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Area forecast discussion...updated 
National Weather Service Pendleton or
405 am PDT sun Sep 21 2014

Updated aviation discussion

Short term...today through Tuesday night...an upper level ridge
will move east into Idaho today. Temperatures will be a little
warmer today than yesterday due to subsidence from the departing
ridge. Winds will be generally light as well. A cutoff low in
central California this morning will move northeast into Nevada by
afternoon. Some middle/high level moisture from the low is moving into
southern Oregon this morning and will spread north during the day.
At this time expect to see some batches of higher based clouds drift
into portions of the area but do not expect any precipitation
through tonight. Upper level flow will become southwesterly by
Monday, and remain southwest through the rest of the short term
period. Models are suggesting precipitation from a weak front Monday
morning along the Cascades. I think the moisture advection is too
fast a transition from a Dry Ridge to precipitation. Soundings show
the moisture is mainly above 14 kft at 12z. Showers may develop
Monday afternoon over eastern Oregon and Washington as the weak cold
front stalls. There will be enough instability in the warm air to
trigger a few thunderstorms as well. Very little precipitation will
occur with this system because the low levels will be very dry
initially. A slow transition into cooler wetter weather will
continue Tuesday as another front approaches the coast. This system
appears stronger on satellite and model forecast but it will be slow
to move inland with winds nearly parallel to the front. Coonfield

Long term...Wednesday through Sunday night...a mature low pressure
system will be located off the Pacific coast on Wednesday with a
cold front just west of the Cascades to start the forecast period.
The progression of this cold front compared to prior model guidance
has been slowed somewhat...with the front expected to move across
the two state area by Thursday night. This slower eastward
progression will place the area under a strong southerly flow...with
adjustments made to the grids to increase daytime highs on Wednesday
as well as southerly winds ahead of the front. Have also slowed
down eastward progression of the anticipated moisture band with the
front and instead have the entire County Warning Area being under a chance of
showers. The steepened lapse rates are still evident on latest
forecast skew T soundings...therefore have left a slight chance of
afternoon thunderstorms along the northeastern Oregon mountains
Thursday afternoon. The main trough axis will slowly move eastward
over the area by Friday...with a good chance of widespread showers
possible over the entire County Warning Area. There is some question as to whether
there is enough instability on Friday for afternoon thunderstorms
along the northeastern Oregon mountains...but in consultation with
neighboring offices...have held with a slight chance of
thunderstorms for now. On Saturday...model solution differences are
evident as to the position of the eventual upper low at the base of
the trough axis. All model guidance solutions place the region
under westerly or northwesterly flow...which would allow for a
gradual end to precipitation in the lower Columbia Basin while
continuing along the higher elevations of the County Warning Area. Have opted to
decrease pop chances in the lower Columbia Basin for Saturday
afternoon and evening given those solutions. Temperatures during
the forecast period will start above normal for the County Warning Area and will
trend to near or just slightly below seasonal norms starting on
Thursday. Bieda

&&

Aviation...12z tafs. Cirrus clouds with ceiling at or above 25k feet above ground level are
spreading into the area from the south this morning due to an upper
low to our southeast. After 21/18z...altocumulus clouds will develop
along higher terrain with scattered ceiling at or above 10k feet above ground level. No significant
weather is expected at this time with VFR conditions. Winds at or below 15
kts will continue through the taf period. Bieda

&&

Preliminary point temps/pops...
PDT 87 57 85 57 / 0 0 10 10
alw 88 63 86 63 / 0 0 10 10
psc 89 56 88 58 / 0 0 10 10
ykm 92 56 87 55 / 0 0 10 10
hri 90 54 88 55 / 0 0 10 10
eln 93 57 85 55 / 0 0 10 10
rdm 90 48 81 47 / 10 0 10 10
lgd 88 54 84 53 / 0 0 20 20
gcd 91 51 86 53 / 10 10 20 20
dls 90 59 84 57 / 0 0 10 10

&&

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

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

$$

76/98/98

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