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Area Forecast Discussion (AFD)

Issued by Portland, OR (PQR)

                            
000
FXUS66 KPQR 161005
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
304 AM PDT Mon Sep 16 2019

.SYNOPSIS...Showers and isolated thunderstorms are expected today as
a cool upper trough moves over the Pacific NW. A cold front will
bring rain and breezy winds to the area on Tuesday, with rain being
heavy at times. Another cool upper trough will continue showers and
bring another threat for isolated thunderstorms on Wednesday. Drier
weather expected late in the week, but temperatures will remain
cooler than usual for this time of the year.

&&

.SHORT TERM...Today through Thursday...Isolated thunderstorms are
reaching the coast early this morning as a cold upper trough
approaches the Pacific NW as isolated to scattered showers cs inland.
The threat for isolated thunderstorms remains on the coast through
the morning, then shifts inland this afternoon as the upper trough
moves inland. The showers will pick up in frequency and intensity
this afternoon as the cool upper trough moves over the region. The
snow levels will lower to around 6500 feet today for a light dusting
of snow in the higher Cascades, but do not expect any winter weather
for the Cascade passes. 

Another strong and moist cold front will bring another round of
moderate to heavy rain on Tuesday. The rain will reach the coast
early Tuesday morning and spread inland by the early afternoon. This
front is very similar to the one that moved through on Sunday, and
expect similar rain rates and totals. Rain totals along the coast and
higher terrain of 0.75 to 1.5 inches are expected between Tuesday
morning and Tuesday evening with 0.5 to 0.75 inch expected for the
interior valleys. Winds will be breezy with the front passage on
Tuesday with gusts of 40 mph possible along
the coast and 30 mph for the Willamette Valley. Temperatures will be
much cooler on Tuesday with daytime highs barely making it to 60
degrees. 

Another cool upper trough follows the Tuesday front that will support
showers through Tuesday night and Wednesday. Cold air aloft will
destabilize the atmosphere and expect isolated thunderstorms along
the coast Tuesday night and inland Wednesday afternoon. The upper
trough moves east of the Cascades Wednesday night and showers will
decrease.  

An upper ridge tries to build on Thursday, but a shortwave trough may
sneak over the ridge and maintain Cascade showers or marine stratus
and drizzle along the coast. Regardless it will be a drier day. 
Temperatures will warm a bit, but still be well below the seasonal
normals. ~TJ
 
.LONG TERM...No Changes. Previous discussion follows...Thursday night
through Sunday...Cannot rule out that some stray showers will
continue into Friday as weak disturbances move through the upper
level flow.  There remains quite a bit of uncertainty in the weather
towards the end of the week and into next weekend.  At this juncture,
looks like late Friday and Saturday could be fairly dry, then another
upper level trough approaches the region on Sunday bringing a chance
of showers. /tw

&&

.AVIATION...Isolated thunderstorms continue over the coastal 
waters overnight with some even reaching the coast. Chances for 
thunderstorms will spread inland today as a cool upper trough 
moves ashore. VFR conditions are expected at the coast today and
tonight. However expect spotty MVFR or lower conditions with 
heavier showers or thunderstorms. For inland areas, widespread 
MVFR conditions with cigs between 1500 and 2500 ft along with
some IFR conditions will affect the terminals this morning. As
the cool upper trough moves over the interior and daytime 
surface heating increases we should see the lower layers begin 
to lift by mid morning with VFR for most areas 18-20Z. Showers 
will increase in the afternoon along with chances for showers and
thunderstorms with may bring brief MVFR or lower conditions. 
Thunderstorm chances should end around 04Z Tue.

KPDX AND APPROACHES...Cigs around 1200-1500 ft should hold 
through about 16Z the lift above 2000 feet before breaking to VFR
20Z. Showers will pick up over the valley in the afternoon. 
Expect mainly VFR conditions Mon afternoon and evening, with the 
potential for some heavier showers or even a thunderstorm or two 
to bring brief MVFR or IFR conditions. /mh Pyle

&&

.MARINE...A broad and weak surface low pressure will drop 
southward across the waters through Monday. This should bring 
relatively benign winds, though cold air aloft will probably 
result in some squally showers and thunderstorms today. Expect 
seas to stay in the 7 to 9 ft range through Monday evening.

The next front is expected to bring gale force winds as it
crosses the waters late tonight and Tue, so have issued a Gale
Warning. It looks like the strongest winds would be brief, 
lasting about 6 hours during the day early Tuesday morning. Seas
will be steep and wind-driven with the front, peaking at 10-11 
ft.

Winds settle Tuesday night into Wednesday with broad low pressure
over the waters, but seas stay in the 8 to 10 ft range with NW
swell. High pressure returns to the waters late in the week for a
more summer type pattern. /mh Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Warning from 3 AM to 2 PM PDT Tuesday for Coastal Waters 
     from Cape Shoalwater WA to Florence OR out 60 NM.

&&
$$

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This discussion is for Northwest Oregon and Southwest Washington 
from the Cascade crest to 60 nautical miles offshore. This area is 
commonly referred to as the forecast area.