Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 260531 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
930 PM PST Sat Jan 25 2020

.SYNOPSIS...A progressive weather pattern will support a series of
fronts impacting the Pacific NW tonight through next week. The first
front tonight, a warm front, will generate a burst of gusty winds
along the coast late tonight. There is potential for another burst of
winds along the coast and inland Monday night. Otherwise rain and
mountain snow will dominate through Tuesday. Snow levels rise
Wednesday behind a strong warm front. Could see some hydro issues
late next week from the prolonged period of rain.

&&

.UPDATE...Rain has spread across the forecast area as expected this
evening. However we did make some tweaks to the forecast this
evening, mainly to lower PoPs Sunday as the tonight`s frontal system
is expected to cross the Cascades by daybreak. There will still be
some scattered showers around Sunday, especially in the higher
terrain. But there may also be some sun breaks for the inland valleys
and much of the day should be dry aside from a few passing showers.
Was tempted to remove thunder mention for the north coast and
adjacent waters, as stability profiles look marginal for convection
deep enough to produce lightning. Will leave it in for now, and allow
the night shift to take a look at it. The next system will push
another warm front across the area Sunday night, bringing another
round of steady light rain during the evening along with another few
inches of snow for the Cascades. More on this system, and those to
follow, in this afternoon`s discussion below.  Weagle

.SHORT TERM...Tonight through Tuesday..A warm front will spread rain
south to north across the region tonight. The isobars tighten as the
low deepens and moves north offshore tonight. The winds are initially
from the SE, but the surface pressure gradient opens up to the S-SW
late tonight where a brief burst of gusty winds up to 50 mph likely
after midnight. The strongest winds will be on the coastal headlands
and open beaches.

The heaviest precipitation is expected overnight tonight with
rainfall totals generally between 0.25 and 0.5 inch, and close to an
inch for the higher terrain of the coast range and Cascades. Snow
levels will be above 6000 feet tonight. Snow levels will lower to
near the Cascade passes Sunday morning as a weaker colder front moves
through for an inch or two of new snow possible for the passes.
Precipitation decreases and turns to showers Sunday afternoon. A
negatively tilted upper trough swings north of the area Sunday
afternoon and may increase instability enough to trigger isolated
thunderstorms offshore and along the north coast for a few hours
Sunday afternoon.

If you are thinking about heading to the coast on Sunday, be extra
watchful of the sea as there will be increased likelihood for sneaker
waves late Sunday morning through Sunday evening This is due to the
potential for a building long-period west swell to increase the
strength and height of the water running up the beaches. THis can
easily catch someone off guard and drag them into the cold ocean
waters. A Beach Hazards Statement has been issued for this coastal
hazard.

The chance for any convection will be brief Sunday afternoon as the
next cold front moves in quickly Sunday evening for more stable rain
and Cascade snow through Sunday night. The snow levels will be around
4000 feet, and expect accumulating snow for the Cascades including
the passes Sunday night with snow amounts of 3 to 6 inches possible.

Another warm front will lift north across the region on Monday for
additional precipitation. This front moves fairly slow compared to
the preceding ones, and has decent moisture with it. Modeled
precipitable water is lower than the previous model runs, but still
high enough (~0.75 inch) to support decent rain and Cascade snow,
with the precipitation to be heavy at times Monday afternoon and
evening. An additional 0.75 to 1 inch of rain is expected Monday
morning through the evening with 2 to 3 inches possible for the coast
range and the Cascades. The Cascades can expect at least 6 to 12
inches of new snow Monday at elevations at and above 4500 feet.

No break in precipitation is expected Monday night and Tuesday as
another frontal system arrives. Snow levels will rise to around 5000
feet Monday night. Current model guidance suggests that the winds
will be stronger with this system with fairly good model agreement of
at least a 997 mb low offshore the Washington coast. Currently do not
anticipate the need for headlines with these winds, but could see
some problems with isolated downed trees due to over saturation
soils.

With all of the rain expected the next few days, and little breaks
between the fronts, the rivers will rise. Although no rivers are
currently expected to exceed flood stage through Tuesday, would not
be surprised to see a few reach close or exceed flood stage mid or
late next week especially as rising snow levels after Wednesday
allows snow melt to contribute to river rises. ~TJ

.LONG TERM...Tuesday night through Saturday...Persistent valley rain
and mountain snow is expected through the end of next week. Models
and their ensembles are in agreement that a trough will move through
the Pacific Northwest Tuesday, bringing heavy rain to the coast and
valley and snow in the Cascades. There will be a brief break from
this precipitation Tuesday night into Wednesday morning before the
next system moves through the area Wednesday afternoon.
Precipitation will transition to predominately rain and continue
Thursday before another brief break on Friday. A westerly flow will
persist through the forecast period keeping highs and low
temperatures above average for this time of the year. Snow levels
will be around 4000ft Tuesday and Wednesday and climb to around
6000ft through Saturday. -Thaler

&&

.AVIATION...The low that is moving through is staying farther
east than expected and is moving at a fairly quick pace. This
should decrease the amount of time spent in deteriorated
conditions. Rain is starting to pick up across the area as the
cold front approaches. MVFR ceilings are expected across much of
the area but visibility should remain VFR.

KPDX AND APPROACHES...VFR conditions are expected to persist
with a brief period of MVFR ceilings late tonight with light
precipitation. -BPhillips

&&

.MARINE...Active weather pattern continues for the foreseeable
future as a series of Pacific frontal systems move across the
coastal waters. A warm front will move north through the waters
tonight. The associated 995 mb low will be about 200 nm west of
Astoria between 10 PM Saturday and 1 AM Sunday as it heads
towards Vancouver Island, BC. The associated cold front will
follow several hours later.

Current guidance is showing a small period of time where the
winds will subside below gale force, but models are showing
differences on timing of a quick moving cold front, have issued
a Gale Watch for the outer waters but this could change as
confidence on the timing of this front is low.

Another storm arrives Monday, but confidence is low on timing
and strength of winds due to large differences in models. Though
it appears gale force winds are possible during that time period.

Seas will build through Saturday night towards 11 to 13 feet, and
continue that trend into Sunday where seas will reach 12 to 14
feet and stay around that level through the early part of the
week.

Overall expect the weather pattern to remain active well into
next week, with seas into the mid to upper teens during the later
part of the week. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Watch from Sunday afternoon through Sunday evening for
     coastal waters from Cape Shoalwater WA to Florence OR from
     10 to 60 NM.

     Gale Warning until 6 AM PST Sunday for coastal waters from Cape
     Shoalwater WA to Florence OR from 10 to 60 NM.

     Gale Warning from midnight tonight to 6 AM PST Sunday for
     coastal waters from Cape Shoalwater WA to Florence OR out
     10 NM.

     Small Craft Advisory until 10 PM PST Sunday for Columbia River
     Bar.

&&

$$

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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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