Scientific Forecaster Discussion
fxus66 kpqr 220415
Area forecast discussion
National Weather Service Portland or
914 PM PDT Sat Oct 21 2017
Synopsis...heavy rain continues over the north part of the forecast
area this evening and will continue tonight into Sunday, decreasing
in the north part of the forecast area late tonight and Sunday
morning and in the south part late Sunday as a strong cold front
moves through. The rain will cause areas of urban and small stream
flooding, likely a few rivers to reach flood stage, and likely some
flash flooding on The Eagle creek burn area. Winds this evening will
decrease from the north later tonight and early Sunday. Higher
pressure builds over region next week, with dry weather for most of
next week, with late night/morning fog, except for one week system
Short term...tonight through Monday...we have a rather strong
atmospheric event ongoing this evening with a lot of moisture
oriented along a baroclinic or frontal zone draped across southwest
Washington and the north half of northwest Oregon. We have strong
winds along the coast and in the Coast Range that are close to high
wind criteria, and will continue the current high wind warnings.
Winds in the valley are brisk and will continue the current Wind
Advisory. Winds will decrease most areas by late tonight or early
The heavy rain is really coming down. Lee's Camp will probably exceed
3 inches in the current 6 hour period ending at 11 PM. Rain in and
around The Gorge is heavy as well, with close to 3 inches in the last
6 hours at higher elevations on the Oregon side of The Gorge, and
over 1.5 inches at lower elevations in The Gorge. The rain will
decrease on the South Washington coast and near Astoria after
midnight tonight, with the remainder of southwest Washington and the
Portland Metro area through The Gorge decreasing during Sunday
morning, and areas to the south decreasing later Sunday.
The Grays River, the Wilson river, and the Trask river look as though
they will reach flood stage tonight. Will be watching a few other
rivers as well, including Hood River which is climbing pretty good.
Will continue the areal flood advisory as rainfall rates and falling
leaves suggest urban and small stream flooding is a good bet.
Adjusted the overnight quantitative precipitation forecast up some, but otherwise the main message of
the forecast remains unchanged.
Look for drying later Sunday and Sunday night with areas of fog and
low clouds possible Sunday night and Monday morning. Tolleson
Long term...no changes. Previous discussion follows...
Monday night through Thursday....models are in agreement, that
shortwave ridging will develop over the Pacific northwest early next week.
This will bring a period of dry weather. But, likely to see
considerable low clouds and fog Mon am and again Tue am. But, should
be very great Fall weather, with dry and mild conditions for most
areas.Weak system will pass to our north later Tue night and Wed,
but will only put a small chance of showers for the region.
Afterwards, models agree that will get back into classic October
offshore flow, with mild days and cool nights. Rockey.
Aviation...previous discussion...overall flight conditions generally
MVFR or worse early this afternoon as a warm front spreads inland.
Rainfall intensity will ease a little late this afternoon and early
evening, but pick up thereafter, which will result in an increase in
IFR coverage. Coastal sites to remain predominant IFR through
tonight. The cold front moves through SW Washington and far northwest Oregon
late tonight and then sags southeast Sun morning. Expect improving
flight conditions from northwest to southeast after 12z sun. Strong south wind will
also develop along much of the Oregon coast with gusts up to 60 kt
along exposed Headland locations. Kast and konp can expect gusts up
to 50 kt. There is also the potential for low level wind shear in the Columbia Gorge
and vicinity through the afternoon hours. East to southeast wind will
continue at the surface, but model soundings and kttd profiler data
suggest SW wind 40-50 kt at fl020.
Kpdx and approaches...previous discussion...MVFR conditions as of 20z
and this should be the primary category through 12z sun. Expect
improvement to VFR after 12z sun behind the cold front. Southeast wind to 15
kt will shift to south 20 to 30 kt with gusts up to 40 kt late this
afternoon and continue tonight. There is the potential for low level wind shear at
the terminal through the afternoon due to southeast surface wind and SW wind
40 to 50 kt at fl020. Weishaar
Marine...previous discussion...wind speeds have eased since this
morning, but are expected to increase through the evening. Latest
guidance suggests solid gale force wind speeds through 12z sun. A few
gusts to 50 kt will be possible during this time frame. Current Gale
Warning ends at 12z, but may need to extend it a little longer for
pzz255 and pzz275. For now, will leave the warning intact. Wind
speeds drop off sun, falling to 10 to 15 kt by early afternoon. A
wind shift from the east occurs Sun night and Mon with speeds
generally 10 kt or less.
Inverted surface trough along the coast strengthens Mon night and
Tue, which will produce north wind gusts around 20 kt late Mon night
and Tue morning. A cold front drops south along the Washington coast
Wed morning and reaches the north and central Oregon waters in the
afternoon. Small Craft Advisory gusts likely with this feature. The
inverted surface trough returns late in the week with Small Craft
Advisory wind speeds possible.
Seas will be rather chaotic through tonight, with a large wind-wave
component. Overall wave heights will be 15 to 20 ft through tonight.
High surf advisory conditions not expected due to the large wind-wave
component. Wave heights ease to around 12 to 14 ft by Sun afternoon
and then just under 10 ft Mon night. Weishaar
or...Flash Flood Watch through Sunday afternoon for central Columbia
River gorge-western Columbia River gorge.
Flood Watch through late Sunday night for central Willamette
Valley-Coast Range of northwest Oregon-greater Portland
Metro area-lower Columbia-north Oregon coast-northern
Oregon Cascade foothills-northern Oregon Cascades.
Wind Advisory until 4 am PDT Sunday for central Willamette
Valley-greater Portland Metro area-south Willamette Valley.
High Wind Warning until 5 am PDT Sunday for central Coast Range
of western Oregon-central Oregon coast-Coast Range of
High Wind Warning until 3 am PDT Sunday for north Oregon coast.
Washington...Flood Watch through late Sunday night for central Columbia
River gorge-Greater Vancouver area-I-5 corridor in Cowlitz
County-South Washington Cascade foothills-South Washington
Cascades-South Washington coast-western Columbia River
Wind Advisory until 4 am PDT Sunday for Greater Vancouver area.
High Wind Warning until 2 am PDT Sunday for Willapa Hills.
High Wind Warning until 11 PM PDT this evening for South
Pz...Gale Warning until 5 am PDT Sunday for coastal waters from Cape
Shoalwater Washington to Cascade Head or out 10 nm-coastal waters
from Cascade Head to Florence or out 10 nm-waters from
Cape Shoalwater Washington to Cascade Head or from 10 to 60 nm-
waters from Cascade Head to Florence or from 10 to 60 nm.
Small Craft Advisory for rough Columbia River bar until 5 PM
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