-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KPQR 032236
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
235 PM PST Wed Mar 3 2021


.SYNOPSIS...Mild dry Spring-like weather will continue through
early Thursday. A series of storm systems will bring valley rain and
mountain snow starting Thursday afternoon and continue moving through
the area into early next week.

&&

.SHORT TERM...Tonight through Saturday...Water vapor satellite
imagery continues to show a shortwave ridge over the region. At the
same time water vapor imagery shows a trough diving southeast into
the eastern Pacific, which will move east towards the region Thursday
into Friday.  As this trough moves east, an atmospheric river looks
to impact the Oregon coast at the same time. Looking at GEFS and EPS
data, Integrated Vapor Transport (IVT) values for this atmospheric
river are around 500-600 kg/(ms), which places it into the moderate
category for atmospheric rivers. The same guidance is showing that
the strongest part of this AR will be focused towards the central
Oregon coast, given that the AR has a south to north orientation the
IVT values farther north will be less than 500 kg/(ms), which lowers
the AR category to low. The exact start time for the precipitation is
still variable but, the high resolution models using the SPC HREF
Ensemble Viewer has the precipitation starting along the coast
sometime between late Thursday morning and Thursday afternoon.

Given that the overall flow of this AR will be south to north the
potential for hydrological concerns continue to be limited. QPF
totals for this event from Thursday afternoon through Friday night
look to be around 1.5 to 2 inches along the coast and 0.75 to 0.25
inches along the eastern flank of the Coast range across to the
Cascades. While overall hydrologic concerns are currently minimal,
the Grays River continues to be the river of highest concern followed
by the the Nehalem River.

As the entire system moves farther south through Friday and into
Saturday, the upper level trough will gradually weaken and drop snow
levels to around 2500 to 3000 feet as 850 mb temperatures fall to
around -3 C to -5 C. However, the majority of precipitation will be
over by then so new snow accumulations are expected to be low at this
time. Shortwave ridging looks to develop Saturday bringing a brief
period of drier weather across the CWA with a some showers lingering
into Saturday night. /42


.LONG TERM...Saturday night through Wednesday...Models remain in
agreement that shortwave ridging will continue to migrate across the
CWA which will result in the few light showers that are lingering to
gradually come to an end.

Models and their ensembles then generally agree the next shortwave
trough will dive into the eastern Pacific from the Gulf of Alaska and
push a weakening front into the region Sunday. Models suggest that
the upper level trough will dig southward and broaden before swinging
eastward into California Monday. Light precipitation will likely
persist through Monday along with cooler temperatures.

Embedded shortwave troughs within the broader trough will likely keep
precipitation chances elevated through Wednesday. Given that the
overall flow pattern and timing of these shortwaves is highly
variable, have not deviated much from the NBM for PoPs and
temperatures at this time. /42

&&


.AVIATION...Dry aloft, with variable flow. But, will see
increasing southwest flow aloft later tonight and especially Thu.
Will remain VFR across the region, with increasing high clouds
later tonight into Thu. The exception will be for areas of MVFR
stratus along the coast, which will become more solidified
overnight, and persist into Thu.

Farther inland, mostly clear skies. But, will see repeat of last
night again tonight, with areas of fog and low stratus after
midnight. This will likely persist into Thu am.

For detailed regional Pac NW aviation weather information, go
online to: https://weather.gov/zse

KPDX AND APPROACHES...VFR, with mostly clear skies through this
evening. But, will have repeat of patchy fog late tonight into
early Thu am, though may not persist as long Thu am as will have
a light east wind by that time. /Rockey

&&

MARINE...Rather benign conditions at the moment, with northerly
winds 10 to 15 kt at most. Seas generally 7 to 9 ft.

That will change later tonight into Thu, as next front
approaches. Winds will turn more southeast overnight, and then
southerly and increase Thu am into Thu afternoon. Still look on
track for strong southerly gales on the outer waters Thu am,
spreading closer to shore in the afternoon. Current Gale Warnings
cover this well for Thu. Still some question for potential storm
force gusts to 50 kt on the outer waters west of Newport and
Florence for time Thu afternoon into early evening. But, for
now, will maintain strong gales.

Seas will be on the increase, but likely to see more increase in
choppy chaotic wind waves during the day. Likely to see 12 to 16
ft seas by Thu mid- afternoon. Larger fetch of swell will arrive
Thu evening, with seas pushing 18 to 22 ft, with 20 to 25 ft on
the outer waters Thu.

Unsettled weather continues through the weekend with possible
gale force winds at times for Fri and Fri night, and again Sat
night./Rockehiga

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 10 PM this evening to 7 AM PST
     Thursday for coastal waters from Cape Shoalwater WA to
     Florence OR from 10 to 60 NM.

     Gale Warning from 7 AM Thursday to 6 AM PST Friday for coastal
     waters from Cape Shoalwater WA to Florence OR from 10 to
     60 NM.

     Small Craft Advisory from 11 PM this evening to noon PST
     Thursday for coastal waters from Cape Shoalwater WA to
     Florence OR out 10 NM.

     Gale Warning from noon Thursday to midnight PST Thursday night
     for coastal waters from Cape Shoalwater WA to Florence OR
     out 10 NM.

     Small Craft Advisory from 6 PM to 10 PM PST this evening for
     Columbia River Bar.

     Small Craft Advisory from 4 AM to 10 PM PST Thursday for
     Columbia River Bar.

&&

$$

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland