466 
FXUS66 KPDT 271636
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
836 AM PST Wed Feb 27 2019

.SHORT TERM...Fairly strong short wave continues to move across
the forecast area this morning. Steady light to moderate snow
associated with this feature from the northeast Oregon mountains
across the Columbia basin. This snow will continue through the
morning before moving off to the northeast by afternoon. Models
and satellite show a break behind the short wave with mostly
cloudy skies. The offshore upper low will then push across the
region with a cold front this evening and overnight. Another round
of accumulating snow likely at this time. 94

&&

.PREV DISCUSSION... /issued 236 AM PST Wed Feb 27 2019/ 

SHORT TERM...Today through Thursday...Two weather systems to
impact the region in rapid succession through tonight and early
Thursday. One is moving across the area now and bringing light to
moderate snowfall. During the next several hours the main focus 
for the moderate snowfall will shift from central Oregon into 
northeast Oregon and extreme southeast Washington. A corridor 
along the foothills of the Blue Mountains could see around 4 
inches of snow this morning. Will be monitoring the foothills of 
Washington zone for a possible upgrade to winter storm warning 
early this morning. Otherwise will leave all current highlights in
place. By late morning most of the snow will taper off before the
next system moves in toward late afternoon or early evening. This
storm will move quickly across the region overnight and produce 
mostly 2-4 inch amounts before exiting to the east Thursday 
morning. There are a couple of complicating factors that may come 
into play. All of the model guidance is warming the areas east of 
the Blue Mountains today above freezing. Even factoring in the 
snow cover and using the GFS model which is the coldest available 
guidance...temperatures and snow levels rise to the point where 
some rain may mix in with the snow briefly in the east this 
evening. Also some of the model guidance is spreading a warm nose 
aloft into the Blue Mountain foothills to the point where some 
freezing rain or sleet would be possible at the onset of the 
precipitation this evening. For now have stuck with all snow but 
this will require a further look on the day shift today. One 
final point is that the Yakima and Kittitas Valleys could need 
winter weather advisories for tonight if the more robust NAM QPF 
in that area looks like it will pan out. Ensemble QPF currently 
keeps snow accumulations around 2 inches. 78

Thursday night through Friday night...It finally looks like there
will be a period of quiet, albeit still cold weather for the 
latter part of the week into the first part of the weekend. 
Thursday night through Saturday morning will feature generally dry
conditions. Some guidance does want to bring some quick hitting 
snow showers through, mainly to southeastern Oregon Friday night, 
but overall QPF is low and confidence remains low enough to not 
include much in the forecast at this time. 

Long Term (Saturday through Next Tuesday)...
It appears we may finally catch a break from the seemingly 
relentless winter weather pattern we have been stuck in as we head 
into the longer term. This will occur as a slow moving cutoff low 
that has been stuck off the Oregon and Washington coasts finally 
moves inland and east of the region, removing the threat of Pacific 
moisture-laden jets streaming over unseasonably cold airmasses. 
Instead, it looks as though we may see a stretch of dry weather from 
the weekend into early next week. Drier is good, but unfortunately, 
the cold air does not appear to be departing anytime soon.

Over the weekend, a drier northwesterly flow regime is expected to 
develop as the large scale trough shifts eastward. A cutoff low 
spinning of central California may bring some very light snow to 
portions of southern and perhaps central Oregon, but it appears any 
accumulating snow would likely be limited to the mountains. Another 
Arctic airmass looks to seep southward through the Columbia Basin 
and into central Oregon Saturday night into Sunday, resulting in a 
continuation of temperatures some 15 to 25 degrees below normal. 
Highs on Sunday only look to rise into the mid/upper 20s to lower 
30s most areas, which is not far from where climatological low 
temperatures are this time of year. While we should catch a break 
in the snow, any snow that melts will refreeze each night with 
slick spots developing on area roads overnight into each morning.

Guidance is showing rather frigid temperatures to start off next 
week with widespread lows in the teens and even single digits Monday 
and Tuesday mornings as an Arctic high settles over the region. 
Temperatures are expected to increase slightly Tuesday afternoon 
into Wednesday as our next storm system approaches, however there 
remains much uncertainty with respect to timing of this system. 
Current guidance suggests with the cold air holding firm, more 
wintry precipitation may be in the works by the middle of next week. 
Stay tuned! 79

AVIATION....12Z TAFS...Most of the near-term guidance has been 
suggesting a break in the snow early this morning, and based on 
the latest radar imagery, that break appears to be materializing. 
The majority of the same guidance suggests snow will redevelop 
around 12Z or shortly thereafter, with the bulk of any snow 
falling during the morning hours before tapering off. Then there 
will likely be a break in the late morning/early afternoon before 
another round of precipitation moves through tonight into early 
Thursday. Guidance has been indicating that temperatures will be 
warming aloft and precip type could become a factor. Confidence is
not high at this point, but there could be a period of FZRA in 
the Columbia basin and foothills.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  26  20  33  19 /  90  80  30  10 
ALW  28  22  33  21 / 100  80  30  10 
PSC  30  21  33  18 /  90  70  20  10 
YKM  32  18  33  17 /  40  70  20  10 
HRI  29  21  34  19 /  80  70  20  10 
ELN  31  17  34  15 /  30  70  20  10 
RDM  25  12  34  18 /  40  50  20  10 
LGD  32  21  34  20 /  90  70  40  10 
GCD  34  23  35  21 /  50  80  30  10 
DLS  29  19  35  24 /  50  60  20  10 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 AM PST Thursday for ORZ041-049-
     050-502-503.

     Winter Storm Warning until 4 AM PST Thursday for ORZ044-505>511.

WA...Winter Weather Advisory until 4 AM PST Thursday for WAZ024-
     028>030-521.

&&

$$

94