al discuss
Office: BMX
FXUS64 KBMX 261336
AFDBMX
Area Forecast Discussion
National Weather Service Birmingham AL
836 AM CDT Sat May 26 2018
.UPDATE...
Morning Mesoscale and Short-Term Updates.
&&
.SYNOPSIS...
Synoptic Analysis:
GOES-R moisture channel imagery along with global numerical model
depictions align well in depicting a trough aloft that extended
from Lake Michigan southward along the Mississippi River and over
the northwest Gulf of Mexico. Deep-layer ridging was depicted
just off the coast of the Carolinas and extended southeast over
the Bahamas and south Florida.
Toward the surface, high pressure was analyzed over the southwest
Atlantic basin that was nosing into our area from the east while
lower pressure was analyzed across New Mexico and Texas.
Subtropical Storm Alberto was analyzed by NHC located south of the
strait between the Yucatan Peninsula and western Cuba.
Mesoscale Analysis:
NEXRAD, GOES-R and surface analysis data reveals a weak low level
boundary across our northern counties associated with light shower
activity. This boundary extended from northern Marion County into
central Blount County and further southeast into south-central
Calhoun County and was lifting northward with time. Another
boundary was nearly stationary and extended from central Dallas
County northeast into western Chilton County with light showers in
the vicinity of this feature, mainly across Dallas County.
Additional boundaries may be present but identification was
hampered by abundant cloud cover.
Sounding Discussion:
The 26/12z BMX sounding continues to maintain a moist profile that
yielded a precipitable water (PWAT) value of 1.66 inches. There
exists a small subsidence inversion from around 940 mb upward to
near 650 mb. Winds were calm at the surface with a southwest flow
present above the surface to around 440 mb with speeds generally
from 10 to 20 knots. A southeast flow was measured higher aloft to
near 230 mb with speeds remaining between 10 and 20 knots. A more
westerly wind was detected above 230 mb with speeds from 10 to 15
knots.
The high PWAT values will again support a risk of localized
flooding in urbanized and poor-drainage areas while light winds
aloft will maintain slow storm motions that will only further
amplify the flash flooding risk. The lack of dry air in the
profile is helping to mitigate the wet microburst risk and today's
risk is in the low category. The best potential for wet
microbursts exists across the western portion of the forecast
area. Modified observed soundings for this afternoon yields a
surface-based convective available potential energy (CAPE) value
over 2500 J/kg with a lifted index of -6. Robust updraft potential
may be realized depending on the how fast the cloud cover mixes
out through late morning and potential exists for a few stronger
storms, especially this afternoon.
05
&&
.SHORT TERM...
Today and Tonight.
The ongoing forecast is in good condition with no changes needed,
short-term higher rain chances will exist across our northern
tier of counties due to showers associated with the northward
moving boundary. Showers may gradually increase in coverage in the
vicinity of the second boundary across our south-
central/southwest counties.
05
Revised Previous short-term discussion:
Convection today will once again be diurnal based with outflows
dominating development. The models are showing a mid level dry
slot moving from the Florida Panhandle and into Southeast Alabama
this afternoon. Based on this feature, lowest rain chances this
afternoon will be across the southeast counties, with likely pops
elsewhere. Activity will diminish in coverage and intensity during
the evening hours.
58/rose
.LONG TERM...
Sunday through Friday.
The main focus in the extended will be on Alberto and its
progression toward the area. Overall we see a west coast trough
swing through Plains on Monday into Tuesday. Until that trough can
make it closer to the region, we are going to remain on the outer
edge of the Bermuda High with the south/southeast flow continuing to
provide very rich moisture ahead of the arrival of Alberto. Rain
chances remain high for this time of the year, as the pattern will
not really change much at all until the trough passes through our
area by Wednesday night, finally getting rid of the tropical
airmass. With that said though this pattern change will place the
area in a northwest flow for Thursday through the weekend. This
could provide those MCS events each night, depending on what
develops to our north. More on that once we get through with
Alberto.
So after speaking with NHC and dissecting the model trends, we are
fairly confident on the overall timing of Alberto and rain chances
based on the track of the system. The consensus of the models take
the center near Mobile Bay Monday night and then slide it northward
along our western counties during the day Tuesday and possibly
exiting by Tuesday night. Look for the center of the low to then
become absorbed by the trough on Wednesday, resulting in front
moving westward through the area.
So to the specifics on impacts from Alberto. The initial band that is
usually 50 to 100 miles north of the center will be exiting the area
Sunday morning, with a second band of rain and storms moving into
the region Sunday afternoon/night and sliding north of the area by
Monday morning, just as models are expecting the center of Alberto
to begin to move into the coastline. The strongest winds will likely
make it into the southwestern areas between 7 and 10 pm Monday
night and only be around 25 to 35 mph with higher gusts (depression
strength). These winds will likely move north and then northeast
during the day Tuesday, all the while weakening as the system moves
north. Flooding and strong winds remain the primary threat but there
is a marginal chance at a brief spin up tornado in the southeast
Monday night into Tuesday as the system moves on shore with banding
on the northeast side of the low. As the system becomes more
organized will evaluate the need to add in brief tornadoes, but for
now will mainly focus on the rainfall and winds. On a whole we are
looking at 3 to 4 inches of rain area wide, with areas in the west
seeing 4 to 5 inches and locally higher totals. Much more on this
system over the coming 24 to 48 hours.
16
&&
.AVIATION...
12Z TAF Discussion.
Cigs and vsbys have been highly variable overnight and very
difficult to establish any trends for short term forecasting.
Overall all sites will experience low cigs thru 15z, with LIFR
conds. Vsbys have not been as low as previous mornings with many
sites aoa 5 miles. Beyond 15z, VFR conds are expected outside
convection. Sct to nmrs tstms will develop after 17z, with the
higher chances for storms across north and west Alabama. Activity
will diminish after sunset. Confidence too low for re-development
of low cigs/fog later tngt, and will let latter shifts evaluate.
58/rose
&&
.FIRE WEATHER...
A moist pattern is expected over the next seven days and should
result in daily rain chances. Heavy rainfall will occur with the
tropical moisture from Alberto on Monday and Tuesday. Patchy fog
and low clouds will be possible each morning particularly where
rainfall occurs during the prior afternoon and evening. No fire
weather concerns at this time.
&&
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 85 67 81 66 81 / 60 40 60 70 60
Anniston 84 67 80 67 81 / 60 40 70 70 60
Birmingham 86 69 82 68 82 / 60 50 60 70 70
Tuscaloosa 87 69 83 69 84 / 60 40 60 70 80
Calera 85 67 80 68 82 / 60 50 70 70 70
Auburn 83 67 77 70 79 / 50 40 80 60 70
Montgomery 87 68 80 71 83 / 50 40 80 60 80
Troy 85 67 76 70 82 / 50 40 80 60 80
&&
.BMX WATCHES/WARNINGS/ADVISORIES/...
None.
&&
$$
FXUS64 KBMX 261336
AFDBMX
Area Forecast Discussion
National Weather Service Birmingham AL
836 AM CDT Sat May 26 2018
.UPDATE...
Morning Mesoscale and Short-Term Updates.
&&
.SYNOPSIS...
Synoptic Analysis:
GOES-R moisture channel imagery along with global numerical model
depictions align well in depicting a trough aloft that extended
from Lake Michigan southward along the Mississippi River and over
the northwest Gulf of Mexico. Deep-layer ridging was depicted
just off the coast of the Carolinas and extended southeast over
the Bahamas and south Florida.
Toward the surface, high pressure was analyzed over the southwest
Atlantic basin that was nosing into our area from the east while
lower pressure was analyzed across New Mexico and Texas.
Subtropical Storm Alberto was analyzed by NHC located south of the
strait between the Yucatan Peninsula and western Cuba.
Mesoscale Analysis:
NEXRAD, GOES-R and surface analysis data reveals a weak low level
boundary across our northern counties associated with light shower
activity. This boundary extended from northern Marion County into
central Blount County and further southeast into south-central
Calhoun County and was lifting northward with time. Another
boundary was nearly stationary and extended from central Dallas
County northeast into western Chilton County with light showers in
the vicinity of this feature, mainly across Dallas County.
Additional boundaries may be present but identification was
hampered by abundant cloud cover.
Sounding Discussion:
The 26/12z BMX sounding continues to maintain a moist profile that
yielded a precipitable water (PWAT) value of 1.66 inches. There
exists a small subsidence inversion from around 940 mb upward to
near 650 mb. Winds were calm at the surface with a southwest flow
present above the surface to around 440 mb with speeds generally
from 10 to 20 knots. A southeast flow was measured higher aloft to
near 230 mb with speeds remaining between 10 and 20 knots. A more
westerly wind was detected above 230 mb with speeds from 10 to 15
knots.
The high PWAT values will again support a risk of localized
flooding in urbanized and poor-drainage areas while light winds
aloft will maintain slow storm motions that will only further
amplify the flash flooding risk. The lack of dry air in the
profile is helping to mitigate the wet microburst risk and today's
risk is in the low category. The best potential for wet
microbursts exists across the western portion of the forecast
area. Modified observed soundings for this afternoon yields a
surface-based convective available potential energy (CAPE) value
over 2500 J/kg with a lifted index of -6. Robust updraft potential
may be realized depending on the how fast the cloud cover mixes
out through late morning and potential exists for a few stronger
storms, especially this afternoon.
05
&&
.SHORT TERM...
Today and Tonight.
The ongoing forecast is in good condition with no changes needed,
short-term higher rain chances will exist across our northern
tier of counties due to showers associated with the northward
moving boundary. Showers may gradually increase in coverage in the
vicinity of the second boundary across our south-
central/southwest counties.
05
Revised Previous short-term discussion:
Convection today will once again be diurnal based with outflows
dominating development. The models are showing a mid level dry
slot moving from the Florida Panhandle and into Southeast Alabama
this afternoon. Based on this feature, lowest rain chances this
afternoon will be across the southeast counties, with likely pops
elsewhere. Activity will diminish in coverage and intensity during
the evening hours.
58/rose
.LONG TERM...
Sunday through Friday.
The main focus in the extended will be on Alberto and its
progression toward the area. Overall we see a west coast trough
swing through Plains on Monday into Tuesday. Until that trough can
make it closer to the region, we are going to remain on the outer
edge of the Bermuda High with the south/southeast flow continuing to
provide very rich moisture ahead of the arrival of Alberto. Rain
chances remain high for this time of the year, as the pattern will
not really change much at all until the trough passes through our
area by Wednesday night, finally getting rid of the tropical
airmass. With that said though this pattern change will place the
area in a northwest flow for Thursday through the weekend. This
could provide those MCS events each night, depending on what
develops to our north. More on that once we get through with
Alberto.
So after speaking with NHC and dissecting the model trends, we are
fairly confident on the overall timing of Alberto and rain chances
based on the track of the system. The consensus of the models take
the center near Mobile Bay Monday night and then slide it northward
along our western counties during the day Tuesday and possibly
exiting by Tuesday night. Look for the center of the low to then
become absorbed by the trough on Wednesday, resulting in front
moving westward through the area.
So to the specifics on impacts from Alberto. The initial band that is
usually 50 to 100 miles north of the center will be exiting the area
Sunday morning, with a second band of rain and storms moving into
the region Sunday afternoon/night and sliding north of the area by
Monday morning, just as models are expecting the center of Alberto
to begin to move into the coastline. The strongest winds will likely
make it into the southwestern areas between 7 and 10 pm Monday
night and only be around 25 to 35 mph with higher gusts (depression
strength). These winds will likely move north and then northeast
during the day Tuesday, all the while weakening as the system moves
north. Flooding and strong winds remain the primary threat but there
is a marginal chance at a brief spin up tornado in the southeast
Monday night into Tuesday as the system moves on shore with banding
on the northeast side of the low. As the system becomes more
organized will evaluate the need to add in brief tornadoes, but for
now will mainly focus on the rainfall and winds. On a whole we are
looking at 3 to 4 inches of rain area wide, with areas in the west
seeing 4 to 5 inches and locally higher totals. Much more on this
system over the coming 24 to 48 hours.
16
&&
.AVIATION...
12Z TAF Discussion.
Cigs and vsbys have been highly variable overnight and very
difficult to establish any trends for short term forecasting.
Overall all sites will experience low cigs thru 15z, with LIFR
conds. Vsbys have not been as low as previous mornings with many
sites aoa 5 miles. Beyond 15z, VFR conds are expected outside
convection. Sct to nmrs tstms will develop after 17z, with the
higher chances for storms across north and west Alabama. Activity
will diminish after sunset. Confidence too low for re-development
of low cigs/fog later tngt, and will let latter shifts evaluate.
58/rose
&&
.FIRE WEATHER...
A moist pattern is expected over the next seven days and should
result in daily rain chances. Heavy rainfall will occur with the
tropical moisture from Alberto on Monday and Tuesday. Patchy fog
and low clouds will be possible each morning particularly where
rainfall occurs during the prior afternoon and evening. No fire
weather concerns at this time.
&&
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 85 67 81 66 81 / 60 40 60 70 60
Anniston 84 67 80 67 81 / 60 40 70 70 60
Birmingham 86 69 82 68 82 / 60 50 60 70 70
Tuscaloosa 87 69 83 69 84 / 60 40 60 70 80
Calera 85 67 80 68 82 / 60 50 70 70 70
Auburn 83 67 77 70 79 / 50 40 80 60 70
Montgomery 87 68 80 71 83 / 50 40 80 60 80
Troy 85 67 76 70 82 / 50 40 80 60 80
&&
.BMX WATCHES/WARNINGS/ADVISORIES/...
None.
&&
$$
Office: MOB
FXUS64 KMOB 261150
AFDMOB
Area Forecast Discussion
National Weather Service Mobile AL
650 AM CDT Sat May 26 2018
.DISCUSSION...Updated for latest aviation discussion below.
&&
.AVIATION...
12Z issuance...
A few widely scattered showers near the coast will persist through
mid morning. After which expect afternoon showers and
thunderstorms to form beginning near the coastline before moving
inland throughout the day. Winds will be generally out of the
southeast during the day before becoming light and variable
overnight. DJ/17
&&
.PREV DISCUSSION... /issued 429 AM CDT Sat May 26 2018/
..Sub-Tropical Storm Alberto Brings a Multitude of Impacts Over
the Central Gulf Coast Into The Memorial Day Holiday Weekend...
NEAR TERM /Now Through Saturday night/...26.00Z upper air analysis
shows a long wave trof positioned from the MS River Valley southward
to off the LA coast. Within the trof axis, a deep layer moist
airmass remains unchanged with PWATs remaining unseasonably high
for the late part of May (resting between 1 and 2 standard
deviations above the climatological mean). That being said and
with the region on the favored east side of the high level trof
axis where a series of subtle mid level impulses eject northeast
atop the local area, an unsettled weather pattern is maintained in
the near term. With daily instability and presence of weak
mesoscale boundaries to help provide for a focus, scattered to
numerous showers and storms are forecast to develop thru the
course of the day. In addition to frequent lightning activity and
brief strong wind gusts, some of the storms will be quite
efficient in dropping locally heavy rains in a short period of
time. This could lead to some isolated cases of mainly nuisance
type flooding over areas subject to poor drainage during heavier
rain occurrences. Forecasters taper off the PoPs going into this
evening.
In the meantime, Alberto over the northwest Caribbean, is
forecast by the National Hurricane Center to begin lifting slowly
northward thru the Yucatan Channel today and emerge into the
southern Gulf tonight. Well north of Alberto, there are
indications that rain bands will begin to spread north and west up
across the coastal waters late tonight. considering this, an
increase in PoPs is aligned along the western Florida Gulf coast
late.
SHORT TERM /Sunday Through Monday night/...Sub-Topical Storm
Alberto will be the big impact player during the short term as it
lifts northward over the southeast Gulf Sunday. The track bends
more to the northwest by Monday. There will be a multitude of
impacts related to Alberto. For specific information on all of
these, including the latest thinking from the National Hurricane
Center on track, please refer to the National weather Service
Mobile AL web site at www.weather.gov/mob.
LONG TERM /Tuesday Through Friday/...Sub-Topical Storm
Alberto continues to be the big impact player early in the long
term as it comes ashore somewhere along the central Gulf coast
early Tuesday morning. The center of Alberto is progged to be
positioned over west central AL Tuesday night, then begin lifting
northeast across the TN River Valley on Wednesday. As the effects
of Alberto begin to move away by mid and late week, chances of
showers and storms taper back to more seasonable then. /10
The following is a breakdown of impacts and confidence levels for
each:
- Flash Flood Threat - Confidence: HIGH. Timing: This evening
through Tuesday evening. Significant rainfall amounts of 6 to 12
inches remain unchanged through this time period, especially
closer to the coast and over our southeastern counties. 5 to 8
inches over portions of the interior. Note: Some areas could see
localized double these amounts. The Flash Flood Watch has been
extended northward as the threat of excessive rain has increased
in latest excessive rain outlooks by the weather prediction
center.
- Storm Surge - Confidence: HIGH. Timing: This evening through
Tuesday. A Storm Surge Watch is in effect for all local coastal
zones, where 2 to 4 feet above ground level (or inundation) is
expected. The timing of maximum coastal water rises looks to be
Sunday night into Monday night.
- High Surf - Confidence: HIGH. Timing: This evening through
Tuesday. Surf heights of 5 to 9 feet will result in pounding
waves and resultant beach erosion. Surf heights could build
upwards of 8 to 12 feet with higher sets possible by Monday. A
High Surf Advisory will likely be required on later forecasts.
- Rip Currents - Confidence: HIGH. A high risk of dangerous to
potentially deadly rip currents remains in effect through the
period.
- Wind - Confidence: HIGH. Timing: Sunday through Tuesday. Given
current track and forecast strength. A Tropical Storm Watch
remains in effect for the entire coast line.
- Severe Storm Potential - Confidence: Low. Timing: Beginning as
early as this evening then increasing potential through Sunday
night into Memorial Day.
MARINE...Sub-tropical Storm Alberto will bring impacts to the
marine area by way of strong winds, high seas over the open Gulf
waters and building waves over area bays and sounds. /10
&&
.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Flash Flood Watch from this evening through Tuesday evening for
ALZ052-053-055-056-059-060-261>266.
Tropical Storm Watch for ALZ263>266.
High Rip Current Risk through Tuesday morning for ALZ265-266.
High Surf Advisory from 1 PM this afternoon to 7 PM CDT Tuesday
for ALZ263>266.
FL...Flash Flood Watch from this evening through Tuesday evening for
FLZ201>206.
Tropical Storm Watch for FLZ202-204-206.
High Rip Current Risk through Tuesday morning for FLZ202-204-206.
High Surf Advisory from 1 PM this afternoon to 7 PM CDT Tuesday
for FLZ202-204-206.
MS...Flash Flood Watch from this evening through Tuesday evening for
MSZ076-078-079.
GM...Tropical Storm Watch for GMZ630>636-650-655-670-675.
&&
$$
This product is also available on the web at:
http://weather.gov/mob
FXUS64 KMOB 261150
AFDMOB
Area Forecast Discussion
National Weather Service Mobile AL
650 AM CDT Sat May 26 2018
.DISCUSSION...Updated for latest aviation discussion below.
&&
.AVIATION...
12Z issuance...
A few widely scattered showers near the coast will persist through
mid morning. After which expect afternoon showers and
thunderstorms to form beginning near the coastline before moving
inland throughout the day. Winds will be generally out of the
southeast during the day before becoming light and variable
overnight. DJ/17
&&
.PREV DISCUSSION... /issued 429 AM CDT Sat May 26 2018/
..Sub-Tropical Storm Alberto Brings a Multitude of Impacts Over
the Central Gulf Coast Into The Memorial Day Holiday Weekend...
NEAR TERM /Now Through Saturday night/...26.00Z upper air analysis
shows a long wave trof positioned from the MS River Valley southward
to off the LA coast. Within the trof axis, a deep layer moist
airmass remains unchanged with PWATs remaining unseasonably high
for the late part of May (resting between 1 and 2 standard
deviations above the climatological mean). That being said and
with the region on the favored east side of the high level trof
axis where a series of subtle mid level impulses eject northeast
atop the local area, an unsettled weather pattern is maintained in
the near term. With daily instability and presence of weak
mesoscale boundaries to help provide for a focus, scattered to
numerous showers and storms are forecast to develop thru the
course of the day. In addition to frequent lightning activity and
brief strong wind gusts, some of the storms will be quite
efficient in dropping locally heavy rains in a short period of
time. This could lead to some isolated cases of mainly nuisance
type flooding over areas subject to poor drainage during heavier
rain occurrences. Forecasters taper off the PoPs going into this
evening.
In the meantime, Alberto over the northwest Caribbean, is
forecast by the National Hurricane Center to begin lifting slowly
northward thru the Yucatan Channel today and emerge into the
southern Gulf tonight. Well north of Alberto, there are
indications that rain bands will begin to spread north and west up
across the coastal waters late tonight. considering this, an
increase in PoPs is aligned along the western Florida Gulf coast
late.
SHORT TERM /Sunday Through Monday night/...Sub-Topical Storm
Alberto will be the big impact player during the short term as it
lifts northward over the southeast Gulf Sunday. The track bends
more to the northwest by Monday. There will be a multitude of
impacts related to Alberto. For specific information on all of
these, including the latest thinking from the National Hurricane
Center on track, please refer to the National weather Service
Mobile AL web site at www.weather.gov/mob.
LONG TERM /Tuesday Through Friday/...Sub-Topical Storm
Alberto continues to be the big impact player early in the long
term as it comes ashore somewhere along the central Gulf coast
early Tuesday morning. The center of Alberto is progged to be
positioned over west central AL Tuesday night, then begin lifting
northeast across the TN River Valley on Wednesday. As the effects
of Alberto begin to move away by mid and late week, chances of
showers and storms taper back to more seasonable then. /10
The following is a breakdown of impacts and confidence levels for
each:
- Flash Flood Threat - Confidence: HIGH. Timing: This evening
through Tuesday evening. Significant rainfall amounts of 6 to 12
inches remain unchanged through this time period, especially
closer to the coast and over our southeastern counties. 5 to 8
inches over portions of the interior. Note: Some areas could see
localized double these amounts. The Flash Flood Watch has been
extended northward as the threat of excessive rain has increased
in latest excessive rain outlooks by the weather prediction
center.
- Storm Surge - Confidence: HIGH. Timing: This evening through
Tuesday. A Storm Surge Watch is in effect for all local coastal
zones, where 2 to 4 feet above ground level (or inundation) is
expected. The timing of maximum coastal water rises looks to be
Sunday night into Monday night.
- High Surf - Confidence: HIGH. Timing: This evening through
Tuesday. Surf heights of 5 to 9 feet will result in pounding
waves and resultant beach erosion. Surf heights could build
upwards of 8 to 12 feet with higher sets possible by Monday. A
High Surf Advisory will likely be required on later forecasts.
- Rip Currents - Confidence: HIGH. A high risk of dangerous to
potentially deadly rip currents remains in effect through the
period.
- Wind - Confidence: HIGH. Timing: Sunday through Tuesday. Given
current track and forecast strength. A Tropical Storm Watch
remains in effect for the entire coast line.
- Severe Storm Potential - Confidence: Low. Timing: Beginning as
early as this evening then increasing potential through Sunday
night into Memorial Day.
MARINE...Sub-tropical Storm Alberto will bring impacts to the
marine area by way of strong winds, high seas over the open Gulf
waters and building waves over area bays and sounds. /10
&&
.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Flash Flood Watch from this evening through Tuesday evening for
ALZ052-053-055-056-059-060-261>266.
Tropical Storm Watch for ALZ263>266.
High Rip Current Risk through Tuesday morning for ALZ265-266.
High Surf Advisory from 1 PM this afternoon to 7 PM CDT Tuesday
for ALZ263>266.
FL...Flash Flood Watch from this evening through Tuesday evening for
FLZ201>206.
Tropical Storm Watch for FLZ202-204-206.
High Rip Current Risk through Tuesday morning for FLZ202-204-206.
High Surf Advisory from 1 PM this afternoon to 7 PM CDT Tuesday
for FLZ202-204-206.
MS...Flash Flood Watch from this evening through Tuesday evening for
MSZ076-078-079.
GM...Tropical Storm Watch for GMZ630>636-650-655-670-675.
&&
$$
This product is also available on the web at:
http://weather.gov/mob
