Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 191729
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1030 AM PDT Thu Oct 19 2017

UPDATED AVIATION DISCUSSION

.SHORT TERM...Today through Saturday...Have increased temperatures
and lowered RH over southern and eastern portion of the area
ahead of this afternoon/evening frontal passage. Prefrontal winds
have already pushed temperatures near the forecast highs in much
of this area especially where aided by downslope warming. Will
continue flash flood watch for burn areas on east slopes of
washington cascades. Rainfall reports overnight show 1 to 1.5
inches have fallen near the burn areas. Latest models continue to
give another 1/2 to 3/4 inch through early evening before
precipitation decreases. Timing of rainfall into central and
eastern portion of area looks good, so no adjustments needed.
Another concern is the winds over mainly just east of the Cascades
today. Although locally very windy, latest HRRR has surface and
850 mb winds staying below highlight criterion.

Most areas will get rain this afternoon and evening as the front
moves across the area. A westerly flow in the base of the trof
will cause rain shadowing east of the Cascades on Friday. This
flow will produce strong downslope winds at times. Showers will be
limited to mainly the crest of the Cascades and upslope mountain
areas over eastern Washington and Oregon. Models continue to
depict another round precipitation ahead of a warm front late
Friday night and Saturday. Snow levels may be low enough to cause
impacts above 3500 feet and will need to look further at this.

.AVIATION...18z TAFs. Increasing clouds with cigs lowering
through the day as a cold front moves into and across the region
this afternoon and exits overnight for improving conditions. Winds
10-20 KT except at KDLS 5-15 kts today but increasing overnight and
Friday to 15-30 kts behind the cold front.

&&

.PREV DISCUSSION... /issued 428 AM PDT Thu Oct 19 2017/


LONG TERM...Saturday night through Wednesday...A warm front will
be moving northwest through the northeast part of the CWA Saturday
night. Rain shadowing will begin in central OR and south central WA.
Snow levels will be 8000-9000 feet so precipitation will be mainly
rain. Sunday a cold front will move southeast across southeastern WA
and eastern OR. Saturday night and Sunday will be very wet over the
Cascades and eastern mountains where one to two inches or more of
rain will be possible. Sunday night moist westerly flow will
transition to drier northwest flow as an upper level ridge begins to
develop offshore. Rain will taper off during this period. The upper
level ridge will slowly shift east over WA and OR Monday night
through Tuesday evening or Wednesday. Subsidence from the ridge will
bring dry and warmer daytime conditions over the area. Light winds
and clear night will provide good radiational cooling at night.
Patchy late night and early morning is possible in the Columbia
Basin. Early Wednesday the ECMWF has flat westerly flow as a weak
front moves through the area. The GFS maintains the ridge. The GFS
ensembles range between the two solutions. I left the forecast dry
but the split in the models lowers confidence. Coonfield



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  71  44  60  39 /  20 100  20  10
ALW  69  48  62  43 /  20 100  30  10
PSC  67  48  63  41 /  50  80  10  10
YKM  60  39  61  35 /  40  20  10  10
HRI  67  45  63  39 /  50  90  10  10
ELN  58  37  56  35 /  50  20  10  20
RDM  66  37  52  33 /  70  80  20  50
LGD  72  42  52  37 /  10  90  50  30
GCD  69  41  52  35 /  10  90  50  20
DLS  59  45  62  43 /  80  50  10  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Flash Flood Watch through this evening for WAZ520.

&&

$$

79/76/91



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