Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 250015 AAB
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
500 PM PDT WED AUG 24 2016

Updated AVIATION Discussion

.SHORT TERM...Tonight through Saturday...A well amplified upper
level ridge of high pressure will remain stationed over the eastern
Pacific through Friday keeping the forecast area under a dry
northerly flow. Then a shortwave riding over the top of the ridge
will intensify as it drops down the Canadian coast Friday night and
Saturday establishing an upper level trough over western Canada.
This will turn the flow more westerly over the Pacific Northwest
with a weak frontal passage expected Saturday afternoon and evening.
The front will bring breezy westerly winds back to the forecast
area and will be a fire weather concern.

.LONG TERM...Saturday night through Wednesday...A Mid/upper level
longwave trough over far NE Pacific and British Columbia Saturday
night puts interior Pacific Northwest on the southern flank of the
trough, yielding a westerly component to the flow aloft across the
forecast area, which produces sinking air that persists through the
extended period for dry conditions through Wednesday. However, there
will be a slight chance of showers along the east slopes of the
central Washington Cascades beginning Sunday and continuing through
Wednesday. A strong mid/upper level closed low moves SE in the Gulf
of Alaska on Monday, which causes the longwave trough to retrograde
westward on Monday. There are differences between the 12Z GFS and
the ECMWF runs with regard to just how progressive the repositioned
longwave will be. Despite the fact that flow aloft over forecast
area backs from west to southwest on Monday through Wednesday, by
virtue of the new low in the Gulf of Alaska causing the longwave to
retrograde, the air mass on the eastern flank of the longwave that
streams across the forecast area will be too dry to support shower
activity away from the Washington Cascades. The 18Z GFS run is
slower than the 12Z ECMWF run in terms of keeping the axis of the
longwave offshore whereas the ECMWF indicates the longwave moving
inland and across the Pacific Northwest. Due to differences in the
amplitude and location of the aforementioned longwave trough, I have
low confidence with respect to showers in the forecast area through
the extended period and have kept the forecast area dry, except for
the east slopes of the central Washington Cascades through
Wednesday.  Polan

&&

.AVIATION...00Z TAFS...VFR conditions through next 24 hours. FEW-SCT
070-090 this afternoon through this evening, then SKC overnight and
Thursday morning. Diurnal, terrain driven winds 5-9KT, except winds
at KPDT, KRDM and KBDN will be 10KT for the remainder of this
afternoon with gusts to 18KT. Thursday will be drier with only a few
cumulus clouds over the Blue Mountains.  Polan

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  55  87  54  88 /   0   0   0   0
ALW  60  88  61  88 /   0   0   0   0
PSC  55  90  57  91 /   0   0   0   0
YKM  57  90  58  92 /   0   0   0   0
HRI  52  89  55  90 /   0   0   0   0
ELN  55  89  56  91 /   0   0   0   0
RDM  45  84  45  88 /   0   0   0   0
LGD  50  82  46  85 /   0   0   0   0
GCD  47  82  48  86 /   0   0   0   0
DLS  58  93  61  95 /   0   0   0   0

&&

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

$$

91/99/99



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