Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 221001

Area Forecast Discussion
National Weather Service Spokane WA
301 AM PDT Thu Mar 22 2018

A wet day is expected across much of the Inland Northwest as a
moist Pacific storm courses its way through the region. Areas of
moderate to locally heavy precipitation are expected near the
Cascades. The threat of precipitation will ease from west to east
late this afternoon and evening as a very strong cold front plows
through. The front will deliver gusty winds, as well as a small
chance of thunder over the eastern quarter of Washington and the
Idaho Panhandle. The air mass behind the cold front will be
considerably colder and unsettled with a chance of rain and snow
showers each day through the weekend. Drier and milder weather
will return to the region early next week.


Today through tonight...This will be an active period as the
region will be impacted by a large trough of low pressure off the
coast with a cold front poised to move through this afternoon and
evening. Current radar is showing a large swath of precipitation
extending from the Wenatchee area eastward through the northern
Columbia Basin and then southward toward the Blue Mountains. Most
of this precipitation is associated with strong warm air advection
at the 850-700 mb level. It is being enhanced even further by
orographic ascent due to southeast winds across western Okanogan
and Chelan Counties. Precipitation during the past 6 hours in this
region has ranged from 0.15-0.32" with a couple more hours of
rain expected. Current snow levels in that area appear to be above
5000` so most is falling as rain. This current batch of
precipitation is expected to shift into BC around sunrise with
most of the region starting the day on a dry note. That will
change abruptly though as a very strong cold front creeps toward
the Cascades toward midday.

This approaching cold front will result in a resurgence of
precipitation near the Cascades as well as a blossoming of
precipitation over the remainder of eastern Washington and north
Idaho during the afternoon. The cold front is expected to pass
through the Cascades by mid-afternoon and shift to the Idaho
Panhandle by early evening. We expect to see widespread
precipitation develop along and ahead of the front. More moderate
to locally heavy precipitation is expected to fall over western
Okanogan and Chelan Counties with amounts possibly nearing a half
inch as the mid-level winds again turn to the southeast. Snow
levels in this area will remain at or above 5000` until the front
passes. Farther east precipitation amounts should be lighter, but
the atmosphere will feature decent lapse rates as a low-level
thermal ridge develops over the eastern Columbia Basin and extends
into the Idaho Panhandle. Ascent ahead of the front will couple
with this instability to produce a line of convection which will
be marginally deep enough to support isolated thunderstorms. The
greatest threat will occur east of a line from Kettle Falls to
Pomeroy and into the Idaho Panhandle. These showers and
thunderstorms will be capable of producing gusty winds, but even
without the convection we should see gusty winds since this is a
vigorous cold front. Wind gust speeds of 25-35 mph will be
possible behind the front will locally higher speeds certainly
possible over the Palouse, southern Columbia Basin, and Camas

The front will push east of the area overnight with a rapid drying
and cooling trend developing. Showers will likely be reserved for
the Idaho Panhandle into the late evening hours with dry
conditions elsewhere and decreasing winds.

We will maintain our current flood watch through this evening over
the northern third of our forecast area however we suspect that
the main threat of flooding will be reserved for Okanogan and
Chelan Counties. The primary flood threat will revolve around low-
land ponding of water or minor flooding and the possibility of
land slides. Mainstem river flooding is not expected at this time.

Friday through Monday: A large closed low off the Washington
coast on Friday will send a moist short wave across the Inland NW
beginning near the Cascades Friday before spreading into Eastern
WA/N Idaho Friday night into Saturday morning. Models show snow
levels Friday afternoon ranging from 2000 feet (Cascades) to 3500
feet (SE WA) before lowering to 1000-2000 feet by Saturday
morning. GFS and ECMWF models show the brunt of the moisture from
this wave near the Cascade crest, and across SE WA into the Idaho
Panhandle while the NAM shows a ribbon of higher qpf further west
from Ritzville to Davenport. Light to locally moderate snow
accumulations are expected even for most valleys with this wave.
This wave exits and is replaced by more hit and miss showers on
Sunday an unstable air mass remains. But the main focus should be
more over the mountains due to an absence of any significant short
waves to initiate convection. On Monday a short wave ridge moves
over the region for dry conditions except for possibly a few light
mountain showers for the Idaho Panhandle in the afternoon due to
lingering low level moisture and shallow instability.  JW

Tuesday through Thursday: A ridge of high pressure will dominate
the weather pattern for this period. This will allow for a drying
trend for the region. Isolated mountain snow showers are possible
but models aren`t too high them occurring. Temperatures around
the region will be in the 40s to low 50s for highs and into the
upper 20s and 30s for lows. /JDC

06Z TAFs: TAFs are rather lengthy in order to time the various
disturbances that are coming up from the south and southwest and
expected to bring precipitation to the area. Ceilings may go down
to MVFR at times associated with what will be rainfall at TAF
sites. Otherwise there may be some weak pulse thunderstorms
forming between 23Z Thursday and 03Z Friday that may affect
locations east of KMWH including the KGEG, KSFF, KCOE and KPUW
sites. After the clutter of this activity ends/diminishes with a
frontal passage an increase in gusty southwest winds is expected
primarily after 04Z Friday. /Pelatti


Spokane        54  30  47  30  41  25 /  80  90  30  60  70  20
Coeur d`Alene  52  29  45  30  40  22 /  80  90  40  70  80  20
Pullman        52  32  47  30  42  26 /  80  90  40  60  80  10
Lewiston       59  35  54  35  50  31 /  60  80  40  60  70  10
Colville       54  30  48  31  44  24 /  80  90  40  60  60  30
Sandpoint      47  29  44  30  38  24 /  80  90  40  70  90  30
Kellogg        50  27  43  29  38  23 /  80  90  30  60  90  20
Moses Lake     57  32  52  31  52  26 /  70  10  20  30  20  10
Wenatchee      52  33  48  30  49  28 /  80  10  40  30  20  10
Omak           51  30  48  30  48  24 /  90  20  50  40  50  10


ID...Flood Watch through this evening for Northern Panhandle.

WA...Flood Watch through this evening for East Slopes Northern
     Cascades-Northeast Mountains-Okanogan Highlands-Okanogan
     Valley-Wenatchee Area.


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