Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 202334
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
434 PM PDT MON APR 20 2015

.SYNOPSIS...

Tuesday will likely be the warmest day in the next 7 to 10 days as
strong high pressure remains over the region for one last day. A
cold front will arrive Tuesday night bringing cooler weather and
breezy conditions into Wednesday. A cool upper trough is expected
to bring showery conditions Friday and Saturday.

&&

.DISCUSSION...

Tonight through Tuesday night...The axis of the ridge of high
pressure influencing the area moves east tomorrow. It does this at
slow enough of a speed to allow for temperatures of the seven day
forecast to peak for most locations tomorrow. Late in the
afternoon and evening with the axis to the east a weak marine push
of sorts allows for winds to increase in the gaps of the cascades
and close proximity to them late Tuesday afternoon and overnight.
The weak push may also fire off a bit of spotty convective showers
and perhaps a thunderstorm or two. Minimum temperatures Tuesday
night should be on the warm side of normal given the mixing
brought about by the wind. /Pelatti

Wednesday: Cooler and breezy weather will arrive Tuesday night
into Wednesday. The high amplitude 500mb ridge responsible for our
recent warm weather will be replaced by a cool polar low
descending out of the Gulf of Alaska. A relatively high spread in
model solutions continues for a day 3 forecast leading to lower
than average confidence for precipitation chances and winds for
Wednesday. The GFS model continues to be an outlier digging an
upper low deeper south into Washington on Wednesday. The ECMWF,
Canadian and NAM models look to have a more reasonable progressive
solution. The deeper/slower low on GFS looks a bit suspect given
the strong upstream kicker in the Gulf of Alaska, so the forecast
for Wednesday and Thursday was largely based on the Canadian
which is a compromise between the ECMWF and NAM.

This Canadian compromise means less chance for thunderstorms since
the heart of the 500mb cold pool will only graze the northern
Washington zones. This solution also entrains a good deal of mid-
level dry air into the region on Wednesday limiting the amount of
deep layer instability. Precipitation chances region-wide don`t
look very impressive. The Canadian and ECMWF solutions are a bit
breezier, so winds have been increased. We will likely see a 10
to 12 degree cool down from Tuesday into Wednesday as chilly
maritime air is squeezed through the gaps in the Cascades. The
change in air mass will likely be accompanied by typical breezy
spring time winds between 15 and 20 mph with some wind prone areas
in the lee of the Cascades gusting in excess of 30 mph on
Wednesday.

Thursday: If we discount the GFS, Thursday has the potential to be
a relatively dry day with fairly light winds. Precipitation
chances have been trimmed, limited to 20 percent or less in the
mountainous. Light winds and a good chance for mainly clear skies
suggest a fairly chilly morning on Thursday. Sheltered areas in
the Idaho Panhandle and northeast Washington will have a good shot
at low to mid 30s...perhaps a frost.

Friday and Saturday: By Friday, the main longwave trough over the
Gulf of Alaska is expected to move into Washington or southern
British Columbia. Seasonably chilly temperatures and showers will
likely accompany the arrival of this broad polar trough. Our
temperature forecast for Friday into Saturday has been cooled in
line with MOS guidance.

Sunday and Monday: Given the model uncertainty in the Wednesday
through Saturday time frame, it is a bit unusual to see the GFS,
ECMWF, and Canadian come into better agreement early next week.
The model consensus is for a mild and wet pattern Sunday and
Monday as a subtropical moisture plume becomes planted over the
Pacific Northwest. Early next week looks like our best shot of
widespread precipitation during the next 7 to 10 day period.
/GKoch

&&

.AVIATION...
00Z TAFS: High pressure will result in VFR conditions and weak
winds at all TAF sites through Tuesday afternoon. /SVH

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        46  74  50  61  36  62 /   0  10  10  20  10  10
Coeur d`Alene  41  73  44  62  34  62 /   0  10  10  20  20  10
Pullman        42  72  46  58  34  61 /   0  10  10  30  10  10
Lewiston       46  78  49  65  38  66 /   0   0  10  30  10  10
Colville       42  77  46  65  37  65 /   0  10  10  40  40  20
Sandpoint      38  72  40  61  33  60 /   0  10  10  30  30  20
Kellogg        40  71  43  59  34  62 /   0  10  10  30  20  20
Moses Lake     44  78  50  67  37  66 /   0  10  10  10   0  10
Wenatchee      51  77  53  65  41  65 /   0  10  10  10   0  10
Omak           44  77  47  65  35  64 /   0  10  10  30  20  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$



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