Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 200054 AAA

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
450 PM PST Sun Feb 19 2017

Updated AVIATION Discussion

.SHORT TERM...Tonight through Tuesday night...The weather pattern
will remain very active through the short term with frequent weather
systems. Moist southwest flow is bringing unstable air into the
area. A thunderstorm may develop early this evening along the Blue
Mountains or foothills where daytime heating has enhanced the
instability and formed cumulus buildups. Scattered showers will
persist in the mountains. A warm front will spread across eastern WA
and OR Monday morning. This will bring widespread precipitation with
snow levels rising to 4500-5500 feet by afternoon and above 5000-
6000 in the evening. This system has good upper level support as a
jet max moves along the front. Some of these stronger winds aloft
may mix down to the surface, particularly in Central and North
Central Oregon. There will be a brief break in rain during the
evening, then another wave will move along the front and bring more
rain and wind Tuesday. These fronts will bring significant rain to
the CWA. Precipitation will decrease and snow levels drop again
Tuesday evening behind the front.  Coonfield

.LONG TERM...Wednesday through Sunday...Upper trough moves to coast
on Wednesday and spreads precipitation east of the Cascades with the
snow level 1000-2000 feet. Lower Columbia Basin should remain dry
through Wednesday afternoon while PoPs increase through the day at
higher elevations. Precipitation amounts will be light and snow
accumulations will be less than an inch even in the higher
mountains. Wednesday night through Thursday night the trough will
remain over the region for unsettled weather. An influx of colder
air from the north will lower snow levels to below 1000 feet during
the day on Thursday. This will yield a chance of light snow showers
and afternoon rain showers at lower elevations. Friday and Friday
night models show another influx of colder air spilling westward
across the Canadian Rockies and entering forecast area thus keeping
snow levels around 1000 feet during the day on Friday with snow
levels lowering to near the floor of the Columbia Basin Friday
night. This results in a chance of snow showers in the mountains and
a slight chance of rain showers and snow showers in the lower
elevations. Next weekend a strong impulse dives south through the
western flank of the aforementioned upper trough, which results in
strong dynamic deepening of the trough with the main energy
developing just offshore and evolving into a strong closed mid/upper
level low that digs south into California. This track for the low
means that the main dynamic lift associated with this system will
miss eastern sections of WA/OR and thus result in only a slight
chance of snow in the mountains of central and NE Oregon. Next
upstream mi/upper level shortwave moves SE along coastal British
Columbia on Saturday/Saturday night and moves into interior Pacific
Northwest by daybreak Sunday spreading moisture east of the Cascades
for a chance of mainly snow from sunup to sundown on Sunday.  Polan


.AVIATION...00Z TAFS...VFR conditions will occur through most of
tonight before the next disturbance moves along a surface frontal
boundary offshore, which approaches the coast this evening. As the
surface low makes landfall along the southern Oregon coast it will
bring a warm front and rain into central Oregon with rain starting
around midnight at KBDN and KRDM. The warm front will spread rain
northward to the other TAF sites as well as NE OR/SE WA generally
prior to daybreak on Monday. Expecting this system will have higher
cloud bases yielding mainly VFR cigs late tonight through Monday
morning. However, KDLS will see conditions worsen to IFR overnight
and then improve to VFR by late Monday morning. KYKM will see
LIFR/VLIFR vsby/cigs forming this evening with these conditions
improving to VFR with onset of -RA by around 10Z/20th. Winds will
generally be less than 10 kts.  Polan


.HYDROLOGY...Significant rain will fall Monday and Tuesday with
these warm fronts. Rising snow levels from the warm air aloft will
add snowmelt to the runoff. Rainfall up to three quarters of an inch
in the Simcoe Highlands and up to one half an inch in the Yakima and
Kittitas Valleys may create localized flooding. A flood watch has
been issued for these areas Monday through Tuesday afternoon. Lesser
amounts of rain will fall in the Lower Columbia Basin and Foothills
of the Blue Mountains. A Hydrological Outlook - product PDXESFPDT -
has been issued for these areas. Coonfield


PDT  35  52  38  49 /  30  90  60  50
ALW  36  53  40  49 /  30  90  80  60
PSC  34  50  37  49 /  20  70  50  70
YKM  32  44  32  45 /  20  80  50  60
HRI  34  52  36  49 /  30  80  50  50
ELN  31  39  31  42 /  20  90  50  50
RDM  33  49  33  47 /  50 100  50  30
LGD  36  48  40  47 /  40 100  60  50
GCD  36  52  38  49 /  50 100  50  50
DLS  34  44  35  45 /  50  90  50  40


WA...Flood Watch from late tonight through Tuesday afternoon for



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