Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 121827 AAB
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1026 AM PST Tue Dec 12 2017

Updated AVIATION discussion

Corrected the issuance time in the PREVIOUS DISCUSSION headline

.SHORT TERM...Today through Wednesday...No change in the weather
pattern over the next 24 to 30 hours. A strong ridge of high
pressure will remain in place over the region. There will be a weak
shortwave passing over the ridge which will produce some cirrus
clouds. There is also the possibility the shortwave could stir the
low level stratus enough to produce some snow flurries. Otherwise
forecast remains the same with low level inversion trapping low
clouds, fog and cold air in the low elevations while mild and warmer
above the inversion.

&&

.AVIATION...18Z TAFS...Low level inversions trapping moisture will
continue to affect the interior Pacific Northwest through the next
24 hours. Thus ceilings will be 1000 to 2500 feet AGL at KDLS, KYKM,
KPSC, KALW and KPDT through the period. Tops of this cloud/fog area
will run between 3500 and 4500 feet MSL. Highest surface pressure is
over SE Oregon. This has been causing an east to west pressure
gradient across central Oregon that has scoured out the fog/stratus
at KBDN and KRDM. This preesure pattern and resultant dryness in the
boundary layer over KRDM and KBDN is expected to last through
Wednesday morning. Since fog/stratus is at KS33 (Madras) this
morning, will keep an eye on the potential for a brief appearance of
fog/stratus overnight into Wednesday morning at KRDM. Winds will
remain light and variable.  Polan

&&

.PREVIOUS DISCUSSION... /issued 300 AM PST Tue Dec 12 2017/

SHORT TERM...Today through Thursday...The current weather pattern
will remain over the area for the next few days with only a few
subtle changes expected. Low clouds remain over the Columbia Basin
and adjacent valleys and into North Central Oregon but has not
returned to Bend and Redmond. A weak low level flow from the
southwest to southeast appears to have pushed the clouds north.
Clouds have been moving back into Madras, Prineville and Redmond but
at around 5000 feet, so it is probably due to a weak wave crossing
the area rather than the low stratus returning. Have the low clouds
returning to central Oregon tonight though without a northerly flow
to push it, confidence is low. The rest of the Columbia Basin and
most northerly areas will see the low clouds continue through
Thursday. A freezing fog advisory remains in effect for north
central Oregon and the southern Blue Mountain Foothills through noon
today. However, the freezing fog advisory for central Oregon was
dropped earlier and do not see any sign it is reforming early this
morning, so I will not issue a new advisory. The low clouds in the
lower elevations will keep temperatures in the current small range
from the mid 20s to lower 30s. Elsewhere skies will be partly cloudy
with highs in the mid 30s to lower 40s and lows mainly in the upper
single digits and teens. There will be a weak wave moving through
the flow late tonight and early tomorrow morning so have added very
light snow flurries to the area under the inversion and low clouds.
Do not expect any locations will see more than a dusting of snow and
precipitation will be just a trace.  Perry

LONG TERM...Thursday night through Monday...A weak disturbance
looks to begin the process of weakening the upper ridge over the
Pacific Northwest late Thursday night into Friday. As such will see
the slow, but gradual elimination of the fog/low clouds across the
lower levels of the Interior Northwest. Some light precip will be
possible as this system moves through the region Friday and Friday
night. Precip Friday morning may be in the form of freezing rain at
many locations. Friday afternoon into Friday night snow levels will
lower, but the low levels should warm due to an intrusion of marine
air. Thus the lower levels would see rain by late Friday while the
higher elevations would see snow. A more westerly flow pattern looks
possible Saturday through Monday. Thus would see periods of precip
with snow in the mountains and rain or snow at the lower elevations
depending on the time of day. 90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  29  26  29  26 /   0   0   0   0
ALW  33  31  33  29 /   0   0   0   0
PSC  34  32  34  30 /   0   0   0   0
YKM  32  31  32  30 /   0   0   0   0
HRI  32  29  32  29 /   0   0   0   0
ELN  30  28  30  25 /   0   0   0   0
RDM  35  10  35  21 /   0   0   0   0
LGD  37  21  37  24 /   0   0   0   0
GCD  45  22  45  23 /   0   0   0   0
DLS  35  32  35  31 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 10 AM PST Friday for ORZ041-044-
     050-505-507>511.

     Freezing Fog Advisory until noon PST today for ORZ508-510.

WA...Air Stagnation Advisory until 10 AM PST Friday for WAZ024-
     026>029-520-521.

&&

$$

91/99/83/90


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