Area forecast discussion 
National Weather Service Pendleton or 
1035 PM PDT Thursday may 5 2016 


Update...showers had developed and were moving west over the Blue 
Mountains. The showers should drift into the Blue Mountain foothills 
and Columbia Basin overnight and the zones were updated to reflect 
this. 


Aviation...showers are expected to move into taf sites kpdt and 
kalw and kpsc with conditions approaching MVFR in and near showers 
until 10z. Otherwise mostly VFR conditions can be expected at all 
tafs sites despite lingering showers into Friday. However an isolated 
thunderstorms and rain is possible at taf sites krdm and kbdn after 22z. 


&& 


Previous discussion... /issued 136 PM PDT Thursday may 5 2016/ 


Short term...tonight through Saturday night...active weather 
pattern continues with a large upper low off the coast and a 
developing closed low over Southern California. An upper ridge is 
moving to the northeast and out of the region. There is abundant 
moisture and instability being pulled northward in a southerly flow 
aloft into the forecast area. So far this afternoon clouds have kept 
convection to a minimum with some weak storms south of the County Warning Area in 
lake and Klamath counties. Expect as afternoon heating continues 
thunderstorms will begin to develop...especially over the eastern 
and northeast mountains where temperatures are the warmest and there 
are the fewest clouds. In addition the eastern and northeast 
mountains is where the best dynamics are to produce forcing to 
trigger thunderstorm development. Shear values are around 40-50 kts 
with precipitable water water values near or just over an inch. In 
addition helicity values are around 300 m2/s2 and negative lifted indice's from 
-2 to -5 c. These are all very favorable parameters for the 
development of thunderstorms...some possibly severe with organized 
rotation to them. Due to the high water content of the atmosphere 
have a Flash Flood Watch in effect from the ochoco-John Day 
Highlands northeast through the northeast mountains and Wallowa 
County through this evening. In particular concern is the burn scar 
from last years Canyon Creek fire in southern Grant County. Elsewhere 
there may possibly be mud or rock slides due to very heavy rainfall 
in steep terrain. Thunderstorms will dissipate this evening after 
dark with the loss of surface heating. On Friday the upper low over 
Southern California will shift eastward into the southern Great 
Basin. This will cause a wrap around northeast flow over the 
forecast area. While this is not always conducive for thunderstorm 
development...there could still be thunderstorm development due to 
the amount of lingering instability and abundant moisture in the 
atmosphere. Have thunderstorms in friday's forecast for the 
southeast third of the County Warning Area for Friday afternoon and evening. The 
upper low will continue to move to the east Saturday and Saturday 
night which will cause a gradual decrease in convective development 
and stabilization of the atmosphere. It will warm up again on Friday 
and Saturday compared to today's highs so far with low elevation 
temperatures in the lower to middle 80s...with 60s and 70s in the 
mountains. Winds will increase this afternoon and it will become 
locally breezy and then they will become light overnight and then 
increase again on Friday and Saturday afternoons and evenings. 88 


Long term...Sunday through Thursday...models are in good agreement 
with respect to bringing another upper level low over portions of 
the forecast area Sunday. This system is expected to mainly affect 
southeast Washington and northeast Oregon as it slowly slips into 
Idaho and Montana Monday night. By Tuesday...drier northerly upper 
level flow in the wake of the aforementioned low should result in 
drier weather over the region. By Wednesday...the models begin to 
differ in their handling of the upper level pattern. GFS tries to 
bring a disturbance over the area while European model (ecmwf) keeps drier 
northwestern flow. At this time...prefer the drier European model (ecmwf) forecast 
so will lean towards it. Daytime high temperatures are expected to 
remain above normal through the period. Earle 


&& 


Preliminary point temps/pops... 
PDT 56 79 56 81 / 30 20 10 10 
alw 55 80 55 82 / 20 20 10 10 
psc 56 84 56 86 / 20 10 10 0 
ykm 53 85 53 86 / 20 10 10 0 
hri 53 82 53 85 / 20 10 10 10 
eln 50 82 50 83 / 20 10 10 0 
rdm 42 74 42 80 / 50 20 30 10 
lgd 46 74 46 77 / 60 40 30 20 
gcd 49 71 49 77 / 70 50 40 20 
dls 53 85 53 88 / 20 10 10 0 


&& 


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


Washington...none. 
&& 


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


$$ 


97/97 



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