418
FXUS66 KPQR 120901
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
201 AM PDT Mon May 12 2025

.SYNOPSIS...A broad low continues to bring cooler temperatures
and precipitation across southwest Washington and northwest
Oregon. Cool and moist conditions will persist through at least
Tuesday which will result in daytime highs in the 50s along the
coast and 60s inland. Slight chance for thunderstorms Monday
afternoon through early evening. A brief period of warm and dry
conditions are expected Wednesday with light precipitation
returning for the latter part of this week.

&&

.SHORT TERM...Today through Wednesday Night...A broad low
pressure system will continue to bring cool and unsettled
weather through Tuesday, with light showers expected. Although
the flow pattern is not especially favorable, cooler air aloft
will boost instability, resulting in around 200-350 J/kg of
CAPE. This supports a 15-30% probability of thunderstorms
through this evening across our CWA. Also, long skinny CAPE seen
within model soundings point towards the probability of small
hail developing within any cell (thunderstorm or not). Any hail
that does develop will likely be less that 0.25 inches in
diameter (pea size or smaller) and will likely not linger too
long once the cell that produced it leaves the area. Still,
there could be very brief periods of time where roads and
sidewalks are covered with small hail and as a result could
bring about slick surfaces. Total rainfall today will generally
range from 0.10 to 0.30 inches in the valleys and along the
coast, with higher totals of 0.25 to 0.60 inches along the
coast and in the Cascades.

On Tuesday, shower activity will gradually taper off as the
upper low shifts southeast. A weak shortwave ridge will follow,
ushering in a slightly drier and more stable pattern. Still, a
few light showers may linger, with up to 0.05 inches of
additional precipitation possible in the interior valley and up
to 0.20 inches for the Cascades. By Wednesday, the shortwave
ridge pattern will develop further and result in warmer and
drier conditions. /42

.LONG TERM...Thursday through Sunday...Precipitation chances
on Thursday return as a another broad trough will likely bring
another round of light precipitation and maintain slightly
warmer than normal temperatures through the weekend. WPC
Clusters are generally points towards ridging over the eastern
Pacific with troughing over the middle of CONUS for the start
of next week. Overall, expect daytime highs in the 50s along the
coast and 60s for inland areas through the latter part of this
week and into the upcoming weekend. /42

&&

.AVIATION...An upper level low offshore will move inland over the
region through today. Scattered rain showers will thus continue
through Monday afternoon, diminishing in coverage by 00-06z Tue,
initially along the coast and subsequently inland. Chances for
MVFR cigs increase to 30-60% after 14-16z Mon before trending back
to VFR as cigs lift by 21z Mon, except along the coast where MVFR
cigs may linger later. There will also be a 15-25% chance of
thunderstorms this afternoon, although confidence in timing and
coverage remain too low to merit PROB30 mention. Any thunderstorm
may be capable of producing small hail, the size of peas or less,
and briefly restricted vis.

Along the coast, south to southeast flow at 5 kt or less will turn
out of the west after 21-24z Mon at 5-10 kt. Inland, light and
variable flow through the morning will increase out of the west to
northwest at 5-10 kt after 21-24z Mon, before diminishing to 5 kt
or less out of the southwest after 06z Tue. Thunderstorms may
produce briefly gusty winds through this afternoon.

PDX AND APPROACHES...Scattered rain showers continue through much
of the period as an upper low moves inland, with shower coverage
finally lessening after 06z Tue. Chances for MVFR cigs at 2-3 kft
increase to around 40-60% after 14-16z Mon, before VFR cigs are
favored to return by 19-21z Mon. There is a 20-25% chance of
thunderstorms this afternoon, which may result in brief vis
restrictions and/or small (pea-sized or less) hail, although
confidence in occurrence and timing of any impacts is low. Light
and variable winds continue through 18z Mon, then increasing to
5-10 kt out of the northwest through the afternoon. Heavier rain
showers or thunderstorms may yield periods of gusty winds through
03z Tue, before winds otherwise diminish to 5 kt or less after 06z
Tue.-Picard

&&

.MARINE...A weak surface low west of Cape Blanco continues to
fill as it tracks to the northeast toward the central Oregon coast
through this morning. Southerly winds will diminish early, then
turn out of the northwest behind the low this afternoon.

High pressure building over the northeast Pacific will yield
northwest flow through at least Wednesday night. Gusts of 20-25
kt beyond 30 NM will see fresh northwest swell rising to 9-11 ft
at 10 seconds Monday night into Tuesday, before diminishing into
Wednesday. Beyond 30 NM, there is a low chance, 10-20%, of maximum
gusts reaching gale force, with the highest likelihood northwest
of the mouth of the Columbia River. An approaching trough will see
flow turn out of the west to southwest Thursday into Friday,
before northwest flow returns for the weekend.-Picard

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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