Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 282144
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
244 PM PDT WED SEP 28 2016

.SHORT TERM...Tonight through Saturday...A ridge of high pressure
over the northern Plains and Rockies will continue to impact the
forecast area with warm dry conditions through Thursday. Then a
trough of low pressure in the eastern Gulf of Alaska will drop south
and off the Pacific Northwest coast Friday and Saturday as the ridge
shifts eastward. This will begin to cool temperatures and increase
the threat of precipitation to the forecast area heading into the
weekend. Could see first the showers occurring Thursday night as the
initial cold front moves over the region and then again Friday night
and Saturday.

.LONG TERM...Saturday night through Wednesday night...Much of the
extended period will feature unsettled weather, as the overall
weather pattern transitions to a mean trough over the Pacific
Northwest. This will mean more clouds, chances for showers and
cooler temperatures....anywhere from about 3 to 8 degrees below
average each day. Snow levels will be between 5500-6500 feet most of
the period.

For Saturday night trough Sunday night a closed upper level low
pressure system will approach the Oregon coast. The latest model
trends are that the core of the energy associated with this low will
slide a little further south, across southern Oregon. Therefore Pops
were decreased slightly with this forecast update, especially for
the northern portion of our CWA. However, there will still be a
slight chance for showers Sunday afternoon across much of northern
and Central Oregon with a chance for showers in the Oregon
mountains. It is now looking possible that the Lower Columbia Basin
of Washington and far northern Oregon could stay dry on Sunday as
the low slides south. Instability looks to be lacking, and current
guidance has it almost non-existent, therefore left out any mention
of thunder for now. Temperatures will be much cooler with highs only
in the 60s for the lower valleys/basins with upper 40s and 50s
mountains Sunday afternoon. Snow levels will be between 5500-6500
feet above MSL during this time...so the higher mountains could very
well see some snow showers or graupel showers at times. The latest
guidance has trended drier for Monday and Monday night, as the area
could be between weather systems. However, with the timing and
placement differences in the models still left in a slight chance to
low end chance for showers, mainly in the mountains during this time
period. Temperatures will remain cool, very similar to Sunday for
Monday/Monday night. Then, for Tuesday and Wednesday the latest
guidance has some significant differences. The latest Euro was
faster, bringing showers back into the forecast area with a deeper
trough Tuesday through Wednesday. Meanwhile the latest GFS keeps
Tuesday and Wednesday mainly dry, before bringing the next system
into the area in a northwest flow next Wednesday night. A blend of
the latest available was used for the official forecast, until these
timing differences can be resolved. 77


&&

.AVIATION...Previous Discussion...18Z TAFS...VFR conditions will
prevail across the entire area through the next 24 hours. There are
SCT high clouds near 25K FT AGL INVOF KYKM late this morning...these
will try to drop southeast toward KDLS and perhaps KPSC into the
early afternoon. Otherwise skies will be mostly clear for the
remainder of the area through the day and the first part of the
overnight. Some additional high clouds will approach the central and
western terminals after 29/15-18z. Winds will be light...diurnal and
terrain driven, generally AOB 10 KTs through the period. 77


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  51  78  52  73 /   0  10  20  10
ALW  54  79  56  75 /   0  10  20  10
PSC  54  80  54  77 /   0   0  20  20
YKM  48  81  47  78 /   0   0  10  10
HRI  51  80  53  76 /   0   0  20  20
ELN  48  79  46  75 /   0   0  10  10
RDM  43  80  40  72 /   0  10  20  10
LGD  47  82  48  78 /   0  10  20  10
GCD  49  84  47  77 /   0  10  10  10
DLS  54  79  51  74 /   0   0  10  10

&&

.PDT Watches/Warnings/Advisories...
OR...None.
WA...None.
&&

$$

91/77/77



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