908
FXUS66 KPDT 152145
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
245 PM PDT Mon Jul 15 2024

.SHORT TERM...
Tonight through Wednesday night...High pressure will build back
over the region from the south. Additionally, an area of low
pressure will move from off the northern California coast Tuesday
afternoon to near the Washington coast by Wednesday and weaken
into an open wave.

As this low/wave moves by it could touch off some thunderstorms,
with the east slopes of the Cascades the most likely location.
However guidance is mixed on thunderstorm potential further east,
with some guidance showing at least some CAPE across the Basin.
The ECMWF EFI is not all that excited about thunderstorm potential
at all on the east side of the Cascades, with its values generally
0.5 or less. The HREF does have some thunderstorm potential across
central Oregon late Tuesday afternoon, and then more potential
toward morning further north.

Based on the best available guidance so far, we will be issuing a
fire weather watch for the east slopes of the Cascades, as this is
where the guidance shows the best chance for thunderstorms. The
biggest question overall is how widespread the thunderstorms will
be. It is possible the the fire weather watch will have to be
extended further east.

The other weather concern is increasing heat, as high pressure
builds northward. Temperatures will once again be in the 101-103
range in the Columbia Basin, Yakima Valley and Blue Mountain
Foothills on Tuesday and probably a degree or so warmer on
Wednesday, with Wednesday likely being the warmest day. Some
guidance doest suggest Thursday will be just as warm, while other
guidance suggests a bit cooler temperatures on Thursday.

A heat advisory is being issued for the Columbia Basin, Columbia
Gorge, Foothills of the Blue Mountains, Yakima Valley and
Kittitas Valley. For the Gorge and Foothills of the Blue Mountains
it will be in effect Tuesday and Wednesday everywhere else it will
run through Thursday. HeatRisk values will be moderate to Major
Tuesday, Major on Wednesday and Moderate to Major on Thursday.

Probabilities of high temperatures >=100 degrees are >80 percent
in most of these areas Tuesday and Wednesday and 80 to 90 percent
in the Basin on Thursday, though much lower elsewhere.

High temperatures during this time will be about 10 to 15 degrees
above normal in the advisory area with overnight lows 5 to 6
degrees above normal.

.LONG TERM...
Thursday through Monday...Models are in excellent agreement in
keeping a persistent upper level ridge over the western states
through most of the long term period with only minor differences
developing Sunday. Differences increase further on Monday when an
upper trough approaches the Pacific NW coast and may flatten the
ridge to our south. Heat will be the biggest concern through the
long term and temperatures will remain well above normal with
temperatures peaking next weekend. While hot and dry conditions
with a southwest flow tends to favor thunderstorm development,
models are showing limited moisture and instability, so the
forecast has no showers or thunderstorms.

Thursday and Friday, models are in excellent agreement in having a
strong ridge centered over the Rockies with a southwest flow over
the area. Temperatures on Thursday will be 95-105 in the lower
elevations and in the 80s and lower 90s in the mountains. Model
guidance suggests a modest marine push through the Columbia Gorge
that will generate west to northwest 10 to 20 mph winds in the
afternoon. Cooler air from the marine push will lower temperatures a
few degrees on Friday to the low 90s to around 100 while the
mountains will be mainly in the 80s.

On Saturday, model clusters are in good agreement in having the
ridge strengthen further and shift the ridge axis westward closer to
our area. This will warm temperatures 3 to 7 degrees in the lower
elevations to 100 to 105 with a few upper 90s in central Oregon. The
mountains will be in the 90s. On Sunday, a few differences develop
between model ensemble members with 65 percent keeping a very strong
ridge centered over Idaho and Montana while the others show an upper
trough approaching the coast and weakening the ridge. Model guidance
shows a few degrees of cooling in central Oregon and over the
Cascades but warms the rest of the area a couple more degrees. This
will raise the Columbia Basin to 102 to 107 while central Oregon
north to the Columbia Gorge will be in the upper 90s. The mountains
will remain in the 90s. Model probabilities show a 70-90 percent
chance of 100 degree temperatures in the Columbia Basin Saturday and
Sunday with a 15 to 20 percent chance of 110 degrees in the eastern
Columbia Basin and eastern Blue Mountain Foothills on Sunday.
Overnight lows in the Columbia Basin will be in the mid 60s to lower
70s so heat relief will be modest. Heat highlights look probable
given these temperatures next weekend.

Differences increase Monday as 65 percent of the models keep a strong
ridge over Idaho with some differences as to the location of the
offshore trough. Those differences affect 500 mb heights over our
area and therefore the temperatures. The other 35 percent have the
trough overhead and a much weaker ridge moving off to the east. The
NBM favors 3 to 6 degrees of cooling and have gone with that. This
gives the Columbia Basin upper 90s to lower 100s while the rest of
the area is in the mid 80s to mid 90s. Models also suggest another
modest marine push Monday afternoon with 10 to 20 mph winds in the
Kittitas Valley and Columbia Gorge. Perry/83

&&

.AVIATION...
18Z TAFs...VFR conditions are expected to prevail at all
TAF sites with just FEW-SCT clouds at or above 18K feet AGL.
However, smoke from area wildfires reduced VSBYs along the Blue
Mountain Foothills earlier this morning from 9S9 to PDT and ALW
though increasing winds and breaking surface inversions have
improved VSBYs in the last couple of hours. Tonight will see
potential once again for FU to reduce overnight and early morning
VSBYs along the Blue Mountain Foothills. Due to the uncertainty of
smoke concentrations, have limited mention of 6SM FU to PDT from 13Z-
18Z tomorrow morning. Westerly to northwesterly winds of 10 to 20
kts with gusts to 25 kts is expected at DLS, PDT and ALW through 03Z
this afternoon and at RDM and BDN from 22Z-03Z. Otherwise, winds
will remain below 12 kts for the next 24 hours. Perry/83

&&


.FIRE WEATHER...
Fire weather watches will be issued for the east slopes of the
Cascades and nearby areas for Tuesday late afternoon/evening
through Wednesday late afternoon/evening. These watches may be
expanded eastward. Fire weather concerns are elevated elsewhere
due to the continued hot and dry conditions and Haines indices of
5. Dry thunderstorm potential begins Tuesday afternoon in central
Oregon and moves northward with time. Guidance has highest
probabilities along the Cascades, but there is at least (20-30%)
along the Columbia Basin on Wednesday. How widespread the
lightning will be is the big question.


.PRELIMINARY POINT TEMPS/POPS...
PDT  58  99  65  99 /   0   0   0  20
ALW  64 102  67 103 /   0   0   0  20
PSC  64 102  67 103 /   0   0   0  20
YKM  61 101  68 100 /   0   0   0  20
HRI  63 103  67 104 /   0   0   0  20
ELN  62 101  67 100 /   0   0   0  20
RDM  53  98  60  96 /   0   0  10   0
LGD  56  98  61  98 /   0   0   0  20
GCD  57  98  64  99 /   0   0  10  10
DLS  63 105  72  99 /   0   0   0  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from noon Tuesday to 10 PM PDT Wednesday for
     ORZ041-507.

     Fire Weather Watch from Tuesday afternoon through Wednesday
     afternoon for ORZ610-611-639-640.

     Heat Advisory from noon Tuesday to 10 PM PDT Thursday for ORZ044.

WA...Heat Advisory from noon Tuesday to 10 PM PDT Wednesday for
     WAZ024-029.

     Heat Advisory from noon Tuesday to 10 PM PDT Thursday for
     WAZ026>028.

     Fire Weather Watch from Tuesday evening through Wednesday
     evening for WAZ690-694-695.

&&

$$

SHORT TERM...77
LONG TERM....83
AVIATION...85