Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/03/21
Area Forecast Discussion
National Weather Service Des Moines IA
546 PM CST Sat Jan 2 2021
...Updated Aviation Discussion...
.SHORT TERM.../Tonight through Sunday Night/
Issued at 202 PM CST Sat Jan 2 2021
Confidence: Medium to High
Main challenge again tonight will be fog potential and the manner
on how this all plays out has lowered the forecast confidence a
bit. Though weak area of low pressure southwest of Iowa today will
be backing in high to mid level clouds over the southeast this
evening, there is little change in the overall light wind pattern
and weak ridge of high pressure situated across the area. In fact,
by 06z through 12z we are lift with nearly the same conditions
over the region as this morning with just a bit of a push of warm
air aloft from the west southwest. This warmer air aloft will
likely strengthen the inversion over the west and along with the
ridge, help to promote additional areas of fog overnight once
again. The HRRR continues to be bullish with fog over the entire
region again tonight. It was a bit overzealous last night,
however. Overall, the same areas from southwest to north central
and a bit farther east are likely to see fog again first tonight
with a few spots taking longer for the fog to initially develop -
most likely around the metro and areas east and southeast where
dewpoint depressions remain larger late this afternoon. Will be
issuing an advisory for all of the forecast area given that most,
if not all should have some areas of dense fog by mid to late
evening and through portions of Sunday. Fog is already backing
into our area near Marshalltown and Waterloo. The ending time of
the advisory is somewhat problematic, but given that today the
thicker fog either never lifted or took to at least 18z... most of
the surrounding offices and us decided to at least continue the
advisory to 18z. It may actually take longer to lift tomorrow in
some areas. Winds will remain light with little mixing Sunday and
this will likely keep the fog around. Tonight lows will once again
bottom out in the single digits and have lowered readings;
especially in the east and in the river valley areas. Sunday is
showing warming aloft by late day, but it may again be a challenge
to burn off all the fog soon enough to bring highs up to
expectation. Have made minor adjustments to the going forecast
today and expect mid 20s east to the upper 20s/lower 30s central
and south. By Sunday night, a more persistent push of warmer air
will be directed into Iowa with light southwest surface winds as
well as increasing southwest flow aloft. This should act to lessen
any risk for areas of fog overnight into early Monday morning.
Along with that, overnight lows will generally be in the upper
teens to lower/mid 20s.
.LONG TERM.../Monday through Saturday/
Issued at 202 PM CST Sat Jan 2 2021
Confidence: Medium With Decreasing Confidence by Wednesday
Another in a series of weak, generally moisture starved waves
will pass over the region early Monday morning. The only real
impact will be a wind shift and a slightly near-neutral, cooler
push of air across the north northeast for the day. Otherwise,
slightly milder air will continue to move over the region from the
west. The model guidance is beginning to shade highs into the 40s
across the south for the day, but snow cover should cut back on
afternoon readings somewhat Monday as melting increases. We
continue this cycle between ridges/approaching weak troughs nearly
every 24 hours through at least Tuesday morning. Though the
impacts from large storms will be nil through Tuesday, we`ll
probably have another chance at fog Monday night into Tuesday
morning if sufficient melting occurs Monday night. Tuesday
remains quiet ahead of the approaching system. Both the Euro/GFS
area in some agreement to continue the warming trend with milder
south winds keeping highs warmer into Tuesday.
Looking into the midweek system next week still brings many
challenges. A look at the last 3 GEFs packages` precip
accumulation ensembles shows that the trends have been for
55%/40%/70% of runs showing central Iowa with higher accumulating
qpf; so the trends are continuing to bounce around, but are
increasing. The GFS has been holding onto an initial more
northerly amplification of the wave- pair in the northern/southern
stream while the Euro is trending to develop the southern wave
initially faster, with more a split configuration across Iowa.
Eventually, by 00z Thursday both models are favoring a low just
south of Iowa but even then some differences in location will play
a huge part in how much precipitation we receive. Along with the
location, precipitation types will then need to be parsed out with
time as well. Currently, the ensemble guidance supports some
solutions with precipitation and will leave slight to chance PoP
for now and continue to evaluate any trends in the next day or
two. At least there is improving confidence as the system departs
with another cold front approaching the region by Friday. Some
differences remain in the amount of available moisture and
expected light precipitation. The Euro is bringing across a bit
more light snow than the GFS deterministic by Friday. Overall next
week will be at or above normal for highs with only a slight cool
down on Saturday. Normal highs range from the mid 20s north to
the lower 30s south and the region will be averaging around 30
north to the mid to upper 30s in the south through the period.
.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 546 PM CST Sat Jan 2 2021
Dense fog to continue at MCW and ALO and is expected to thicken
elsewhere across central Iowa later tonight into Sunday morning.
High confidence in the long duration LIFR visibility from the
dense fog, just lower confidence when it`ll actually settle in
over DSM, OTM and FOD this evening. Once it does thicken, it looks
to linger for much of the Sunday morning and even MVFR visibility
into the afternoon hours seems highly probable. Medium to high
confidence in the IFR/LIFR ceilings as expect them to bounce
between the two flight categories.
Dense Fog Advisory until noon CST Sunday for IAZ004>007-015>017-
Minimal changes from the previous forecast discussion, with the
exception of increasing confidence of the timing of next weeks
storms system. Used mostly Pops from WPC with NBM lagging behind
the latest updates from deterministic model runs. Rain showers
are expected to move in by Thursday morning and exit mostly on
Friday. Some snow will also be possible with some wrap around
precip, but with discrepancies with the timing of the system and
lingering moisture, we went with rain/snow mix with minimal
forecast snow accumulations Friday morning. Previous discussion
LONG TERM /Sunday Night through Friday/...
The beginning of the extended period will be characterized by a dry
airmass behind the exiting cold front. Relative humidity values are
expected to drop into the upper 20s and 30s across the area and
precipitable water values will be limited to 0.5 inches or less.
Temperatures will also start the period near or just above
climatological normals, with morning lows mainly in the 30s and
afternoon highs mainly in the 50s to low 60s. A fast-moving upper-
level shortwave will traverse the Tennessee Valley on Monday
morning. However, considering the limited moisture over the region,
very little to no impact will be observed over north and central
Georgia from this disturbance. As the disturbance continues to move
eastward to the mid-Atlantic coast, upper-level ridging will build
in over the southeastern CONUS on Tuesday and remain in place
through late Wednesday. A surface high associated with this ridge
will lead to continued clear skies and a gradual warming trend
In the later part of the week a synoptic trough will set up over the
eastern CONUS, bringing another storm system to the area on Thursday
and Friday. Some model discrepancies remain with the evolution and
timing of this system, and ultimately the impacts to our forecast
area. The latest GFS and ECMWF both develop a closed-off low in the
ArkLaTex region on Thursday, which extends a cold front towards the
forecast area. However, the models diverge on the speed at which the
cold front and associated precipitation approaches north and central
Georgia, with timing discrepancies still up to 12 hours in the
guidance. Considering the lingering uncertainty with respect to this
system, rain chances remain limited to chance PoPs across the
majority of north and central Georgia during the day on Thursday and
into early Friday. The chance also remains for light snow showers
and a light rain/snow mix across far northeast Georgia on Thursday
night and into Friday morning due to wraparound moisture behind the
system and below freezing temperatures in the far north behind the
cold front. However, the potential for frozen precipitation will
need to be monitored as model guidance trends towards better
Expect some return of IFR/MVFR ceilings mainly after 02z with
abundant low level moisture. Main area of rain should continue
to push east of KMCN and KAHN overnight...although isolated
showers are possible elsewhere. Fairly quick improvement and
scattering after 14z Sunday behind the upper system with
increased west to northwest winds 9-12 kts gusting up to 20 kts.
//ATL Confidence...00Z Update...
Medium on overall cigs/precip trends.
High on all else.
.PRELIMINARY POINT TEMPS/POPS...
Athens 43 53 34 58 / 50 5 0 0
Atlanta 40 51 34 56 / 20 5 0 0
Blairsville 37 44 29 50 / 30 10 0 0
Cartersville 39 50 30 56 / 20 5 0 0
Columbus 40 56 35 60 / 40 0 0 0
Gainesville 41 50 34 56 / 30 5 0 0
Macon 44 57 34 61 / 70 5 0 0
Rome 39 51 30 58 / 10 10 0 0
Peachtree City 38 52 32 58 / 30 5 0 0
Vidalia 51 60 38 60 / 100 5 0 0
Area Forecast Discussion
National Weather Service Fort Worth TX
554 PM CST Sat Jan 2 2021
...New Short Term, Aviation...
.SHORT TERM... /NEW/
/Through Sunday Evening/
Light south/southwest winds and sunny skies allowed afternoon
temperatures to climb a tad higher than forecast this afternoon,
with several of the western zones topping out around 60. Dry air
and light winds should still lead to a good radiational cooling
night with lows in the 30s area-wide. Temperature/dewpoint
spreads will approach zero during the pre-dawn hours across the
northwest zones, and patchy fog has been added in those areas for
Meanwhile, water vapor imagery reveals one shortwave near Memphis
and moving away from the area, while another is beginning to take
shape near the Nebraska/Colorado state line. The lee-surface
cyclone induced by the upstream wave will move into northwest
Texas overnight into Sunday. The resulting pressure gradient will
increase southwest winds to 10-15 MPH during the day Sunday. This
should allow Sunday temperatures to climb into the 60s for all
but the northwest, where lingering fog will keep conditions quite
a bit cooler.
The entire system will move quickly southeast through the Plains,
dragging a cold front through the area Sunday afternoon and
evening. Northwest winds around 10 MPH behind the front will
become light and variable Sunday night, likely setting up the area
for a more widespread round of radiation fog.
.LONG TERM... /Issued 304 PM CST Sat Jan 2 2021/
/Sunday night through next weekend/
Expect another cold night Sunday night with lows in the upper 20s
across the far western zones to low/mid 30s elsewhere. One issue we
will have to monitor is the potential for fog/stratus to develop
across parts of North Texas during this time period. Some of the
deterministic models like the HRRR and NAM continue to be more
aggressive with the fog/stratus, and even NBM probabilities are
showing reduced visibilties or low clouds through Monday morning.
Surface winds will be calm or light enough to support the fog
and/or low clouds, but moisture is expected to be limited and
shallow. Confidence is not high enough to include it in the
forecast at this time, but we can`t rule some patchy ground fog
especially along the Red River counties. We will have to keep an
eye on the latest trends through tomorrow.
Otherwise, a pretty quiet start of the week with above normal temps
thru Wednesday. As a surface high pressure and an upper ridge moves
over the region, we will enjoy nice temperatures (60s) under mostly
clear skies. Winds will shift to the south on Tuesday as the next
trough/upper low moves across the Rockies. Overall forecast details
about this system have not changed much, with the best potential for
showers and isolated storms east of I-35 Wednesday afternoon.
Despite the uncertainties on the track of the low, ensemble
analysis show a more progressive pattern keeping the best lift
north of our area. For now, we kept PoPs between 20% and 30%
mainly across East TX. Instability is forecast to be fairly weak,
but we can`t rule out some isolated storms. No severe storms are
Due to the Pacific nature of this system, we don`t anticipate a
extreme drop in temperatures. Our mid-late week forecast include
nice temperatures, no rain, and north winds. Highs will stay on the
cool side ranging from the low 50s across North TX to upper 50s to
low 60s across Central TX. Overnight lows will drop into the 30s to
near 40s each night.
It looks like our next rainmaker will arrive sometime next weekend.
As expected, long range models diverge on the progression of the
upper trough, but overall consensus show a slight chance of
precipitation either Saturday night or next Sunday.
Light south winds will increase to 10-15 kt after 15Z Sunday ahead
of the next cold front. FROPA in the DFW area looks to be around
22Z Sunday, then just after 00Z Monday for KACT. Northwest winds
around 10 kt can be expected behind the front. Winds will become
light Sunday night as high pressure enters the area, which could
lead to for formation after 06Z Sunday, and may need to be
addressed in future forecasts.
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 36 60 34 62 36 / 0 0 0 0 0
Waco 36 66 34 63 36 / 0 0 0 0 0
Paris 33 58 32 59 33 / 0 0 0 0 0
Denton 33 57 29 63 31 / 0 0 0 0 0
McKinney 33 58 32 61 33 / 0 0 0 0 0
Dallas 37 61 36 63 38 / 0 0 0 0 0
Terrell 34 61 32 61 33 / 0 0 0 0 0
Corsicana 37 63 37 63 38 / 0 0 0 0 0
Temple 34 66 34 64 36 / 0 0 0 0 0
Mineral Wells 32 54 29 62 33 / 0 0 0 0 0
Area Forecast Discussion
National Weather Service Lincoln IL
824 PM CST Sat Jan 2 2021
Issued at 305 PM CST Sat Jan 2 2021
Light drizzle will continue to impact the region through the
evening as the next weather system moves through the area tonight.
This will bring another chance for accumulating snowfall to
location se of the Illinois River Valley, with upwards of 2 inches
by Sunday morning. The best chance for snowfall exists across
eastern Illinois, while locations in central Illinois will see
upwards of 1 inch. Cloudy skies will also persist through the
overnight, along with the return of dense fog conditions northwest
of the I-55 corridor. Behind this system, High pressure arrives to
end the weekend and begin next week.
Issued at 824 PM CST Sat Jan 2 2021
Evening water vapor imagery shows our upper low located south of
St. Louis, with a noticeable curl in the radar imagery over that
area. Not a significant amount of precip shown on radar mosaics,
likely due to the beam overshooting in this low cloud regime.
Local radar in the more sensitive coverage pattern does show an
increase in light snow and drizzle over central Illinois in the
last 20 minutes or so. HRRR suggests a more organized increase in
snow as we get closer to 06Z and the upper low moves into southern
Illinois, with the focus continuing to be in the Bloomington to
Decatur area and east, with amounts of 1-2 inches. No significant
changes being made to the snow amounts in the forecast at this
Regarding the fog advisory, there is some concern about the
eastern extent of it, and high-res guidance showing more of a
focus after midnight extending east into the Illinois River
valley. Lower visibilities along I-55 may be more from the snow
versus the fog, as visibility thus far north of the low have been
more in the 1 to 2 mile range on the lower end and the dense fog
has been near Quincy. Will continue to monitor this over the next
.SHORT TERM...(This evening through Sunday)
ISSUED AT 305 PM CST Sat Jan 2 2021
Low clouds continue to impact the Midwest as more moisture is
ushered into the region tonight. This is evident on radar as light
bands of precip are currently pushing through the state. As this
evening progresses, the upper level Low pressure system will track
towards the Ohio River Valley from the lower Mississippi River
Valley. This will track mostly snowfall through the region
overnight, as temperatures will drop below freezing after sunset.
Some light mixed precip could occur to begin, south of the I-70
corridor, as temps are slightly above freezing...however this will
change to snowfall as the Low passes south of the area.
With winds coming out of the ne currently, low clouds are expected
to linger throughout the overnight into the morning. This will
finally begin to shift out of the area Sunday as winds shift to
the west behind Low pressure passage and exit. As with most winter
time clouds, expecting lingering low ceilings through Sunday
morning. Issued a Dense Fog Advisory for tonight through Sunday
morning, as these clouds are expected to persist throughout the
period. With the light winds lingering into Sunday morning, will
have the chance to hold the clouds in place. Only question this
afternoon was the possibility of clouds increasing as the Low
pressure slides through the region. Thinking was that it will be
far enough southeast that the low clouds and excessive moisture
would be enough to hold fog in place.
This system will slide out of the region Sunday, allowing for the
return of High pressure to the area.
.LONG TERM...(Sunday night through Saturday)
ISSUED AT 305 PM CST Sat Jan 2 2021
Weak High pressure slides through the Midwest late Sunday into the
start of the week. However there is some model depiction of
another weak frontal system to track through the upper Midwest
Monday night into Tuesday. This could swing another weak frontal
boundary through the region late Monday. The big question here
will be if there is enough moisture to spark a few showers
throughout the area. The best energy looks to be east of the
Midwest, however some models hint at a chance for precip.
Currently left the mention of any precip out of the forecast, as
this is a weak system, and not expected to bring any precip to the
area. Behind this boundary, a stronger High pressure system slides
into the area from the south. Unfortunately, this week`s setup
really will be a mixed bag.
Heading into mid-week, a large-scale Low pressure system develops
across the central Plains and tracks slowly eastward. This will
bring the next weather maker to the Midwest Wednesday evening
through Thursday. However, models do have some hint that this
system might slide south of the area, so there is some detail that
needs to be worked out over the next couple of days. If High
pressure takes dominance over eastern Canada mid-week, this will
help to push the system south of the Midwest Wednesday night,
moving the best chance for precip across the se US. If High
pressure cannot hold control, then this system is likely to slide
into the Tennessee Valley, which would provide some precip to
southern Illinois during the second half of the week.
Models have differing solutions heading into the weekend, so this
will need to be held of for now. But High pressure looks to take
control again, as of now Saturday looks dry.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 519 PM CST Sat Jan 2 2021
While widespread ceilings of a few hundred feet are present over
much of central Illinois, areas from KCMI east and south have
recently seen MVFR ceilings rise over 2,000 feet at times.
Deterioration there is expected later this evening as light snow
moves into the area, reducing visibilities down below a half mile.
Elsewhere, there has been some periods of light snow or drizzle
recently, but more widespread light snow is expected toward mid
evening. No real improvement in ceilings expected through the
period, though perhaps getting closer to 1,000 feet at KPIA/KBMI
westward Sunday afternoon.
Dense Fog Advisory until noon CST Sunday for ILZ027>031-036>038-
Area Forecast Discussion
National Weather Service Jacksonville FL
904 PM EST Sat Jan 2 2021
Mid to upper level trough over the srn U.S. will continue to push
the slow-moving cold front toward our area with a band of showers
and embedded thunderstorms. Latest radar trends over the past hour
or so has shown a general weakening trend of higher reflectivities
but broad low level southwest fetch and PWATs values approaching
1.8 inches will continue to lead to numerous to widespread rain
showers rest of tonight. Localized flooding is still possible but
the threat is low given the radar presentation. Light to moderate
showers still occurring in the flash flood watch area so will
keep the watch up through the 11 PM expiration at this time. Recent
lightning imagery showing no strikes but weak buoyancy and frontal
forcing could still result in a couple of isolated t-storms
through late tonight. HRRR shows the band of showers will continue
moving east and move off the southeast GA coast around 5 AM and
for the northeast FL coast by 8-9 AM. Current forecast handles
this well, and only minor adjustments made to the forecast. Min
temps may end up just slightly lower so adjusted southeast GA min
No change made at this time with marginal winds offshore from the
south ahead of the approaching front so will maintain SCEC
headline. Seas from nearshore buoys are in line with the current
forecast as well.
.PREV DISCUSSION [627 PM EST]...
.NEAR TERM [Through Tonight]...
A stalled front stretching from the northeastern Gulf into the Florida
Big Bend into southern Georgia has maintained a band of moderate
to briefly heavy showers mainly over our interior southeast
Georgia counties today. Troughing, associated with an upper low,
extends into the northern Gulf helping to reinvigorate convection
across our area by lifting shortwave energy from the Gulf of
Mexico along the frontal boundary. This will increase rainfall
intensity along with the chances for stronger thunderstorms with
gusty winds that will push out ahead of the boundary into inland
SE GA into the evening hours. A Flash Flood Watch is in effect
into this evening for portions of inland southeast Georgia. Around
1 to 2 inches of rainfall have fallen today. An additional 1 to 2
inches are expected in the watch area with locally higher amounts
possible. The trough will cause the front to move eastward
tonight and approach the Atlantic coast by Sunday morning. The
upper low driving this system will lift northeastward into the
Great Lakes which will lift much of the energy aloft away from the
region. This will bring an end to heavier rainfall after midnight
and a scattering of showers. Precip will begin to end from
northwest to southeast tonight. Cooler, drier air begins to filter
in behind the front allowing lows tonight to dip into the 50s
across southeast georgia and Suwannee Valley and the low 60s in
.SHORT TERM [Sunday Through Monday Night]...
A cold front exits the region by Sunday afternoon with scattered
lingering showers in the morning hours mainly south of
Jacksonville. Cooler, drier air filters into the region behind the
front. Low level ridging will build in over the southeast into
early next week in the wake of the cold front. Despite cooler air
advecting in, highs on Sunday will reach above climo with
increasing sunshine. Temperatures then drop to around climo with
lows in the upper 30s to low 40s and highs on Monday in the 60s.
.LONG TERM [Tuesday Through Friday]...
Surface high pressure over the lower Mississippi valley on Tuesday
will move northeastward and expand across the eastern CONUS
continuing dry weather for the region. Tuesday night into
Wednesday morning will be the coolest night with lingering cold
air advection and clear skies. Lows will be in the mid 30s inland
and patchy frost will be possible. Around mid-week, another upper
low will move into the Plains and develop the next cold front to
approach the region. The cold front will move through Thursday
night into Friday bringing chances for precipitation with its
passage. Temperatures will be above climo on Thursday with
southerly flow ahead of the front.
[Through 00Z Monday]
VFR at this time but expect showers and possible brief, isolated
embedded t-storm to move over southeast GA and northeast FL
tonight. Low cigs and vsby restrictions are expected at TAF sites
developing after midnight, with MVFR-IFR cigs and MVFR vsby at
times. Main period will be from about 06Z to 13Z period for the
precip and lowest cigs. We can`t rule out LIFR cig for 2-3 hrs
during this period. South-southwest winds 10 kt or less much of
tonight and then cold front moves thru around the 09Z to 12Z time
frame, shifting southwest winds to west. A chance of LLWS possible
around 08Z to 12Z Sunday, mainly over northeast FL, as a low
level jet strengthens just ahead of the cold front.
Clearing starts developing after about 14Z-15Z Sunday...with VFR
likely by 15Z to 18Z.
A cold front will move across the coastal waters tonight into
Sunday bringing showers and an isolated thunderstorm. Winds will
continue to linger around 15 to 20 knots over our offshore waters
through Sunday, then slacken behind the cold front. High pressure
will then build along the northern Gulf coast region early next
week, with a prevailing offshore flow.
Rip Currents: SE GA - low risk this weekend. NE FL - moderate
risk today, low risk tomorrow with offshore flow
A Flash Flood Watch is in effect for portions of inland southeast
Georgia into this evening. Around 1 to 2 inches of rainfall have
fallen today. An additional 1 to 2 inches are expected in the
watch area with locally higher amounts possible. Highest amounts
will likely be areas northwest of Jasper, FL, Waycross, GA, and
Jesup, GA. Some localized flooding possible with mainly ponding of
water on roads and creeks and streams rising out of their banks.
Expect significant river rises following the event for next week
on the main stem river basins.
.PRELIMINARY POINT TEMPS/POPS...
AMG 53 61 37 60 38 / 100 0 0 0 0
SSI 58 66 42 61 43 / 70 20 0 0 0
JAX 60 69 41 63 41 / 70 30 0 0 0
SGJ 62 70 44 63 43 / 70 50 0 0 0
GNV 60 69 39 64 37 / 80 30 0 0 0
OCF 62 70 42 66 39 / 70 30 0 0 0
FL...Flash Flood Watch until 11 PM EST this evening for Hamilton.
GA...Flash Flood Watch until 11 PM EST this evening for Appling-
Northern Ware-Pierce-Southern Ware-Wayne.
Area Forecast Discussion
National Weather Service Pendleton OR
254 PM PST Sat Jan 2 2021
Updated Aviation Discussion
.AVIATION...00z TAFs...VFR conditions expected through the TAF
period. Currently strong S to SW winds impacting most sites,
having gusted up to and over 30 kts already this afternoon. A
front will move through this evening and bring a chance of light
showers for most sites. MVFR conditions may briefly occur during
rainfall. Cigs will be bkn-ovc around 5-10 kft, decreasing to 4-5
kft overnight. Winds will decrease and cigs will lift and become
sct by daybreak Sunday. 74
.PREV DISCUSSION... /issued 115 PM PST Sat Jan 2 2021/
SHORT TERM...Tonight through Monday night. Active weather pattern
for the next few days. A cold front will move across the region
tonight bringing high mountain snow and windy conditions. Most of
the snow will be along the crest of the Cascades and over the Blue
Mountains where winter weather advisories remain in effect.
Considered upgrading to warning for the Blues above 4500 feet
where HREF is pinging some hefty snow amounts tonight but some of
the model guidance is suggesting that snow levels will rise above
5000 feet and NBM snow ratios are only about 8 to 1 which will
cut down on accumulation efficiency. Still the situation at the
snotels and Tollgate will need to be monitored through the
evening. Other concern is the wind. Models are emphatic in
showing limited mixing of the winds to the surface with the cold
frontal passage tonight. Thus have held off on issuing any
wind advisories except for the southern foothills where the HRRR
is showing some gusts AOA 50 mph tonight. Winds will diminish
quickly tomorrow and snow will end by 18Z. It will be a short
break as a warm front lifts north across the area Sunday night
spreading mountain snow across the region...with the biggest
impact over the east slopes of the Washington Cascades. High
mountain snow and valley rain will continue on Monday and as a
low pressure tracks across the region...strong winds will be
possible Monday afternoon and Monday night. 78
LONG TERM...Tuesday through Saturday...Organized trough will depart
our area early Tuesday, leaving behind dry conditions until a
southwesterly jet brings another round of valley rain and mountain
snow early Wednesday. Global ensembles varying a decent degree with
this system, but another few tenths of precip could fall given
potent moisture advection as depicted by deterministic GFS and
ECMWF. Snow levels will start at around 2000 ft early Tuesday,
gradually rising to above 3500-4000 ft as warm air noses into our
area via SW flow, before dropping off toward 2000-2500 ft by the end
of the long term period. As a result, wintry precip threat will
remain in the mountains, as the synoptic pattern favors generally
mild conditions given the time of year. Highs will start in the mid
to upper 40s Tuesday, dropping off toward the low 40s/upper 30s by
the end of the week. Lows will have trouble dropping below freezing
before next weekend due to abundant cloud cover expected given upper-
level flow pattern.
Deterministic guidance diverges a bit after Wednesday`s system, but
general pattern favors dry conditions outside of the Cascades, as
models back off on the strength of the flow aloft. Ensemble QPFs
generally agree with this, with generally dry weather beyond
Wednesday. ECMWF tries to bring in a trough by Friday, while
westerly flow continues within the GFS. Will stick with NBM for now,
which keeps most of the CWA outside the crests of the Cascades dry
and quiet Wednesday night through next weekend. 74
.PRELIMINARY POINT TEMPS/POPS...
PDT 41 50 39 50 / 40 50 40 70
ALW 44 50 41 51 / 60 60 50 80
PSC 42 52 40 51 / 30 20 40 60
YKM 33 48 33 45 / 60 10 80 90
HRI 41 52 40 53 / 30 30 40 60
ELN 30 43 32 42 / 60 10 80 90
RDM 37 49 38 50 / 40 50 30 70
LGD 36 43 34 43 / 80 70 50 90
GCD 37 46 37 47 / 70 50 40 80
DLS 40 49 39 49 / 80 50 80 90
OR...Wind Advisory until 7 AM PST Sunday for ORZ508.
Winter Weather Advisory until 10 AM PST Sunday for ORZ502-509.
WA...Winter Weather Advisory until 10 AM PST Sunday for WAZ030-520.
Area Forecast Discussion
National Weather Service Portland OR
155 PM PST Sat Jan 2 2021
.SYNOPSIS...An active weather pattern will continue through at least
the middle of next week. A cold front moves onshore late this evening
with increasing rain and wind. Another system impacts the area Sunday
and Sunday night, followed by addtional weather systems through
mid-week. A brief break in the action is expected Wednesday night or
Thursday, but a return to wet conditions is likely Friday.
.SHORT TERM...Tonight through Tuesday...Early afternoon GOES-17 water
vapor imagery revealed an upper level low pressure area just west of
Hadai Gwaii with an extensive moisture feed across the Pacific into
the Pacific Northwest fed by a strong west upper level jet.
Wind is the first weather concern. The 12Z 4km WRF-GFS has backed off
slightly regarding coastal wind. The 12Z run shows a swath of 50 kt
10m wind gusts along the coast 03Z Sun. By 06Z, this 50-kt core is
located from KTMK to K6S2. There is a dramatic wind shift associated
with the cold front immediately behind the south to southwesterly
wind core max. The current high wind warning timing for the coast
looks on track, but max wind gusts may end up a little lower than
forecast. The WRF-GFS and 19Z HRRR 80m wind product indicate 35-40 kt
gusts this evening through midnight for the Willamette Valley, mainly
south of KSLE. South to southwest wind ramps up in the north
Willamette Valley early this evening and gradually works south
through the remainder of the evening. The HRRR 80m wind gust product
and NBM wind gust forecast suggest 25-35 kt gusts for Clark County.
Will maintain the current advisory at this time. Wind speeds will
quickly drop off behind the cold front. Expect the cold front to
reach KAST around 06Z Sun, KPDX 09Z and KEUG 10Z to 111Z.
The other weather concern will be precipitation and potential hydro
issues. The ECMWF Precipitable water ensemble mean valid 00Z Sun
shows 1.0 to 1.2 inches. Combine this with 50-70 kt 850 mb southwest
flow into the Oregon Coast Range and southwest Washington Willapa
Hills and the result in impressive orographic lift. Per WPC Mesoscale
Precip Discussion, rainfall rates up to 0.5 inches per hour will be
possible on southwest-facing slopes in the higher terrain. In
addition, the GEFS ensemble mean Integrated Water Vapor Transport
(IVT) valid 06Z Sun shows a band of 500-700 kg/m/s directed into much
of the forecast area. The ECMWF IVT valid 06Z has slightly higher
values. Fortunately, this will be a fairly fast-moving cold front
such that these high rainfall rates should be short-lived. Rainfall
totals through early Sun morning will be on the order of 2 to 4
inches for the Oregon Coast Range, Willapa Hills and south Washington
Cascades. The expected QPF looks to be enough to result in minor
flooding on the Greys River. Thus, a flood watch has been issued.
Snow levels have risen to 5000 to 5500 feet early this afternoon per
the Astoria profiler. Snow levels are expected to lower to around
3000 feet overnight in the south Washington Cascades to near pass
level in the Lane County Cascades. However, the bulk of the
precipitation will have already occurred by the time snow levels
start falling. Expect total snowfall by Sun morning on the order of 6
to 12 inches above 5000 feet.
The cold front does not completely go away Sun. The remnants will
reside over southwest Oregon Sun morning and then transition to a
warm front Sun afternoon due to surface low development well
offshore. Rain will increase across the south part of the area late
Sun morning or early afternoon and then lift north. Another cold
front reaches the coast between 06Z and 12z Mon. The 12Z model runs
continue to struggle with the evolution and strength of the surface
low. The GFS has been insistent the past couple of runs developing a
compact sub-990 mb low pres center just west of Cape Arago 18Z Mon.
The NAM shows multiple low pres centers along the baroclinic
boundary, all of which are in the mid to upper 990s. The 12Z ECMWF
ensembles show a high variability regarding surface low placement and
strength. All of which leads to lower-than-average forecast
confidence. It appears a lull in the action occurs Mon night and most
of Tue, followed by another weather system nearing the coast late
The long period (18-19 seconds) westerly swell is expected to build
early this morning then last into the afternoon before slowly losing
energy as the dominant wave period drops to 16 to 17 seconds. This
supports keeping the High Surf Advisory for today, and also brings
an enhanced threat of sneakers waves. Weishaar
.LONG TERM...Tuesday night through Saturday...The active weather
pattern continues Tue night and Wed as the 12z deterministic runs are
in general agreement showing another weather system moving through
the area. Some of the model details differ, with the GFS suggesting
another possible coastal wind event while the ECMWF has a much weaker
pressure gradient. The ECMWF MSLP ensemble mean valid 00Z Thu
indicates weak ridging over the area while the deterministic GFS
shows a 980 mb low center near KUIL. Favor the ECMWF ensembles, which
line up reasonably well with the total mean 500 mb cluster analysis.
There is moderate confidence that Wed night through Thu will be
rather quiet, but not confidence enough to go completely dry. Model
discrepencies become more pronounced Fri and Sat. The 12Z model runs
show another frontal system moving into the area Fri. However, the
ECMWF shows a wide range of surface low solutions. The 12Z GFS
solution would suggest another possible high-wind event for the
coast. All in all, rather wet and mild conditions look to persist
through the extended period. Weishaar
.AVIATION...Conditions will get worse the rest of today as a
strong cold front approaches. Mix of MVFR and IFR along the
coast will persist, though cigs will lower a tad more. Southerly
winds will gust 40 to 50 kt, with strongest winds occurring
between 02Z and 07Z this evening. Cold front will push to Astoria
between 05Z and 06Z, then push gradually to the south to Newport
by 08Z. Winds will quickly ease behind the front, but MVFR CIGS
will persist rest of the night.
Farther inland, MVFR will dominate. Current VFR to south and east
of KMMV to KUAO line will gradually fall to MVFR by 02Z as rain
spreads farther southward. Will remain mostly MVFR overnight into
early Sun. Expect south winds gusting 25 to 35 kt at times for
most interior lowlands of Willamette Valley this evening, with
strongest winds between 03Z and 08Z. Also, expect southerly
gusts 40 to 45 kt over the higher ridges of Coast range and
Cascades through 08Z.
For detailed regional Pac NW weather information,
go online to: http://weather.gov/zse
KPDX AND APPROACHES...MVFR will persist tonight, with rain
through midnight. Will maintain breezy south winds, with gusts
20 to 30 kt at times through 08Z. Still think strongest of those
winds will be between 03Z and 07Z as cold front draws closer to
the region. Winds will ease quickly behind the front after
midnight. MVFR will persist through 14Z, with gradually
improvement to VFR with broken clouds Sun am. /Rockey
.MARINE...Deep low pressure over the southeast Gulf of Alaska
will persist for next several days, maintaining rather active
weather on the coastal waters.
Strong cold front offshore will push to the Washington coast
later this evening. As of 2 pm, southerly winds gusting 35 to 45
kt on the coastal waters, with seas running 20 to 21 feet. As
the front draws bit closer, should see boost in the winds, as
gradients tighten and strong winds aloft arrive. Current
expectation of storm force winds looks reasonable, so no changes.
Gusts 45 to 50 kt this evening. Cold front will drop to Astoria
between 9 and 10 pm, pushing southward and reaching Newport
around midnight, and past Florence by 1 or 2 am. Winds will
ease quickly behind the front. Seas will stay at 20 to 25 ft
range this evening, peaking between 8 pm and midnight.
Afterwards, winds much less overnight, with seas subsiding.
But, still a lot of long period westerly swell offshore, so will
maintain seas at 17 to 20 ft overnight through next several days.
More tranquil later tonight and Sunday, as region sits between
fronts. Warm front to the south will lift back to the north later
Sun afternoon and Sun night, with another round of strong gales.
May have to watch this, as models suggest some potential of storm
force gusts Sun night, especially south of Cascade Head. No
headlines yet, as have enough with current weather, but overnight
shifts will likely issue new gales or storm watch for Sun night.
OR...Winter Weather Advisory until 4 AM PST Sunday for Northern
Winter Weather Advisory from 10 PM this evening to 10 AM PST
Sunday for Cascades in Lane County.
Wind Advisory until midnight PST tonight for Central Willamette
Valley-Greater Portland Metro Area-South Willamette Valley.
High Surf Advisory until 4 PM PST Sunday for Central Oregon
Coast-North Oregon Coast.
High Wind Warning until 1 AM PST Sunday for Central Oregon
Coast-North Oregon Coast.
WA...Winter Weather Advisory until midnight PST tonight for South
Wind Advisory until midnight PST tonight for Greater Vancouver
High Wind Warning until 9 PM PST this evening for South
High Surf Advisory until 4 PM PST Sunday for South Washington
PZ...Storm Warning from 6 PM this evening to 1 AM PST Sunday for
coastal waters from Cape Shoalwater WA to Florence OR out
Gale Warning until 6 PM PST this evening for coastal waters
from Cape Shoalwater WA to Florence OR out 60 NM.
Small Craft Advisory until midnight PST Sunday night for
Columbia River Bar.
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