Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/12/17
Area Forecast Discussion
National Weather Service Denver/Boulder CO
712 PM MDT Mon Sep 11 2017
.UPDATE...
Issued at 712 PM MDT Mon Sep 11 2017
A weak upper level low spinning over central Wyoming has helped
trigger showers and thunderstorms over south central Wyoming and
north central Colorado. Elsewhere, isolated to scattered convection
has formed over the higher terrain and across the eastern plains.
Not much has occurred over the Urban Corridor. General trend has
been decreasing convection across the area. Adjusted pops to line
up with the current trends.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 340 PM MDT Mon Sep 11 2017
Dirty upper ridge remains anchored over the central Rocky Mtn region
with the upper high sitting over srn Colorado. Moisture trapped
beneath the ridge as indicated by integrated PW values in the 0.70-
0.80 inch range around here. Gentle upslope pressure gradient across
the high plains will continue to move low-level moisture up against
the Front Range and along the Palmer Divide for the remainder of the
afternoon. Diabatic heating has been slow and steady today due to
variable cloud cover, but with more sun than clouds past hour, CIN
has given way to CAPE as evident by the isolated showers popping up
over Elbert and lincoln Counties. Meanwhile the line of showers and
isolated t-storms along the South Platte River downstream from
Greeley earlier today have pretty much fallen apart. In the high
country, convection is now well underway, notably up along the
Continental Divide. A weak upper air disturbance in light w-nwly
flow aloft now spinning over swrn Wyoming/nwrn Colorado and clearly
discernible on GOES-16 6.19 um WV imagery, is progged to translate
sewrd over our nrn mtns ranges later this afternoon and ern sections
of the forecast area this evening. NAM latches onto this feature and
generates around an inch of pcpn over Park County by mid-evening,
with lesser amounts extending across the Denver metro area and
northeast to Washington County. GFS and the HiRes models show about
the same idea, but amounts are much lower. Although the HRRR and to
some extent show a line of storms moving off foothills around 00z
with the passing u/a disturbance. They indicate anywhere from 0.20
to around a half inch of rain from them, with the WRF indicating
around 0.75 inch of rain over Douglas County. The timing and
eastward progression of these showers/t-storms appears reasonable,
but amounts look overdone. See cutting these amounts in half, if not
more than that since models have been overdoing QPF quite a bit the
past few days. While the shortwave swings very slowly southeastward
over the area overnight, the convection rolling off the foothills
appears to fizzle out just east of the I-25 urban corridor by mid to
late evening. On the back side, should see gradual clearing late,
except over far sern sections of the CWA in the vicinity of the
shortwave. Looking for lows tonight similar to those last night.
For Tuesday...the shortwave mentioned above should move southeast of
the CWA by mid morning bringing most of the mid-level cloudiness
with it. Meanwhile, the upper ridge begins a slow westward migration
placing the fcst area under a slightly stronger and somewhat drier
northwest flow aloft. Flow will also be more stable with slight
warming above 500 mbs. Therefore, should see less shower/t-storm
coverage tomorrow, esply on the plains. Don`t expect to see too many
storms drifting off the high terrain with south-southeast storm
motions. Highs tomorrow should be about the same as today, and still
several degs above the seasonal norm.
.LONG TERM...(Tuesday night through Monday)
Issued at 340 PM MDT Mon Sep 11 2017
Models continue to forecast a change in the upper air pattern over
the western U.S. which will begin bringing more precipitation to
the state. The first system to move over the state will be the
upper level circulation which is currently off the northern
California coast. It will be in the process of shearing out as it
gets drawn into increasing southwesterly flow aloft across the
Great Basin. This disturbance will cross over the state Thursday
night and Friday morning. A stronger trough is expected to follow
right on the heels of the first system and move over Colorado
Saturday night and Sunday. This system will have a pretty good
shot of cold temperatures aloft, bringing much cooler temperatures
by Sunday. At this time, the ECMWF is more aggressive than the GFS
with this system. Have therefore favored the GFS solution when it
comes to temperatures. Afternoon and evening showers are going to
become the pattern each day of the forecast period, as these two
systems affect the weather starting as early as Wednesday
afternoon and continuing through Sunday. The amount of cold air
that the second trough brings with it will determine whether or
not the mountains see any snowfall Sunday morning. Will wait to
see if later runs of the ECMWF continue to bring the cold
temperatures with the latter trough. After all, it is getting to
be the latter half of September.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 712 PM MDT Mon Sep 11 2017
Can`t totally rule out a thunderstorm affecting a Denver airport
through 05Z, however chances are very low, less than 10 percent.
Outflow from convection on the eastern plains may produce one more
wind shift. Eventually winds will settle at a southerly direction
by 06Z. On Tuesday, light winds in the morning will become south-
southeast. Chances for a thunderstorm will be very low Tuesday
due to a drier airmass.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Meier
SHORT TERM...Baker
LONG TERM...Dankers
AVIATION...Meier
Area Forecast Discussion
National Weather Service Glasgow MT
905 PM MDT Mon Sep 11 2017
.SHORT TERM...for northeast Montana...tonight through Tue...
Update:
Quiet weather is expected tonight with mainly clear skies and
light winds allowing for efficient radiational cooling even as
850mb temperatures rise. Given this information, expect much of
the forecast area to see lows a few degrees higher than last
night. However, some deeper valleys where more drainage can occur
could see low temperatures reach the 40s. Maliawco
Previous Discussion:
Today, the Rocky Mountain and High Plains ridge of high pressure
is rebuilding and expanding through the region - bringing warmer
temperatures and drier humidity to most locations.
For the most part, the short term forecast is rather benign. The
major forecast challenge revolves around the impact of haze and
smoke drifting into NE Montana from western wildfires. Some
reduced visibilities in Glasgow and Miles City seem to confirm
this thinking. Online HRRR smoke plume model shows some of this
coming in on the SW surface winds through tonight and part of
tomorrow. Temperatures tomorrow should be very similar to today,
ahead of an approaching large-scale low pressure trough, set to
change the seasons through the latter part of the week.
BMickelson
.LONG TERM...Tue night through Mon...
Attention continues to be drawn to this period as a major shift in
the pattern occurs. Cooler temperatures are a certainty, but how
much rainfall occurs continues to be a question. Models are coming
into agreement with things and blended current low but good qpf
forecast grids to 12z models, as models tend to out run reality
this far out. The wettest period for our area looks to be Thursday
Night where about a quarter to a third of an inch is what we are
expecting today. Stay tuned to changes as we go through the week.
TFJ
Previous Discussion...
Weather change expected past midweek to cooler and potentially
wetter conditions with a strong upper low moving across the
region. Main question mark for eastern Montana will be how much
rain to expect if any.
Upper trof begins digging south from BC into the Pacific Northwest
on Tuesday night with upper flow turning southwest and lee trof
beginning to form in central Montana. Low level winds turn briefly
southeast across the plains but moisture feed appears to be
limited due to blocking by the remnants of Irma over the mid-
Mississippi valley.
Cooler air continues to filter south as the trof digs into the
northern Rockies. Pacific moisture also continues to spread across
the divide in the southwest flow aloft. Dynamics and upper level
moisture in place for a good rain event from around Wednesday
afternoon through Saturday morning, with the current focus on
Thursday night over eastern Montana. With current drought
conditions and weak low level moisture flux, along with known wet
bias of the models, undercut the qpf for the region by quite a
bit. With the cool conditions expected Thursday night, RH should
increase enough to allow rain to reach the ground.
Ridge begins to rebound by late in the weekend, with another
upper trof approaching for the middle of next week. Ebert
&&
.AVIATION...
VFR conditions are expected tonight with light winds. A little
haze and smoke from upstream wildfires will likely not be enough
to reduce visibility. Do expect that winds will increase from the
northwest at 10 to 15 kts on Tuesday morning. Maliawco
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
weather.gov/glasgow
Area Forecast Discussion
National Weather Service Hastings NE
630 PM CDT Mon Sep 11 2017
.SHORT TERM...(This evening through Tuesday)
Issued at 219 PM CDT Mon Sep 11 2017
Potentially Hazards Weather: None.
Aloft: RAP analyses of the tropopause along with aircraft/
sounding obs reveal the Westerlies were far the N over Canada.
While there were many features over/near the CONUS...the only ones
of immediate interest to the fcst here are the ridge/subtropical
high over the Rockies and a shear-induced barotropic vort max over
WY. A small high will develop over SD/Neb tonight and gradually
drift E thru tomorrow...while the WY vort max slowly drifts E as
well. By tomorrow afternoon it will be over Wrn SD and the Neb
Panhandle.
Surface: The tail end of a Canadian cool front was near the
SD/Neb border. It will dissipate tonight leaving high pres E of
the rgn dominating the wx here thru tomorrow.
Rest of this afternoon: Sunny and very warm. Highs will peak
around 4 PM.
The subtle tail end of the shortwave trof well to the NE of the
rgn has resulted in persistent weak spotty mid-lvl shwrs from the
Sandhills SW into CO. The forcing for these shwrs is extremely
subtle and it is very uncertain what happens to these shwrs. For
now the fcst is dry...but there is a very slight chance some of
these shwrs (and more likely sprinkles) could meander into the NW
fringe of the CWA (LXN-ODX). The good things is movement is very
slow. So they could dissipate before ever reaching the CWA.
Tonight: M/clear with very light/calm winds. Temps a little above
normal.
.LONG TERM...(Tuesday night through Monday)
Issued at 219 PM CDT Mon Sep 11 2017
Potentially Hazards Weather: some tstms possible Tue night and
then again at times Thu-Sun...and maybe Mon.
The Westerlies will be progressive thru this weekend. That means
the longwave trof currently over the NE Pac will move into the Wrn
USA Wed. Amplification will occur due to upstream adjustments
over the Bering Sea...forcing the trof to dig and a low to form in
vicinity of ID/UT/NV by Fri. This will draw the cut-off low
(currently off CA) northward and weaken it. The remaining vort max
is currently slated to move thru here Fri. Overall the last 2
runs of the EC/GFS/CMC/UKMET are in agreement on this scenario...
along with the EC/GFS ensemble means. This low is fcst to lift NE
into the Canadian Prairies this weekend. For the fcst here...the
vort max currently over WY will move thru Neb Tue night. The Wrn
ridge moves in Thu...then its SW flow thru the weekend with one
or more vort maxima moving thru or nearby.
At the sfc...S flow will gradually strengthen as the week
progresses with a strong cool front fcst to slide thru late Fri-
early Sat.
Rain: spotty tstm potential exists at times...but the best chance
for some beefier tstms clusters that could put down some good rain
is slated for Sat night. The fcst probably doesn`t fully depict
the real potential for rain just yet due to modeling blending in
Thu-Mon. POPs are likely to increase for some time frames.
Typically...an upr low moving well NW of the CWA is not good for
much rain here...but slow movement of the front is in our favor.
Temps will be warmer than normal...slowly creeping upward and
peaking Fri. Then a BIG cooldown next weekend. Our fcst most
likely does not fully depict how cool Sat could be just yet. It
depends on when the front moves thru. Sat could be a transition
day.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 629 PM CDT Mon Sep 11 2017
VFR conditions are forecast through the forecast period for both
KGRI and KEAR with light winds.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&
$$
SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...NOAA/NWS/Moritz
Area Forecast Discussion
National Weather Service Green Bay WI
959 PM CDT Mon Sep 11 2017
Updated aviation portion for 06Z TAF issuance
and new information added to update section
.UPDATE...
Issued at 949 PM CDT Mon Sep 11 2017
Have increased fog coverage across north central and far northeast
WI, issued a Special Weather Statement for potentially hazardous
travel through the Tuesday morning commute, and updated the
Hazardous Weather Outlook.
The fog will develop in the shallow cool air in the wake of a weak
cold frontal passage overnight.
Also allowing the Small Craft Advisory and Beach Hazard Statements
to expire at 10 pm.
&&
.SHORT TERM...Tonight and Tuesday
Issued at 250 PM CDT Mon Sep 11 2017
The latest RAP analysis and satellite/radar imagery show high
pressure centered over the eastern Great Lakes, but extending west
into the mid-Mississippi Valley. Meanwhile, a weak cold front is
moving southeast over northern Minnesota and remains void of any
precip early this afternoon due to a dry and stable airmass in
place over the western Great Lakes. As this front moves across the
region, cloud trends and fog potential are the main forecast
concerns.
Tonight...The front will move into north-central WI late in the
evening or early overnight, then into central and northeast WI late
tonight. The atmosphere will remain too dry for precip. But low
level moisture will increase along the front, which is already
evident by dewpoints rising into the low to mid 50s across the area
this afternoon. With winds becoming calm, will have a decent setup
for the development of ground fog late. There was not much fog
upstream early this morning, but they also had a scattered to broken
mid-level cloud deck overhead. Will increase patchy fog coverage.
Lows ranging from the mid 40s near the U.P. border to the mid 50s
over the southern Fox Valley.
Tuesday...Once morning fog burns off, should have few to scattered
cu pop with heating of the day over central and east-central WI,
where the front is projected to wash out. Northern WI should enjoy
mostly clear skies. Low level temps will continue to warm, which
should bring highs into the upper 70s to lower 80s, but cooler near
the Lake.
.LONG TERM...Tuesday Night Through Monday
Issued at 250 PM CDT Mon Sep 11 2017
With the westerlies to the north and an upper low to
the south, upper ridging is forecast to continue across Wisconsin
through the end of the week. This should provide dry weather with
temperatures about ten degrees above normal. Some showers and
thunderstorms are possible Saturday night and Sunday as an upper
trough and surface cold front approach the region.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 949 PM CDT Mon Sep 11 2017
The main aviation concern will be fog development overnight into
early Tuesday. The fog will be most prevalent in north central and
far northeast WI, where a shallow cool air mass will settle in
the wake of a weak cold frontal passage. Will probably see
IFR/LIFR conditions in this region, with patchy VLIFR conditions
in dense fog. Farther southeast, only expect spotty MVFR/IFR
vsbys. The fog should mix out by around 14z/Tuesday.
Aside from the fog, mainly VFR conditions are anticipated, along
with light winds.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE.........Kieckbusch
SHORT TERM.....MPC
LONG TERM......RDM
AVIATION.......Kieckbusch
Area Forecast Discussion
National Weather Service Indianapolis IN
1145 PM EDT Mon Sep 11 2017
.UPDATE...
The AVIATION Section has been updated below.
&&
.SYNOPSIS...
Issued at 348 PM EDT Mon Sep 11 2017
Beginning late tonight and continuing at times into Thursday, the
remnants of Hurricane Irma will bring chances for showers to
central Indiana. Temperatures will remain cool. Friday and into
next weekend, the departure of the trough associated with Irma
will allow an upper ridge to build into the area, bringing dry
weather and warmer temperatures back to the area.
&&
.NEAR TERM /Tonight/...
Issued at 906 PM EDT Mon Sep 11 2017
Short range model guidance suggests the more organized lift
probably won`t reach the far southern zones until at least around
sunrise Tuesday, and possibly later. This evening`s upper air
indicates the air mass is quite dry up to about the 400mb level.
As a result, will trim back the PoPs during the pre dawn hours on
Tuesday to more towards sunrise and restrict them more towards the
far south.
Satellite indicates high level cloud cover is quite thick, so will
go more pessimistic on the cloud cover tonight.
Previous discussion follows.
Ample cloud cover streaming into the area today as Irma moves into
Georgia. Irma will continue to steadily weaken overnight and push
into the Tennessee Valley. Latest HRRR runs suggest precipitation
from Irma will reach the southern forecast area near daybreak, and
thus will carry low pops across the south the last few hours of
the night tonight.
Consensus temperatures appeared reasonable given low level thermal
progs and were generally accepted.
&&
.SHORT TERM /Tuesday through Thursday/...
Issued at 348 PM EDT Mon Sep 11 2017
Irma will continue to move into the central Mississippi Valley
Tuesday into Tuesday evening, before slowly pushing eastward as
the system begins to get drawn into the prevailing midlatitude
flow. As a result, mid to high chances for showers will be
required Tuesday into Wednesday, with chances ramping down
gradually Wednesday night into Thursday as the system departs.
Will carry only showers as thunder does not appear likely.
Precipitation amounts with the remnants of Irma are not expected
to be significant and should not pose a major threat to area
waterways.
Consensus temperatures continued to appear reasonable with minor
tweaks during the highest chances of precipitation mainly Tuesday
and Wednesday.
&&
.LONG TERM /Thursday Night Through Monday/...
Issued at 206 PM EDT Mon Sep 11 2017
Mainly quiet late summer weather will be expected during the
period. The ECMWF suggests the remnants of Irma will finally be
exiting the area to the northeast on Thursday night. This allows
strong ridging over the middle Mississippi valley to build
eastward across Indiana and the Ohio valley. This feature will
bring dry weather to Central Indiana for the weekend. Temperatures
this weekend will be warmer than last weekend though. The High
Pressure system associated with the ridge is expected to set up
over the northeastern United States...leading southerly flow
across Indiana. This will allow warmer and more humid gulf air
into Central Indiana.
The ECMWF then suggests an upper trough moving across the plains
states and pushing into the Great Lakes and Indiana on Sunday
Night and Monday. Forecast builder has included some pops
here...and this seems reasonable considering decent moisture that
should be in place ahead of the approaching dynamics.
&&
.AVIATION /Discussion for the 120600Z TAFS/...
Issued at 1145 PM EDT Mon Sep 11 2017
Ceilings above 050 expected through the midday hours of Tuesday.
Short term model data suggest organized lift will begin moving over
the terminals around the mid morning hours of Tuesday from the
south. As a result, there will be an increasing threat for some
shower activity in the vicinity of the terminals after that time. At
this point, it appears any precipitation will be light enough that
any visibility restrictions will be minimal.
Surface winds 040-060 degrees at 4-7 kts overnight will become 050-
070 degrees at 10-14 kts by midday Tuesday. Occasional surface gusts
around 18 kts possible as well.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...Nield
NEAR TERM...Nield/JAS
SHORT TERM...Nield
LONG TERM...Puma
AVIATION...JAS
Area Forecast Discussion
National Weather Service Reno NV
1255 PM PDT Mon Sep 11 2017
.SYNOPSIS...
Slow moving low pressure over California combined with above
normal moisture will produce good chances for showers and
thunderstorms each day through Wednesday. The first solid cold
front of the fall season will bring gusty winds Thursday followed
by much colder temperatures Friday into the weekend.
&&
.DISCUSSION...
* Stubborn upper low off the California coastline combined with
precipitable water anomalies 2-4 SD above normal will produce
daily chances for showers and thunderstorms through Wednesday.
Tough call however on which days could "go big" in terms of
storm intensity and coverage.
* Storm development today has been slow with the exception of
ongoing thunderstorm clusters over Inyo and Esmeralda Counties.
These are lifting NW and the HRRR picks up on this. Overall
expect these clusters plus additional development to favor the
Sierra and far W Nevada through the evening with a continued NW
motion. Instability is a bit on the weak side so storm intensity
may not get super strong, but the usual hazards of heavy rain,
lightning, gusty outflow winds, and small hail still apply.
* One quick diversion - there`s a definite haze in the air today
and it appears there`s a veil of high-altitude smoke
overspreading the region from fires in S Sierra. Latest near-
surface smoke models don`t show significant PM2.5 levels in our
region through tomorrow but some localized smoke impacts could
still occur with low predictability.
* Tuesday and Wednesday the ingredients are there for stronger
storms and flash flood concerns, but we may end up with a cloud-
over scenario with more showers vs storms either day. Forecast
precipitable water values, especially Tuesday, are getting high
enough to make me consider that. Will have to wait to see how
the early morning environment looks before tipping the scales
one way or the other.
* Upper low finally scoots out of here Thursday but at the same
time a larger trough coming out of the NE Pacific drops in.
This will bring an increase in wind ahead of the associated cold
front. Nothing outrageous but widespread gusts on the order of
25-35 mph are possible. Showers along the cold front are looking
more likely for Thursday and could become widespread.
* Temperatures Friday into the weekend are expected to be below
normal, a big change from the last few months of record heat.
Possibly well below normal if ECMWF verifies. GFS even has the
700mb 0C line down to Minden Friday morning. While not unheard
of for this time of year, long-term averages typically don`t
bring 700mb zero line down to Reno until late October or early
November. Could see some frost in typically cold Nevada and NE
California valleys Saturday and Sunday mornings, with freezes
for the mountain valleys. Plan ahead with this in mind for
outdoor activities Friday and this weekend.
* Looking further out for next week, there appears to be another
potent early-fall trough into the Pacific NW Monday-Tuesday in
both the GFS and ECMWF guidance. This could bring even stronger
winds to our region, along with light showers and another shot
of even cooler temperatures. Confidence remains medium on this
scenario since we`re still 7+ days out.
-Chris
&&
.AVIATION...
* Daily chances for showers and thunderstorms through Wednesday.
Hard to pin down which day will see the most coverage and
strongest cells. For late this afternoon and evening - MMH,
TRK, TVL have the highest risks for storms 40-50%, with RNO, CXP
at 30%. Chances increase Tuesday and Wednesday with broad
40-60% probabilities for showers and storms at any given point.
* Impacts look to be: temporary 1-3 hour MVFR-IFR
ceilings/visibility in SHRA or TSRA, erratic outflow winds to
40 kts, frequent lightning, and small hail.
* Cold front through the region Thursday will bring more showers,
mountain obscuration, and increased winds with mountain wave
turbulence. Some of that may persist into Friday morning, before
a big improvement in flying conditions Friday afternoon through
the coming weekend with lighter winds and VFR conditions.
-Chris
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno
Area Forecast Discussion
National Weather Service Seattle WA
825 PM PDT Mon Sep 11 2017
.SYNOPSIS...A ridge of high pressure over the area will break
down tonight and Tuesday as an upper level trough approaches the
area from the northwest and a weakening frontal system moves into
the area. Expect an increase in morning clouds and fog Tuesday
across the lowlands. An upper trough and onshore flow will result
in cooler conditions Tuesday through Thursday. A ridge of high
pressure will build into the area Friday through Saturday giving
some warming and less cloud cover.
&&
.SHORT TERM...Upper level high pressure over the area is weakening
this evening as weakening cold front extending southwest from
about Central Vancouver Island, and an associated upper trough
over the eastern Gulf of Alaska, drops southeastward. The
incoming front and trough are mainly dry.
Infrared and multispectral satellite imagery this evening shows
stratus and some fog from about the NW tip of Vancouver Island
southwestward moving into the area. The latest HRRR and NAM12
solutions generally show the fog and stratus remaining over the
coastal zones and through the Strait of Juan de Fuca, while the
University of Washington WRFGFS solution and statistical guidance
from the NAM and GFS show more extensive stratus and some fog
moving into most of the interior lowlands Tuesday morning. The
forecast will be updated to include the areas of fog, especially
near the inland waters, Tuesday morning.
Expect temperatures to fall to near or below normal for Tuesday
through Thursday with the air mass change. Highs are expected to
be only in the 60s to around 70 and lows in the 40s to lower 50s.
It looks like fall is here! The high temperature of 80 that
occurred at SeaTac airport today may be the last one for this
year as climatology shows that after mid-September, the 80 degree
mark becomes very difficult to reach due to the shortening days
and lower sun angles.
The incoming front and upper trough do not have much moisture or
lift, so conditions are expected to remain rather dry, perhaps
just a few showers. Albrecht
Key messages in the short term:
1) Temperatures will be near or slightly below normal Tuesday
through Thursday.
2) A few showers will be around the area Wednesday
into Thursday, but nothing significant.
.LONG TERM...From the previous long term discussion: Following
the trough exiting southeast of the area by late Thursday and into
Friday, ridging is expected to quickly build back in from the
west. However the ridging is not extreme, and will probably only
push high temps back to near or slightly above normal by Saturday.
Then the focus will shift to the potential for a more substantial
low pressure system by late Sunday and into Monday. The timing
was different between the GFS and ECMWF in earlier runs, but this
mornings guidance depicts that rain would arrive during the day
Sunday and so have increased pops on Sunday and reduced high
temperatures.
Key Messages in the long term
A more substantial rainfall possible by Sunday into Monday.
&&
.AVIATION...Westerly flow aloft will increase late tonight and
Tuesday as an upper level trough in the Gulf of Alaska pushes
gradually southeastward. At the surface, low level onshore flow
will increase on Tuesday behind a dissipating frontal system. The
air mass is dry and stable. The lower levels will moisten somewhat
late tonight into Tuesday in the onshore flow behind the front
while the air mass above about 5000 ft MSL remains mainly dry.
Infrared and multispectral satellite imagery show stratus or fog
extending southwestward from Cape Flattery early this evening. The
latest HRRR and 00Z NAM solutions continue to show this low level
moisture pushing into the coastal zones late tonight through
Tuesday morning with some pushing eastward through the Strait and
into Admiralty Inlet and Whidbey Island, but not into the interior
zones. The University of Washington WRFGFS solution as well as
guidance from the NAM and 18Z GFS show more fog and stratus in the
interior. All models show the fog and stratus burning back to the
coastal zones by mid afternoon.
The previous forecast took the more foggy and cloudy route, and
that forecast will be maintained. Albrecht
KSEA...Clear skies, northerly breeze. Expect fog and LIFR stratus
to move into the terminal about 13Z, then to lift to an MVFR
stratus about 17Z. The northerly wind speeds late tonight through
Tuesday morning are expected to be less than 5 knots. Albrecht
&&
.MARINE...Onshore gradients are producing small craft advisory
westerly flow in the eastern two thirds of the Strait of Juan de
Fuca. Northwesterly winds of 10 to 20 knots are occurring over the
coastal waters. Expect the winds to ease overnight as the remnants
of an old frontal system extending southwestward from Central
Vancouver Island moves into the waters.
While the front will dissipate as it moves southeastward Tuesday
morning, expect pressures to fall east of the Cascades during the
day on Tuesday as an upper level trough moves into the region.
This will result in the development of stronger onshore flow late
Tuesday afternoon through about Thursday. A small craft advisory
will likely need to be issued for Tuesday afternoon and evening
for the eastern two thirds of the Strait of Juan de Fuca and for
the coastal waters with the forecast package late tonight.
Albrecht
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Tuesday for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca.
&&
$$
www.weather.gov/seattle
You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html