Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS66 KPQR 132115
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
215 PM PDT Sun Oct 13 2019

.SYNOPSIS...Mostly dry weather is expected through Monday. High
pressure will build into the region tonight with areas of fog and 
low clouds forming overnight, especially in the valleys. Areas of 
fog will linger into mid-morning on Monday, but will clear for a 
sunny and seasonable October afternoon. Clouds will increase on 
Tuesday as the first in a series of frontal systems approaches the 
Pacific Northwest coast. This will mark a shift toward a much more 
active and wet weather pattern for the middle to latter part of the 
week. 

&&

.SHORT TERM...Tonight through Wednesday...The upper level trough that
moved through the region last night into this morning will move east 
of the area tonight. High pressure aloft and at the surface will 
build across the region tonight and Monday. Time-height cross 
sections show a fairly moist boundary layer throughout the 
Willamette Valley that persists through about 18z Monday. With the 
low level moisture and light winds, expect to see a mix of fog and 
low stratus in the valleys late tonight into early Monday morning. 
The low clouds and fog should clear by midday, giving way to a 
mostly sunny afternoon on Monday. High temperatures on Monday will 
be 3 or 4 degrees warmer on Monday with temperatures at the coast 
near 60 and in the lower to mid 60s inland. 

The ridge of high pressure will transit the area Monday with the
ridge axis over the northern Rockies on Tuesday. The first in a
series of storms will approach the region late Tuesday. NWP models
have slowed the progression of this front with the front moving into
the coastal region Tuesday night into early Wednesday.Another
slightly stronger front will follow on it's heels later Wednesday.
/tw

.LONG TERM...Wednesday night through Sunday...Models and their 
ensembles are in good agreement a series of shortwave troughs will 
slide east-southeastward across the Pacific Northwest during the 
second half of the work week. This will result in a multi-day 
stretch of wet weather. While no one day looks unusually wet, 
rainfall amounts will likely add up over time. Based on the GEFS and 
EC, it appears an additional 0.50-2.00" of rain on top of Tuesday 
night/Wednesday's rain will be possible in the Willamette Valley 
Wednesday night through Saturday with an additional 1-3" along the 
coast and an additional 2-5" rain in the Coast Range and Cascades. 
Given these rainfall amounts will be spread out over several days, 
mainstem river flooding appears unlikely at this point...even at our 
most flood prone rivers including the Grays River at Rosberg. 
Nonetheless, rivers will certainly be on the rise and the weather 
will be reminiscent of many past November days.

It should be noted that subtle differences exist between models and 
various ensemble members in timing and amplitude of upper level 
shortwave troughs so there is still some uncertainty on when showers 
will be more or less numerous across the region. Nonetheless, there 
is at least some indication Thursday afternoon or evening could see 
a spike in rain coverage as an occluding front drops southeastward 
into the region. In addition, it appears the region will be on the 
edge of the 500mb cold pool Wednesday night and again on Thursday 
night or Friday so there will be a risk for a thunderstorm or two 
over the northern waters, and perhaps even inland, but there remains 
enough uncertainty to leave it at that for now. 

Pressure gradients will also be favorable for breezy to windy 
conditions along the coast late Wednesday and Thursday, but at this 
point models suggest wind fields should be weak enough to 
prevent any high wind issues along the coast. 

Finally, wet weather may very well continue into Sunday, but models 
and their ensembles suggest it's less likely than Saturday so PoPs 
were maintained in the chance to low end likely range per NBM 
guidance for now. It should be noted that the some of the recent 
operational EC and GFS runs do suggest an atmospheric river riding 
up and over the shortwave ridge building across the eastern Pacific 
could take aim at the Pacific Northwest late Sunday and beyond so 
that will be worth monitoring, particularly given the rain 
anticipated to fall this week. /Neuman
&&

.AVIATION...Generally VFR conditions expected to continue through 
about 09Z tonight, although there is a chance for seeing a few areas 
with MVFR ceilings along the coast until about 01Z this evening. 
Between 09Z and 13Z expect to see areas of fog and low stratus to 
develop along the coast and in inland valleys, reducing flight 
conditions to IFR or low end MVFR categories. Expect the fog and low 
stratus to lift and break up between 18Z and 20Z for a return to VFR 
conditions.

KPDX AND APPROACHES...Generally VFR conditions expected through 12Z 
Monday. After about 12Z IFR conditions appear likely to develop with 
a low stratus layer or fog. VFR conditions then expected to return 
after 18Z to 20Z Monday.  

&&

.MARINE...North to northwest post-frontal winds expected to weaken 
late Sunday afternoon and evening as high pressure moves back over 
the coastal waters. A fresh swell that had seas up to 9 to 11 feet 
Sunday afternoon will likewise subside overnight.

The weather pattern becomes much more active beginning Tuesday, and 
continuing into next weekend. Beginning Tuesday night and continuing 
into Saturday expect winds gusting to 20 to 30 kt as a series of 
front move east across the waters. At this point, the Wednesday 
system appears to be the strongest, and some gale force gusts with 
this system may not be out of the question. Seas are likely to build 
above 10 ft by Tuesday evening, and expected to build as high as 15 
to 20 ft from late Wednesday into Friday, which will be the biggest 
seas since spring. 

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 6 PM PDT this evening for coastal 
     waters from Cape Shoalwater WA to Florence OR from 10 to 
     60 NM.

&&

$$

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

National Weather Service Glossary of Abbreviations