018
FXUS66 KOTX 022147
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
247 PM PDT Thu May 2 2024

.SYNOPSIS...
With the exception of widely scattered showers along the Canadian
border Friday afternoon, the Inland Northwest will experience
mild and dry day. A slow moving frontal system will bring
increasing chances for rain to central Washington Friday night
into Saturday. Sunday will be a chilly and rainy with portions of
north Idaho and eastern Washington experiencing highs in the 40s
Sunday. Cool and showery weather will be in store Monday through
Wednesday followed by warmer temperatures late next week.

&&

.DISCUSSION...

Tonight: Afternoon temperatures are several degrees warmer than
they were at this time yesterday which is an indication that our
air mass is moderating. Even though are dewpoints continue to be
very dry (mid 20s to low 30s), warming aloft should prevent
widespread freezing temperatures overnight. It will still be
chilly with light winds and mostly clear skies, but we don`t see a
need for a Freeze Warning tonight. The National Blend of Models
(NBM) morning lows in the mid 30s for the valleys of northeast
Washington, the West Plains, Palouse, and Moses Lake area. There
will be pockets that dip below freezing, so folks that have
planted sensitive vegetation and live in cold spots should take
measures to protect their gardens.

Friday: A slow moving front will bring widespread rain to the
Inland Northwest this weekend, and we will begin to experience
effects of that front by Friday afternoon. In the morning, skies
will be mostly clear and winds will be light. By the afternoon,
southeast winds will increase with the most notable increases
over the Waterville Plateau and up the Okanogan Valley. Guidance
from the High Resolution Ensemble and the NBM produce sustained
winds of 15 to 20 mph with gusts up to 30 mph for Waterville,
Mansfield, Tonasket, and Omak. Similar winds can be expected on
exposed ridges in the north Washington Cascades. Frontal
precipitation will be slow to arrive with only a 50 percent chance
after midnight at Stevens Pass and a 20 percent chance of light
rain at Wenatchee by daybreak Saturday morning. There will be
enough residual instability over the mountains along the Canadian
border Friday afternoon for a 20 percent chance of light rain
showers over the high terrain of near Republic, Kettle Falls,
Metaline, and Bonners Ferry. With the reversal of our mid-level
flow (ahead of the front), these showers will move from south to
north...the opposite cell motion we have had the last 3 days.

Saturday: The eastward progress of the front on Saturday will be
slow. The upper low pushing it east will slide down the coast and
into Oregon during the day. North Idaho and the eastern third of
Washington should experience a relatively decent day. Morning
temperatures will be significantly warmer with overnight lows in
the 40s. Chances for measureable precipitation through 4PM
Saturday are only 20 percent for Spokane, Coeur d`Alene, Lewiston,
and Colville with highs in the 60s (low 70s in Lewiston). Ensemble
based guidance suggests a different story for Wenatchee,
Leavenworth, Chelan, and the Methow Valley with 50 to 70 percent
chance of rain and highs in the 50s. The NBM spreads a band of
much needed rain across the Columbia Basin, West Plains, Palouse,
and L-C Valley Saturday night. The month of April was quite dry.
Pullman fell nearly a half inch below average, Spokane almost
seven tenths below average, and Moses Lake nearly four tenths
below average. It`s unfortunate that rain will fall over the
weekend, but the regional wheat crop can certainly use the
moisture. /GKoch

Sunday through Thursday: Transition to wet and cool conditions is
well underway at this point, and very much apparent in numerous
tools utilized to view the NBM data. Very apparent there will be
significant cooling in daytime highs Sunday however the members show
a large spread with 1D viewer showing whisker plots (spread) between
44 and 67 for KGEG`s Max temperatures for Sunday and is very similar
elsewhere in the CWA. The whiskers show the 10th and 90th
percentiles)...even the boxes showing the 25th and 75th percentiles
are rather tall varying between 47 and 57....SO its still reasonable
to say Sunday will be quite cool and wet. NBM is noting Saturday`s
high temperature for Spokane (KGEG) could fall very close to past
record low max of 47 degrees set back in 1961. Precipitation amounts
in the NBM have increased and as such our rain amounts in the
forecast for Sunday and Sunday night have increased. They area
approaching near one half inch overall accumulation for Spokane area
if one adds the rain amounts expected Saturday night, Sunday, and
Sunday night. This is due to a wet frontal zone wrapped up along the
northeast edge of an upper level area of low pressure centered over
the northern great basin moves slowly east. This frontal zone has a
moderate, yet very effective, tap into subtropical moisture and
this is reflected in high forecast precipitable water values
approaching 160 percent of normal for the forecast area. The
moisture plume and the associated upper level trof moves east,
however any resulting shortwave ridging is still embedded in a
general longwave trof continuing to linger over the Western US. With
this in mind a rain-shadow of sorts can be expected in places
between the lee of the Cascade Crest and the higher terrain of North
Idaho that expands with time heading into Thursday with remaining
periphery holding onto varying pops and QPF as well as minor
mentions of short-lived weak low topped thunderstorms and all are
favoring the afternoon and early evening hours. /Pelatti

&&

.AVIATION...
18Z TAFS: VFR conditions will prevail at the TAF sites today and
through Friday. Convective showers will develop over the
mountainous terrain of the Idaho Panhandle as well as northeast
and north central Washington mainly between 20-02z. Showers won`t
be heavy rain makers since the lower atmosphere is quite dry.
Light rain and virga that occurs around Sandpoint, Bonners Ferry,
Colville, Republic, Deer Park, Winthrop, and Kellogg may be
accompanied by gusty outflow winds. Gusts as high as 30 mph will
be possible as precipitation evaporates in the dry air leading to
chilly outflow gusts.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is a 20 percent chance of lightning and pea hail mainly over
the high terrain around Bonners Ferry, Sandpoint, and Colville. A
few lightning strikes will be possible between 20z-02z as well.
/GKoch

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

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  65  46  68  41  47 /  10   0   0  20  50  70
Coeur d`Alene  36  63  44  68  41  46 /  10   0   0  10  40  70
Pullman        35  62  46  65  37  44 /   0   0   0  20  70  80
Lewiston       40  70  47  73  45  52 /   0   0   0  20  70  80
Colville       34  65  41  67  41  52 /  20  10  10  20  40  70
Sandpoint      37  61  42  66  44  48 /  50  10   0  10  40  80
Kellogg        37  61  44  65  44  45 /  20  10   0  10  50  80
Moses Lake     37  71  52  68  44  54 /   0   0  10  50  60  60
Wenatchee      43  67  52  59  47  56 /   0   0  20  60  60  40
Omak           40  70  50  67  48  59 /  10   0  10  40  40  50

&&

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

$$