Special Weather Statement, NWS Spokane, WA

Area Forecast Discussion
National Weather Service Spokane WA
502 PM PDT Wed Jun 20 2018

.SYNOPSIS...
Showers and thunderstorms will continue over the Cascades and
northern mountains this evening. The threat for rain and
lightning is expected to spread into eastern Washington and north
Idaho overnight. Slow moving cells will have the potential to
produce locally heavy rainfall. Breezy weather is expected Friday
and Saturday with the chance for mountain showers. The beginning
of next week currently looks dry but breezy.

&&

.DISCUSSION...

...Scattered wet thunderstorms possible through Thursday...

This afternoon and evening: Very active next 36 hours. Showers
and thunderstorms have developed across the higher terrain of the
Cascade mountains and northern WA mountains. They are remaining
in the higher terrain and are nearly stationary. Very heavy
rainfall as well as some small hail and cloud to ground lightning
is expected through the evening hours. Have issued a areal flood
advisory for part of eastern Okanogan county and northern Ferry
county through 6pm. Radar estimates of precipitation occurring
with these stronger storms is 1-2 inches an hour. While the radar
is likely overestimating the rates, think there is still heavy
rain occurring that could cause problems to some roads and
properties.

Tonight through Thursday Night: A trough is moving onto the west
coast and pushing up a strong shortwave into Oregon this evening.
Some strong storms are already developing along the Oregon
Cascades. This wave will move northeast and toward southern WA
and the southern ID Panhandle overnight. So as thunder and heavy
rain showers end for the Cascades and northern mountains of WA and
ID late this evening, showers and thunderstorms will be
approaching the Blue Mountains. Overnight expect that area to
expand across portions of the Palouse/LC Valley and the Camas
Prairie. Then during the early morning hours that will expand
further north into the Spokane/COE area. Thursday could be a very
active day with numerous rain showers and scattered thunderstorms
across most of eastern WA and north ID. These storms will move a
bit faster than the storms currently occurring, but will still
put down some very heavy rain. The heavy rain will be the main
impact, but small hail and frequent lightning will also be likely.
The wave will quickly exit the region late Thursday afternoon.
This will push the best chance of showers and thunderstorms to
extreme eastern WA and the ID Panhandle in the evening and then to
the Panhandle for the overnight hours. With the drier air moving
over the Cascades in the afternoon and evening, winds will
increase across the gaps 15-20 mph with gusts up to 30 mph
possible. /Nisbet

Friday through Wednesday: The general longwave pattern appears to
keep Eastern Washington and Northern Idaho on the outer western
edge of a longwave ridge of not too substantial amplitude. The end
result of such a position is that the longwave ridge does not have
enough amplitude to block any synoptic scale disturbances. As such
the models are inferring of at least two additional synoptic scale
disturbances, either in the form of a front or possibly even another
cut off low (if one looks far enough back at past model runs for
this Friday) with Friday and Monday standing out as the two days
with the most significant sensible weather in the form breezy/gusty
southwest winds and possibly some thunderstorms up across the
northern third of Eastern Washington and North Idaho. Otherwise the
exiting trof marks Saturday with some showers as it takes a bit of
time for the short amplitude ridge to come in and allow for
temporary warmer and drier weather on Sunday. With the additional
trof or low pressure system passage Monday a similar scenario sets
up but this time the models are suggesting the general trof and
associated northwest flow lingers longer afterwards thus some minor
mention of showers and/or thunderstorms may again linger over
portions of the northern third of Eastern Washington and Northern
Idaho along Tuesday and Wednesday. This scenario is likely to result
in forecast temperatures near or ever so slightly on the warm side
of climo for this time of year but far from being extreme or close
to breaking any record temperatures with the brief interval of
shortwave ridging on Saturday marking the warmest day of the seven
day forecast (not including today). /Pelatti

&&

.AVIATION...
00Z TAFs: Thunderstorms this evening will avoid most TAF sites
with VFR conditions through the overnight hours. However 11 miles
south of KEAT on Mission ridge there will be thunderstorms on the
ridge which could bring wind gusts to 15 mph out of the southwest
until 02Z which is not typical for KEAT. General convection will
diminish after sunset. Moisture moving outh of the south will
begin to impact KLWS after 12Z moving north toward KPUW,KGEG,KSFF
and KCOE through the remaining TAF period. Showers with embedded
thunderstorms in this area can be expected with MVFR conditions
forecast at KPUW. Confidence is low bringing VIS and CIGS down for
KGEG, KCOE and KSFF but the weather will certainly be more
unsettled. TC

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        62  75  58  80  55  76 /  10  70  50  10  20  20
Coeur d'Alene  61  73  56  78  53  75 /  10  70  70  10  20  20
Pullman        60  74  55  76  51  73 /  40  70  70  10  10  10
Lewiston       65  81  59  85  57  80 /  60  70  40   0  10  10
Colville       60  79  55  82  52  81 /  20  70  40  50  50  20
Sandpoint      58  71  55  75  52  73 /  10  80  70  30  30  30
Kellogg        58  69  53  74  50  70 /  20  70  70  10  20  30
Moses Lake     65  89  56  87  55  84 /  40  30  10   0  10  10
Wenatchee      68  85  60  83  58  83 /  40  10  10   0  10  10
Omak           64  86  57  85  54  85 /  30  40  10  10  20  20

&&

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

&&

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Special Weather Statement
National Weather Service Spokane WA
705 PM PDT WED JUN 20 2018

WAZ037-038-210245-
Northeast Mountains WA-Okanogan Highlands WA-
705 PM PDT WED JUN 20 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN STEVENS AND
NORTHEASTERN FERRY COUNTIES UNTIL 745 PM PDT...

At 703 PM PDT, Doppler radar was tracking a strong thunderstorm
near Laurie moving southwest at 10 mph.

Nickel size hail will be possible with this storm along with
torrential rain possibly causing water runoff issues.

Locations impacted include...
Laurier and Pierre Lake Campground.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4894 11805 4876 11838 4899 11860 4901 11854
      4900 11811
TIME...MOT...LOC 0203Z 058DEG 9KT 4899 11822

TC