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Area forecast discussion...update 
National Weather Service Pendleton or
1005 am PDT sun Sep 21 2014

Updated aviation discussion

Short term...morning update...the upper ridge over the western U.S.
Will continue to shift east today in advance of a deepening upper
trough over the eastern Pacific. The flow over the pacnw will become
southwesterly today as a result. An upper low moving into Nevada at
the moment will continue to move northeast today reaching southern
Idaho this evening. Mostly thin high cloudiness will continue to
drift north from this low and will cover much of central and
northeast Oregon today. As such, increased cloud cover over our
Oregon zones into the 10-20 percent range for today. Some middle level
moisture may begin to reach our southern most zones late this
afternoon and this evening. Instability remains marginal, and expect
some cumulus clouds to develop over the mountains of Deschutes,
Crook and Grant counties this afternoon. At this time do not expect
any showers or thunderstorms in these areas, but will have to
monitor as a stray shower or storm could develop this evening. Will
be unseasonably warm again today, and did make a few minor
adjustments to high temperature forecasts. 90

Long term...previous discussion...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.


Aviation...18z tafs...winds will be at or below 15 kts for the next 24
hours. Cirrus clouds have developed across central and northeast
Oregon and will spread northward as the day progresses. Middle level
altocumulus and/or altostratus clouds will increase today and this
evening. By 06z tonight in central Oregon and 12z Monday morning
elsewhere...there will be variable middle and high level clouds with
broken-overcast ceilings at or above 10,000 feet above ground level. Wister


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


PDT watches/warnings/advisories...

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