647
FXUS66 KPDT 102335
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
435 PM PDT Wed Jul 10 2024

.Updated for Aviation...


SHORT TERM...Tonight through Friday night...The heat has reached
its peak, and the Excessive Heat Warnings and Heat Advisories are
set to expire at 11 PM. Unfortunately, our forecast area will
remain in the minor to moderate HeatRisk through Friday.
Additional heat related statements may be issued for the upcoming
weekend as confidence is high (80%) that we will be pushing in the
moderate or even major HeatRisk category. No significant cooling
is in sight for the next several days.

Red Flag Warnings are in effect for most of the forecast area--dry
and unstable conditions along the Blues, Wallowas, and the John
Day-Ochoco Highlands and wind/RH threats for the Lower Columbia
Basin, Kittitas Valley, the eastern CR Gorge, and central Oregon.
The warning was expanded to include fire zone OR610 which covers
the east slopes of the northern Oregon Cascades, including the
Warm Springs area. These are in effect through 11 PM this evening
with the exception of fire zone 690 which covers the Kittitas
Valley which is in effect until 8 PM Thursday.

The upper level ridge has shifted eastward with the axis along the
northern Rockies. WA/OR are on the backside of the ridge and under
a southwest flow aloft. The weakening ridge has enhanced the
instability with dry air at the surface and aloft. At the surface,
the inverted thermal trough east of the Cascades has strengthened
the cross-Cascade gradients with breezy winds observed through
the CR Gorge and Cascade gaps. Fortunately, this is not a strong
onshore flow and marine push as evident by the lack of stratus
clouds along the coastline. Otherwise, there would be much
stronger wind speeds that would result in more pronounced red flag
conditions. The pattern changes little through Friday, therefore
winds will be locally breezy in central and north central Oregon.
Wister/85

LONG TERM...Saturday through Wednesday...

Bottom Line Up Front

1. Breezy conditions return along Cascade east slopes and through
   the Cascade Gaps could leave to fire weather concerns.

2. Thunderstorm potential Saturday and Sunday.

3. Dry and warm conditions remain in place.

Models are in firm agreement with the upper level high perched over
the Four Corners and an upper level low sits off the coast of
California. This synoptic set up will cause west to south west flow
aloft. This will create the tightening of the surface pressure
gradients across the Cascades. A diurnal wind pattern will set
itself up each day with winds becoming breezy along the east slopes
of the Cascades especially through the Cascade Gaps. NBM is showing
a near 88% probability of the Columbia River Gorge, foothills of the
southern Blues and the lower Columbia Basin will see daily sustained
wind speed averaging between 10 to 15 mph. 60-80% of the raw
ensembles are in agreement with what the NBM is showing. Moving on
to the Kittitas and Yakima Valleys, NBM in showing 90% probabilities
of sustained winds of 15 to 20 mph with 90 to 100% of the raw
ensembles in agreement. Daily daytime relative humidities will be in
the teen with a few scattered locations being in the 20s. With the
elevated winds, dry RH values and the incoming instability, fire
weather concerns may become elevated as the event draws nearer. As
of right now, confidence in fire weather conditions is low (10-20%).

Models remain in firm agreement through the period with the synoptic
patter with the upper level low remaining off the coast of
California and the upper level high over the Four Corners. However,
models show the low to strengthen just a bit and the high to move
slightly southward a touch. Just enough that there is some upper
level moisture that gets wrapped around the high and ushered into
the region Saturday night with the majority ushering in Sunday. This
set up will allow for thunderstorm probabilities through central OR
and along the Ochoco-John Day Highlands before spreading across the
rest of the eastern mountains and into Wallowa County. Model derived
soundings for Deschutes and  Grant counties show MUCAPE values
cresting 500 J/kg, lapse rates of 9.5 C/km, lifted index of -2 and
bulk shear of 49 kts. PWATs within the sounding is 0.63 inches and
with the dry layer beneath the moisture, these thunderstorms on
Saturday will be dry. The ingredients are there for thunderstorms on
Saturday, however, raw ensembles are only showing a probability of
15% due to the model variances in the amount of moisture that will
make its way into the region. Sunday shows a tad more promise with
raw ensembles showing upwards of 25% probabilities for thunderstorms
with model derived sounding showing a much more moist and unstable
atmosphere. Model derived sounding along the eastern mountains have
areas where MUCAPE values are cresting over 500 J/kg with some
locations seeing values as high as 900 J/kg, lapse rates of 8.9
C/km, lifted index of -4 and bulk shear of 50 kts. PWATs are still
in the 0.65 inch range and with the continued dry and warm surface
conditions, any rain associated with these storms will again be
light to nil. This will also lead to some potential fire weather
concerns and will be monitored as the event draws nearer.

Lastly, even with the synoptic pattern shift, models are still
showing the region to be under dry and warm conditions through the
long term period. EFI is showing temperatures to remain above normal
through the beginning of the long term before slowly teetering more
towards climatological normal by mid work week. 90% of the raw
ensembles have the Pendleton area back in the mid to upper 90s, 62%
has the Basin, Gorge, Yakima Valley and central OR to be in the
upper 90s and into the 100s. Temperatures will steadily decrease
through the long term period before leveling off by Wednesday.
Bennese/90

AVIATION...
00Z TAFS...VFR conditions with gusty winds lingering through the
evening. Winds will gust to around 30 kts at DLS and 20 to 25 kts
at PDT, RDM, BDN and YKM. Winds will decrease overnight to 10 kts
or less everywhere except DLS. Winds will gust 20 to 25 kts on
Thursday afternoon at DLS, PDT, BDN and RDM.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  96  60  97 /   0   0   0   0
ALW  66  99  65 100 /   0   0   0   0
PSC  65 100  64 101 /   0   0   0   0
YKM  62  98  61  99 /   0   0   0   0
HRI  65 100  63 101 /   0   0   0   0
ELN  64  94  62  99 /   0   0   0   0
RDM  53  95  55  96 /   0   0   0   0
LGD  60  95  59  98 /   0   0   0   0
GCD  59  98  60 102 /   0   0   0   0
DLS  64  95  63  98 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 10 PM PDT this evening for ORZ041-
     044-505-507-508-510-511.

     Red Flag Warning until 11 PM PDT this evening for ORZ610-639>645.

     Heat Advisory until 10 PM PDT this evening for ORZ049-050-502-
     503.

WA...Excessive Heat Warning until 10 PM PDT this evening for WAZ024-
     026>029-521-523.

     Red Flag Warning until 11 PM PDT this evening for WAZ691>693.

     Heat Advisory until 10 PM PDT this evening for WAZ030.

     Red Flag Warning until 8 PM PDT Thursday for WAZ690.

&&

$$

SHORT TERM...85
LONG TERM....90
AVIATION...77