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Office: MFR
FXUS66 KMFR 050525
AFDMFR
Area Forecast Discussion
National Weather Service Medford OR
1025 PM PDT Sat May 4 2024
...New Aviation Section...
.AVIATION (06Z TAFs)...
Precipitation has diminished across the region, but expecting
isolated showers to pick back up around sunrise and continue
through the day. The hard part is timing if the terminals will be
impacted or not, but due to isolated nature will go with vicinity
mention for now unless it becomes clearer for impacts at the
terminals. Otherwise, terminals should be mostly VFR with stints
of MVFR. Confidence was not high enough to introduce IFR at this
time, but low level saturation could lead to brief periods of IFR
and may need to be reevaluated tonight if confidence increases in
timing.
-Guerrero
&&
.PREV DISCUSSION... /Issued 839 PM PDT Sat May 4 2024/
DISCUSSION...An upper low is moving onshore into the region this
evening as our recent wet front finally exits. Precipitation has
become scattered and showery this evening. Showers will start to
decrease in coverage tonight but see a re-surgence tomorrow
(Sunday) morning as the low spins another round of moisture into
the region. Cold temperatures from the low will lead to snow
levels continuing to fall slightly to 2,500-3,000 feet early
Sunday morning before rising again Sunday afternoon. This will
also lead to chilly morning temperatures, and a Freeze Warning for
the Shasta and Scott valleys in northern CA is in place from 2 AM
to 8 AM Sunday. For more details, please see the previous
discussion below. -CSP
AVIATION...05/00Z TAFs...A strong frontal system has mostly passed
through the region this afternoon, but low pressure following the
main frontal band will lead to intermittent, showery precipitation
continuing for most of the weekend. Widespread MVFR conditions and
terrain obscurations are expected to continue, though some
improvement to VFR tonight is expected in areas, including the Rogue
Valley. This improvement may not be linear, with conditions bouncing
between MVFR and VFR. Snow levels will continue to lower this
evening and tonight, and rain showers will transition to snow east
of the Cascades. Winds will continue to be gusty along the coast and
east of the Cascades with the low pressure. Precipitation will begin
tapering off later Sunday afternoon and conditions are expected to
improve area wide. -CSP
MARINE...Updated 830 PM Saturday, May 4, 2024...Showers will
dissipate through this evening, with a very low chance for a
thunderstorm before sunset. Isolated showers are expected to
redevelop tomorrow around sunrise and go throughout the day.
Moderate west winds and steep fresh short period west swell will
continue through tonight, then southwest winds increase Sunday
ahead of another front that will move through late Sunday night
into Monday. Seas are likely to remain elevated Monday night into
Tuesday with building west-northwest swell. After that, we expect
high pressure to build in mid-late next week with a thermal trough
strengthening along the coast. This will bring a return of
stronger north winds and steep seas, highest south of Cape Blanco.
PREV DISCUSSION... /Issued 234 PM PDT Sat May 4 2024/
SHORT TERM...Through Tuesday morning...A low pressure system
continues to bring activity across northern California and southern
Oregon. Reports have indicated 2 to 3 inches of rain along the
Oregon coast in the past 24 hours, as well as 4 inches of snow in
areas around Mount Shasta. The main band of rainfall is moving
across Klamath and Lake counties while scattered showers continue
west of the Cascades. Existing daytime hazards have all expired, as
elevated winds over east side areas have slowed and the heaviest
snowfall over western Siskiyou County and the Cascades has passed.
Other hazards will continue through the night. Instability from the
low pressure system brings the possibility of thunderstorms through
the night tonight. Current chances are at 20-25% across areas west
of the Cascades, with lower 10-20% chances to the east. These
chances will remain into the last hours of Saturday before
decreasing through Sunday morning.
Additionally, a Freeze Watch has been elevated into a Freeze Warning
for the Shasta and Scott Valleys in Siskiyou County. Temperatures in
these valleys are forecast to be in the high 20s to low 30s tonight
into early Sunday morning. The Freeze Warning will be in place from
2 AM until 8 AM on Sunday morning. Other areas, including the
Illinois Valley and the southern Rogue Valley, may see temperatures
at or near freezing. But the possibility of substantial periods of
freezing temperatures are low (10-20%), so warnings were not issued
for these areas. Near-freezing temperatures in the mid-30s are
forecast, so extra care for sensitive plants and animals may still
be beneficial.
The low pressure system will follow the Oregon-California border
through Sunday, keeping cooler temperatures and precipitation in the
Forecast for Sunday. Snow levels are expected to rise to about 4000
feet, limiting snowfall to the Cascades and the highest terrain to
the east. Thunderstorm chances are not in the forecast.
A warm front will follow behind the low pressure system on Monday,
bringing another round of precipitation across the area. This front
looks to be non-impactful, with some limited thunderstorm chances
over Klamath and Lake counties on Monday evening. Precipitation
will be highest over the Cascades, with 3 to 6 inches of snow
forecast over the Cascades and unremarkable rainfall amounts over
lower elevations.
-TAD
Long Term...Tuesday (05/07) through Saturday (05/11)...The
extended period starts as "third winter" comes to an end, and a
familiar pattern of high pressure builds in. During this period of
high pressure strong, gusty north winds will be present along the
coast and east winds will develop inland. The warm bubble around
Brookings due to the Chetco effect is expected to be on display at
the end of the work week.
This diurnal pattern of wind flow will bring in drier air to the
region, but the magnitude of the warmth will be limited. The current
forecast calls for the heat to peak either Friday or Saturday in the
low to mid 80s and overnight lows barely scraping into the upper 40s
or low 50s. The reason for this low peak in high temperatures
appears to be a retrograding low pressure center, which is expected
to undercut the ridge as it moves in from around Utah.
-Miles
AVIATION...05/00Z TAFs...A strong frontal system has mostly passed
through the region this afternoon, but low pressure following the
main frontal band will lead to intermittent, showery precipitation
continuing for most of the weekend. Widespread MVFR conditions and
terrain obscurations are expected to continue, though some
improvement to VFR tonight is expected in areas, including the Rogue
Valley. This improvement may not be linear, with conditions bouncing
between MVFR and VFR. Snow levels will continue to lower this
evening and tonight, and rain showers will transition to snow east
of the Cascades. Winds will continue to be gusty along the coast and
east of the Cascades with the low pressure. Precipitation will begin
tapering off later Sunday afternoon and conditions are expected to
improve area wide. -CSP
MARINE...Updated 200 PM Saturday, May 4, 2024...Showers will
dissipate through this evening, with a very low chance for a
thunderstorm before sunset. Moderate west winds and steep fresh
short period west swell will continue through tonight, then
southwest winds increase Sunday ahead of another front that will
move through late Sunday night into Monday. Seas are likely to
remain elevated Monday night into Tuesday with building west-
northwest swell. After that, we expect high pressure to build in mid-
late next week with a thermal trough strengthening along the coast.
This will bring a return of stronger north winds and steep seas,
highest south of Cape Blanco. -BPN
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...Freeze Warning from 2 AM to 8 AM PDT Sunday for CAZ080-081.
PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT Monday
for PZZ350-356-370-376.
&&
$$
Office: PQR
FXUS66 KPQR 050439
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
939 PM PDT Sat May 4 2024
.SYNOPSIS...
Steady light to moderate rain will continue across the
lowlands of SW Washington and NW Oregon through Sunday with
light to moderate snow over the Cascades above 4000 feet.
Travel impacts in the Cascades will largely occur tonight into
Sunday morning when road temperatures become cool enough for
snow to stick. Another round of rain and Cascades snow is
expected Monday as the next system moves onshore, with post-
frontal showers lingering into Tuesday. A significant warming
and drying trend is expected later in the week as high pressure
builds over the region.
&&
.SHORT TERM...through Tuesday...Radar imagery shows showers
continuing across NW Oregon and SW Washington this afternoon.
The surface front has pushed into eastern Oregon through the
morning with satellite imagery indicating the associated upper
closed low pressure system approaching the Oregon/California
border. Ensemble guidance remains in solid agreement that the
closed low will move onshore along the Oregon/California border
this evening, moving slowly east through northern California
into Nevada tonight through Sunday morning. NW Oregon and SW
Washington is currently situated on the northeastern side of the
closed low and will remain on the north side of this closed low
through Sunday. Enough moisture will wrap around this low to
allow precipitation to continue across the region through
Sunday. The heaviest bought of precipitation for most locations
should taper off tonight and become lighter as the region
transitions from the northeast to north side of the low except
for over the Cascades where orographics will keep precipitation
more steady. The following precipitation amounts have been
recorded since rain began Friday: 1.25 to 2.5 inches along the
coast and Coast Range, 0.75 to 2 inches in the lowland valleys,
and 0.4 to 1.5 inches for the Cascades and adjacent western
foothills. Highest amounts have been roughly in and south of
Lincoln County. Additional QPF amounts through 5pm Monday are as
follows: 0.5 to 2 inches along the coast and Coast Range, 0.5
to 1.25 inches in the interior lowlands, and 1 to 3 inches along
the Cascades and adjacent foothills.
Since this is a colder weather system, snow levels have lowered
to around 4000 feet this morning and will lower to around
3000-4000 feet tonight through Sunday. Webcams show snow did
begin right around 10am this morning over mountain passes.
However, as of 2pm, a limited amount of snow seems to be
sticking to roads due to warm road temperatures lingering. Only
in the past hour do webcams show slushy snow beginning to stick
along Willamette Pass. As temperatures remain cool this
afternoon and lower overnight, expect more snow to begin
accumulating along roadways. Despite the higher QPF for the
Cascade passes, snow accumulations should remain fairly low for
the passes due to the marginal thermal profile and resulting low
snow-to- liquid ratios. By far, the most significant deviations
our forecast makes from NBM were in the snow-to- liquid ratios
(SLRs). Our SLRs were largely based on the more reasonable WPC
guidance, though we lowered the SLRs 10-15% from even the WPC
guidance (and 30-40% below NBM guidance). This was necessary to
get the SLRs below 10:1 for the passes, where NBM was showing
SLRs in the 13:1 to 16:1 for the passes and even higher than
that for higher elevations. Such SLRs would be difficult to
achieve for the passes even in the middle of winter, much less
the middle of spring. Even then, a Winter Weather Advisory
remains in effect through 6 pm Sunday as at least 4 to 8 inches
of snow are expected at pass level. NBM and HREF (SLR of 10:1)
indicate a 60-90% probability of at least 8 inches above 4000
feet generally along and south of Highway 20 through 5pm Sunday.
Since the snow ratios on both these are both a bit high, would
expect 8 inches to be the higher end of snow accumulation at the
passes, with up to 14 inches above 5000 feet.
A relative lull in precipitation is possible Sunday night except
for lingering Cascades showers as the upper low and its
deformation zone shift into the Rockies. However, ensembles are
in good agreement that a shortwave trough and reinforcing cold
front will move onshore Monday morning, bringing another round
of widespread precipitation Monday night through Monday
afternoon with post- frontal showers persisting through Tuesday.
Upper level flow will be westerly with this system which will
lead to quite a bit less accumulation in the lowlands (0.5-0.25
inch) than the Cascades (0.5-1 inch). Snow levels will remain
around 3500-4000 feet with lower SLRs, so a few more inches of
snow is possible over passes. Temperatures will remain below
seasonal normal, with lowland highs stuck in the 50s through
Tuesday. -HEC/Weagle
.LONG TERM...Wednesday through Friday...Ensemble guidance
confidence is high for a rapid shift in the weather pattern from
cool and wet to warm and dry. This abrupt shift is the result
of an upper level ridge that is set to build over the region,
and all four clusters shown in WPC's 500 mb cluster analysis
depict this ridge with varying amplitudes. The deterministic NBM
currently suggests lowland highs in the 60s Wednesday, 70s
Thursday (except 60s at the coast), and 80s Friday (except low
70s at the coast). The coolest model solutions are similar to
the NBM 10th percentile, showing inland high temperatures
peaking in the mid to upper 70s on Friday. Meanwhile, the
warmest model solutions show highs near 90 degrees for the
inland valleys. Either way, temperatures will be running above
normal for this time of year by Thursday. The probability for
high temperatures at or above 80 degrees on Friday has raised to
75-90% across the interior lowlands, which is quite high for a
forecast that is six days out. Overall, the warmest temperatures
of the year so far are likely to occur late this week high
confidence this pattern will continue into at least Saturday.
This may draw some people to area rivers and/or lakes, but keep
in mind water temperatures are still very cold and river
currents will be swift with mountain snowmelt. If you make
plans near area waterways, be very vigilant and wear a life
vest as cold water shock and hypothermia will be a very real
risk for anyone who goes into the water. -TK/HEC
&&
.AVIATION...An upper level trough across southern ORegon/northern
California continues to support a surface low now located across
eastern Oregon. Precipitation has lightened up but will
continue as wrap-around moisture continues to move into
northwest Oregon and and southwest Washington. Conditions range
from VFR to IFR and guidance suggests sub-VFR conditions
developing or persisting at all terminals by 12Z and persisting
into early Sunday afternoon. There is a small (10-30%) chance of
IFR CIGs developing between 12-20Z but confidence is low at
this time. Winds are generally westerly across the coast and
southerly along the interior valley at 5-10 knots and will
maintain these relative directions and speeds through Sunday.
PDX AND APPROACHES...A mix of VFR/MVFR conditions will drop to all
MVFR as the night continues. There is a 40-80% chance of MVFR CIGs
developing by 12Z. Light rain is expected to continue but
shouldn't bring VIS below VFR. S/SW winds between 5-10 knots will
continue into Sunday afternoon. -Batz
&&
.MARINE...The active weather pattern continues into early next
week before a shift to generally calmer conditions and a more
summer-like pattern. A broad upper level low off the far
southern Oregon coast will continue to progress inland into
northern California tonight leading to a decrease in 15 to 25
knot gusts over the waters (highest beyond 10nm) and subsiding
seas. After a quick break the next frontal system arrives Sunday
bringing another round of gusts up to 25 kt as well as steep
seas across most of the waters Sunday morning through Monday
morning. Following this front high pressure over the east-
northeast Pacific begins build over the waters and bring breezy
west to northwest winds (gusting 20-25 kt) across the waters
later Monday into Tuesday. Also expect the arrival of a pounced
WNW 9-11 ft swell at ~12 seconds Monday night. The high pressure
shifts closer to the waters later next week followed by a
larger offshore component to the wind in the Friday/Saturday
timeframe. -Schuldt
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 6 PM PDT Sunday for ORZ126>128.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210-
251>253-271>273.
Small Craft Advisory from 11 AM Sunday to 8 AM PDT Monday for
PZZ251-271.
Small Craft Advisory from 5 AM Sunday to 8 AM PDT Monday for
PZZ252-253-272-273.
&&
$$
www.weather.gov/portland
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Office: PDT
FXUS66 KPDT 050505
AFDPDT
Area Forecast Discussion
National Weather Service Pendleton OR
1005 PM PDT Sat May 4 2024
Updated Aviation Discussion
.AVIATION...06z TAFs...Light to moderate rain showers will impact
all sites through the period, leading to MVFR and even IFR
conditions at times as showers lead to reduced cigs and even
lowered vsby's at times. The bulk of the rain associated with this
ongoing weather system is expected to occur during the overnight
hours, with locally heavy showers possible for PDT and ALW around
sunrise Sunday. Elsewhere, showers will be of a lighter intensity,
however cigs for most of the period are expected to be bkn-ovc
between 2 and 7 kft. Rain chances will end earliest across sites
near the Cascades, spreading eastward throughout the period,
before rain is largely expected to end for all sites by nightfall
Sunday night. Winds will remain gusty at times as well, peaking
during the day Sunday as many sites see westerly gusts up to 35
kts, especially DLS and PDT. Evans/74
&&
.PREV DISCUSSION... /issued 854 PM PDT Sat May 4 2024/
EVENING UPDATE...A wet and windy 24 hours is in store for the
forecast area as a deep low pressure system continues to move
onshore right around the Oregon/California coastline. The main
band of wraparound moisture has been late to materialize based on
what models originally foresaw, but latest radar imagery this
evening shows the band finally starting to develop, with much of
the forecast area expected to be enveloped with rain by midnight
tonight, gradually spreading northward as we head into tomorrow
morning.
Latest HREF has come in a bit wetter than previous runs, with the
latest CAMs putting quite the bullseye over the Oregon Basin early
tomorrow morning. NBM QPF is not quite as bullish, but this wrap
around banding does have the potential to produce pretty
respectful amounts of moisture potentially exceeding half an inch
by tomorrow afternoon in the Oregon Basin. Whether that actually
materializes is another question, as CAMs have been a bit off with
regards to the start of rainfall, but did update QPF based on
latest HREF as well as recent trends.
Overall messaging with the winds and mountain snow remains the
same. Webcams show accumulating snow starting to occur over the
Oregon Cascade passes, with snow expected to spread into the John
Day/Ochoco Highlands as this oncoming low pulls in colder air into
the forecast area. Wind gusts also look fairly consistent compared
to the latest HREF. Overall changes to the forecast package
focused primarily on updating PoPs to reflect the drier-than-
anticipated conditions this evening, but that is expected to
change quickly as this band of wraparound moisture is expected to
materialize overnight. Evans/74
PREV DISCUSSION... /issued 443 PM PDT Sat May 4 2024/
SHORT TERM...Tonight through Monday night...A deep low currently
centered about 130 miles west of Coos Bay has brought widespread
overcast skies and a band of light precipitation over south
central WA and north central OR since early this morning. This
weak deformation band is only a precursor to a stronger band
from the Cascades westward where numerous rainfall amounts of 1-2
inches have been observed over the past 24 hours. This is all
associated with an AR in the range of 500-600 kg m-1 s-1 aimed
directly over the OR Cascades. Areas east of the Cascades will not
observe as much precipitation as this band tracks to the east,
but this is definitely one to bring above average rainfall to the
area. For the next 24 hours, many areas will have 0.25-0.75" and
locally around 1". The east slopes of the OR Cascades have already
received 0.25-0.5" already, and the Mt. Wilson RAWS site in Wasco
County measured 0.78".
A Winter Weather Advisory is in effect for the Cascade east
slopes of OR above 4000 feet (public zone OR509) through 11 AM
Sunday. Based on current temperatures and dewpoints, the snow
levels in OR509 are around 5000 feet--a little higher than
previously expected. However, temperatures at Santiam Pass are in
the mid 30s and precipitation will soon change over the snow as
snow levels fall to around 3500 feet tonight. As the low travels
to the ESE, colder air behind the system will cause snow levels to
lower to around 3500-4500 feet over the southern Blues (public
zone OR503) and the John Day- Ochoco Highlands (public zone
OR506). A Winter Weather Advisory is also in effect for OR506
above 4000 feet tonight through 11 PM Sunday. OR503 will have snow
accumulations around 3-6 inches, but mainly along the higher
peaks. The only location along HWY395 with several inches of snow
in the forecast is Long Creek Mountain. The northern Blue Mtns
will also have around 3-6 inches of snow, but mainly above 5000
feet which includes Tollgate. There are no plans to issue any
Winter Weather Advisories for the Blue Mtns. It's important to
note that the probability progs from the NBM and HREF use a 10:1
ratio which will indicate higher than the current forecast, as
10:1 is a little too high with our warm temperatures we have
observed today.
The upper low will weaken as it travels east across southern OR
and NV and into southern ID tomorrow. This will be followed by a
northwest flow aloft Sunday night. Precipitation will decrease
during this time, but numerous snow and rain showers will continue
over the mountains and valleys. Snow levels will be around
3500-4500 feet. A second system will follow as a shortwave trough
on Monday, keeping snow levels down around 4000 feet along with
light orographic showers. Even though QPF and snow amounts will be
light, snow covered roads in early May will catch some unprepared
travelers by surprise and this will be addressed the next couple
of days. The air mass will be marginally unstable, and an isolated
thunderstorm cannot be ruled out, mainly over southeast OR.
Not only will forecasters focus on precipitation amounts and snow,
but wind is another concern. A Wind Advisory is in effect Monday
for many areas across south central WA and north central OR.
Surface gradients have been tight today, and the increasing winds
aloft and tighter gradients on Sunday will result in very windy
conditions gusting to 45-50 mph. Confidence in the wind advisory
is around 80% but warning criteria (i.e. 58 mph or stronger gusts)
is low (20%). Wister/85
LONG TERM...Tuesday through Saturday...Cool, breezy, and showery
weather is forecast on Tuesday with a significant warming and drying
trend through the remainder of the period, especially Thursday
through Saturday.
Synoptic Overview: The period will start out on Tuesday with a broad
upper-level closed low downstream over the Great Plains and an upper-
level ridge building in upstream offshore in the Pacific. This will
place the forecast area under a cool northwest flow with light rain
and snow showers forecast for the mountains. Wednesday, flow aloft
turns north to northeast, and any lingering shower activity will
likely be confined to the northeast mountains, mainly in Wallowa
County. Thursday, ensemble guidance is in excellent agreement that
the low downstream over the Great Plains will eject eastward with a
piece of shortwave energy likely (>80% chance) facilitating the
formation of another closed low over the Great Basin into
California. Ensemble clusters show some spread in solutions
regarding the development and evolution of the closed low over
California, primarily with regard to the magnitude of the 500-mb
heights over northern California and southern Oregon. Pattern
details aside, all clusters are advertising some flavor of a Rex
block pattern setting up Thursday and persisting through Friday
(>80% chance) or Saturday (75-80% chance). This will favor a warming
trend as the upper-level ridge/high sets up over the PacNW to the
north of the closed low. There is a low chance (22% of members) that
the closed low will migrate far enough north over NW CA/SE OR that
showers will develop on Saturday over the mountains (mainly the
Blues.
Regarding the chances of any watches, warnings, or advisories, the
NBM is suggesting a 60-95% chance of advisory-level winds Tuesday
for the Kittitas Valley, Simcoe Highlands, Columbia Gorge, foothills
of the Blue Mountains of Oregon, and portions of the lower Columbia
Basin of Oregon.
The probability of maximum temperatures exceeding 80 degrees
increases Thursday, Friday, and Saturday (peaking Saturday at 60-90%
chance for the Columbia Basin and adjacent valleys and foothills).
Moreover, the Columbia Basin and Yakima Valley have a 45-65% chance
of highs exceeding 85 degrees on Saturday, and there is a very low
chance of exceeding 90 degrees (<15% chance). While NWS HeatRisk
values increase Thursday, Friday, and Saturday, they are currently
forecast to stay at a category 1 (minor). This level of heat
primarily affects individuals extremely sensitive to heat,
especially when outdoors without effective cooling and/or adequate
hydration. The chance of any heat-related highlights is extremely
low (<5% chance). Plunkett/86
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 39 50 40 56 / 100 90 70 60
ALW 44 52 44 58 / 90 80 80 60
PSC 47 59 47 65 / 80 90 40 20
YKM 44 61 39 63 / 40 60 10 20
HRI 42 56 43 62 / 100 90 40 40
ELN 45 58 40 60 / 40 40 20 20
RDM 33 49 34 52 / 70 70 10 60
LGD 39 48 38 52 / 100 80 90 80
GCD 34 44 35 50 / 90 100 70 90
DLS 45 57 46 57 / 90 70 30 50
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 2 AM to 11 PM PDT Sunday for ORZ041-044-507-
508-510.
Winter Weather Advisory until 11 PM PDT Sunday for ORZ506.
Winter Weather Advisory until 11 AM PDT Sunday for ORZ509.
WA...Wind Advisory from 2 AM to 11 PM PDT Sunday for WAZ024-521.
&&
$$
SHORT TERM...74
LONG TERM....86
AVIATION...74
