342
FXUS66 KPQR 202144
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
244 PM PDT Sat Jul 20 2024

.SYNOPSIS...Hot inland today, with bit cooler weather along the
coast where morning clouds will give way to sunshine. Upper
disturbance offshore will lift north across the region Saturday
night and Sunday, with some light showers and a few
thunderstorms Saturday night through Sunday afternoon. Bit
cooler with mix of sunshine and clouds Sunday. Afterwards,
increased onshore flow will maintain near normal temperatures
for Monday and next week.

&&

.SHORT TERM...Saturday afternoon through Monday...

Key Messages:
  1) Hot inland today, with highs in the 90s.

 2) Scattered showers and a chance of thunderstorms Saturday
    night into Sunday morning, beginning in Lane county late
    tonight then spreading northward through Sunday morning.

  3) Cooler air spreads inland Sunday night, with temperatures
     near what is expected for late July (lower 80s inland
     with 60s on the coast) for Monday into next week.

Water vapor satellite imagery this afternoon shows our incoming
shortwave situated off of the central California, slowly moving
north, with dry air associated with weak high pressure over
western Oregon and Washington. This high pressure is producing
another day of above normal temperatures. As of 2pm,
temperatures are in the upper 80s to low 90s across the inland
valleys, and are forecast to peak in the mid 90s. Some hazy
skies from wildfire smoke in the Cascades seem to be limiting
temperatures somewhat in the southern Willamette Valley, so
these areas may only reach the low 90s today.

Ensemble guidance is in good agreement that the aforementioned
shortwave trough will move north through NW Oregon and SW
Washington tonight through Sunday. This shortwave will merge
with monsoonal moisture currently situated over the Sierra
Nevada as it moves north, which will allow enough moisture for
the potential of showers over the area tonight through tomorrow
afternoon. CAMs indicate the negative tilt of this trough along
with the midlevel moisture will provide enough elevated
instability for thunderstorm chances tonight, shifting to
surface based thunderstorms along the Cascades tomorrow
morning and afternoon. The locations with the best chances for
thunderstorms are along the coast, Coast Range, and Cascades due
to orographic lift, especially south of a line from Tillamook
to Clackamas County, but a few thunderstorms could meander into
the inland valleys from the terrain. Scattered showers and
thunderstorms will begin in Lane County around 10 PM to
midnight tonight, spreading north/northeast in a line from the
northern Oregon/southwest Washington coast to the central
Willamette Valley by daybreak, then continuing to spread
northeast through the morning and afternoon hours. The majority
of showers should move east of the Cascade crest by 5 PM
tomorrow, with dry weather returning tomorrow night into next
week.

Cooler temperatures will follow this shortwave. Daytime
temperatures tomorrow will drop to the low to mid 80s, then
fall again to the upper 70s to low 80s for Monday for inland
locations. Onshore flow brought behind the shortwave will
continue into Monday due to a longwave trough situated over the
eastern Pacific. -HEC

.LONG TERM...Tuesday through Saturday...Ensemble guidance is in
agreement that a longwave trough will remain situated over the
eastern Pacific through most of next week, keeping high pressure
east of the Pacific NW. NBM guidance indicates temperatures are
expected to hover right around seasonal normals, in the low to
mid 80s inland and 60s along the coast, with onshore flow and
dry weather persisting. -HEC

&&

.AVIATION...Marine stratus from the morning has cleared out of
northern terminals, but the central/southern coast continues to
see marine stratus. KONP is still seeing IFR cigs, and there is
70-80% chance of KONP remaining IFR throughout Saturday as
stratus never fully clears. NNW winds at the coast will continue
picking up going into the afternoon, with gusts up to 25 kt
possible at times during Saturday afternoon and evening.


Small chance of thunderstorms at times after 06-09z Sun beginning
at the coast. The Willamette Valley will see chances beginning
around 18z Sunday, with even lower chance than the coast. Should
generally expect VFR conditions inland, though a high overcast
deck is possible.

PDX AND APPROACHES...VFR conditions expected through the forecast
period. NW gusts to 20 kt possible Saturday evening, between
00-06z Sun. Very low chance of a stray thunderstorm at the end of
the TAF period, around 18z Sunday. /JLiu

&&

.MARINE...High pressure continues to dominate, and wind pattern is
dominated by diurnal cycle. Northerly gusts up to 25 kt possible
at times, mostly during afternoon and evening hours. Seas 3 to 6
ft range, with a mix of variable period swell, but with gusty
winds, will have choppy, steep seas.

Beginning around 8-9pm, slight chance of intermittent
thunderstorms for all waters as a system passes through the area.
Chances are fairly low, 10-20%, but threat exists for an isolated
strike or two. /mh/JLiu

&&

.FIRE WEATHER...Only minor changes in forecasts, but overall
pattern remains on track. An upper level disturbance offshore
will lift across the region late tonight and Sunday. As such,
will see isolated to scattered showers, with a chance of
thunderstorms. Generally, looks like a 15-30% of thunderstorms
over the region, with highest chance being over the
Cascades/foothills, Coast Range, and along the coast. These
zones along with the southern Willamette Valley have been
upgraded to a Red Flag Warning for the potential of abundant
lightning. Even though there is a chance of similar conditions
and a lightning ignition here and there across the north Oregon
Coast Range and Willapa Hills, the forest fuels in those areas
are not dry enough for significant fire spread. That is why
those areas are not in the Red Flag Warning. Additionally, the
central and northern Willamette Valley and Clark County zones
have not been upgraded as the potential for abundant lightning
is much lower, though a few isolated weak thunderstorms are
still possible. -HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Heat Advisory until 11 PM PDT this evening for ORZ111-112-115-
     117-118-120>122.

WA...Heat Advisory until 11 PM PDT this evening for WAZ205>207-209-
     210.

PZ...Small Craft Advisory until midnight PDT tonight for PZZ251>253.

     Small Craft Advisory until midnight PDT Sunday night for
     PZZ271>273.
&&

$$

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