Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 212327
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
325 PM PST Tue Jan 21 2020


.SYNOPSIS...Showers will persist through the evening hours as the
postfrontal air briefly settles in. A warm front will then lift
northeast through the region Wednesday bringing another round of
widespread rain along with rising snow levels. A continued series of
embedded weak disturbances will continue training into the Pacific
Northwest later this week and through the weekend, which will
continue the rainy weather pattern.

&&

.SHORT TERM...Tonight through Friday...Showers will continue to
persist through the overnight hours as the post frontal air mass briefly
settles in tonight. Looking at the 500mb heights we can see the the
vort max outline of the upper level trough will move over the
Cascades by this evening. In addition 500mb heights over the area
will start to lift, this lifting will cause the overall energy of the
system to lower, which will cause the shower potential to slowly
decrease across the area. Multiple models are showing a weak warm
front moving across the area on Wednesday ahead of a developing ridge.
This will keep temperatures on the mild side, will raise snow levels
and keep the area covered with precipitation. Enough snow will fall
through Wednesday that the Winter Weather Advisory has been extended.
As the ridge develops over the area a more zonal flow pattern can be
seen in the 500mb level. A weak cold front along with some trailing
perturbations can be seen within this zonal flow pattern. There is a
suggestion among a few models that a band of precipitation will stall
over the area Thursday and Thursday night. Looking at guidance a
generally strong south/southwesterly flow pattern develops towards the
surface, which could bring a fair amount of precipitation to the area
through the latter part of this week. The amount of precipitation and
increasing snow levels could cause some hydrological issues late
Thursday into Friday. /42

.LONG TERM...Friday night through Tuesday...Overall, models
and their ensembles are in good agreement an active weather pattern
will continue to bring periods of valley rain and mountain snow for
much of the extended forecast period. Weak shortwave ridging over
the region early Friday evening appears likely to shift east of the
region quickly and will be replaced by shortwave troughing over the
northeast Pacific this weekend. This will result in a front
spreading widespread rain into the area late Friday night into early
Saturday. There is some hint among the models that a weak low
pressure may develop along the trailing front off the northern
California coast late Saturday. This would likely result in the
front and attendant band of rain stalling out Saturday night into
early Sunday. At this point, this appears most likely to happen
south of our CWA, but these have a tendency to drift northward with
time so it bears watching. Otherwise, the jet stream appears likely
to consolidate across the eastern Pacific early next week, which
will keep precipitation chances elevated. /Neuman

&&

.AVIATION...Post-frontal showers will continue chances for MVFR
cigs and gusty south winds this evening. Isolated thunderstorms
are possible over and west of the coast range early this
evening. The showers should become less frequent later this
evening for more widespread VFR conditions. A warm front will
increase rain overnight tonight with lowering CIGS and VSBY.
Expect mostly MVFR conditions Wednesday morning with pockets of
IFR associated with rain, fog, and low ceilings with the warm
front. Gusty south winds are expected along the coast Wednesday.

KPDX AND APPROACHES...Mostly VFR this evening with rain showers,
but an occasional heavier shower could result in brief MVFR
conditions at times. MVFR becomes more likely Wednesday morning
as rain increases with a warm front, and should continue through
Wednesday afternoon. Could see 15-20 kt gusts with the S-SE winds
Wednesday after 17z. ~TJ

&&

.MARINE...Gales have ended this afternoon, with solid small craft
conditions tonight through Wednesday morning. Seas have peaked
around 18 feet this afternoon and will subside to around 15 feet
by Wednesday morning.

A warm front moves south to north across the waters on Wednesday
with Gales filling in behind it. The front will stall north of
the waters keeping the gale conditions mostly south of the
Columbia River Bar, and small craft conditions offshore the
Columbia bar and northward. Visibilities may be low at times if
low clouds accompany the the warm front and rain. The seas will
remain around 15 feet through Wednesday night. Gales are
possible with the next front Wednesday night through Thursday
night. Seas will be between 12 and 14 feet Thursday.

A strong high tide may result in tidal overflow flooding for the
south Washington coast Thursday morning. The current forecast is
for a total tide of 11 feet which has historically resulted in
minor flooding for low lying areas. Since this tide is out 24+
hours will wait to see if the forecast continues to how the
possibility for at or below 11 feet before issuing a coastal
flood advisory. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Winter Weather Advisory until 10 PM PST this evening for South
     Washington Cascades.

PZ...Small Craft Advisory until 7 AM PST Wednesday for Coastal
     waters from Cascade Head to Florence OR out 10 NM-coastal
     waters from Cape Shoalwater WA to Florence OR from 10 to
     60 NM.

     Gale Warning from 7 AM to 4 PM PST Wednesday for Waters from
     Cape Shoalwater WA to Cascade Head OR from 10 to 60 NM.

     Gale Warning from 7 AM to 10 PM PST Wednesday for coastal
     waters from Cascade Head OR to Florence OR out 60 NM.

     Small Craft Advisory until 4 PM PST Wednesday for Columbia
     River Bar.

     Small Craft Advisory until 10 AM PST Wednesday for Coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 10
     NM.

     Gale Warning from 10 AM to 4 PM PST Wednesday for Coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 10
     NM.

&&


$$

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This discussion is for Northwest oregon and Southwest Washington
from the Cascade crest to 60 nm offshore. This area is commonly
referred to as the forecast area.



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