Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 291745

Area Forecast Discussion
National Weather Service Pendleton OR
1045 AM PDT Mon May 29 2023

.Updated Aviation Discussion.

.MORNING UPDATE...An upper closed low continues to sit along the
central CA coast this morning, with a westerly flow between it and
a broad upper trough over the western Canadian coast. This is
creating a westerly flow over the CWA. There is some moisture and
instability over extreme southeast portions of the forecast area
today. A slight chance of afternoon showers and thunderstorm will
exist over the extreme southeast portions of the CWA where the
moisture and instability is. SPC has a general risk of
thunderstorms in this area. In addition, both the HREF Paintball
and NBM 4.1 WSUP viewer are showing isolated showers and
thunderstorms this afternoon and evening over extreme southwest
portions of the forecast area. The rest of the CWA looks to be dry
today. Temperatures will be a little warmer than Sunday, with
lower elevations highs expected to climb well into the mid and
upper 80s, possibly 90 degrees in the Lower Columbia Basin, which
will be mainly near HKRI and KPSC. In the mountains, highs will be
in the mid 60s to mid 70s. Temperatures will be cooler where
there are showers and thunderstorms. It will also become breezy to
windy through the Cascade gaps today, especially in the eastern
Columbia Gorge, north central OR into the Lower Columbia Basin and
the Kittitas Valley this afternoon and evening.

SPC has the general risk of afternoon and evening thunderstorms
again on Tuesday again over SE portions of the CWA and again on
Wednesdays. Temperatures on Tuesday are expected to be a couple
degrees cooler than today, with lower elevation highs in the lower
to mid 80s, and mostly lower 60s to lower 70s mountains. Winds
will develop again in the same areas as today.

The winds combined with minimum RH`s will not be enough to
create critical fire weather conditions, or to warrant any fire
weather highlights. However, this will be need to be monitored.
With the warm temperatures, fine fuels will continue to cure.
Critical fire weather conditions are not expected to develop as
RH`s will be mostly in the 20s percent. However the Basin will
have minimum RH`s from 10-20 percent. Will highlight low RH`s
with very warm temperatures and breezy winds in the Fire Weather
Forecast, but there is not yet a need for any fire weather

Wednesday will be cooler, with high temperatures in the lower
elevations in the 70s to around 80 (back to near normal). RH`s
will also be slightly higher, with minimum RH`s in the 20s to
lower 30s. It will become breezy again, in the same areas, except
it will expand to include also the Blue Mountain Foothills on
Wednesday. 88


.AVIATION...18Z TAFs...VFR conditions are likely (95-100% chance)
and forecast over the next 24 hours for all TAF sites. Afternoon
convection will be focused across the central and eastern
mountains of Oregon and southeast Washington with SCT-BKN cumulus
yielding isolated showers and thunderstorms. Cloud cover for TAF
sites is forecast to be limited to FEW cumulus around 080-100 for
non-basin sites. Winds through the Cascade gaps will increase
through the morning and afternoon with KDLS seeing the strongest
winds of around 15 kts sustained with gusts of 25-30 kts.
Elsewhere, sustained winds of 10 kts or less are forecast with a
few afternoon gusts of 15-20 kts for KPDT/KRDM/KBDN/KYKM.


.PREV DISCUSSION.../issued 234 AM PDT Mon May 29 2023/

SHORT TERM...Today through Wednesday...A stretched out upper level
trough extends from the northern Plains back to a closed low off the
California coast. This is allowing a more westerly flow to settle
over the forecast area today which will primarily provide a warm
and dry Memorial day to most of the forecast area. Just a little
moisture from the trough lingering over SE Oregon will lead to some
potential afternoon and evening showers or thunderstorms over the
mountains from southern Grant county to southern Wallowa county.
Will see the continuation of some locally breezy to windy conditions
along the east slopes of the Cascades with high temperatures around
5 to 10 degrees above normal across the forecast area.

The flow aloft over the region begins to buckle and turn
southwesterly Tuesday due to a deepening upper level trough in the
Gulf of Alaska. This will also begin to nudge the closed low into
California with a continued fetch of moisture cutting across SE
Oregon. Again this will lead to a slight chance of afternoon and
evening showers and thunderstorms from Grant county to Wallowa
county but continued dry and mild over the rest of the forecast area
with some locally breezy conditions.

On Wednesday the Gulf of Alaska trough begins to push into the
Pacific Northwest and SW Canada. This will usher cooler and
generally breezy conditions across the forecast area. This will
bring high temperatures back to near normal levels. It will also
push the moisture over SE Oregon a little further east limiting the
shower potential to mainly Wallowa county.

LONG TERM...Thursday through Monday...The long term sees a drying
trend early as we begin to warm into summer heat, with perhaps
finally a chance at precipitation late in the weekend into early
next week.

Thursday begins with a shortwave trough passing through the region
as models have begun to align with the timing of this feature
compared to yesterday`s forecast. This feature is unlikely to
produce any noteworthy weather concerns, however, as precipitable
water values and instability remain dreadfully low, keeping this a
dry system. Speaking of dry spells, this will likely be the case
through the beginning of the weekend as moisture and instability
continue to remain incredibly limited, though perhaps we could see a
very isolated shower on Saturday in either the Cascades or Wallowa
County. Southwesterly flow persists through Saturday, finally being
disrupted on Sunday as a deep low just south of the Gulf of Alaska
gets shunted eastward into Canada. This should then allow for high
pressure to build back over portions of the Intermountain West with
low pressure off of southern California spinning moisture up towards
our region which may then allow for better chances of precipitation.
Instability should jump notably, so we`re likely to see some
thunderstorm activity in the high terrain on Sunday with a more
widespread thunderstorm threat then possible on Monday.

With the building of the aforementioned ridge however comes the
heat. High temperatures on Thursday should be seasonable to perhaps
just a degree or two above in the mid 70`s to low 80`s, but by
Sunday models are coming into agreement that the heat is on. Highs
for the lower elevations should reach between the low 80`s to mid
90`s, around 10 to 15 degrees above seasonable average. The ECMWF
Extreme Forecast Index in showing a swath of above normal
temperatures for the region in good agreement with the deterministic
outlook. Compared to yesterday`s forecast as well the ensembles all
show some sort of ridging building in with the low stuck in
California, also noting solid agreement with their deterministic
counterparts. There is high confidence (80-90%) in the upward trend
of temperatures late next week into the weekend, with moderate to
high confidence (60-70%) in precipitation remaining limited until
late in the weekend into early next week. Goatley/87


PDT  83  51  80  48 /   0   0   0   0
ALW  87  54  84  51 /   0   0   0   0
PSC  89  56  86  52 /   0   0   0   0
YKM  85  51  82  47 /   0   0   0   0
HRI  87  55  84  52 /   0   0   0   0
ELN  80  54  74  44 /   0   0   0   0
RDM  80  45  76  41 /   0   0   0   0
LGD  81  50  78  46 /  10  10  20  20
GCD  80  49  78  44 /  20  20  20  20
DLS  84  53  79  48 /   0   0   0   0




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