Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 300006
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
506 PM PDT Wed Mar 29 2017

.SYNOPSIS...
Rain will be on the decrease this evening with the bulk of the
shower activity lingering across extreme southeast Washington and
into the southern to central Idaho Panhandle. A rare dry day is
expected on Friday. The weekend and early next week will feature
average temperatures and scattered light showers, mainly over the
mountains.


&&

.DISCUSSION...
Tonight through Thursday morning: A cold front is beginning to
move into western WA late this afternoon and then will sweep
across the Inland Northwest overnight. The moisture tap out ahead
of the front is becoming less with time and the axis of best
moisture will be across northern California into southern Idaho.
Isentropic ascent out ahead of the front will also weaken through
this evening with mid levels of the atmosphere exhibiting some
drying over much of the region. What we will be left with is
scattered showers over the Panhandle into the very extreme
portions of eastern WA; however, the Camas Prairie into the
southern ID Panhandle will continue to see stratiform rainfall
continue into at least late hours of this afternoon. This is good
news since we have seen a lot of rainfall so far this year and
soils are very saturated.

The upper level trough will push in behind the cold front and be
squarely over the top of the region by early Thursday morning.
Colder air will move in as well with snow levels dropping down
across all mountain passes. Stevens Pass will continue to see slop
over precip with another 4-6 inches of snow possible overnight.
Snow showers are likely to continue over Lookout Pass with a
couple of inches possible. All other mountain passes will be lacking
moisture for much in the way of appreciable snow accumulations. We
will also need to keep an eye on the lower portion of the upper
level trough as it moves over eastern OR. The upper level
dynamics will be strongest over this portion of the Inland
Northwest and models spin up a surface low over SE OR/SW ID.
Moisture will wrap around this low and push up as far north as the
Camas Prairie. The trend has been to keep much of this moisture
south of the our forecast area, but light snow with 1-2 inches of
accumulation will be possible on the Camas Prairie.

Thursday afternoon through Thursday night: Weak surface based
instability will spark off scattered showers Thursday afternoon
that should die off rather quickly in the evening. Skies will then
clear out with fog forming in the mountain valleys and out into
the Spokane/Coeur d`Alene Area. /SVH

Friday through Thursday...This period will be characterized by
generally drier conditions than we have been experiencing with
alternating periods of dry and showery weather through mid to late
next week. Temperatures will remain around their seasonal normals
with highs in 50s and lows in the 30s.

On Friday, an upper level ridge begins to nose into the region as
a closed low sets up over the four corners region of the desert
southwest. This will bring us dry weather for Friday. A weak
shortwave moves by to our north with associated frontal boundaries
Saturday. This could spark a few mountain showers but I still
expect most locations to remain dry. The boundary layer will
remain moist allowing for some fog or low stratus potential in the
favored sheltered mountain valleys for Friday and Saturday
mornings.

Our upper level ridge begins to break down for Sunday and Monday
as a series of disturbances drop through from the northwest.
Models indicate a 500 mb cold pool of -26 to -28 C as the trough
moves overhead which should be enough to enhance the shower threat
over our eastern zones, particularly in the orographically
favored areas. The GFS advertises enough instability for Sunday
afternoon to perhaps warrant a small chance of thunderstorms but
for now will leave out forecast until there is better model
agreement.

Shortwave ridging again builds back in for Tuesday and the first
part of Wednesday limiting any precipitation threat to a small
chance of mainly mountain showers. Our reprieve from widespread
rainfall looks to come to an end by late Wednesday and Thursday,
as our upper level flow turns more to the southwest and we receive
a glancing blow from another good moisture tap, rebounding PWATs
back to the 0.6 to 0.8 inch range. /Kalin

&&

.HYDROLOGY...
No changes will be made to the Flood Watch that is in effect until
Friday morning. Rainfall will be on the decrease tonight;
although around an additional quarter of an inch of rainfall can
be expected for the Northeast Blue Mtns, Camas Prairie and south-
central ID Panhandle. Rivers and streams across the Northeast Mtns
to the central-northern Idaho Panhandle are expected to crest by
tonight. Some of the rivers over the southern Idaho Panhandle will
take a little longer before they crest around Thursday night or
Friday morning. All of the counties in the Flood Watch will see a
continued risk of landslides/mudslides because of how saturated
the soils are. We will allow the rain from this afternoon to
filter through their respective watersheds before removing any
counties from the Flood Watch. /SVH

&&

.AVIATION...
00Z TAFS: An upper-level trof ushers a cold front through the
region tonight bringing an end to the precipitation. Breezy west
to southwest winds will deliver VFR skies to KEAT and KMWH and
low stratus into the rising terrain of Ern WA and N ID impacting
KGEG, KSFF, KCOE, and KPUW with moderate confidence. KLWS carries
lower confidence for restrictions and opted to leave out attm.
Stratus lifts aft 18z with shallow convective showers 19-00z at
the eastern terminals. /sb

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        37  51  32  54  37  56 /  20  30  10   0   0  10
Coeur d`Alene  38  49  32  53  35  54 /  60  40  10   0   0  10
Pullman        40  49  32  52  37  55 /  60  40  20   0   0  10
Lewiston       43  54  37  56  39  60 /  70  60  10   0   0  10
Colville       36  53  31  54  36  54 /  20  30  10   0   0  20
Sandpoint      38  48  31  51  33  53 /  70  30  10   0   0  20
Kellogg        37  45  31  50  34  52 /  80  40  30  10   0  20
Moses Lake     38  60  31  60  39  62 /   0  10   0   0   0  10
Wenatchee      38  55  35  57  38  59 /   0  10   0   0  10  20
Omak           36  55  30  57  37  59 /  10  10   0   0  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch through Friday morning for Central Panhandle
     Mountains-Coeur d`Alene Area-Idaho Palouse-Lewis and
     Southern Nez Perce Counties-Lewiston Area-Northern
     Panhandle.

WA...Flood Watch through Friday morning for Lower Garfield and Asotin
     Counties-Northeast Blue Mountains-Northeast Mountains-
     Spokane Area.

&&

$$


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