Area forecast discussion...updated
National Weather Service Pendleton or
402 am PDT sun may 19 2013
Updated aviation discussion
Short term...today through Monday night...an upper level ridge will
build along the coast today. This will bring a drier northwest flow
to eastern Washington and Oregon. Lingering moisture will combine
with upslope effects to trigger a few showers from Grant County to
the northern blues and Wallowa County. These showers will increase
with afternoon heating. The ridge axis will shift east tonight and
move over eastern Washington and Oregon Monday. Subsidence from the
building ridge will warm daytime temperatures a few degrees today
and even more Monday. Clearing skies tonight will allow some
radiational cooling with cooler overnight temperatures. An
approaching Pacific system will bring increasing clouds Monday night
and may spread some light precipitation to the Washington Cascades.
Coonfield
Long term...Tuesday through Saturday...a large middle/upper level
trough will be over the NE Pacific west of Vancouver Island around
daybreak Tuesday. The trough evolves into a large middle/upper level
low Tuesday morning with the low moving southeast. The center of the
low approaches the coast just west of the Columbia River by late
Tuesday afternoon. A cold front on the eastern flank of the low will
move into the western sections of the forecast area late Tuesday
afternoon. The cold front will then move east and spread increasing
moisture and showers across southeast Washington and northeast
Oregon Tuesday evening. Marginal instability may trigger some
isolated thunderstorms Tuesday afternoon and Tuesday evening in the
Wallowa Mountains and Wallowa County. The cold upper low will usher
in a cooling trend and periods of unsettled showery weather, as the
upper low center moves over the forecast area and persists through
Friday. The upper low moves northeast into southwest Canada Saturday
in response to a trough moving east into the Gulf of Alaska. Daytime
high temperatures will be slightly cooler than normal for Tuesday
through Friday. High temperatures will warm to near normal on Saturday.
Temperature lapse rates from 5000 feet to 20000 feet in the middle levels
of the atmosphere of seven degrees celsius or larger suggest that
there may be enough marginal instability, combined with very strong
dynamic lift and vertical wind shear of 40 to 60 knots from the
surface to 20000 ft, which would favor development of a few isolated
thunderstorms during the daytime on Wednesday, especially in the
afternoon and early evening over the mountains of NE Oregon and southeast
Washington. However, will await Storm Prediction Center guidance before introducing a
slight chance of thunderstorms on Wednesday afternoon/evening at
this time since this far out confidence is low with respect to areal
coverage of thunderstorm potential. Cannot rule out some isolated
thunderstorms Wednesday afternoon/evening given 500mb temperatures
around -28 degrees celsius, which is cold enough to yield steep
temperature lapse rates and thus marginal instability favorable for
thunderstorm development. Polan
&&
Aviation...12z tafs. VFR conditions will occur for the next 24
hours at all taf sites. However, MVFR conditions are expected today
along the air traffic Route over the Blue Mountains from kpdt to
kbke due to low ceilings. Otherwise, cloud cover will be scattered-broken
5000-8000 feet above ground level this morning as a weak upper trough is moving
through. The upper trough exits into Idaho by midday with scattered
5000-8000 feet above ground level this afternoon. Winds 5-15 kts except 10-20 kts at
kdls. Polan
&&
Preliminary point temps/pops...
PDT 70 44 76 49 / 10 0 0 0
alw 71 49 79 53 / 10 0 0 0
psc 76 43 81 48 / 10 0 0 0
ykm 74 44 78 46 / 10 0 0 0
hri 75 43 80 47 / 10 0 0 0
eln 71 45 79 46 / 10 0 0 0
rdm 66 32 75 44 / 10 0 0 0
lgd 64 39 73 45 / 20 0 0 0
gcd 64 40 74 42 / 10 0 0 0
dls 71 46 80 51 / 10 0 0 0
&&
PDT watches/warnings/advisories...
or...none.
Washington...none.
&&
Threat index
today : green
Monday : green
Tuesday : 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
$$
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