Hail in Oregon, August 11, 2022

Area Forecast Discussion
National Weather Service Pendleton OR
210 PM PDT Thu Aug 11 2022

.SHORT TERM...The forecast area remains in a south to southwest
flow aloft between an upper low pressure system off the PacNW
coast, and an upper ridge over the center of the country. There is
moisture and instability in this southwest flow, which has begun
to cause thunderstorm development over NE Wallowa county within
the last hour. This area, as well as the northern Blue Mountains
of OR and southeast WA will continue to have convective
development through the afternoon and evening. There is a
Marginal Risk for severe thunderstorms as predicted by the Storm
Prediction Center (SPC). This Marginal Risk area is mainly from
the Blue Mountains eastward. There is a slight possibility of a
thunderstorm west of the Blue Mountains, but the chance is very
small and if any do form, they are not expected to become severe.
Thunderstorm development on Friday will be over the same areas as
today, but they will just be general non-severe thunderstorms. The
HREF Dbz Paintball is showing the best areas for thunderstorms
today to be over the Northern Blues and Wallowa County. On Friday,
there is some indication for more thunderstorms by the HREF Dbz
Paintball, but just by a slight amount.

Elsewhere, it will be dry and warm, but not as warm as Wednesday.
For example, the temperature difference across the forecast area
is an average of 2 degrees F cooler than yesterday. Pendleton is
currently 4 degrees cooler than Wednesday at this time. This
cooling will continue through Friday and Saturday, before
temperatures begin to warm back up to around the century mark
early next week during the extended period.

The upper low off the coast will weaken and become an open trough
as it moves northeast into Canada. The forecast will remain in a
southwest flow aloft, but it will be drier and more stable during
the next few days after today. It will become locally breezy in
the afternoons and evenings, mainly through the Cascade gaps and
passes, including the eastern Columbia River Gorge and the
Kittitas Valley.

The flow aloft will begin to become more westerly by Saturday
night into Sunday morning, before an upper ridge pattern develops
during the extended period with a significant warming trend, and
another heat wave. 88

.LONG TERM...SUNDAY THROUGH THURSDAY...The extended period is
characterized by a building upper level ridge originating in the
desert southwest, which allows for hot and dry conditions to return
through much of the week. The lingering low pressure center that has
been located just off the Washington/Oregon coasts over the past
week will finally make its way into British Columbia over the
weekend. This will allow for westerly flow aloft to take over,
keeping temperatures near normal on Sunday as highs peak into the
low 90s across the Lower Columbia Basin. However, the infiltrating
upper level ridge will allow highs to increase into the mid to upper
90s for the Basin Monday, before triple digit high temperatures
return through the Lower Columbia Basin on Tuesday. As the ridge
builds into the area from the south, associated monsoonal moisture
will allow for a slight chance of thunderstorms for our southern
zones through Central Oregon and the John Day Highlands and
extending into northeast Oregon on Tuesday. Current confidence is
rather low due to the discrepancies between models regarding the
strength of the incoming ridge and location of the trough located in
the Gulf of Alaska.

Guidance is in good agreement with the overall pattern, though
differences in trough/ridge location, strength, and timing arise
midweek. The ECMWF hints at a stronger building ridge Monday into
Tuesday, and a stronger and closer trough in the Gulf of Alaska than
that of the GFS. This would provide warmer and drier conditions
than the GFS through midweek. However, recent guidance has
trended weaker in terms of the building ridge and deepening
trough. Current EFI values highlight the only weather concerns in
the long term being associated with the hot temperatures returning
on Tuesday and extending through the remainder of the workweek.
The 500mb EOF patterns mirror deterministic outcomes as ensemble
differences regarding ridge strength are indicated. The cluster
phase space does show the ECMWF being more representative and more
in line with its associated ensembles. Thus, the extended
period's forecast does lean slightly toward the ECMWF outcome of a
stronger ridge, warmer temperatures, drier conditions, and
isolated thunderstorms for Central and Northeast Oregon Tuesday
and Wednesday. 75

&&

.AVIATION...(Previous Discussion)...18Z TAFS...VFR conditions
currently at all sites, which will stay the course through the
period. Convection is expected over the NE Oregon mountains later
this afternoon, but should remain east of PDT and ALW. However,
there could be some periods of gusty and erratic winds occurring
at PDT and ALW due to passing thunderstorms moving through the
Blue Mountains. Winds will slowly increase through the morning,
leading to northwest winds of 10-20 kts this afternoon and evening
for DLS/PDT/BDN/RDM. 75

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  93  59  87 /   0   0  10   0
ALW  63  95  63  89 /  10   0  10  10
PSC  65  98  65  92 /   0   0  10   0
YKM  58  96  58  89 /   0  10   0   0
HRI  63  97  62  91 /   0   0  10   0
ELN  60  94  59  85 /   0  10  10   0
RDM  52  90  48  86 /   0   0   0   0
LGD  58  93  55  86 /  10  20  10   0
GCD  55  96  53  91 /   0  10  10   0
DLS  63  90  62  86 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.

&&

SHORT TERM...88
LONG TERM....75
AVIATION...75