Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 192256
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
255 PM PST Sun Feb 19 2017

.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 coming 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 upper trough, which results in strong dynamic
deepening of the trough with the main energy developing just
offshore, evolving into a strong closed mid/upper level low that
digs south into California. This track for the low means that t;he
main dynamic lift associated with this system will miss eastern
sections of WA/OR and thus only a slight chance of snow in the
mountains of central and NE Oregon.  Polan

&&

.AVIATION...18Z TAFS...A weather system continues to move through
the area and is producing scattered light rain showers at lower
elevations in the Foothills of the Blue Mountains and light
rain/snow showers in the northern Blue Mountains AOA 4000 feet MSL.
Marginal instability this afternoon in the Lower Columbia Basin for
a slight chance of a thunderstorm, but probability is too low to
include in TAFs. Conditions will be mostly VFR with periods of MVFR
when showers pass through. Improvement to VFR expected at KPSC this
afternoon there will happen by the late afternoon. Other TAF by
around midday sites. Showers ending around 19-20Z. Another round of
showers will move in from the south 06Z-10Z tonight with MVFR/VFR
conditions. Winds will generally be less than 15 kts though KRDM and
KBDN will have gusts to 20 kts this afternoon and early this
evening.  Polan

&&

.HYDROLOGY...Significant rain will fall Monday and Tuesday with
these warm fronts. Rising snow levels will from the warm air aloft
will add snow melt 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
has been issued for these areas. Coonfield

&&

.PRELIMINARY POINT TEMPS/POPS...
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

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Flood Watch from late tonight through Tuesday afternoon for
     WAZ026-027-521.

&&

$$

76/99/99



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