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000
FXUS66 KOTX 230924
AFDOTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
224 AM PDT Thu May 23 2013

.SYNOPSIS...
Cool, showery weather will continue over the Inland Northwest due
to a lingering upper low. Snow will also be possible over the
mountains. Conditions could moderate a bit by the weekend, as the
low moves out of the area, but it will be replaced by another cool
low sometime early next week.


&&

.DISCUSSION...
Today and tonight: An upper low provides continued hit-and-miss
shower chances and cool temperatures. The low was centered just
south of Seattle this morning. As a shortwave pivots around its
northwest side today, the low is expected to retrograde toward the
mouth of the Columbia River. This will keep the Inland Northwest
in a south to southeasterly flow and in the path of weaker
vorticity maxima. One vort max strings by northeast WA and
northern ID early today and a second slips by the Cascades later
this afternoon and evening. Finally, a third slips across Oregon
toward the Clearwaters late this afternoon and evening too. With
the afternoon heating, models depict increased convective
instability. Agreement on where this instability will lay is
highest over the Cascades to Waterville Plateau and secondarily
across the lower Columbia Basin into the Blue Mountains. One to
two hundred J/kg of CAPE is depicted.

The weak forcing from the passing vort max, coupled with the
south/southeast flow, will support the highest shower chances
across the Cascades, Wenatchee area and Waterville Plateau.
Secondary chances will be found near the Blue Mountains. Given the
unstable nature of the upper trough a slight chance of
thunderstorms will be found here this afternoon and early evening
too. Tertiary chances will be found in northern mountains, largely
due to the orographics. The lowest threat will be of the upper
Columbia Basin through the central Panhandle, including the
Spokane/C`dA area and Palouse as models continue to entrain a fair
amount of dry air into southeast Washington and the Idaho
Panhandle. By tonight waning instability and exiting vorticity max
will diminish the threat of showers throughout much of the region.
The main exceptions will be near the Cascades and near the
Blue Mountains as the main shortwave pivots around from the
northwest to the south side of the low and begins to push swing
across Oregon overnight into Friday morning). /J. Cote`

Friday through Wednesday...Models are in good agreement for Friday
in maintaining a deep upper low pressure over the forecast area.
While the main deformation axis with widespread showers will have
pivoted north and east and be well clear of the region...the
forecast area will reside underneath the destabilizing cold pool
aloft in the center of the upper low. Thus...scattered showers are
a good bet and just about all zones will be susceptible. In
addition...if any sunbreaks occur...which is a distinct
possibility...the prospect for at least isolated thunderstorms
will be very real...again just about anywhere. Temperatures will
remain well below normal through Friday.

From Saturday onward model agreement decreases somewhat...especially
with sub-synoptic details...however the general model consensus is
to weaken or eject the upper low north into Canada and leave a
distinct but weaker troffy pattern over the Northwest US. This is
good news for holiday weekend outdoor planning as it implies that
there are likely to be considerable periods of dry or minimal
shower activity and the main shower activity expected each
afternoon and evening will be concentrated over the mountains
ringing the Columbia Basin. This is not to say that random showers
will not prowl the basin from time to time...just that the
activity will not be as sure a bet as when the upper low was
sitting right over the forecast area.

For the new work week the latest GFS and ECMWF both hint at the
arrival of a new and deeper trough into the region on or about
Tuesday or Wednesday...with the potential for a well defined and
moist frontal surface leading to more widespread showers.

Through this period temperatures will start out well below normal
on Friday and gradually increase day by day to around seasonal
normals by Sunday. /Fugazzi

&&

.AVIATION...
06Z TAFS: An upper level low pressure area centered in the vicinity
of the aviation area will keep the threat for -shra vcnty KEAT and
KMWH through much of the night and Thur morning.  Aftn heating will
promote light but widely sct -shra across the region for just about
any location.  Some showers may produce MVFR ceilings at times.
Additionally some late night and early morning fog could produce
brief IFR/LIFR visibilities with KSFF/KLWS carrying the highest
threat for fog formation. Patchy frost will be possible near KPUW
and KDEW.  All terminals are expected to receive a break from pcpn
and VFR skies aft 02z. /sb


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        60  41  60  42  64  45 /  20  20  40  30  20  10
Coeur d`Alene  59  39  59  41  64  43 /  20  20  50  40  20  20
Pullman        60  38  56  40  64  42 /  20  20  50  20  20  20
Lewiston       66  45  63  45  71  49 /  20  10  50  20  20  20
Colville       63  38  67  42  69  43 /  30  30  50  50  40  30
Sandpoint      57  36  62  40  63  40 /  30  20  60  50  30  30
Kellogg        55  39  56  41  60  44 /  20  20  60  50  40  40
Moses Lake     66  43  68  46  72  47 /  20  20  30  20  10  10
Wenatchee      62  44  66  48  69  49 /  40  30  40  20  10  10
Omak           64  38  68  42  69  43 /  30  30  40  30  30  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Freeze Warning until 7 AM PDT this morning for Central Panhandle
     Mountains-Idaho Palouse-Lewis and Southern Nez Perce
     Counties.

WA...Freeze Warning until 7 AM PDT this morning for Washington
     Palouse.

&&

$$