Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
321 am PDT Monday Mar 17 2014
Synopsis...a strong cold front had moved east of the Cascades early
this morning with decreasing precipitation but snow levels down near
1500 to 2000 feet. Northwest onshore flow will give scattered showers
today with a couple more inches of snow in the mountains. A weak wave
continues to be forecast to drop southeast into the Pacific northwest
for a little light precipitation Monday night and Tuesday...with snow
levels remaining unseasonably low. A more organized frontal system is
forecast to bring more valley rain and mountain snow to southwest
Washington and northwest Oregon especially on Wednesday. Post frontal
showers will linger through Thursday. We may see some drier weather
Short term...the strong cold front that brought a period of heavy
rain and heavy mountain snow to southwest Washington and northwest
Oregon late Sunday and Sunday night has moved east of the Cascades
early this morning. Snow levels have dropped dramatically to near
1500 to 2000 feet over much of the area. Northwest onshore flow
behind the front will keep scattered showers going much of today...
but amounts look insufficient to keep the Snow Advisory going in the
Cascades...so have dropped it this morning. Nevertheless...a couple
more inches of snow are possible over the Cascades today...and this
will help keep roads snow covered and will likely impact travel over
The models still show the moisture band out near 135w from 45n and
northward will spread into the Pacific northwest tonight and Tuesday.
Amounts will be light...but we should see some areas of light
precipitation. Snow levels will continue to be rather low...so it is
not out of the question we may see a few flurries mixed in at the
higher elevations around the valleys late tonight and early Tuesday.
However...the air mass will be rather moist and the low level flow
light...so this should limit any impacts and prevent the snow level
from getting too low. The overrunning weak isentropic lift should
decrease much of our area later Tuesday into Tuesday night...perhaps
lingering north of the Columbia River.
The next decent frontal system moves in on Wednesday. Snow levels
will be a bit higher with this system...up near pass elevations. We
should get more snow in the Cascades...but probably just below
All in all...this week looks unsettled with temperatures below seasonal
Long term...no changes. Previous discussion follows...
Wednesday night through Sunday... a cold frontal passage on Wednesday will
leave a cool and showery air mass in its wake for Wednesday night and Thursday.
Snow levels behind the front may reach into the higher elevations of
the Coast Range and Cascade foothills. Fortunately...quantitative precipitation forecast values from
the showers are quite light in the latest model runs...so any
potential snow accumulations would be light. The upper level trough
pushes east into The Rockies and then the central U.S. Later Thursday into
Friday. At the same time...weak ridging begins to develop over the NE
Pacific. It appears that the Pacific northwest may remain in between the trough to
the east and ridging to the west through the end of the week into
next weekend. This would leave US with cool northwest flow aloft...with very
little if any precipitation. If any clearing develops... overnight
lows on Thursday and Friday may be quite chilly. The latest model guidance
indicates valley lows could drop into the middle or even low 30s. The
upper level ridging is prognosticated to move over the Pacific northwest later next
weekend...which should help to moderate temperatures. Pyle
Aviation...cold unstable aloft will lead to occasional showers today
under mainly VFR conditions. Brief MVFR conditions will be possible
under any heavier shower...but again these conditions should not last
terribly long. Otherwise...surface high pressure will shift over the
region this evening and lead to clearing skies. Some low clouds near
1.5-3kft will likely shift eastward into the northwestern half of the
forecast area towards 12z Tuesday. Kast appears the most likely taf
site to be impacted...but certainly konp and the Portland metropolitan taf
sites could see impacts as well.
Kpdx and approaches...expect mainly VFR conditions today and
tonight...except for brief MVFR conditions under any heavier shower
this morning...and then again towards 12z Tuesday as clouds between
1.5kft and 3kft above ground level push eastward towards the terminal. /Neuman
Marine...seas are currently in the 13 to 15 feet range...and will
continue to ease today...dropping below 10 feet late this evening.
Gusty northwest winds with gusts of 25 to 30 knots will continue this
morning before dropping below 20 knots early this afternoon. A weak
front will push into the waters tonight...briefly turning winds
southerly...but should have little impact the magnitude of winds.
Another storm system will slide north and east of the area
Wednesday...bringing another round of gusty northwest winds and a
swell in the 10 to 12 feet range.
High pressure will then build over the waters for the end of the work
week and weekend...bringing a more Summer like quiet weather and sea
Pz...Small Craft Advisory for winds until 2 PM PDT this afternoon
for coastal waters from Cape Shoalwater Washington to Florence or out
Small Craft Advisory for hazardous seas until 11 PM PDT this
evening for coastal waters from Cape Shoalwater Washington to Florence
or out 60 nm.
Small Craft Advisory for rough Columbia River bar until 9 PM
PDT this evening.
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This discussion is for northwest Oregon and southwest Washington from
the Cascade crest to 60 nautical miles offshore. The area is commonly
referred to as the forecast area.