sc discuss
Office: CHS
FXUS62 KCHS 261433
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
1033 AM EDT Sat May 26 2018
.SYNOPSIS...
High pressure over the Atlantic will extend westward into the
forecast area today. A conveyor belt of deep tropical moisture
on the east side of Tropical Cyclone Alberto will move overhead
Sunday then linger, resulting in unsettled weather through the
middle of next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
10:30 AM: Very minor changes made to the forecast, mainly to the
current temperature and dew points to mesh them with the ongoing
forecast. Showers and thunderstorms are starting to form along
the sea breeze and expect them to trend inland, into areas of
higher instability. But the severe threat remains low. Depending
on the convective coverage, we may need to adjust the hourly
temperatures further.
Rest of today: Deep layered ridging extends from offshore into
eastern GA and the coastal Carolinas. Sufficient moisture and
diurnal instability/thermodynamics look to exist for scattered
showers and tstms along and inland from the sea breeze. Somewhat
deeper convection is probable this afternoon over inland GA
zones where over 2500 J/KG SB Capes are possible and environment
lapse rates are just a bit steeper adjacent to the
CSRA/Midlands. Moisture is also deeper in this region thus
DCAPES should be unimpressive. The overall risk of severe storms
remains low although a few stronger updrafts could pulse up at
times.
Tonight: Although even deeper tropical moisture will be
approaching from the south overnight, most areas are expected to
squeak out a dry night after early evening convection inland
wanes. We will probably see patchy low clouds form again well
inland and perhaps some fog adjacent to the upper Savannah
River. Lows will remain quite consistent in the upper 60s to low
70s.
&&
.SHORT TERM /SUNDAY THROUGH TUESDAY/...
A plume of exceptionally deep tropical moisture (PWats 2-2.5 inches,
3 standard deviations above normal) advecting northward on the
eastern side of Alberto will spread over the area Sunday as the
tropical cyclone approaches the Gulf Coast. Guidance continues to
consistently show a rainband-type structure containing widespread
moderate to heavy rainfall forming along a surge of high theta-e air
and a coupled jet structure that will begin to approach the area
from the south Sunday morning, slowly working across the area Sunday
afternoon through early Monday morning. We have collaborated with
WPC to bring a slight chance of excessive rainfall across the area
for Sunday and Monday. Much of the area will see 2 to 3 inches of
rainfall during this time, with amounts in excess of 3 inches mainly
focused across the Charleston Tri-County area. Given the relatively
wet antecedent conditions currently in place (several inches of rain
have fallen across most areas away from the immediate coast over the
past week), localized flooding issues are possible. Additionally,
any heavy rain falling near the coast around the time of high tide
Sunday evening could result in significant issues as high tide is
currently forecast to approach coastal flood level.
A more diurnal rainfall pattern will ensue Monday evening, with
storm coverage and intensity waning overnight, then becoming greater
with the increase in thermodynamic instability during the day
Tuesday. A few strong thunderstorms producing gusty winds are
possible Monday and Tuesday afternoons as CAPE values climb to near
1500 J/kg for areas that receive some sunshine, but the overall
severe risk is low in such a deeply moist environment lacking
substantial shear/winds aloft.
&&
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Active weather will persist through the middle-to-end of the week as
deep tropical moisture remains in place. The lack of any larger
scale forcing will result in a primarily diurnal trend for the POP
forecast, with chance-to-likely most days and low-end-to-slight
chance overnight. The flooding threat will decrease, though local
issues cannot be ruled out given the ample moisture available to
storms mainly Wednesday and Thursday afternoons.
High pressure centered near the Bahamas will slowly assume control
of the local pattern as we head into next weekend, bringing more
settled conditions. Temps will trend from near to marginally above
normal through the period.
&&
.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions likely to persist through the 12Z TAF cycle into
daybreak on Sunday. The main forecast quest is convective
initiation and advancement inland with the sea breeze from late
morning through early this afternoon. We maintained VCSH through
early afternoon at both sites with thunder a possibility but
too uncertain at this juncture. South to southeast breezes will
strengthen a bit in the wake of the sea breeze this afternoon.
Extended Aviation Outlook: Occasional to frequent ceiling and/or
visibility restrictions can be expected at the terminals Sunday
evening through Monday morning as an area of moderate to heavy
rainfall crosses the area. VFR conditions will prevail thereafter,
though continued unsettled conditions mean that brief periods of
flight restrictions in showers and thunderstorms are possible mainly
in the afternoons.
&&
.MARINE...
South to southeast winds remain light this morning, but should
begin a gradual uptick with the onset of the sea breeze along
with a slightly tighter low level pressure gradient later today
and tonight. Speeds should increase closer to 15 kt both in the
Intra-coastal and adjacent waters later today with 10-15 kt
speeds tonight across the marine waters. Seas will range from 2
ft this morning to 2-4 ft by tonight, highest beyond 20 NM
offshore.
Persistent southerly winds will bring increasing windswell into the
coastal waters Sunday into Monday. A Small Craft Advisory will
likely be needed beginning midday Sunday as seas climb over 6 ft for
the offshore Georgia waters, and possibly the nearshore South
Carolina waters as well. Seas will return to the 2 to 4 foot range
with moderate southwest winds mid-week as high pressure near the
Bahamas takes control.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
NEAR TERM...
SHORT TERM...
LONG TERM...CEB
AVIATION...
MARINE...
FXUS62 KCHS 261433
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
1033 AM EDT Sat May 26 2018
.SYNOPSIS...
High pressure over the Atlantic will extend westward into the
forecast area today. A conveyor belt of deep tropical moisture
on the east side of Tropical Cyclone Alberto will move overhead
Sunday then linger, resulting in unsettled weather through the
middle of next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
10:30 AM: Very minor changes made to the forecast, mainly to the
current temperature and dew points to mesh them with the ongoing
forecast. Showers and thunderstorms are starting to form along
the sea breeze and expect them to trend inland, into areas of
higher instability. But the severe threat remains low. Depending
on the convective coverage, we may need to adjust the hourly
temperatures further.
Rest of today: Deep layered ridging extends from offshore into
eastern GA and the coastal Carolinas. Sufficient moisture and
diurnal instability/thermodynamics look to exist for scattered
showers and tstms along and inland from the sea breeze. Somewhat
deeper convection is probable this afternoon over inland GA
zones where over 2500 J/KG SB Capes are possible and environment
lapse rates are just a bit steeper adjacent to the
CSRA/Midlands. Moisture is also deeper in this region thus
DCAPES should be unimpressive. The overall risk of severe storms
remains low although a few stronger updrafts could pulse up at
times.
Tonight: Although even deeper tropical moisture will be
approaching from the south overnight, most areas are expected to
squeak out a dry night after early evening convection inland
wanes. We will probably see patchy low clouds form again well
inland and perhaps some fog adjacent to the upper Savannah
River. Lows will remain quite consistent in the upper 60s to low
70s.
&&
.SHORT TERM /SUNDAY THROUGH TUESDAY/...
A plume of exceptionally deep tropical moisture (PWats 2-2.5 inches,
3 standard deviations above normal) advecting northward on the
eastern side of Alberto will spread over the area Sunday as the
tropical cyclone approaches the Gulf Coast. Guidance continues to
consistently show a rainband-type structure containing widespread
moderate to heavy rainfall forming along a surge of high theta-e air
and a coupled jet structure that will begin to approach the area
from the south Sunday morning, slowly working across the area Sunday
afternoon through early Monday morning. We have collaborated with
WPC to bring a slight chance of excessive rainfall across the area
for Sunday and Monday. Much of the area will see 2 to 3 inches of
rainfall during this time, with amounts in excess of 3 inches mainly
focused across the Charleston Tri-County area. Given the relatively
wet antecedent conditions currently in place (several inches of rain
have fallen across most areas away from the immediate coast over the
past week), localized flooding issues are possible. Additionally,
any heavy rain falling near the coast around the time of high tide
Sunday evening could result in significant issues as high tide is
currently forecast to approach coastal flood level.
A more diurnal rainfall pattern will ensue Monday evening, with
storm coverage and intensity waning overnight, then becoming greater
with the increase in thermodynamic instability during the day
Tuesday. A few strong thunderstorms producing gusty winds are
possible Monday and Tuesday afternoons as CAPE values climb to near
1500 J/kg for areas that receive some sunshine, but the overall
severe risk is low in such a deeply moist environment lacking
substantial shear/winds aloft.
&&
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Active weather will persist through the middle-to-end of the week as
deep tropical moisture remains in place. The lack of any larger
scale forcing will result in a primarily diurnal trend for the POP
forecast, with chance-to-likely most days and low-end-to-slight
chance overnight. The flooding threat will decrease, though local
issues cannot be ruled out given the ample moisture available to
storms mainly Wednesday and Thursday afternoons.
High pressure centered near the Bahamas will slowly assume control
of the local pattern as we head into next weekend, bringing more
settled conditions. Temps will trend from near to marginally above
normal through the period.
&&
.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions likely to persist through the 12Z TAF cycle into
daybreak on Sunday. The main forecast quest is convective
initiation and advancement inland with the sea breeze from late
morning through early this afternoon. We maintained VCSH through
early afternoon at both sites with thunder a possibility but
too uncertain at this juncture. South to southeast breezes will
strengthen a bit in the wake of the sea breeze this afternoon.
Extended Aviation Outlook: Occasional to frequent ceiling and/or
visibility restrictions can be expected at the terminals Sunday
evening through Monday morning as an area of moderate to heavy
rainfall crosses the area. VFR conditions will prevail thereafter,
though continued unsettled conditions mean that brief periods of
flight restrictions in showers and thunderstorms are possible mainly
in the afternoons.
&&
.MARINE...
South to southeast winds remain light this morning, but should
begin a gradual uptick with the onset of the sea breeze along
with a slightly tighter low level pressure gradient later today
and tonight. Speeds should increase closer to 15 kt both in the
Intra-coastal and adjacent waters later today with 10-15 kt
speeds tonight across the marine waters. Seas will range from 2
ft this morning to 2-4 ft by tonight, highest beyond 20 NM
offshore.
Persistent southerly winds will bring increasing windswell into the
coastal waters Sunday into Monday. A Small Craft Advisory will
likely be needed beginning midday Sunday as seas climb over 6 ft for
the offshore Georgia waters, and possibly the nearshore South
Carolina waters as well. Seas will return to the 2 to 4 foot range
with moderate southwest winds mid-week as high pressure near the
Bahamas takes control.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
NEAR TERM...
SHORT TERM...
LONG TERM...CEB
AVIATION...
MARINE...
Office: CAE
FXUS62 KCAE 261239
AFDCAE
Area Forecast Discussion
National Weather Service Columbia SC
839 AM EDT Sat May 26 2018
.SYNOPSIS...
The region will remain moist and unstable the next few days
between a ridge offshore and weak low pressure to the west.
Scattered to numerous showers and thunderstorms, mainly during
the afternoon and evening, are expected. Periods of heavy rain
are possible Sunday and Monday as a plume of tropical moisture
from Subtropical Storm Alberto is directed into the area.
&&
.NEAR TERM /THROUGH TONIGHT/...
Upper trough to our west along the Miss valley extending south
into the GOMEX. Upper ridge to our SE off the SE coast. Embedded
short wave just to our north to push farther north, with some
slight upper height rises for our FA today. Slightly drier air
aloft today, but projected PW values still a respectably moist
1.8 inches. Scattered diurnal convective coverage anticipated.
Moderate instabilities provides an isolated severe threat.
Slightly lower PW may reduce localized heavy rain/flooding
threat slightly, but will still be possible with any slow
moving, training, or merging cells. Model blend on weather
elements looks good. Will expect diurnal decrease in convective
coverage this evening, with drier air moving in tonight.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Subtropical storm Alberto is expected to be located somewhere
in the central Gulf of Mexico at 12z Sunday with a somewhat
drier airmass over the forecast area and precipitable water
values at or below 1.5 inches. Though there are still some
differences among models in the track of Alberto there is
reasonable agreement it will stay well to the west of our area
so a wind threat is not expected. However, atmospheric moisture
will surge over the forecast area by Sunday afternoon and
evening as a plume of tropical moisture moves northward on the
eastern side of the system.
Precipitable water values rise well over 2 inches by 00z Monday
across the region with increasing moisture transport into the
area and widespread rainfall expected late Sunday and continuing
through Monday night. This will bring the potential for flash
flooding to the region given the generally wet pattern we have
been in for the past week or so and saturated soils, especially
in the CSRA where precipitation has been 300-600 percent of
normal. A flash flood watch may be needed. Severe weather
potential looks minimal, especially on Sunday due to drier air
in place and marginal instability. Forecast soundings indicate a
moist adiabatic profile Sunday night through Monday night so
think flooding from heavy rain remains the primary concern. WPC
has outlooked the area in a slight risk of excessive rainfall.
Temperatures this period will be near normal for highs in the
mid 80s and above normal for lows in the upper 60s to lower 70s.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
Active weather continues through the extended forecast period
with abundant moisture in place and remnants of Alberto and
upper trough to the west early in the period then shifting
northeastward with the upper trough crossing the region late in
the week.
The remnants of Alberto are expected to be somewhere along the
central Gulf Coast states on Tuesday then moving northward into
the Tennessee Valley by 12z Wednesday. While the forecast area
will be relatively displaced from Alberto, significant moisture
will remain over the region with precipitable water values near
maximum values for this time of year. Will continue to carry
high chance to likely pops, primarily diurnally driven, through
the extended forecast Tue- Thu. The deeper moisture will finally
shift east of the forecast area by Friday but enough moisture
will remain combining with shortwave energy diving through the
upper trough to provide the chance for showers and
thunderstorms. High temperatures during this period will be near
normal to above normal, in the mid to upper 80s Tue-Wed and
upper 80s to around 90 Thu-Fri, and above normal for lows, in
the upper 60s to lower 70s.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Widespread LIFR to IFR CIGs this morning, with a return to VFR
expected by late morning. Will expect scattered mainly afternoon
and evening showers and thunderstorms, diminishing by early
tonight. Will handle with VCSH and tempo SHRA for now. Lowering
CIGs/VSBYs expected again late Sat nt into Sun morning.
EXTENDED AVIATION OUTLOOK...Late night and early morning IFR to
MVFR ceilings and visibilities along with mainly diurnal
showers and thunderstorms through the middle of next week as a
very moist air mass remains over the region.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
SYNOPSIS...99
NEAR TERM...99
SHORT TERM...99
LONG TERM...99
AVIATION...99
FXUS62 KCAE 261239
AFDCAE
Area Forecast Discussion
National Weather Service Columbia SC
839 AM EDT Sat May 26 2018
.SYNOPSIS...
The region will remain moist and unstable the next few days
between a ridge offshore and weak low pressure to the west.
Scattered to numerous showers and thunderstorms, mainly during
the afternoon and evening, are expected. Periods of heavy rain
are possible Sunday and Monday as a plume of tropical moisture
from Subtropical Storm Alberto is directed into the area.
&&
.NEAR TERM /THROUGH TONIGHT/...
Upper trough to our west along the Miss valley extending south
into the GOMEX. Upper ridge to our SE off the SE coast. Embedded
short wave just to our north to push farther north, with some
slight upper height rises for our FA today. Slightly drier air
aloft today, but projected PW values still a respectably moist
1.8 inches. Scattered diurnal convective coverage anticipated.
Moderate instabilities provides an isolated severe threat.
Slightly lower PW may reduce localized heavy rain/flooding
threat slightly, but will still be possible with any slow
moving, training, or merging cells. Model blend on weather
elements looks good. Will expect diurnal decrease in convective
coverage this evening, with drier air moving in tonight.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Subtropical storm Alberto is expected to be located somewhere
in the central Gulf of Mexico at 12z Sunday with a somewhat
drier airmass over the forecast area and precipitable water
values at or below 1.5 inches. Though there are still some
differences among models in the track of Alberto there is
reasonable agreement it will stay well to the west of our area
so a wind threat is not expected. However, atmospheric moisture
will surge over the forecast area by Sunday afternoon and
evening as a plume of tropical moisture moves northward on the
eastern side of the system.
Precipitable water values rise well over 2 inches by 00z Monday
across the region with increasing moisture transport into the
area and widespread rainfall expected late Sunday and continuing
through Monday night. This will bring the potential for flash
flooding to the region given the generally wet pattern we have
been in for the past week or so and saturated soils, especially
in the CSRA where precipitation has been 300-600 percent of
normal. A flash flood watch may be needed. Severe weather
potential looks minimal, especially on Sunday due to drier air
in place and marginal instability. Forecast soundings indicate a
moist adiabatic profile Sunday night through Monday night so
think flooding from heavy rain remains the primary concern. WPC
has outlooked the area in a slight risk of excessive rainfall.
Temperatures this period will be near normal for highs in the
mid 80s and above normal for lows in the upper 60s to lower 70s.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
Active weather continues through the extended forecast period
with abundant moisture in place and remnants of Alberto and
upper trough to the west early in the period then shifting
northeastward with the upper trough crossing the region late in
the week.
The remnants of Alberto are expected to be somewhere along the
central Gulf Coast states on Tuesday then moving northward into
the Tennessee Valley by 12z Wednesday. While the forecast area
will be relatively displaced from Alberto, significant moisture
will remain over the region with precipitable water values near
maximum values for this time of year. Will continue to carry
high chance to likely pops, primarily diurnally driven, through
the extended forecast Tue- Thu. The deeper moisture will finally
shift east of the forecast area by Friday but enough moisture
will remain combining with shortwave energy diving through the
upper trough to provide the chance for showers and
thunderstorms. High temperatures during this period will be near
normal to above normal, in the mid to upper 80s Tue-Wed and
upper 80s to around 90 Thu-Fri, and above normal for lows, in
the upper 60s to lower 70s.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Widespread LIFR to IFR CIGs this morning, with a return to VFR
expected by late morning. Will expect scattered mainly afternoon
and evening showers and thunderstorms, diminishing by early
tonight. Will handle with VCSH and tempo SHRA for now. Lowering
CIGs/VSBYs expected again late Sat nt into Sun morning.
EXTENDED AVIATION OUTLOOK...Late night and early morning IFR to
MVFR ceilings and visibilities along with mainly diurnal
showers and thunderstorms through the middle of next week as a
very moist air mass remains over the region.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
SYNOPSIS...99
NEAR TERM...99
SHORT TERM...99
LONG TERM...99
AVIATION...99
Office: GSP
FXUS62 KGSP 261512
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1112 AM EDT Sat May 26 2018
.SYNOPSIS...
Very moist conditions will persist over the region through the
weekend as Alberto develops across the Gulf of Mexico. Tropical
moisture will likely affect our area through much of next week,
bringing the potential for continued heavy rainfall and associated
flooding to the region.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 1050 am: One small area of moderate to heavy showers
(responsible for producing locally heavy rain across the Upstate
earlier this morning) is dissipating across the northwest NC
Piedmont, while another area has been gradually building into the
northern NC Piedmont. These will be the two areas that see the
highest pop over the next 1-3 hours, while the remainder of the
forecast area will only see 20-30 pops during that time. In terms of
the redevelopment potential later today, instability is limited by
morning cloud cover and poor mid-level lapse rates in semi-tropical
environment. Meanwhile, PWATs per the 12Z regional RAOBs are around
1.5": certainly juicy, but not a slam dunk to yield widespread
showers and storms this afternoon in light of modest-at-best
instability and forcing. In fact, guidance is in relatively good
agreement in building in weak subsidence and lower PWAT air from the
south in association with a mid-level short wave ridge. As such,
will continue to highlight the high terrain with likely pops this
afternoon and evening, with mainly 40-50 east of the Blue Ridge.
Halfway decent mid-level flow will allow cells and clusters of
convection to move toward the NE at around 15 kts, so excessive
rainfall concerns will remain localized and by and large limited to
anchoring along terrain features, cell training, and/or locations
with poor antecedent conditions due to heavy rain that has fallen in
the past 24-ish hours.
850 mb flow will stay mainly southwesterly through the evening
before starting to back to light southeast in southern sections
early Sunday morning. We should see a repeat of this morning, with
very mild minimum temperatures and showers continuing, especially in
and near the mountains, but with enough steering flow to continue to
keep any hydro issues quite isolated. This will continue to saturate
soils, however, and likely set the stage for later hydro issues.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 AM EDT Saturday: With sfc high pressure shifting into the
OH Valley and a (slightly weakening) subtropical ridge persisting
with it's westward extension into the Carolinas, focus remains on
Subtropical Storm Alberto and it's affect it'll have on our FA over
the next several days. Unfortunately, discrepancy continues with the
latest 00Z runs of the GFS and ECMWF. The GFS places the center of
Alberto just south of the AL coastline Sunday morning, while the
ECMWF is just about 24 hours slower with the progression, bringing
it just south of the AL coastline Monday morning and not moving
onshore until Monday night. The timing of the heaviest rainfall
across our FA will absolutely rely on the Alberto's progression,
thus do note the general timing mentioned below is not set in stone.
Noticeable mid-level dry air in place which allowed for a brief lull
in shower/thunderstorm activity coming into the short term forecast
period will (per the GFS) quickly be dismissed into Sunday afternoon
as a surge of deep tropical moisture makes it's way northward
through portions of the Southeast and into the FA (not until Monday
morning per the ECMWF), re-saturating the atmospheric column. As has
been discussed the past few days, model guidance continues to
support PWATs ranging between 1.5 to 2.0 inches late Sunday into
Monday (again, depending on which model you reference), which is 2+
standard deviations above climo. With the tropical airmass in place
as Alberto meanders across MS/AL through Monday night/early Tuesday,
and weak instability becomes available, expect isolated to scattered
showers and thunderstorms to become widespread in nature beginning
Sunday evening. The potential for heavy rainfall and localized flash
flooding remains the primary threat attm with the rainfall
rates of most interest (through both the short term and medium
range forecast period). Taking into account the recent rainfall
over the past week which caused flooding/landslide issues, this
will be especially a concern for areas across the NC mountains
and the Escarpment, overnight Sunday into Monday per the GFS (or
moreso Monday, based on ECMWF). To give an idea of the rainfall
we've seen across the NC mountains this past week, for the
month of May, the all-time monthly total precipitation record
for Asheville which was 9.18 inches (set in 2009) has already
been broken - with 9.69 inches already recorded for May 2018,
and we still a few days to go yet in the month. Even so, with
rainfall being the primary concern, will note that while winds
attm look to be minimal, any brief gusts in thunderstorms along
with the already saturated soils - it won't take much to bring
down weak trees. While not issued with this update, a flash
flood watch remains a possibility. High temperatures will remain
just below normal, with overnight lows hovering around normal.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 315 AM EDT Saturday: Given both the temporal and spatial
discrepancy of Alberto between the 00Z runs of the GFS and ECMWF, a
general consensus will be used for this forecast period. With
Alberto gradually weakening as it moves up through the TN valley
around midweek, latest guidance continues to suggest the opening of
it's associated 500 mb low as it eventually merges with the upper
trough in place across the upper midwest into the latter part of the
week. With the persistent SSW flow/moisture supply, heavy
downpours/localized flooding will remain a concern, especially
across the upslope areas, as long as showers and thunderstorms
continue to develop and move across the FA. Even as the remnant sfc
low tracks west of the FA, from the TN Valley to the OH Valley and
then into the northeast into the weekend, guidance continues to
depict an upper longwave trough north of the area with weak
disturbances traveling within the feature and nearing the FA. Thus
keeping an overall unsettled weather pattern through the end of
the week, with coverage gradually transitioning from widespread
to isolated/scattered in nature by Friday. High temperatures
will continue to teeter around normal, climbing to above normal
at the end of the week, with overnight lows remaining fairly
mild.
&&
.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Showers departing the Upstate this
morning will likely work over the region from KHKY to KCLT through
14Z or 15Z. Then, expect mainly scattered showers and occasional
TSRA this afternoon, especially over the mountains, with profiles
remaining very moist across the region and upslope triggering
persisting. Surface winds will remain south to southwesterly through
the period. IFR cigs this morning will gradually improve through
MVFR through late morning, with some lower end VFR likely for much
of the afternoon hours. Lowering restriction ceilings will develop
once again this evening.
Outlook: The moist and unsettled pattern will continue through the
period. Tropical moisture will increase by late weekend into
Memorial Day, further increasing the frequency and intensity of SHRA
and associated restrictions. Morning stratus/fog are possible each
day, especially following any heavy rainfall the previous day.
Confidence Table...
15-21Z 21-03Z 03-09Z 09-12Z
KCLT Med 75% High 100% High 100% Med 77%
KGSP Med 73% High 100% High 100% Med 69%
KAVL Med 75% High 100% Med 77% Med 66%
KHKY High 81% High 100% High 100% Med 74%
KGMU Med 75% High 100% High 100% Med 65%
KAND High 85% High 100% High 100% Med 69%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
www.weather.gov/gsp/aviation
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...HG
NEAR TERM...HG/JDL
SHORT TERM...SGL
LONG TERM...SGL
AVIATION...HG
FXUS62 KGSP 261512
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1112 AM EDT Sat May 26 2018
.SYNOPSIS...
Very moist conditions will persist over the region through the
weekend as Alberto develops across the Gulf of Mexico. Tropical
moisture will likely affect our area through much of next week,
bringing the potential for continued heavy rainfall and associated
flooding to the region.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 1050 am: One small area of moderate to heavy showers
(responsible for producing locally heavy rain across the Upstate
earlier this morning) is dissipating across the northwest NC
Piedmont, while another area has been gradually building into the
northern NC Piedmont. These will be the two areas that see the
highest pop over the next 1-3 hours, while the remainder of the
forecast area will only see 20-30 pops during that time. In terms of
the redevelopment potential later today, instability is limited by
morning cloud cover and poor mid-level lapse rates in semi-tropical
environment. Meanwhile, PWATs per the 12Z regional RAOBs are around
1.5": certainly juicy, but not a slam dunk to yield widespread
showers and storms this afternoon in light of modest-at-best
instability and forcing. In fact, guidance is in relatively good
agreement in building in weak subsidence and lower PWAT air from the
south in association with a mid-level short wave ridge. As such,
will continue to highlight the high terrain with likely pops this
afternoon and evening, with mainly 40-50 east of the Blue Ridge.
Halfway decent mid-level flow will allow cells and clusters of
convection to move toward the NE at around 15 kts, so excessive
rainfall concerns will remain localized and by and large limited to
anchoring along terrain features, cell training, and/or locations
with poor antecedent conditions due to heavy rain that has fallen in
the past 24-ish hours.
850 mb flow will stay mainly southwesterly through the evening
before starting to back to light southeast in southern sections
early Sunday morning. We should see a repeat of this morning, with
very mild minimum temperatures and showers continuing, especially in
and near the mountains, but with enough steering flow to continue to
keep any hydro issues quite isolated. This will continue to saturate
soils, however, and likely set the stage for later hydro issues.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 AM EDT Saturday: With sfc high pressure shifting into the
OH Valley and a (slightly weakening) subtropical ridge persisting
with it's westward extension into the Carolinas, focus remains on
Subtropical Storm Alberto and it's affect it'll have on our FA over
the next several days. Unfortunately, discrepancy continues with the
latest 00Z runs of the GFS and ECMWF. The GFS places the center of
Alberto just south of the AL coastline Sunday morning, while the
ECMWF is just about 24 hours slower with the progression, bringing
it just south of the AL coastline Monday morning and not moving
onshore until Monday night. The timing of the heaviest rainfall
across our FA will absolutely rely on the Alberto's progression,
thus do note the general timing mentioned below is not set in stone.
Noticeable mid-level dry air in place which allowed for a brief lull
in shower/thunderstorm activity coming into the short term forecast
period will (per the GFS) quickly be dismissed into Sunday afternoon
as a surge of deep tropical moisture makes it's way northward
through portions of the Southeast and into the FA (not until Monday
morning per the ECMWF), re-saturating the atmospheric column. As has
been discussed the past few days, model guidance continues to
support PWATs ranging between 1.5 to 2.0 inches late Sunday into
Monday (again, depending on which model you reference), which is 2+
standard deviations above climo. With the tropical airmass in place
as Alberto meanders across MS/AL through Monday night/early Tuesday,
and weak instability becomes available, expect isolated to scattered
showers and thunderstorms to become widespread in nature beginning
Sunday evening. The potential for heavy rainfall and localized flash
flooding remains the primary threat attm with the rainfall
rates of most interest (through both the short term and medium
range forecast period). Taking into account the recent rainfall
over the past week which caused flooding/landslide issues, this
will be especially a concern for areas across the NC mountains
and the Escarpment, overnight Sunday into Monday per the GFS (or
moreso Monday, based on ECMWF). To give an idea of the rainfall
we've seen across the NC mountains this past week, for the
month of May, the all-time monthly total precipitation record
for Asheville which was 9.18 inches (set in 2009) has already
been broken - with 9.69 inches already recorded for May 2018,
and we still a few days to go yet in the month. Even so, with
rainfall being the primary concern, will note that while winds
attm look to be minimal, any brief gusts in thunderstorms along
with the already saturated soils - it won't take much to bring
down weak trees. While not issued with this update, a flash
flood watch remains a possibility. High temperatures will remain
just below normal, with overnight lows hovering around normal.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 315 AM EDT Saturday: Given both the temporal and spatial
discrepancy of Alberto between the 00Z runs of the GFS and ECMWF, a
general consensus will be used for this forecast period. With
Alberto gradually weakening as it moves up through the TN valley
around midweek, latest guidance continues to suggest the opening of
it's associated 500 mb low as it eventually merges with the upper
trough in place across the upper midwest into the latter part of the
week. With the persistent SSW flow/moisture supply, heavy
downpours/localized flooding will remain a concern, especially
across the upslope areas, as long as showers and thunderstorms
continue to develop and move across the FA. Even as the remnant sfc
low tracks west of the FA, from the TN Valley to the OH Valley and
then into the northeast into the weekend, guidance continues to
depict an upper longwave trough north of the area with weak
disturbances traveling within the feature and nearing the FA. Thus
keeping an overall unsettled weather pattern through the end of
the week, with coverage gradually transitioning from widespread
to isolated/scattered in nature by Friday. High temperatures
will continue to teeter around normal, climbing to above normal
at the end of the week, with overnight lows remaining fairly
mild.
&&
.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Showers departing the Upstate this
morning will likely work over the region from KHKY to KCLT through
14Z or 15Z. Then, expect mainly scattered showers and occasional
TSRA this afternoon, especially over the mountains, with profiles
remaining very moist across the region and upslope triggering
persisting. Surface winds will remain south to southwesterly through
the period. IFR cigs this morning will gradually improve through
MVFR through late morning, with some lower end VFR likely for much
of the afternoon hours. Lowering restriction ceilings will develop
once again this evening.
Outlook: The moist and unsettled pattern will continue through the
period. Tropical moisture will increase by late weekend into
Memorial Day, further increasing the frequency and intensity of SHRA
and associated restrictions. Morning stratus/fog are possible each
day, especially following any heavy rainfall the previous day.
Confidence Table...
15-21Z 21-03Z 03-09Z 09-12Z
KCLT Med 75% High 100% High 100% Med 77%
KGSP Med 73% High 100% High 100% Med 69%
KAVL Med 75% High 100% Med 77% Med 66%
KHKY High 81% High 100% High 100% Med 74%
KGMU Med 75% High 100% High 100% Med 65%
KAND High 85% High 100% High 100% Med 69%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
www.weather.gov/gsp/aviation
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...HG
NEAR TERM...HG/JDL
SHORT TERM...SGL
LONG TERM...SGL
AVIATION...HG
