NWS Pendleton, OR wrote its last area forecast discussion before the first event at Aug 7, 7:04 AM PST, 1 hour 26 minutes earlier.
Area forecast discussion, Aug 7, 7:04 AM PST, 1 hour 26 minutes before
Area Forecast Discussion
National Weather Service Pendleton OR
804 AM PDT Mon Aug 7 2023
.UPDATE...Nocturnal convection persist this morning, mainly over
north central OR, south central WA, and the southern Blues to the
Foothills of the northern Blues up into the Lower Columbia Basin.
Convection is producing mainly heavy rain and lightning, but not
severe. WPC has a SLGT for excessive Rainfall Outlook over a small
portion of Wallowa County, and a larger area of MRGL ERO for much
of the rest of Wallowa County...and it may be expanded to include
the Cascade east slopes, especially the WA Cascades. PWATs are
about 150-200 percent of normal. Dew points are in the 50s, with a
few lower 60s across the CWA, hence the atmosphere is quite
moist. Thunderstorms today will likely produce heavy rain, with
most of not all storms being wet with wetting rains expected from
them (70-90%). Therefore, no critical fire weather concerns today,
even with LALs of 2-3 (less than a 10% chance of critical fire
weather). Flash Flood Watch over Wallowa County looks good.
An upper low forms again today over the forecast area, with
abundant moisture and QPF by the deterministic, ensembles, and
the CAMs models. This upper low will persist through the day, and
then exits to the east-southeast this evening. Most of the
forecast area is under a thick overcast at this time, however,
any clearing that takes place today will be the best areas for
afternoon convection due to heating with abundant moisture and
instability.
The flow, from east to west, on the north side of the upper low
will produce heavy rainfall with showers and thunderstorms against
the WA Cascades, and possibly the N Oregon Cascades (80-90%
chance). This upper low will exit the area this evening with a
weak ridge over the CWA on Tuesday. This will be followed by
another shortwave trough on Wednesday for more showers and
thunderstorms.
High temperatures today will be cooler than normal, with highs
only in the upper 70s to mid 80s in the Basin, and mid 60s to mid
70s mountains. Minimum RHs will be in the mid 30s to mid 40s
percent, except central OR, with have minimum RHs from 25-35
percent. Tuesday will be much warmer, with near normal
temperatures. Highs will be in the mid 80s to lower 90s lower
elevations, and 70s to lower 80s in the mountains. Wednesday will
have a slight cool down again due to the next short wave trough,
which will produce more clouds and showers/thunderstorms. Minimum
RHs will be mostly in the teens and 20s on Tuesday, but then
mostly 30s to lower 40s percent again on Wednesday. 88
&&
.PREV DISCUSSION... /issued 251 AM PDT Mon Aug 7 2023/
SHORT TERM...Today through Wednesday...A shortwave in the northwest
flow is coming onto the coast this morning and then will pass over
the forecast are today before exiting into central Idaho this
evening. This shortwave will serve as the trigger for another day of
convective showers and thunderstorms over most of the forecast area,
except central Oregon where no precipitation is expected. The
showers will begin to decrease west to east across the forecast area
this afternoon and evening as the shortwave exits. Some brief
locally heavy rain will be possible mainly over the eastern
mountains. A transitory upper level ridge will move over the area
tonight and Tuesday for a dry period before the next shortwave
trough arrives. This trough will pass further to the north, mainly
through Canada, but will clip the region with some rain showers
mainly along the Washington Cascade crest and the northern Blue
Mountains. It will also bring back some breezy to windy conditions
across the forecast area. At this point it appears that humidities
will remain high enough that Red Flag criteria will not be met but
still the winds could present fire spread issues especially in the
fine grassy fuels. Cloud cover today will help hold temperatures to
a little below normal before returning to near normal on Tuesday.
LONG TERM...Thursday through Monday...The long term is expected
to be hot and dry, with the only scenario of any sort of relief
unlikely at this time.
Deterministic guidance is at odds for much of the long term forecast
period. The long term begins with a trough passing to the east with
westerly to northwesterly upper level flow in its wake. Models agree
we continue to remain under a mostly zonal flow pattern through the
end of the week, but by the weekend a Pacific ridge becomes the
primary disagreement amongst the major models. Both the ECMWF and
Canadian expect that the high will build into the coast and over our
region, bringing dry conditions and increasing warmth; whereas, the
GFS expects we'll stay under the zonal pattern before a deep
Canadian low brings cooler temperatures early next week, which the
ECMWF/Canadian believe gets pushed too far east to affect us.
Cluster analysis of the ensembles provides little faith in the GFS,
as the ECMWF and Canadian remain in much better alignment with their
ensemble counterparts.
With the likely scenario a dry ridging pattern, temperatures will
see a steady increase through the long term. By next week, highs in
the mid to upper 90's are possible, bringing another shot of summer
heat to the later portion of the season. The NBM illustrates these
increasing chances, with a 50-70% chance of greater than 90 degree
temperatures on Friday, and by next Monday those chances skyrocket
to a widespread 70-95% chance. Meanwhile the pressure gradients
remain weak under this pattern with little in the way of significant
winds and nil chances of precipitation.
Goatley/87
AVIATION...12Z TAFs...VFR conditions outside of -SHRA or -TSRA
that could bring brief heavier rain, expected primarily for
PSC/PDT/ALW. Rain begins around 12Z and continue through the
afternoon, ending around 19-20Z. Otherwise, expecting mid to high
level clouds with winds generally lighter, 10-15kts, with some
breezier gusts at DLS around 25kts.
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 80 58 87 60 / 60 20 0 10
ALW 82 62 90 63 / 80 30 0 10
PSC 83 65 90 66 / 60 20 0 10
YKM 85 60 89 63 / 30 10 0 10
HRI 85 62 91 66 / 50 20 0 10
ELN 82 59 86 61 / 40 10 0 10
RDM 82 50 88 53 / 10 0 0 0
LGD 78 55 87 57 / 80 50 0 10
GCD 81 52 87 56 / 60 30 0 0
DLS 87 61 90 65 / 20 0 0 10
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Flash Flood Watch from noon PDT today through this evening for
ORZ050.
WA...None.
&&
UPDATE...88
SHORT TERM...91
LONG TERM....87
AVIATION...87