886
FXUS66 KPDT 141724
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1024 AM PDT Sun Jul 14 2024

.UPDATED AVIATION...VFR conditions will prevail through the
forecast period. CIGs will remain mostly clear with a few
scattered upper level clouds with a bit of smoke aloft across the
eastern TAF sites. Breezy conditions across all sites at 10 to 15
with gusts near 25 kts before settling down and returning to
diurnally driven and below 10 kts near/after 4Z. Bennese/90

&&

.PREV DISCUSSION... /issued 255 AM PDT Sun Jul 14 2024/

SHORT TERM...Today through Tuesday...The high pressure ridge over
the western USA continues to be centered over the Four Corners area.
This combined with a weak upper level low pressure off the
California coast is lifting some moisture north through the western
Great Basin into southern and southeast Oregon. This is spreading
some clouds over central and northeast Oregon this morning.
Convective instability this afternoon will be mainly focused over
southern and southeast Oregon but could reach northward into
southern Grant and Crook counties while also clipping SE Deschutes.
Chances are low at 10-20% probability. Yesterday the Fall Fire in
northern Harney County formed a pyrocumulus on top of the smoke
column that produced some lightning strikes and todays weather is
very similar so could see that happen again today. The rest of the
forecast area will be under the influence of a dry westerly flow
with some breezy westerly winds forming along the east slopes of the
Cascades in the afternoon and then pushing out into the Columbia
Basin. The combination of some cloud cover over portions of the
forecast area and the westerly winds will result in high
temperatures being a couple of degrees cooler today. This will still
result in some highs topping the 100 degree mark around the Columbia
Basin and the Heat Advisory continues through this evening.

Weather pattern remain fairly constant on Monday but the westerly
flow looks to be a little stronger over central Oregon which should
suppress convection just a tad southward keeping it out of the
forecast area. The weak upper level low off the California coast
begins to open up and shift northward as a shortwave approaching the
northern California coast. This shortwave looks to combine with
another shortwave rounding a large scale upper level trough over the
eastern Pacific. The trough then begins lifting north into western
Oregon late Tuesday. This brings a return of a southerly flow aloft
into central Oregon increasing moisture and instability parameters
leading to a slight chance (10-15%) of thunderstorms in the late
afternoon and evening. The trough continues lifting northeast into
Washington overnight through early Wednesday. At this point there is
roughly a 5-10% chance of some nocturnal convection impacting the
forecast area mainly from the Columbia Basin over the Washington
Cascades through Wednesday morning. Or, it could just produce some
midlevel Altocumulus clouds. At this point the POPs are less than
10% and prefer to see how subsequent model runs perform before
introducing any showers or thunderstorms for this period of time.

LONG TERM...Wednesday through Sunday...Models remain in good
agreement on the majority of the long term being monotonous and
similar day to day as the region sits between upper high pressure to
the southeast and low pressure troughing off the coast. Under this
pattern southwesterly flow will prevail, generally conducive of
orographically induced thunderstorms, but with moisture lacking the
risk of thunderstorm activity is minimal to nil. The one exception
to this could be at the very beginning of the period, where a few
models indicate a shortwave rounding the ridge producing some
isolated nocturnal convection. But with low confidence (10-20%),
have elected to keep this out of the early morning grids for now
after collaborating with the short term forecaster.

Temperatures throughout the long term are not expected to see much
change as we remain locked into similar conditions daily. Highs will
sit between 95-105 (10-15 degrees above normal), with the NBM
presenting a near daily chance of highs 100+ at 40-80% probability,
with the best chances in the Columbia Gorge/Basin, Yakima Valley,
and foothills of the Blues, giving high confidence (80-90%) in the
temperature forecast. Meanwhile this flow pattern produces minimal
concerns in the way of winds aside from the usual breezes through
the Cascade Gaps, which should help to temper critical fire weather
concerns despite daily minimum RH values into the teens.

At the end of the long term there is a chance to finally see a
breakdown of the pattern but this is where model discrepancies
increase. Current ensemble forecast reasoning suggests a deep upper
low from the Gulf of Alaska will descend along the Canadian
coastline, finally moving inland across our region sometime late in
the weekend or early next week. Either way, this should bring a more
westerly to then northwesterly flow as it does move inland, which
should help to lessen the notable warmth of the region when it does
finally occur. But with models varying when this breakdown occurs,
there is low confidence in the overall forecast beyond Saturday (20-
30%) with high confidence leading up to the weekend (70-80%).
Goatley/87

FIRE WEATHER...Red Flag Warnings are in effect today for a couple
of concerns. A warning for hot dry and unstable conditions (Haines
6) continues for zone 642 over southern Grant and northern Harney
counties. This could result in another day of a plume dominated fire
such as occurred Saturday on the Fall Fire NW of Burns. Conditions
remain similar Monday and Tuesday but with a Haines level of 5
expected. However, these conditions will still be capable of
producing another plume dominated fire scenario.

Other concern will be breezy afternoon through evening winds (10-
20mph) combined with low humidities (8-15%) along the east slopes of
the Cascades and Lower Columbia Basin. Main area of concern will be
from the Warm Springs reservation northward up to the Kittitas
Valley and then eastward to the Hermiston area. This will produce
prime conditions for a period of rapid fire spread on new or
existing fires.

The hot dry conditions will continues Monday but with winds generally
below criteria for another warning. The next concern comes on
Tuesday as the low off the California coast opens and lifts north
into western Oregon. This has a low chance (10-15%) of generating
thunderstorms over central Oregon late in the day through evening.
As the low continues moving northeast overnight there remain a very
low chance (5-10%) of some nocturnal thunderstorms moving north
through the Columbia Basin and east slopes of the Washington
Cascades.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  98  60  95  58 /   0   0   0   0
ALW 101  64  98  63 /   0   0   0   0
PSC 102  66 100  63 /   0   0   0   0
YKM  99  62  98  63 /   0   0   0   0
HRI 101  65  99  62 /   0   0   0   0
ELN  95  64  94  60 /   0   0   0   0
RDM  96  55  94  53 /   0   0   0   0
LGD  96  57  93  56 /   0   0   0   0
GCD  99  58  95  57 /  10  10   0   0
DLS  98  63  97  62 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 10 PM PDT this evening for ORZ041-044-049-
     503-505>508-511.

     Red Flag Warning until 9 PM PDT this evening for ORZ641.

     Red Flag Warning until 11 PM PDT this evening for ORZ642.

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

     Red Flag Warning until 9 PM PDT this evening for WAZ690-691.

&&

$$

SHORT TERM...91
LONG TERM....87
AVIATION...90