Area forecast discussion 
National Weather Service Pendleton or 
735 PM PDT Monday Jul 27 2015 


Update...convection has dissipated over the County Warning Area though some showers 
still persist north and east of Wallowa County. Ridge will build 
into Washington Tuesday. With clearing skies expect good 
radiational cooling overnight. Current forecast on track. Coonfield 


&& 


Previous discussion... /issued 412 PM PDT Monday Jul 27 2015/ 


Short term...tonight through Thursday afternoon...a middle/upper level 
long wave trough has moved into Idaho/western Montana this 
afternoon. The western flank of the trough will bring a few more 
hours of wrap around moisture into early this evening to the 
northern Blue Mountains, Wallowa County and the Wallowa Mountains. 
As such isolated showers and perhaps a few isolated lightning 
strikes will be possible until sunset this evening in the 
aforementioned areas. The long wave trough will usher in a cooler and 
drier airmass tonight and Tuesday night. The cooler air will be most 
noticeable in the mountains above 3000 feet above mean sea level over 
the next couple of nights. Low temperatures around daybreak on 
Tuesday and Wednesday mornings will be near record lows, in the 
lower to middle 30s, especially in the Blue Mountains and in the Grande 
Ronde Valley, and also in the Wallowa Mountains with below normal 
lows expected in other mountainous areas. Campers and hikers should 
pack extra warm clothing and extra warm thermal sleeping bags with 
them for overnight sojourns in the Cascades mountains of Oregon and 
Washington, the Blue Mountains, the Wallowa Mountains, the Elkhorn 
and Strawberry mountains, the ochoco-John Day Highlands and the 
Aldrich Mountains by virtue of significantly below normal low 
temperatures at higher elevations tonight and Tuesday night. 


Looking upstream across the northeast Pacific, a ridge of middle/upper 
level high pressure will be moving east to the coast overnight with 
the ridge axis moving into the forecast area on Tuesday. The ridge 
flattens out a bit Tuesday night over the region and then merges 
with the middle/upper level ridge of high pressure over The Four 
Corners area on Wednesday. The western states high pressure ridge 
then amplifies northward into the Pacific northwest Wednesday night 
and Thursday. Therefore, expect dry conditions overnight and on 
Tuesday through Thursday afternoon. A warming trend commences on 
Wednesday with daytime high temperatures getting into the lower to 
middle 90s for Wednesday and Thursday. Polan 


Long term...Thursday night through Monday...an upper level ridge of 
high pressure will be firmly in place over the region for Thursday 
night and Friday. This will allow above average temperatures and 
generally clear/dry conditions to continue. Temperatures will be in 
the upper 90s to low 100s for the lower elevations on Friday...which 
is 10-15 degrees above average. By Saturday...Sunday and Monday middle 
and upper level monsoonal moisture will begin to pivot into the 
region from the south. This added moisture will likely act to 
increase the elevated instability during the afternoon and evening 
hours...therefore added a slight chance for showers and 
thunderstorms into the forecast...mainly in the Oregon mountains 
during this time. As is typically the case with monsoon moisture 
cloud bases are prognosticated to be rather elevated...likely between 10- 
15k feet above ground level (at least to start). Model soundings are showing the 
classic inverted "v" shape...with dry low level air present below 
10k feet above ground level. However an indication of the increased moisture is the 
rising precipitable waters ...which are forecast to be between 0.75 and 1.10 inches 
by Saturday night and Sunday. If storms do form dry lightning could 
certainly end up being an issue (again at least to start)...and this 
is a threat that will need to be watched carefully in the coming 
days. Temperatures are expected to remain 8 to 15 degrees above 
normal into the weekend and early next week...with exact 
temperatures likely dependent on the amount of cloud cover over the 
area. In general expect temperatures in the middle-90s to low 100s 
through Monday for the valleys and basins with 80s to lower 90s in 
the mountains. Overnight lows will also be on the rise for the 
weekend with the increased moisture and cloud cover around. Lows 
will be in the 60s for the lower elevations with upper 40s and 50s 
in the mountains. 77 


Aviation...00z tafs...VFR conditions are expected to persist 
through the next 24 hours. Some scattered middle-level (6 to 10k feet agl) strato- 
cumulus clouds are currently affecting most of the north-central taf 
sites this evening. These clouds will dissipate toward and just 
after sunset giving way to mainly clear skies areawide overnight and 
through the day on Tuesday. Winds will stay a bit breezy at 
kdls...kykm...krdm and kpdt through about 28/04z before diminishing 
overnight. Winds will be lighter tomorrow afternoon...at or below 12kts at 
all taf sites. 77 


&& 


Preliminary point temps/pops... 
PDT 50 84 53 95 / 0 0 0 0 
alw 55 86 58 95 / 0 0 0 0 
psc 52 87 51 97 / 0 0 0 0 
ykm 51 84 53 93 / 0 0 0 0 
hri 50 87 52 96 / 0 0 0 0 
eln 53 86 51 96 / 0 0 0 0 
rdm 38 83 43 93 / 0 0 0 0 
lgd 39 80 42 90 / 10 0 0 0 
gcd 42 85 46 94 / 0 0 0 0 
dls 56 90 57 99 / 0 0 0 0 


&& 


PDT watches/warnings/advisories... 
or...none. 
Washington...none. 
&& 


For additional weather information, check our web site at... 
www.Weather.Gov/Pendleton 


$$ 


76/76/76 



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