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236
FXUS66 KPDT 290329
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
829 PM PDT Tue May 28 2024

.SHORT TERM UPDATE...
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Thunderstorms over far eastern Oregon are
decreasing this evening, and the forecast was updated to end the
thunderstorm threat for areas west of Union and Baker Counties.
Cooler and more stable air has followed the surface cold front,
and the air mass over the rest of northeast Oregon will stabilize
later this evening. This is evident on SPC Mesoscale Analysis that
shows little to no instability over the past hour. Earlier today,
a thunderstorm over Wallowa County prompted the issuance of a
Severe Thunderstorm Warning. Spotters reported hail as large as
penny size in the town of Wallowa. Heavy downpours were also
associated with many of the storms in Wallowa and Baker Counties.
Winds also increased with the frontal passage and are a little
slower to decrease than previous forecast, and winds were adjusted
to extend the breezy conditions until 06Z. Wister/85
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&&

.PREV DISCUSSION... 
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/issued 445 PM PDT Tue May 28 2024/

SHORT TERM...Tonight through Thursday...Still on track to see
scattered thunderstorms across eastern portions of our CWA this
afternoon with a low-end risk of some stronger to very isolated
severe activity as this precipitation evolves this afternoon and
early evening from a cold front moving across. This brings breezy
winds as well, with a northwesterly flow promoting some chances of
mountain precipitation tomorrow that will give way to drier and
calmer conditions by Thursday.

Current analysis of ongoing activity as of this writing shows
plentiful thunderstorm activity developing in a favorable
environment just to our east. Immediate concerns lie with
developing precipitation in Baker County lifting up into a
favorable environment of Union and Wallowa Counties. Mesoanalysis
indicates around 500 J/kg of MUCAPE and around 40-50 knots of
effective shear. Mid-level lapse rates have faltered a bit,
generally around 7-8 C/km, but still favorable enough to be
supportive of thunderstorm structures. This will be the primary
activity to watch this afternoon for any chance of seeing
stronger, possibly isolated thunderstorms, with gusty winds the
primary hazard in this type of environment, though heavy rain and
occasional small hail are also possible. Shower and thunderstorm
chances will continue from the Ochoco-John Day Highlands up into
the Foothills of the Blue Mountains and eastwards through the
Wallowas during the evening hours, with thunderstorms expected to
exit by the late evening and early nighttime hours, around 06-08Z.
Lingering showers are still possible in the Blues/Wallowas and in
the Cascades through Thursday under northwesterly flow, but no
further significant activity is expected.

In the post-frontal environment, breezy winds have been ongoing,
lining up quite nicely with forecast expectations. Gusts just
under 40 mph have been seen, with a few stronger breezes in the
foothills of the Southern Blues and Lower Columbia Basin of Oregon
expected to reach the low 40`s, but expected to continue to remain
just under wind advisory levels of 45 mph. The NBM expects around
a 40-60% chance of gusts near 45 mph with some bullseye of 60-80%
chance in Morrow and western Umatilla counties, likely isolated at
best if they do occur, with similar bullseyes in the Simcoe
Highlands across the high terrain. Tomorrow the probabilities drop
for both Northern Oregon and the Simcoe Highlands, but increase
slightly for the Kittitas Valley; though once again, the forecast
falls on the lower side, with any stronger gusts of 45-50 mph
expected to be isolated at best, precluding a wind advisory in
this region.

Otherwise, as the troughing departs and a weak ridging sets up on
Thursday, conditions both dry and calm with no sensible weather
concerns expected after today. High temperatures in the post-
frontal environment will drop around 5 to 10 degrees on Wednesday,
in the 60`s to low 70`s, with highs then rebounding on Thursday by
around 3 to 8 degrees. Goatley/87

LONG TERM...Friday through Tuesday...Models in better agreement
today, but they are still struggling with the impacts of a
deepening upper level low over the Gulf of Alaska. The EOFs
show discrepancies increasing Saturday and continuing into next
week as the position of the low and how deeply it develops will
determine if we have southwest flow (more likely to see convection)
or westerly flow (drier outside Cascades and the Blues) next week.
WPC cluster analysis shows a weak upper trough moving through
Saturday, but members begin to diverge Sunday. 56% of members are
leaning towards zonal flow while 44% show northwest flow with a
shortwave ridge developing off the coast.  By early next week, all
but one cluster show southwest flow developing over the area which
should open the door to a few days of convection over our mountains.
The ensemble means show a similar pattern so confidence is growing
(40-50%) that we could see a few days of afternoon/evening showers
and thunderstorms, mainly over the mountains next week. At this
time, there is a moderate chance (40-50%) to see 0.10 of an inch of
rain Monday and Tuesday over the mountains. In fact, the mountains
have a 2X better chance of seeing a wetting rain than does the basin.

Looking beyond this period, there is a moderate to high chance (60-
70%) a strong upper level ridge will develop over the four corners
area nosing northwestward resulting in well above normal daytime
highs by next weekend. Earle/81

AVIATION...00Z TAFs...VFR conditions will prevail through the
period. Variable mid to high level clouds can be expected as a
system moves through the area with decreasing clouds overnight.
Winds will be 15-25 kts with higher gusts, decreasing to 12 kts or
less overnight.  However, winds will increase to similar magnitudes
on Wednesday. Wister/85
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&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  44  64  40  69 /  20  10   0   0
ALW  47  67  44  71 /  20  10  10   0
PSC  49  71  45  74 /  10  10   0   0
YKM  39  67  38  72 /  10  10   0   0
HRI  47  70  43  74 /  10  10   0   0
ELN  41  62  41  66 /   0  10   0   0
RDM  39  62  33  70 /   0   0   0   0
LGD  42  60  38  66 /  30  10  10   0
GCD  42  63  36  69 /  40   0   0   0
DLS  48  66  44  73 /  10   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...87
LONG TERM....81
AVIATION...85