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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

FXUS66 KPDT 260227

Area Forecast Discussion
National Weather Service Pendleton OR
727 PM PDT Tue Jun 25 2019

.UPDATE...Convection is beginning to wind down this evening with
the loss of solar heating and increasing clouds to prevent 
solar heating. Thunderstorms were fairly numerous earlier, but 
none of the storms were either strong or severe. The amount of 
lightning is rapidly decreasing now with mainly just some showers 
left over. This is likely the result of less development of new 
storms, when lightning is the most numerous. An upper low 
pressure system will move to the PacNW coast on Wednesday with a 
deep southerly flow ahead of it and a decent amount of shear and 
instability as well as moisture. This combined with surface 
heating will lead to showers and thunderstorms. The Storm 
Prediction Center (SPC) is still advertising possible strong to 
severe storms over the northeast portion of the forecast area on 
Wednesday. Wednesday will have the best chance for strong to 
severe storms and also the most numerous. Then as the upper trough
moves inland for the rest of the week conditions will become 
showery and it will remain cooler than normal. There is a good 
chance for precipitation in most areas if not all areas of the 
forecast area. Due to the abundant number of lightning strikes 
over the lower elevations where fine vegetation has cured and 
dried out a Fire Weather Watch will remain in effect through the 
afternoon and evening Wednesday. After that the fire weather 
threat will diminish as the atmosphere becomes more moist and the 
amount of lightning decreases and rain increases with storms. 
Outside of gusty and erratic winds with thunderstorms, winds will 
be mostly light. 88


.AVIATION...06Z TAFs...Tonight, the amount of lightning and
precipitation is decreasing. However, it will increase again at
all TAF sites on Wednesday due to a strong upper low pressure
system and an unstable atmosphere this will move into the region.
There may be brief periods of MVFR conditions under the stronger
shower or thunderstorm cores on Wednesday afternoon and evening,
otherwise it will be mainly VFR. Winds will be light, except for
gusty and erratic winds near any thunderstorms Wednesday afternoon
or evening. 88


.PREV DISCUSSION... /issued 230 PM PDT Tue Jun 25 2019/ 

SHORT TERM...Tonight through Friday evening...Showers and 
thunderstorms are developing across portions of the forecast area at 
this time due to the deepening closed upper level low pressure 
system off the coast. Todays showers and thunderstorms will continue 
into the evening then decrease to a few showers overnight. The low 
will nudge closer to the coast on Wednesday providing a little better 
dynamic situation in which we are expecting stronger thunderstorms 
with the potential for some severe storms. The main concern for 
severe storms will be from central Oregon across northeast Oregon 
and southeast Washington. The upper level low will move onto the 
coast Thursday bringing some cooler conditions to the forecast area. 
Some showers and thunderstorms will continue to be possible but the 
threat of stronger storms will be to the east in Idaho. The low will 
lift northeast across Washington on Friday for continued cool 
conditions along with showers and some thunderstorms. 

LONG TERM...Friday night through Tuesday...Models somewhat agree 
through the weekend with the upper-level low slowly working into 
southern Canada by early Saturday, but with the area remaining under 
some form of troughing through the weekend. Some model guidance even 
suggesting another upper-level low developing near the coast again 
and slowly shifting inland. Expect a slight chance of showers over 
the mountains and possibly a stray thunderstorm or two. The better 
chance looks to be Saturday with a bit more instability expected and 
stronger upper level support. Beyond the weekend model agreement is 
quite poor, but expect an overall troughing pattern to continue over 
the PacNW in some way shape or form. Expect a slight chance of 
showers and isolated storms over the mountains to continue into 
early next week. Highs Saturday (upper 60s to around 80) will be 
around 5 degrees below normal with a steady increase through the 
period to around 5 degrees above normal early next week (upper 70s 
to around 90).

FIRE WEATHER...A fire weather watch is being issued for abundant 
lightning in conjunction with dry fuels for Wednesday afternoon 
and evening. This watch is for the grassland regions in the zones 
covered under the watch. The storms will be wet which will aid in 
the suppression and or moistening of the fuels but nonetheless, 
numerous fire starts will be possible due to lightning.


PDT  53  77  52  72 /  20  50  60  20 
ALW  56  80  52  74 /  20  60  70  20 
PSC  61  83  56  78 /  20  20  70  10 
YKM  55  78  52  73 /  20  30  60  40 
HRI  58  81  55  76 /  20  40  60  10 
ELN  51  74  50  68 /  20  40  60  50 
RDM  46  68  42  66 /  20  70  60  50 
LGD  49  74  47  66 /  40  60  60  60 
GCD  52  74  46  65 /  40  60  50  50 
DLS  56  74  53  71 /  20  30  40  20 


OR...Fire Weather Watch from Wednesday afternoon through Wednesday 
     evening for ORZ610-639>641.

WA...Fire Weather Watch from Wednesday afternoon through Wednesday 
     evening for WAZ639-641-675.