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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

                            
000
FXUS66 KPDT 230847
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
147 AM PDT Sun Jun 23 2019

.SHORT TERM...Today through Tuesday night...Weak ridging will give 
way to mostly zonal flow this afternoon through early Tuesday. 
Breezy to locally windy conditions through and downwind of gaps 
through the Cascades will subside a little this morning before 
strengthening again late this afternoon and into the evening. With 
slightly weaker onshore flow expected tonight think these will be a 
bit weaker than last night. Will need to keep an eye on afternoon
RH trends in WA675, the diurnal increase in winds downwind of the
Kittitas Valley could produce an hour or so of marginal Red Flag 
conditions if RHs reach criteria, mostly limited to the Hanford 
area. Cascade gap winds will weaken further Monday and Tuesday
as the west side warms up a bit in response to weakening onshore
flow.

Flow begins to turn southwesterly Tuesday morning in response to an 
upper level low dropping south along the WA/OR coast. Models are in 
reasonable agreement in a plume of steepening mid-level lapse rates 
advecting into the southeastern third (all model consensus) or half 
(WRF based consensus) Tuesday afternoon. This coupled with surface 
dewpoints in the mid 40s to lower 50s and adequate surface warming 
should yield some marginal surface based instability with 
thunderstorms possible. The highest confidence in storm coverage 
will be over the Blue Mountains, with less confidence in coverage in 
the Blue Mountain foothills, Oregon Cascades and Central Oregon 
where both lapse rates and surface fields are somewhat in 
question. Strengthening southwesterly mid-level flow associated with 
the aforementioned upper low combined with southerly/southeasterly 
flow at the surface will yield some 0-6KM shear in the 50-60KT 
range with cloud layer shear 60+KTs. With rather marginal 
instability west of the Blues storms may struggle to avoid getting
sheared apart in an environment like this. In the Blues where 
MLCAPE is forecast in the 500-1000J/kg range should see a little 
better chance of persistent storms with at least a conditional 
threat of large hail and damaging winds. Storms will also be quite
fast moving (around 35KTs), so while they are not expected to be 
dry, will have a limited temporal window for rain after fresh 
strikes to mitigate any ignitions. For now, have continued with a 
slight chance of thunder (LAL 2) for all of the previously 
mentioned areas, but will likely need to bump this up for portions
of the area as confidence in placement increases. Peck

.LONG TERM...Wednesday through Saturday. The extended period will
be dominated by a slow moving upper low. Models are in reasonable
agreement with the location of the low through Friday as it moves
across the Pacific northwest. Some differences though in timing 
and placement of precipitation. This mainly due to jet streaks and
short waves moving through. The low will be centered just offshore
Wed then move slowly across Washington and Oregon Thu and Fri. 
Expect there will be showers with a chance of thunderstorms each 
day. Skies will be mostly cloudy and temperatures below normal 
with highs in the 60s and 70s. Lighter winds than what we have 
seen the past few days. By Saturday the upper low is moving off 
to the east however a weak upper trough remains over the region.
94

&&

.AVIATION...06Z TAFs...Previous Discussion...VFR conditions will 
prevail for the next 24 hours. There will be some high thin cirrus
and possibly some high based cumulus Sunday afternoon. Skies will
become mostly clear tonight, except for a few high then cirrus 
clouds. Winds will diminish overnight, but they will increase 
again in the eastern Columbia River Gorge and north central Oregon
as well as the Kittitas Valley by Sunday afternoon. 88


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  75  50  75  52 /   0   0   0   0 
ALW  77  53  78  55 /   0   0   0   0 
PSC  81  53  81  55 /   0   0   0   0 
YKM  77  49  77  53 /   0   0   0   0 
HRI  78  53  80  55 /   0   0   0   0 
ELN  67  48  71  50 /   0   0   0   0 
RDM  72  43  75  46 /   0   0   0  10 
LGD  70  45  72  48 /   0   0   0  10 
GCD  70  45  72  49 /   0   0   0  10 
DLS  71  53  76  56 /   0   0   0   0 

&&

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

$$

74/94/94