216
FXUS66 KPQR 022127
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
227 PM PDT Sun Jun 2 2024

.SYNOPSIS...A late season atmospheric river continues to push
inland this afternoon producing ample rain over the region. Some
localized flooding possible, especially over the Coastal areas
and Cascades. Rain will taper through Tuesday but another weak
front arrives on Wednesday morning. Strong high pressure builds
through the remainder of the week which will increase chances
for very warm temperatures.

&&

.SHORT TERM...Now through Wednesday Night...Today has not
necessarily worked out exactly as forecast, but overall the
impacts will remain similar. The late season atmospheric river
has been slow to transition inland this morning. By 1100 this
storm was already expected to be producing heavy rainfall.
However, the heaviest rains have just started falling around
1300. They are robust though with over a half inch of rain
falling over the Coast Range within the last 3 hours. Radar and
satellite do not show a break in the rain anytime soon though so
expecting those accumulation amounts to continuously rise. With
these precipitation rates and amounts, cannot rule out localized
river flooding or urban ponding. A hydrological outlook as been
issued so please turn to that for more details. With the rain on
going what will end up happening over the next 24 hours? Lets
start that analysis by looking aloft.

At 250 mb (~35,000 ft) the jet stream the stronger winds are
beginning to move over the region which is supporting the rain
thus far. As we move into Monday, the strongest winds (the jet
streak) will pass over northwest Oregon and southwest
Washington. There, winds are around 110 kt and nearly zonal.
Shifting to the mid-elevations (500 mb), this jet is coupled
with west to northwesterly winds around 110 kt as well. As we
reach the surface, winds become more south to southwesterly
around the trough that sits over the northeast Pacific. With
the westerly flow aloft, the Coast Range and Cascades are
orographically lifting the system and thus enhancing
precipitation in those areas. The southerly winds are making
their mark though as wind gusts are exceeding 20 kt in most
places, with the coast seeing the highest winds with peak gusts
around 40 kt.

Behind this system temperatures will cool aloft, but not
necessarily significantly enough to increase chances for
thunderstorms. 850 mb temperatures only lower to around 0 deg C
(32 F) but we usually are looking for much cooler conditions for
higher thunderstorm potential. The NBM has suggested around a
15% chance in southwest Washington, but with a fully saturated
atmosphere and really no forcing mechanism, those chances are
likely lower. On Monday night a shortwave trough and a weak warm
front pushes inland once again. Will see another round of
stratiform rain but it will quickly move and will not be
impactful. However if the atmospheric river from today
overperforms, then the added precipitation could have an impact
on more triggery and full rivers. High resolution models are
showing quite the precipitation accumulation spread. In
Portland, the 6 hour rainfall totals, ending at 0400, range from
0.05-0.11 inch, with the 90th percentile at 0.15 inch. In
Tillamook, the range is around 0.08-0.19 inch with the 90th
percentile around 0.25 inch. As you get into the Cascades, the
Gifford Pinchot Natl Forest could see rainfall totals as high as
0.80 inch. Ultimately, this system will once again be
orographically driven.

Rain will ease through the day on Tuesday with a few lingering
showers into the afternoon. Wednesday starts the first day of
the drying and warming conditions that will round out the
remainder of the week. -Muessle



.LONG TERM...Thursday through Sunday...If you enjoy warm, clear,
and dry weather, then the later half of the week is perfect for
you. We are starting off meteorological summer out right with a
broad ridge of high pressure which encompasses most of the West.
This high pressure system is turning out to be robust with high
confidence and consensus in the ensembles. Sensible weather
wise, Wednesday will be dry and clear but near normal for high
temperatures. Through the week into Saturday upper levels
temperatures too will rise. 850 mb temperatures during this
time frame will rise to around 20 degrees C by Saturday. This
will create a deep layer of warm air with little to no reprieve.

Looking at high temperatures, values range from the mid 60s
along the coast to the mid 70s inland. Upper Hood River Valley
and western Columbia River Gorge will trend warmer within the
forecast area due to the proximity to a bulk of the warm air and
the very slight easterly downslope flow. This will be the trend
over the next several days.

As we transition into Thursday and Friday, the ridge will only
intensify and temperatures will compound on one another; each
day will be warmer than the previous. The models have finally
started to come together on this range as it once was a 20
degree spread, and now is a 10 degree spread between the
25-75th percentile. High temperatures could rise to near 90
inland but heightened concerns occur with the overnight
temperatures. Specifically pointing to the Upper Hood River
Valley and the Columbia River Gorge near Carson, models are
showing around a 35% chance that low overnight temperatures
could be greater than 70 degrees F early Saturday morning.
Combine that with dewpoint temperatures in the upper 50s to mid
60s, overnight recovery could be less favorable. There still
remains some level of uncertainty though so be sure to continue
to watch the forecast for more information on the heat risk late
in the week. -Muessle


&&

.AVIATION...Currently, IFR/MVFR conditions at the coast along
with a mixture of VFR and MVFR inland with widespread rain across
the airspace. These conditions are expected to persist through the
overnight hours. Rain, which could be heavy at times result in
periods of reduced visibility across the airspace. Also, mountains
will remain obscured in clouds and precipitation.

Southerly winds across the airspace with gusts up to 35 kt along
the coast and up to 25 kt inland through around 08Z Monday.
Afterwards, southerly winds will persist, but gusts are expected
to weaken to 25 kt along the coast and 20 kt for inland locations.

PDX AND APPROACHES...MVFR conditions persist. However, around 00Z
Monday expect a slow improvement towards high-end MVFR/low-end VFR
as precipitation decreases. Locally heavy rain could bring
visibility down to MVFR thresholds. Expect southerly gusts around
20 kt through around 08Z Monday. Afterwards, winds will continue
to be southerly with gusts up to 15 kt. /42

&&

.MARINE...A strong storm system, will continue to slowly move
eastward through the overnight hours. Current buoy and land based
observations are showing south/southwesterly gusts up to 40 kt.
Therefore, have extended the current Gale Warnings out through the
early evening. Afterwards, have a Small Craft Advisory for all
waters through Monday night for winds and/or seas. Will extend the
current Small Craft Advisory for the Columbia River Bar through
Monday night as well. Winds will subside by Monday night and
become northerly. Currently, seas around 8-10 ft. Expect seas to
build towards 10-12 ft on Monday.

Winds will remain northerly, but will likely increase towards
Small Craft conditions by the middle of the week. Seas will also
continue building through the middle of the week towards 12-14 ft
as another westerly swell enter the waters. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT Monday for PZZ210.
     Gale Warning until 5 PM PDT this afternoon for PZZ251>253-
     271>273.
     Small Craft Advisory from 5 PM this afternoon to 11 PM PDT
     Monday for PZZ251>253-271>273.
&&

$$

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