National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KPQR 021208
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
318 AM PST Tue Mar 2 2021


.SYNOPSIS...Mild and mainly dry Spring-like weather will hold through
early Thursday before a series of storm system bring a return to
valley rain and mountain snow late in the week into next weekend.


&&


.SHORT TERM...Today through Thursday...Water vapor satellite imagery
early this morning reveals an upper level low pressure digging
southward off the California coast and cutting off from the mean jet
stream currently plowing into British Columbia. This has left a
dying front more or less stalled along our north coast. Weak onshore
flow should continue to allow marine clouds tied to this dying front
to expand inland this morning before gradually scattering out this
afternoon. Surface observations and the KRTX and KLGX radars have
detected few, if any, precipitation returns overnight and do not see
a big reason that will change today so kept PoPs below mentionable
thresholds.

A low amplitude shortwave trough currently centered near the Aleutian
Islands will dig southeastward into the eastern Pacific over the
coming days. This will result in shortwave ridging transitioning
across the Pacific Northwest and amplifying over the Rocky Mountain
states through Thursday. This will leave the region under a quiet
weather regime with high temperatures gradually climbing from the
mid 50s today to the low 60s by Thursday.

As the aforementioned shortwave trough approaches the region, the
next front and accompanying band of rain will most likely reach the
coast Thursday afternoon per the latest ensemble guidance. Strong
southerly flow tied to the front will minimize orographic
precipitation. In fact, NBM guidance suggests just a 40-50% chance
that one inch of rain will fall in the Willapa Hills and our wetter
points in the north Oregon Coast Range Thursday afternoon through
early Friday despite this atmospheric river likely falling into the
low end moderate category per the GEFS and EPS. As a result,
hydrology concerns remain relatively low for most of the region.
Nonetheless, will need to watch the Grays River, particularly
considering how responsive it was less than a week ago and there is
still some snow lingering in the upper elevations of the basin per
NOHRSC. Theoretically, the past couple of days and next several days
of dry weather will allow some of the rain this coming Thursday to
soak in vs. runoff as efficiently as it did last week, but how much
so, remains quite uncertain.

Despite 50-70 kt 925-850mb southerly winds developing offshore ahead
of the front late Thursday, modeled pressure gradients appear
unfavorable to result in these stronger winds surfacing along most,
if not all, of our coastline. As a result, we may be able to scrape
by without any wind headlines Thursday. /Neuman


.LONG TERM...Thursday night through Monday...Models and their
ensembles are in good agreement the aforementioned front and
attendant band of rain will slowly shift eastward into the rest
of northwest Oregon and southwest Washington Thursday night into
Friday. This will result in temperatures returning closer to average
with off and on light valley rain expected Friday. Snow levels
will generally be above the Cascades passes to begin, but should
lower below the passes some time late Friday or Saturday. However,
the bulk of the precipitation will likely be over at that point so
winter travel impacts will be quite a bit more limited than our most
recent storm cycle.

Model and ensemble guidance suggests a series of colder storm
systems dropping southeastward out of the Gulf of Alaska appear
likely to impact the Pacific Northwest late in the weekend into
early next week. Timing and details remain uncertain, but most model
and ensemble guidance suggests temperatures will drop back below
average, at least a couple bouts of valley rain and more significant
mountain snow will move through the Pacific Northwest late in the
weekend into early next week. /Neuman


&&


.AVIATION...Remnants of a dying front with MVFR to IFR cigs on
the north Oregon and south WA coast. Clouds expected to lift and
dissipate around midday today. Up the lower Columbia river to
KPDX poses a more challenging forecast. Will it be VFR or MVFR
this morning. There is enough model support to say yes with weak
lift in the lower levels and enough moisture to form the lower
cigs. But the observed onshore flow is weak, would like to see
KAST-KPDX near 2 mb, it is near zero. But that is not the tell
all for determining cigs reaching KPDX and vicinity. For now,
with moderate confidence, think cigs will develop around
1500-3000 ft from 15-19Z. For the remainder of the interior
should remain VFR today with patchy fog for a few hours this
morning, best TAF locations for fog would be KHIO and KEUG.

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

KPDX AND APPROACHES...VFR to start the TAF forecast, but there is
enough guidance showing MVFR cigs 1500-3000 ft for a few hours
this morning what does form should dissipate around 19Z for a
return to VFR. Surface winds should remain light today.
/mh


&&


.MARINE...Winds will trend more northwest today as high pressure
builds in from the west. Seas still holding at 10 to 12 ft today
through this evening. Not much change into Wed, as winds stay
relatively benign with weak pressure gradients.

But, it is still March, a month of transitions. As such,
transition is Thursday, as a strong but slow moving cold front
approaches. Moderate to high potential for strong southerly
gales, along with seas building back to 17 to 22 ft. A Gale Watch
will likely be needed in the next 24 hours. Winds and seas will
drop back a bit on Fri, but unsettled weather continues into the
coming weekend. Still though some models variations, but various
models are in better agreement then 24 to 48 hours ago. /mh


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until midnight PST tonight for coastal
     waters from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory until midnight PST tonight for Columbia
     River Bar.

&&


$$

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