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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

                            
000
FXUS66 KPDT 210608
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1005 PM PST Wed Feb 20 2019

.SHORT TERM...Still have scattered snow showers over the southern
portion of the forecast area associated with the upper low. Expect
these will slowly decrease later this evening and overnight.
Models continue to indicate a weak disturbance rotating back into
Wallowa county and the Blues overnight and Thu morning with snow
showers. Otherwise for Thu ridge building into the region for a
short time with dry northerly flow aloft and partly to mostly
cloudy skies. This will continue into Thu night with cold
temperatures. The next system to move across the Pacific northwest
is currently over the Gulf of Alaska. This system will spread
clouds and rain/snow over the forecast area Friday. Models linger
this upper trough over the Pacific northwest through the weekend
with the potential for another significant snow event. 94

.AVIATION...06z tafs. Isolated snow showers possible at PDT ALW DLS 
RDM BDN through the overnight period. Ceilings mostly 010-040. Winds 
less than 10kt. Decreasing clouds Thu becoming sct for most 
locations by afternoon. 94

&&

.PREV DISCUSSION... /issued 226 PM PST Wed Feb 20 2019/ 

SHORT TERM...Tonight through Saturday...Rain/snow instability
showers across the region will weaken with loss of surface heating
this evening. Given steep mid-level lapse rates, surface temps in
the mid to upper 30s and ELs around -30C some of these showers in
north central and central Oregon may become locally intense at 
times with brief periods of heavy snow and/or graupel over the
next couple hours. Snow will become confined to the Blue 
Mountains and Wallowa County where a weak backdoor cold front will
approach early Thursday morning with upslope flow producing an 
additional 2 to 4 inches of snow accumulation. Will drop all 
winter highlights with the afternoon package except for Wallowa 
County where a Winter Storm Warning will be downgraded to a Winter
Weather Advisory and run through early Thursday morning. 
Transient ridging builds in for Thursday and early Friday with dry
conditions expected. Partially clearing skies with a rather dry 
airmass in place Thursday night will allow overnight lows to 
plummet into the teens for the lower elevations and down into the 
single digits for some the higher valleys. The next system 
approaches during the day Friday with the best precipitation 
chances primarily confined to the Cascades and Blues with 
significant precipitation shadowing elsewhere. Accumulations look 
to remain on the light side, 3 to 7 inches near the crest of the 
Cascades and 2 to 5 inches in the Blues with generally an inch or 
less for the lower elevations. Peck 

LONG TERM...Saturday night through Wednesday...Saturday night 
through early Monday an upper level low will slide along west
coast from northern Vancouver Island to WA while a surface front
will stall over OR. This will keep a prolonged period of snow.
over the southern half of the CWA, Although snow levels at the
surface snow amounts in WA and the Lower Columbia Basin, amounts
will be limited. 

Confidence in the deterministic models is low for the remainder of
the forecast period. Flat westerly flow will remain over WA and OR
Monday transitioning to an upper level ridge Tuesday and
Wednesday. However an occluded front (GFS or warm front (ECMWF)
will be embedded in the ridge so precipitation will persist over
the area. The ECMWF and GFS solutions would have very different
snow levels so I trended toward the NBM, but confidence in
precipitation type is low. Since temperatures will remain below
normal I kept type snow, occasionally mixed with rain in the
afternoon. Coonfield 

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  20  31  13  36 /  20  10  10  10 
ALW  20  30  15  37 /  30  10  10  10 
PSC  21  33  18  38 /  10  10   0  10 
YKM  19  35  18  37 /  10  10   0  30 
HRI  22  33  16  39 /  10  10   0  10 
ELN  15  34  15  33 /  10  10   0  50 
RDM  18  31  14  39 /  50  10  10  10 
LGD  21  30  11  34 /  30  20  10  10 
GCD  20  30  11  35 /  30  10  10  10 
DLS  25  38  23  41 /  40  10   0  40 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 AM PST Thursday for ORZ050.

WA...None.
&&

$$

94