Severe Thunderstorm Warning 30, NWS Spokane, WA

Area Forecast Discussion
National Weather Service Spokane WA
449 AM PDT Fri Aug 12 2022

.SYNOPSIS...
Moisture rounding a low pressure system in the eastern Pacific
will keep showers and thunderstorms in the forecast at times
early Saturday morning. Once again a few of the thunderstorms
could be strong and produce large hail and damaging winds
especially over extreme eastern Washington into north Idaho. A
cold front passage on Saturday will result in breezier winds for
the afternoon and usher in much drier air. After a brief cool down
for the weekend, hotter weather is expected to return through at
least midweek.

&&

.DISCUSSION...

Today and tonight: Another round of thunderstorms is expected for
the Inland Northwest. The Low off the coast continues to promote
instability across the Pacific Northwest. Today is expected to be
similar to yesterday but the areas impacted will generally be the
Idaho Panhandle and the Northern Mountains. The thunderstorm
threat is expected to start late morning and continue through the
evening. The thunderstorm activity will diminish behind a cold
front overnight and early Saturday morning.

The environment in these areas is expected to support strong
thunderstorms. Cape values are 2000-3000 Joules. Lapse rates are
around 8C/KM. Shear values are expected to be 35-40 kts. PW
amounts are expected to be near one inch.

The threats from the storms are expected to be abundant lightning,
hail, gusty winds, and heavy downpours. Some storms could produce
severe hail of an inch or greater. Wind gusts of 35 to 45 MPH are
possible. Luckily these storms are expected to bring decent
amounts of rain and dampen any possible fire starts.

Winds across the Basin will generally be in the teens with gusts
near 25 MPH. Highs for the day are still expected to be above
normals. The region can expect widespread 90s.

Saturday: As the Low continues to move North, high pressure will
begin to build into the region. It will lead stable dry
condition. Winds will continue to be breezy across the Basin
leading to increase fire concerns as RHs are in the upper teens
and low 20 percents. Highs will dip into the 80s. Lows will be in
the 50s and low 60s. /JDC

Sunday through Wednesday...The ensemble suites are in very good
agreement through this period by showing a gradual rebound of the
upper level ridge over the Inland Northwest. So what does this
mean? It means we are looking at a period with dry weather and
increasingly warm temperatures. Each day we expect to see about
1-2C of warming at 850 mbs and likely peaking on Wednesday. On
Sunday we will start with 850 mb temperatures ranging from 19-21c
which equates to seasonable temperatures with highs in the mid 80s
to mid 90s. By Wednesday those values will range from 27-29C (and
a little cooler from the Canadian ensemble means) which equates
to another day of potential triple digit heat. Right now we have
forecast highs ranging from the mid 90s in the far northern Idaho
Valleys to the mid 100s over the Okanogan Valley, Wenatchee
Valley, and LC Valley. Some of the forecast values are near record
highs for the date including:

Wenatchee: Forecast: 102F  Record: 104F set in 1977
Omak: Forecast: 104F  Record: 104F set in 2020
Ephrata: Forecast 102F  Record: 104F in 1977

Meanwhile we expect conditions to be considerably drier than our
current air mass as the precipitable water values drop from over
an inch today to nearly half that by Saturday night/Sunday.
Fortunately this dry air mass isn’t expected to be accompanied
by any strong wind events during this period. Nonetheless the
combination of the much drier air, clear skies, and increasing
heat will continue to desiccate the fuels and any possible
holdovers from recent and upcoming lightning. As the week
progresses, precipitable water values will gradually increase as
we transition from westerly flow to more of a southerly one by
midweek with the retrogression of the Four Corners High.

From Thursday and Friday, the confidence in the forecast begins to
plummet somewhat, as about a quarter of the ensemble members
(mostly from the Canadian) shove the ridge into Montana and bring
a stronger trough in western Washington. Meanwhile about 40
percent of the ensemble members amplify the ridge even further. If
the former were to occur, we’d be looking at a significant cool
down, likely accompanied by some breezy winds and the possibility
of more precipitation. However if the latter occurs its more of
the same and in fact it could be hotter than Wednesday. The
ensemble trends of the Euro and Canadian means is toward the
cooler solutions, but we shall see. fx

&&

.AVIATION...
12Z TAFs:
VFR conditions will are expected for TAF sites. Late morning and
afternoon convection is expected to produce isolated thunderstorms
in the Idaho Panhandle and Northern Mountains. There is the slight
chance of storms impacting LWS- PUW-CDA-SFF but confidence is
very low. Winds will increase across the Basin with gusts near 25
kts. /JDC

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        95  60  86  56  87  56 /  10  10   0   0   0   0
Coeur d'Alene  95  59  85  53  86  53 /  10  20   0   0   0   0
Pullman        90  54  82  51  84  52 /  10  20   0   0   0   0
Lewiston       98  67  91  61  93  62 /  20  20   0   0   0   0
Colville       96  52  88  47  88  48 /  20  20  10   0   0   0
Sandpoint      93  57  85  51  86  50 /  20  20  10   0   0   0
Kellogg        93  62  83  59  84  60 /  20  30  10   0   0   0
Moses Lake     96  58  89  53  90  56 /  10   0   0   0   0   0
Wenatchee      96  62  86  59  90  63 /  10  10   0   0   0   0
Omak           98  61  91  56  92  59 /  20  20   0   0   0   0

&&

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

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SPOKANE WA
751 AM PDT FRI AUG 12 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0720 PM     HAIL             8 SE NORTHPORT          48.85N 117.63W
08/11/2022  E0.75 INCH       STEVENS            WA   TRAINED SPOTTER

            DELAYED REPORT FROM THURSDAY EVENING.

&&