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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

FXUS66 KPDT 211720 AAA

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
920 AM PST Thu Feb 21 2019

Updated Aviation Discussion

.SHORT TERM...Today and tonight...A deep upper level trough 
continues to push south of the region into the southwestern U.S. 
This is leaving the Pacific Northwest under a cold northerly flow. 
There is enough lingering moisture that the northerly flow banking 
up against the higher terrain of Oregon is generating some snow 
showers with minor accumulations. This will persist into the 
afternoon and then taper off and end going into tonight. 
Temperatures will remain below normal today and clearing skies 
tonight will allow temperatures to drop into the teens and single 


.AVIATION...18Z TAFs...Upslope flow northerly flow keeping light 
SNSH at RDM BDN PDT and ALW. Low level moisture at PSC and DLS 
producing BR/FZFG which will also dissipate as drier air moves in. 
By this afternoon, most sites will be VFR. Radiational fog may 
reduce visibilities tonight, particularly along the Blue Mtn 
Foothills. A northerly gradient may cause stratus clouds to develop 
at BDN and RDM. 76


.PREV DISCUSSION... /issued 330 AM PST Thu Feb 21 2019/ 

SHORT TERM...Today through Friday Night...Although snow has tapered 
off across most of the forecast area, WSR-88D is picking up on 20-25 
dBZ returns over the Blue Mountains and foothills.  Scattered snow 
showers have been observed early this morning, and web cams are 
showing snow-covered roadways that were earlier plowed.  The center 
of the upper low is over SE Oregon and Nevada with continued wrap-
around moisture.  The HRRR forecasts QPF up to 0.1 of an inch for 
areas east-southeast of Pendleton and the Oregon Blues through 18Z. 
Forecast will reflect scattered morning snow showers with 
accumulations up to 1.5 inches. Typically, these wrap-around 
patterns can cause snow to accumulate fast in Wallowa County but the 
web cam at Joseph is showing very light accumulations since 
midnight. Snow has also tapered off or ended over central Oregon. No 
winter highlights are planned for this morning, but we will keep a 
close eye on precipitation over the Blue Mtn Foothills.  

Snow showers will taper off to isolated mountain snow showers over 
eastern Oregon this afternoon and end everywhere tonight.  Clearing 
skies will cause temperatures to plummet into the single digits and 
teens for most of the area.  Clouds will increase from the west 
Friday morning and will be mostly cloudy and cold Friday afternoon. 
The next front will bring snow to the Washington and northern Oregon 
Cascades Friday afternoon then over the remainder of the forecast 
area Friday night.  Frontogenesis begins to develop south of the 
Washington border after midnight with the front forming a line from 
Walla Walla to Heppner to Madras by 12Z Saturday.  More details on 
this upcoming system can be found in the long term discussion. There 
will be weak warm air advection ahead of the front increasing snow 
levels to around 1500 feet, therefore some of the lowest elevations 
will have a rain/snow mix Friday evening.  Wister

LONG TERM...Saturday through next Friday...The models are in good 
agreement to start with a mostly zonal flow with a northwest to 
southeast direction. This is where the jet stream will be, which 
will divide the cold air north of it in Washington and warmer air 
from north central Oregon southward. A weather system will move into 
the region again by Sunday. This next system will affect mostly the 
southern CWA with the cold/warm air boundary over north central 
Oregon. 1000-850 thicknesses are marginal for snow for elevations 
below 1500 feet MSL, but precipitation will be widespread this 
system will eventually bring a little light snow as the colder air 
moves into the CWA on Sunday. This wet pattern will persist for and 
through the beginning of the extended period, which will be around 
Monday. After conditions will dry out fast.  Then a short visit with 
an upper ridge will develop over the Pacific Northwest. Cold air 
will be trapped at the surface in the Lower Columbia Basin south 
through central Oregon. This time of year, the mixing out of warmer 
air under a ridge may transport warmer air and may cause rain or 
freezing rain through Wednesday and the rest of next week. 88


PDT  28  14  35  27 /  20  10   0  40 
ALW  29  16  36  28 /  20  10  10  50 
PSC  31  19  36  26 /  10   0  10  10 
YKM  34  18  35  22 /   0   0  30  10 
HRI  31  17  37  28 /  10   0   0  20 
ELN  34  15  33  19 /  10   0  60  20 
RDM  32  15  40  28 /  20  10   0  30 
LGD  30  12  34  25 /  30  10  10  60 
GCD  31  13  36  27 /  20  10   0  50 
DLS  37  23  39  31 /  10   0  30  40