727
FXUS66 KOTX 192136
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
236 PM PDT Sun May 19 2024

.SYNOPSIS...
Showers and isolated thunderstorms will quickly subside this
evening. Cold temperatures will lend to frost formation for
portions of the region overnight, especially across the northern
mountain valleys. There will be a brief break between weather
systems Monday into Tuesday. Then a wet low pressure system is
expected Late Tuesday night and Wednesday, lingering Thursday. The
series of cold upper level low pressure systems through the week
will keep temperatures below normal.

&&

.DISCUSSION...

Tonight through Monday night: A low pressure trough over the Inland
Northwest with colder temperatures aloft will keep the atmosphere
conditionally unstable. Shower development this afternoon will
dissipate quickly with the loss of surface heating. Only a handful
of cloud to ground lightning strikes have been observed from the
Northeast Mountains to the Northern Panhandle. I don`t expect much
more coverage of thunderstorms for the rest of this afternoon with
weak surface based CAPE and little to no wind shear. Clouds are
expected to clear out across much of eastern Washington through the
evening with some lingering over the Idaho Panhandle. Dew points
sitting in the lower 30s will lead to frost formation across the
northern mountain valleys as clear skies and weak winds promote
strong radiational cooling. A frost advisory has been issued for the
Okanogan Highlands and Northeast Mountains in effect late tonight
through early Monday morning. This includes the communities of
Republic, Northport, Metaline Falls, Colville, Chewelah, and Deer
Park. Tonight is expected to be the last cold night this week with
widespread frost potential. It`s also possible that patchy frost
will be observed over the northern portions of the Upper Columbia
Basin, Palouse, and Northern Panhandle. Elected not to include
these areas in the frost advisory as it will be much more patchy
in nature.

Chances for showers and isolated thunderstorms will mainly be
confined to the Idaho Panhandle into extreme eastern Washington for
Monday. These areas will see a -24 Celsius cold pool aloft at 500
mbs. Shortwave ridging will be building across central Washington
with temperatures warming aloft and having a stabilizing effect
on the atmosphere. Temperatures will see a bump up with highs
warming into the mid 60s to mid 70s across much of the Inland
Northwest on Monday. /SVH

Tuesday through Sunday: As a low pressure slides into the region,
rain showers will increase throughout the day on Tuesday. Rain will
start over the Cascades, spreading eastward by the afternoon. Rain
will become widespread overnight and into Wednesday morning. Some
areas, like the lower lee of the Cascades and the deeper Columbia
Basin will receive less rain. Rain totals will be upwards of 0.5
inches to over an inch in the mountains, with a quarter to half an
inch in the lower elevations. The Columbia Basin will miss out on
much of the rain with less than 0.05 inches expected. Snow will be
limited to the highest terrain, with less than an inch forecasted at
Washington Pass, and Stevens Pass will remain as all rain, with the
possibility of a few snowflakes mixed in. This rain, along with
additional snowmelt from the mountains will lead to rivers rising,
but should remain below action stage. During the day on Wednesday,
an isolated lightning strike is possible but don`t expect to see
any. Tuesdays temperatures will be near normal, dropping about 10
degrees cooler for highs on Wednesday as the system passes through.
In areas that receive limited rain could see breezy winds with gusts
up to 25 mph.

For Thursday and beyond, scattered showers will continue, especially
in northeast WA and ID Panhandle. Another low arrives late Friday
into Saturday, with additional rain to the area. Temperatures will
conintue to stay slightly below normal for this time of year. /KM

&&

.AVIATION...
18Z TAFS: An upper level cold trough of lower pressure over the
Inland Northwest will promote a convection through the day today.
Covective temperatures are already being achieved over the higher
terrain of northeast Washington into the northern Panhandle with
isolated showers forming. Expect coverage of convection to expand
as the surface continues to warm up into the afternoon. Thunderstorms
will be single cell pulse type featuring infrequent lightning,
brief heavy rain, and small hail. Thunderstorms are most likely to
impact KCQV-KDEW-KSZT-KGEG-KSFF-KCOE today. Convection is
expected to dissipate clouds see a clearing trend between 02-04Z
this evening.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is low
with a 20-25% chance that thunderstorms will develop at KGEG-KSFF-
KCOE terminals today. Lower chances that thunderstorms will
develop at KEAT-KEPH-KMWH (5% chance) and KPUW-KLWS (10-15%
chance). There is low to moderate confidence for ceilings
producing MVFR conditions at KCOE Monday morning. /SVH

-----------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https://www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        37  68  41  62  45  53 /  30  20  10  20  70  90
Coeur d`Alene  37  65  41  61  45  51 /  50  30  20  20  80  90
Pullman        37  62  42  60  44  52 /  10  20  10  10  80  90
Lewiston       44  70  46  69  50  60 /  10  20  20  10  80  80
Colville       35  69  42  63  40  53 /  40  20  10  30  80  90
Sandpoint      36  62  39  61  45  51 /  60  50  20  20  80 100
Kellogg        38  60  42  59  47  49 /  50  40  20  20  80 100
Moses Lake     41  75  44  66  45  63 /  10   0   0  10  20  50
Wenatchee      44  72  49  63  47  64 /  10   0   0  20  20  40
Omak           39  74  44  66  45  63 /  30  10  10  20  50  70

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Frost Advisory from 2 AM to 8 AM PDT Monday for Northeast
     Mountains-Okanogan Highlands.

&&

$$