Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 252142
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
242 PM PDT Fri May 25 2018

.SYNOPSIS...
Thunderstorms are expected to develop this afternoon/evening, and
some may be capable of producing hail and heavy rain over the
southern Idaho Panhandle. A few showers may linger into Saturday
morning before drier weather arrives for the Memorial Day weekend.
Cooler weather is expected by the middle of next week.

&&

.DISCUSSION...
Tonight: A closed upper level low pressure system over California
will feed moisture up into primarily the southeastern portion of
the region. Best mid level moisture and instability will reside
from around the Northeast Blue Mtns to the Central Panhandle Mtns
and points southeastward. Afternoon convection across this area is
expected to continue into the evening hours. Surface based CAPE
values of up to around 1,000 J/kg with 0-6 km shear of between
25-30 kts will be sufficient for isolated stronger thunderstorms
resulting in gusty outflow winds and small hail. The severe
thunderstorm threat doesn`t look promising however as storms will
be moving into a less favorable storm environment. Synoptic level
forcing with shortwave energy rotating around the low will be
better south of our area. P-wats will be at around 1 inch meaning
that thunderstorms will contain very heavy rain. The good news is
that thunderstorms will be moving, albeit at a slow pace of
around 15 kts to the northeast. A Flash Flood Watch is in effect
for portions of the Northeast Blue Mtns, Lewiston-Clarkston areas
and the Camas Prairie through this evening. The primary threat
for flash flooding will be in steep terrain and in urban areas
such as in the Lewiston-Clarkston Valley. The good news is that I
don`t think any one thunderstorm will create a flash flooding
scenario since storms will be moving, but the threat will increase
substantially if multiple storms track over the same area.

Shortwave energy off of the Northwest coast will also track across
the region tonight as an open wave. Models show a small chance for
shower developing along the frontal boundary. I decided to address
this potential by adding sprinkles to the forecast tonight. The
front will push across overnight with drier air filtering by
Saturday. This will reduce our potential for precip over the
weekend. Temperatures will be cooler on Saturday, especially over
the Idaho Panhandle, but warm back up on Sunday with highs back up
into the upper 70s to low 80s.

Winds will pick up through the Cascade gaps this evening with
gusts of 20-30 mph expected across the Wenatchee Area tonight.
Winds will be a little breezy across the basin on Saturday behind
the cold front, but not expected to cause any impacts. /SVH

Monday through Friday: We`ll start the week hot and dry then cool
down with shower chances later in the week. It will be a great
Memorial Day to usher in the summer season for anyone with outdoor
plans. The upper low to our south stays over Utah, far enough
away to keep any of that wrap around precipitation to our
southeast in central Idaho. Under the high pressure ridge we`ll
enjoy sunny skies and temperatures around 10 degrees above average
for late May, reaching in the 80s.

Tuesday begins our transition from our dry and warm ridge to a
cooler and more moist pattern. A cool trough of low pressure
begins to move inland on Tuesday bringing increased moisture and
cloud cover. We`ll start sunny and clouds will increase from the
northwest through the afternoon/evening, as well as some breezy
winds in the Columbia Basin in the afternoon. The cold front will
swing through around late Tuesday night/early Wednesday through
there is still some uncertainty about exact timing. This cold
frontal passage will come with a line of showers likely early in
the day Wednesday. The latest run of the EC has actually come in
line with the GFS in showing this precip Wednesday morning, so
confidence it increasing that we`ll see some showers, especially
for the northern mountains and Panhandle mountains given the
upslope flow trajectory. Along with showers the front will bring
gusty post frontal winds to the basin and in the lee of the
Cascades, generally gusting up to 20-30 mph. Under this cold pool
we`ll see instability increasing as well and some Wednesday
afternoon thunderstorms are possible, mainly for the northern
mountains. Beyond Wednesday we`ll generally stay under this cool
and more unsettled pattern through late week, with high
temperatures in the 60s on Wednesday increasing to the low 70s by
Friday. /bw

&&

.AVIATION...
18Z TAFS: Mid and high clouds will move over most the area today
and this evening. Evening thunderstorms are possible for KPUW and
KLWS. Some of these storms could be strong with heavy rain, hail
and strong winds. None of these have a high enough probability to
put into the TAF. Elsewhere gusty evening winds are expected to
develop at KEAT and KMWH.  RJ

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        79  57  71  49  78  54 /  10  10  20   0   0   0
Coeur d`Alene  80  55  70  47  78  52 /  10  30  20  10  10   0
Pullman        76  54  65  46  73  51 /  10  60  40  10  10   0
Lewiston       82  61  71  52  80  56 /  10  70  50  10  10  10
Colville       82  54  80  49  86  51 /  10  10  10   0   0   0
Sandpoint      80  53  74  46  79  49 /  10  20  20  10  10   0
Kellogg        78  54  67  46  76  50 /  20  60  40  10  10  10
Moses Lake     82  54  78  49  84  53 /   0  10   0   0   0   0
Wenatchee      81  53  76  52  84  55 /   0   0   0   0   0   0
Omak           82  54  79  51  85  53 /  10  10   0   0   0   0

&&

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

&&

$$



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