016
FXUS66 KPQR 232152
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
251 PM PDT Mon Sep 23 2024

.SYNOPSIS...The upper level trough has moved through the area, with
no more remaining precipitation. High pressure returns tonight
through Wednesday morning. Warm temperatures on Tuesday. Another
front arrives on Wednesday night which brings higher probability for
rainfall through the remainder of the week.

&&

.SHORT TERM...Now through Thursday...The region has dried out as the
previous front moves out of the area. Winds in the central and
southern Willamette Valley are currently gusting up to 16-20 mph, but
will continue decreasing and become light and variable overnight.
Over Monday night, high pressure builds into the region, with dryer
and warmer conditions Tuesday. The thermal trough shifts offshore
late Monday night, with a brief period of easterly flow late Monday
night and early Tuesday morning. Easterly wind gusts up to 20 mph
will be possible through the Columbia Gorge during this time. By
midday Tuesday winds will shift westerly as the thermal trough moves
well inland, east of the Cascades. Tuesday sees much warmer
temperatures, with around a 60% chance of high temperatures
throughout the Willamette Valley being over 90 degrees. Chance of
high temperatures being higher than 95% is less than 5%.

Wednesday sees a pattern change as another trough enters the area.
Model trends continue to show the jet stream shifting north, and it
looks like wind speeds will remain under 25 mph for all regions. Rain
amounts will be higher further north, with 80% chance of exceeding
0.25" in the Willapa Hills. This decrease down to 40% near Eugene.
Thursday sees relatively zonal flow; some morning showers may be
possible, but any accumulation will be minimal. Wednesday and
Thursday both look much cooler, with highs around 70 degrees in the
lowlands. /JLiu

.LONG TERM...Thursday night through Monday...Brewing in the
northeast Pacific is a low pressure system which will move
eastward on Thursday and Friday. This incoming low will cause
the flow to become more zonal which can be observed in the jet
stream motion. The forecast area sits on the cool side of the
jet with a 145 kt jet streak just to the north along the
Washington-Canadian border. The low will enhance precipitation
on Thursday into Friday. Because this low is moving inland to
the north, we currently are sitting on the southern portion of
the front. Will note that similar to the jet on Wednesday, this
upper air pattern too has shifted northward which will result
on lower probability for precipitation Friday night into
Saturday. High pressure returns on Sunday into Monday. -Muessle

&&

.AVIATION...High pressure with northwest to northerly flow aloft
today will maintain predominately VFR conditions with variable
high clouds. Widespread stratus over the waters from this morning
has dissipated, but right along the coast streams of stratus (likely
IFR cigs) extending downwind from coastal headlands. KONP forecast
will be a bit of a challenge as winds have a slight offshore
component, but with heating inland could see a change to onshore
wind to bring clouds to the airport. Guidance keeps the coastline
right on the edge of IFR conditions through about 05Z Tue then
chances for IFR increase. Slightly different conditions at KAST
where a weak surface trough just offshore maintaining a deeper
marine layer there with MVFR cigs. May see SCT-BKN layer around
2000-2500 at KAST this evening, then a IFR later developing
overnight.

VFR prevails at inland TAF sites with mainly mid and high clouds.
Then after about 12-14Z Tue there is about a 30-50% chance for
MVFR or lower conditions, particularly south of KUAO in the
Willamette Valley.

PDX APPROACHES...VFR prevailing into Tuesday. But there is about
10% chance for MVFR cigs around 14-16Z Tuesday. Light northwest
winds expected to increase to around 6-8 kt this afternoon. / mh

&&

.MARINE...Small Craft Advisory wind gusts of 21 kt or more are
expected across the coastal waters off the central coast of Oregon
into early Tuesday morning. High pressure weakens on Tuesday
while thermal troughing shifts inland, allowing for northerly
winds to decrease substantially through the day. An approaching
front will turn the winds southerly late Tuesday night into
Wednesday. NBM Probabilistic guidance has backed off on chances
for winds 20-25 kt range later Tue into Wed. The highest chances
area now 25-35% for wind gusts above 21 kt Wed morning. However
the latest deterministic NBM shows widespread gust 20-25 kt
briefly Wed morning, though GFS and ECMWF are weaker. So still
some room for models to come to better consensus.


Further on, still uncertainty in forecast details late this week
as a stronger low pressure system is expected to develop and
rapidly intensify across the far NE Pacific, but there is much
better agreement among the latest model runs. The surface low is
very likely (>90% chance) to take the northerly track toward Haida
Gwaii on Thursday. The majority of models suggest the associated
front only brings Small craft Advisory level wind gusts to the
coastal waters. However, there is a 10-20% chance of Gale Force
southerly winds gusts 35 kt spreading across at least the northern
waters.

Seas around 5 to 7 ft today build to around 8 to 9 ft on Tuesday
as a fetch of northwest swell moves into the coastal waters. Seas
likely linger around 7 to 9 through Thursday. Another west to
northwest swell is expected to move in behind the front on Friday
with seas likely building in the 10 to 14 ft range. /mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ253.

     Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Tuesday for PZZ272.

     Small Craft Advisory until 5 AM PDT Tuesday for PZZ273.
&&

$$

www.weather.gov/portland

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