Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 301116

Area Forecast Discussion
National Weather Service Spokane WA
415 AM PDT SAT AUG 30 2014

The Labor Day weekend will be cooler than normal with locally
breezy conditions over portions of central and eastern
Washington. With the exception of some isolated mountain showers,
the majority of the Inland Northwest will remain dry through the
weekend. A continuation of the cool weather pattern is expected
through next week. The best chance for showers and thunderstorms
will probably occur in the Wednesday or Thursday time frame.


Today through Sunday night: A cold front is slowly pushing its
way across the central ID Panhandle early this morning. This has
opened the door for much cooler temperatures to filter in across
the region. This will be most notable in the Panhandle as 850 mb
temps will drop from between 18-20 Celsius yesterday to around 16
Celsius this afternoon. High temperatures today are anticipated to
be in the 70s for most locations. This front will also result in
breezy conditions across the region today with winds up to 15-20
mph and gusts to around 25 mph. A weak upper level disturbance
pushing onshore early this morning may keep showers continuing in
the Central Panhandle Mtns. We will then see a splitting shortwave
trough of lower pressure push across the region this afternoon. A
moderately strong jet is oriented from NW to SE into western
Oregon. This where the southern portion of the energy is expected
to track. As such, generally only the very southeastern portion of
the region and the Cascade crest is expected to see some showers
with this portion of the upper level energy. The northern portion
of the splitting trough will largely track across BC and may
produce some isolated showers across the northern mountains. Areas
in between will see a lesser chance for showers today and the
basin will likely only just see some mid to high level cloud
cover. A lighting strike or two will be possible over the higher
terrain, but I don`t like our prospects for thunderstorms today.

Moist upslope flow into the ID Panhandle will keep showers
possible through tonight into Sunday. This will also be the case
up at the Cascade crest. Temperatures on Sunday will be a few
degrees cooler compared to this afternoon. There are timing
difference amongst the model guidance as when the next disturbance
will push into the region. The NAM and ECMWF show a weak entering
the region Sunday night. The GFS is much weaker and slower with
this energy. The NAM is slightly wetter with showers possible
across the northwest portion of the forecast area, whereas the GFS
and ECMWF are drier. I elected to keep the forecast as is for
Sunday night with the potential for some showers in the Northeast
Mtns and in the ID Panhandle, but confidence is low. /SVH

Labor Day: The 500mb trough responsible for the mountain showers
on Sunday will migrate eastward into the Upper Plains on Monday.
The Inland Northwest will likely experience dry weather on Labor
Day as the next shortwave trough approaches the British Columbia
coast. Afternoon temperatures in the mid to upper 70s will
continue to be several degrees below average.

Tuesday through Friday: There is decent model agreement that the
next upper level trough will arrive on Tuesday. The 0z ECMWF is
quicker and a bit deeper than the GFS with this system. Both
models depict the best best chance for showers over the northern
Cascades and along the Canadian border. The best combination of
mid-level cooling and moisture availability will be over the
mountains north of Lake Chelan, Republic, Colville, and Sandpoint
Tuesday afternoon and evening.

By Wednesday, the medium range models differ on the evolution of
the elongated 500mb trough over the region. Both models show the
trough splitting with part of the trough tracking into the
southern Canadian prairies while a portion of the trough lingers
over the interior Northwest. The best chance for showers and
thunderstorms during this split will probably be on Wednesday
depending on the placement of the 500mb cold pool. Given the
uncertainty, precipitation chances for Wednesday were changed
little with the best chances over the north Idaho Panhandle and
adjacent portions of extreme northeast Washington. There may be
enough shallow instability lingering into Thursday for isolated
mountain showers, but by Friday none of the models suggest enough
instability for anything more than some shallow cumulus. /GKoch


12Z TAFS: VFR conditions expected through 12Z Sunday. A couple of
weak weather disturbances today will produce mainly mountain
showers. A cold front passage last night will tighten pressure
gradients across the region with winds becoming breezy by the
afternoon. Models are hinting at some low level moisture advection
across southeastern WA Saturday night. This is expected to produce
some mid level cloud cover across eastern WA and showers ongoing
over the ID Panhandle through Saturday night. /SVH


Spokane        75  51  71  51  74  50 /  10  10  10  10  10   0
Coeur d`Alene  74  48  69  47  73  47 /  10  10  10  10  10   0
Pullman        73  47  71  45  73  43 /  10  10  10  10  10   0
Lewiston       79  55  77  55  80  54 /  10  10  10  10   0   0
Colville       77  45  74  43  77  44 /  10  10  10  10  10  10
Sandpoint      73  43  68  43  71  45 /  10  10  20  20  10  10
Kellogg        69  48  65  47  68  47 /  20  30  30  20  10  10
Moses Lake     80  51  78  50  80  51 /   0  10   0   0   0   0
Wenatchee      78  57  76  56  79  56 /  10  10   0   0   0   0
Omak           79  52  77  51  80  52 /  10  10   0  10   0   0



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