447
FXUS66 KPQR 171102
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
401 AM PDT Wed Jul 17 2024

.SYNOPSIS...An upper level disturbance will continue to move
northeastward today, maintaining a slight chance of thunderstorms
for northern portions of the forecast area early this morning, with
best chances remaining from near Mt Hood northward into the
Washington Cascades. Morning clouds give way to clearing skies with
above-average temperatures expected to continue inland through the
weekend, while onshore flow persists at the coast. Slight cooling
trend to near normal temps likely early next week.

&&

.SHORT TERM...Today through Friday...Water vapor satellite imagery
early this morning shows the upper level low spinning off the
southern Oregon coast. Combined with mid-level moisture and
instability, this has produced isolated to scattered elevated
thunderstorms across parts of northwest Oregon overnight, producing
lightning and gusty outflow winds, with little rainfall. The upper
low and associated 500 mb shortwave trough will gradually lift
northeastward across NW Oregon this morning, pushing into central WA
this evening. Will maintain at least a slight chance (10-20%) of
thunderstorms across northern portions of the forecast area through
8 am this morning. Then, appears the threat of thunder remains
confined to the Cascades near Mt Hood northward through this
afternoon. Will largely depend on the speed of the upper low and the
amount of mid-level moisture available. Will maintain the Red Flag
Warnings currently in place through this afternoon. See the fire
weather section for more details.

Mix of clouds this morning, with most areas clearing by the
afternoon. Should see most interior valley locations warm into the
mid to upper 80s. If marine stratus in the southern Willamette
valley holds on longer, temperatures may struggle to get much above
80 degrees. More stable and dry southwest flow aloft returns on
Thursday. Should see high temperatures once again approach 90
degrees inland, while the coast remains under the influence of
morning marine stratus and onshore flow. An upper shortwave trough
will likely deepen the marine layer Thursday night into Friday
morning. Then, the upper level ridge strengthens again over the
Pacific NW by Friday afternoon with 500 mb heights building over 590
dam. Highs once again likely (50-70% chance) around 90 degrees. /DH

&&

.LONG TERM...Saturday through Tuesday...Cluster analysis indicates
good agreement among ensemble guidance showing the upper level ridge
amplifying and shifting back west for Saturday. This will likely
cause temperatures to bump up a few more degrees with highs in the
90-95 degree range. The ECMWF ensemble suggests 850 mb temps peak on
Saturday around 20-22C across the Willamette Valley. NBM guidance
suggests a slight cooling trend into early next week as upper level
troughing begins to nudge into the Pacific NW. This could bring
temperatures closer to normals. Something to watch will be the
potential for another cut-off low and shortwave trough to slide
across the area again Sat night, which could produce another round
of thunderstorms, but confidence remains low at this time.  /DH

&&

.AVIATION...Low pressure off the south Oregon coast, with
southerly flow aloft over the region. Air mass remains unstable,
with scattered showers and isolated TS. Though, high potential of
any TS will be along the Oregon Coast from KTMK to near KONP, and
inland from Portland to Salem, and to the east across the south
Washington and far North Oregon Cascades. As the low offshore
lifts north and east today, will see the TS potential shift east
of the Cascades by mid to late afternoon.

Otherwise, VFR inland with variable mid and high clouds into early
this am, then those clouds will thin out through rest of the am.
Moderate onshore flow will maintain somewhat persistent MVFR CIGS
along the coast through the day. That onshore flow will also
keep areas of MVFR inland from just south of KSLE to KEUG and
K77S. This inland MVFR will break apart and clear by 18Z.

PDX AND APPROACHES...VFR today, with variable mid/high clouds
through 16Z today, then clouds decreasing. A few showers will pass
across the OPs area through 16Z. And, there remains a small
chance (less than 20%) for thunderstorms in/near the terminal area
until 15Z. If does, could see brief wind gusts to 25 kt. The
thunderstorm potential shifts eastward afterwards, staying over
the Cascades after 16Z, and east of Cascades by late afternoon.
/Rockey &&

.MARINE...Upper low pressure sites over the south Oregon coastal
waters early this am, with southeast flow aloft. This maintaining
showers and a few thunderstorms on the coastal waters through
early morning, mainly to south of Cascade Head. As the low lifts
northeast and inland today, will see thunderstorm potential
come to an end by mid morning. Overall, southerly winds 10 kt, but
will see gusts up to 25 or 30 kt around the thunderstorms.

Low pressure remains over the waters today into tonight, with
winds mostly south at 5 to 15 kt. As high pressure builds Thu and
Fri, will see winds becoming more west to northwest at that time.
Still, winds stay in 10 to 15 kt range. Seas mostly a mix of
swell fetches, one out of the west at 2 to 4 ft and another from
the south at 2 to 3 ft. As such, overall combined seas will hold
at 4 to 5 ft.

&&

.FIRE WEATHER...Red Flag Warnings remain for locations north of
Salem through 8 am this morning, and through 5 pm for southwest
Washington Cascades. The upper level disturbance will maintain a 15-
25% chance for elevated thunderstorms, leading to increased fire
weather concerns. Lightning strikes and critically dry fuels east of
the Coast Range may result in numerous fire starts. Expect little
rain with this system, as the surface is very dry. Any rain that
falls from these elevated thunderstorms could evaporate before
reaching the surface, which may result in gusty outflow winds.
Outflow winds from thunderstorms may also result in erratic fire
spread. DH/Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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