422
FXUS66 KOTX 182139
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
239 PM PDT Sat May 18 2024

.SYNOPSIS...
Cooler and unsettled weather will continue through the weekend.
Frost in the northern mountain valleys will be more patchy in
nature with more cloud cover hanging around through the night. A
brief break between weather systems Monday into Tuesday. Then a
wet low pressure system is expected Wednesday into Thursday. The
series of cold upper level low pressure systems through the week
will keep temperatures below normal.

&&

.DISCUSSION...

Tonight through Monday night: Cold pool aloft nested in a general
trof pattern overhead consisting of 500mb temperatures hovering
near -25 degrees C will allow for a conditionally unstable airmass
to linger over Eastern Washington and North Idaho through at
least Monday until some positively tilted shortwave ridging drops
down from the northwest and allows the upper levels to warm up and
bring some stability. Short term high resolution models suggest a
vort maxes and other such small scale disturbances will utilize
this instability to allow for continued showers and isolated weak
low topped short lived pulse thunderstorms as the tropopause
brought about by the cold trof overhead remains low. In addition
the forcing at play, brought about by this vort max and any other
additional disturbances, may allow for any convection to occur
during the overnight hours. Thus pops don`t drop off after sundown
but more or less follow where the vortmax is expected to track
which is northwest to southeast through Eastern Washington and
North Idaho. Additional, though less resolved in the high res
models, disturbances are expected to make similar travels through
the cold trof overhead thus additional pops for spotty showers and
thunderstorms remain in place Sunday and Sunday evening. Some
clearing is suggested Sunday night into Monday morning, enough to
merit mention of areas of frost. A repeat of minor mention of
spotty convection lingers over portions of the Idaho Panhandle
Monday afternoon as the earlier mentioned incoming upper level
positively tilted ridge moves in and the resulting incoming
stability should suppress convection over Eastern Washington.
Clouds then increase from west/northwest Monday night, mainly west
of the upper level ridges positively tilted ridge axis but for
the most part Monday night looks to remain mostly dry. Delayed
onset of the incoming clouds may allow for another repeat of
spotty frost late Monday night. As to be expected with a cold trof
aloft forecast temperatures will tend to remain near or slightly
on the cool side of what would be considered normal for this time
of year. /Pelatti

Tuesday through Thursday: Confidence is increasing for a deep closed
upper level low pressure system to drop down out of BC into the
Northwest Tuesday night into Wednesday. The center of the low will
pass across northwest Washington into north-central Oregon Tuesday
night into Wednesday morning. A deformation band will track across
the region and become hung up across the Idaho Panhandle, northeast
Washington, and over into the northern Cascades. This area is
expected to receive good soaking precipitation with a 70% chance for
at least a quarter of inch of precipitation, a 50% for at least a
half an inch, and a 20% chance of up to 0.75 inches of
precipitation. The official forecast calls for between 0.50 to 0.75
inches of precipitation across the Idaho Panhandle into the
Northeast Mountains and Okanogan Highlands. Extreme eastern
Washington from the Spokane Area to the Palouse will more likely
see rainfall amounts in the range of 0.25 to 0.50 inches.
Temperatures will be much cooler under the low with temperatures
on Wednesday likely to struggle to warm into the upper 50s.

Thursday night through Saturday: There is more uncertainty with the
ensembles on the overall pattern later in the extended portion of
the forecast period, but the leading cluster is indicating another
deep upper level low to drop down over the region around Memorial
Day weekend. This second upper level low doesn`t look quite as wet.
It will continue to keep the region unsettled though and cooler than
normal. Anyone with camping plans for the holiday weekend should
prepare for cool and showery conditions. /SVH

&&

.AVIATION...
00Z TAFS: Conditionally unstable airmass with a disturbance
dropping down northwest to southeast across the aviation area will
allow for some mention of showers and possible weak short lived
pulse thunderstorms. Still for the most part VFR conditions are
expected. /Pelatti

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Of course the
disturbance dropping down could very well take a different
trajectory through and miss some of the TAF sites that have
mention of potential precip in them. In addition some stratus
could form tonight into Monday morning due to any resulting
rainfall today and tonight. /Pelatti

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

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        40  61  39  68  44  66 /  40  40  20  10   0  10
Coeur d`Alene  39  57  39  65  42  66 /  40  50  20  20   0  10
Pullman        37  57  38  63  41  64 /  30  20  10  10   0  10
Lewiston       44  64  45  70  46  72 /  20  10  10  20   0  10
Colville       33  63  34  70  38  67 /  70  80  40  20   0  20
Sandpoint      37  55  38  63  41  64 /  60  80  30  40  10  20
Kellogg        40  52  40  60  44  62 /  50  60  20  40  10  20
Moses Lake     40  69  42  75  44  71 /  10  10  10   0   0   0
Wenatchee      43  67  44  72  49  68 /  10  10   0   0   0  10
Omak           39  69  41  75  45  71 /  30  30  10   0   0  10

&&

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

$$