Area forecast discussion...updated
National Weather Service Pendleton or
321 PM PDT Tuesday may 21 2013
Updated for aviation discussion
Short term...tonight through Thursday night...an upper low will
continue to move into the Pacific northwest late this afternoon and
tonight. The cold front associated with this system has pushed
through most of our area, except the eastern half of Wallowa County.
This front should be through Wallowa County by 5 PM. Will continue
to indicate a threat of isolated thunderstorms, though the threat
seems to be diminishing. Storms will be possible from Grant County
north to The Blues and east to Wallowa County late this afternoon,
and over Wallowa County this evening. A band of steady showers just
behind the front continues to slide northeast and east through the
area. This band currently runs from eastern Grant and Baker counties
north-northwest into Walla Walla and Franklin counties. This band
should largely be through the area by sunset this evening. With the
upper low over the region tonight, will continue to see bands of
showers rotate through the area. There remains some uncertainty as
to the timing and track of these bands, but data indicates some
decent precipitation over many location overnight into Wednesday morning.
Snow levels will fall to around 4500 feet this evening, then down to
2500 to 3000 feet by daybreak Wednesday. The one area that looks to
see enough precipitation for some decent late season snow is the Blue
Mountains. Will issue a low end advisory for the Blue Mountain zones
as much for impact potential as for the actual snow amounts. Other
areas that may see snow should see an inch or less.
The upper low will remain over the region Wednesday afternoon
through Thursday night. As such the area will remain within a cool
and unsettled weather pattern with waves rotating around the low
causing periods of showers. Snow levels look to slowly rise through
this period, though some spotty snow will be possible late at night
into the hours around daybreak. Daytime heating and cold air aloft
could create lapse rates strong enough to support stray afternoon
and evening thunderstorms Wednesday and Thursday. At this time will
continue to mention storms only on Thursday as there appears to
better focusing on this day. 90
Long term...Friday through Tuesday night...upper level low will
continue to circulate over the area. Expect a continued chance to
likely showers along the mountains of northeast Oregon and east
slopes of the Cascades...as the low remains over the area.
Confidence is still fairly high with the overall pattern...but there
is some divergence when it comes to favoring thunder along the
mountains of northeast Oregon. Right now the best agreement that
would support thunderstorms is for Sunday afternoon. So have kept
thunder in the forecast for the ochoco John Day...blue and Wallowa
mountain areas...as well as the Grande Ronde Valley. Otherwise have
back off to just showers for the other time periods. As we get
closer to the near term...it may be better pinpointed and we can add
the thunder as needed. Although the models keep the circulation over
the area for most of the extended...hence keeping a slight chance
showers over the lower elevations and a chance to likely showers
over the mountains...the circulation does appear to weaken gradually
after Saturday. This will allow for warmer air to intrude and return
lower elevation temperatures into the middle to upper 70s for the
remainder of the extended. Weber
&&
Aviation...00z tafs...MVFR and VFR conditions are expected over the
next 24 hours. Upper level low will continue to circulate over the
interior Pacific northwest. Expect lowered ceilings...on and off
showers...and breezy conditions at all taf sites over the next 24
hours. Winds will generally be 15 to 25kts. Expect breezy to windy
conditions this afternoon as well as tomorrow afternoon at most taf
sites. Weber
&&
Preliminary point temps/pops...
PDT 40 56 37 62 / 60 50 20 30
alw 43 57 41 65 / 60 50 20 30
psc 46 62 38 69 / 70 40 20 30
ykm 41 58 35 64 / 60 30 20 30
hri 44 62 35 67 / 60 40 20 30
eln 45 56 37 64 / 60 40 30 40
rdm 30 53 29 57 / 40 40 20 30
lgd 39 51 33 58 / 60 50 30 30
gcd 35 54 33 59 / 60 40 20 30
dls 44 56 41 65 / 30 50 30 40
&&
PDT watches/warnings/advisories...
or...Winter Weather Advisory from 9 PM this evening to 10 am PDT
Wednesday above 4000 feet for the orz502-503.
Washington...Winter Weather Advisory from 9 PM this evening to 10 am PDT
Wednesday above 4000 feet for the waz030.
&&
Threat index
Wednesday : green
Thursday : green
Friday : green
Green: none or limited need for watches, warnings, or advisories.
Yellow: a few watches, warnings, or advisories possible or in effect.
Red: numerous watches, warnings, or advisories possible or in effect.
For additional weather information, check our web site at...
www.Weather.Gov/Pendleton
$$
90/89/89
