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 Washington 
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 County Warning Area. 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 Washington/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 southeast 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/southeast Washington 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 


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


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