270
FXUS66 KPQR 201702
AFDPQR

Area Forecast Discussion...Updated Aviation
National Weather Service Portland OR
1002 AM 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 Sat night and Sun, with
some light showers and a few thunderstorms at that time. Bit cooler
with mix of sunshine and clouds, and maybe a few showers on Sunday.
Afterwards, increased onshore flow will maintain more comfortable
temperatures for Monday and next week.
&&

.SHORT TERM...(Saturday 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, first in Lane county, with that
     potential spreading northward.

  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.

Typical mid-summer pattern over the region, with strong high pressure
over the Great Basin states. This is maintaining warm air mass across
the western USA. Overall, have seen slow warming of the 850 mb to 700
mb temperatures over past few days, with models showing 850 mb
peaking today at 22 to 25 deg C. As such, with modeled soundings,
seems reasonable to expect afternoon highs across the interior
lowlands to reach the middle 90s. Cooler along the coast, where
morning clouds and fog will break up and give way to sunshine. But,
afternoon temperatures on the coast only rising to the upper 60s to
lower 70s. Current forecast look on track, so no changes for
temperatures, and will maintain current Head Advisory.

Skies will gradually become more hazy as the day progresses,
especially to south and east of Salem. This due to all the smoke that
will be caught in the southerly flow aloft. Areas to east and
southeast of Albany may have areas of smoke as well, as light winds
will allow for smoke from the Ore Fire (near Blue River, Oregon) to
drift westward, with somewhat limited dispersion.

Now, bit of excitement returns Saturday night, as upper trough
offshore will send a bit of energy towards the region. As it
approaches, it will coincide with a plume of monsoonal moisture over
the Sierras. Moisture pool is not all that deep, but think will be
similar scenario that saw earlier in the week, with isolated to
scattered showers developing over southern Oregon later Sat afternoon
into the evening. With the south to southeast flow, will see the
convective debris clouds (whats left of weakening showers over time)
drifting north to northwest overnight. Models have been bit weak on
depicting the thunderstorm potential. But, based on mid-level lapse
rates for Sat night into Sun, seems will have a two areas of concern
for higher potential of thunderstorms. First, with the convection
drifting to the northwest out of south central Oregon into the Lane
County Cascades, and then drifting westward over the west slopes of
the Cascades and lower foothills. This activity will spread north and
westward Sat night, likely reaching the Columbia River by daybreak
Sunday. Again, moisture will be limited, so looks like another round
of low-rainfall production from these storms. Then, as the main upper
disturbance offshore nears closer to the region, will have another
area of showers and few thunderstorms form over the west-central
Oregon Coast Range and offshore Sat night into Sun am. So, bottom
line: isolated to scattered light rain showers expected Sat evening
over Lane County, with that spreading to the north and west through
Sun am. Add to that, a chance of thunderstorms, though best chance
will be over the Cascades and along the coast/over the Pacific
waters.


On Sunday, will see the showers/thunderstorms potential lift farther
northward, mainly to north of a Tillamook to Salem line for Sunday
am, then that shifting to the Cascades by mid-afternoon. So, mix of
sunshine and clouds with lingering haze expected. But, with the
clouds and bit more onshore flow, will see inland temperatures down a
bit, with highs in the 80s. Onshore flow will gradually strengthen
later in the day, as the upper system passes on the north and east of
the region. So, will see chance of showers/thunderstorms end from
west to east in the afternoon. The haze will gradually thin as well,
as the south winds aloft turn more west to southwesterly and the haze
is pushed towards the east-northeast.

.LONG TERM...Monday through Thursday...Temperatures return to that
more expected for mid to late July for next week. Upper level
troughing nudges into the Pacific NW on Monday with strong onshore
flow. Marine stratus more likely to push inland Monday morning, with
inland highs in the upper 70s to near 80s. WPC cluster analysis
remains in good agreement with model ensembles showing upper level
low centered near Haida Gwaii on Tuesday, slowly shifting east into
British Columbia by mid-week. NBM guidance suggests temps will likely
trend closer to the mid-80s as near seasonal normals and dry weather
persists next week.
&&

.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, and along the coast. Now,
given the forest fuels that are more conducive to ignition and
carrying a fire, will maintain the current Fire Weather Watch. 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 Fire
Weather Watch.

&&

.AVIATION...Marine stratus this morning continues to affect
coastal terminals, with IFR conditions persisting at the moment.
Northern coast likely clears to VFR within an hour or two (by 20z
Sat), with 60-80% chance of IFR ceilings returning around 06z Sun.
Southern coast sees 50-60% chance of 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 offshore will gradually strengthen today
and with thermal low pressure on south Oregon coast, will see
return of northerly winds. As pressure gradients tighten today,
expect gusts up to 25 kt into Sunday. Seas 3 to 5 ft range, with a
mix of variable period swell, but with gusty winds, will have
choppy, steep seas.

Cold water and shallow marine stratus will result in patchy,
dense fog for near shore waters (visibility 1 NM or less) through
mid morning.

/mh

&&

.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...Dense Fog Advisory until 11 AM PDT this morning for PZZ210-
     251>253.

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

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

$$

www.weather.gov/portland

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