129
FXUS66 KPDT 152328
AFDPDT

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

Updated Aviation Discussion

.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...00Z TAFs...VFR conditions to prevail through the
period. CIGS will be mostly few-sct AOA 12kft AGL through this
evening, and developing again by tomorrow afternoon. Smoke from
area wildfires may impact vsby at sites PDT/ALW after 10Z,
lowering CIGS down to 6SM, though confidence in MVFR or lower
conditions is low (20-30%). Winds of 12-15kts will impacts sites
PDT/RDM/BDN/YKM through this afternoon, becoming less than 12kts
overnight. Site DLS will see winds 15-20kts with gusts up to 30kts
through 4Z this evening, becoming less than 12kts overnight. All
other sites will see light winds, less than 12kts, through the
period. Lawhorn/82


.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...82