Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 290948

Area Forecast Discussion
National Weather Service Spokane WA
248 AM PDT FRI MAY 29 2015

Scattered showers and thunderstorms will continue today. Expect a
warming trend into the weekend, with highs in the 80s, with a
lingering threat of mainly mountain showers and thunderstorms. The
next best chance of showers and thunderstorms arrives by next
Monday and Tuesday with the potential for some stronger storms
and the return of cooler temperatures.


Today and tonight: The region will be under a moist and unstable
zonal flow pattern over the next 24 hours with a pair of shortwave
disturbances passing through the region. The first will move
through this afternoon and the second overnight. No big changes
with the air mass is expected today. Dew points continue to remain
in the mid 40s to low 50s and temperatures will top out in the
80s. Another day of warm temperatures combined with a mildly juicy
air mass will once again result in afternoon convection. There
figures to be a bit more mid to high level cloud cover to start
out the day compared to yesterday. This may hold down surface
temperatures a little bit, but models indicated surface based
CAPEs of around 500-1000 J/KG across the northern mtns where the
best chances of thunderstorms are expected today. There will be
some shear to work with as well of up to around 25 kts between 0-6
km that will coincide with these stronger CAPEs. Some added lift
with the weak disturbance moving through is expected to result in
at least a chance for some isolated stronger thunderstorms to
develop across the northern mtns this afternoon. Possible hazards
will include small hail, gusty outflow winds up to around 40 mph,
and frequent cloud to ground lightning strikes.

P-wats will continue to run above normal at around 0.80 inches.
This result in very heavy rain under the stronger storm cells.
Isolated low land flooding or urban flooding will be possible with
these storms. There will also be the potential for mud or debris
flows in steep terrain. The east slopes of the northern Cascades
will not escape convection this afternoon. This will raise
concerns for flash flooding or debris flows in and around recent
burn scars from the 2013 and 2014 fire seasons. The Carlton
Complex and Devils Elbow burn scars will see the best potential
for heavy rain from thunderstorms. Chances are not as high south
of Lake Chelan, but thunderstorms will still be possible and I can
not rule out problems due to flash flooding or debris flows across
these areas as well. The good news is that there will be at least
some steering flow this afternoon; it will be weak, but should at
least result in some movement to the east and northeast instead of
storms remaining nearly stationary.

The second weak shortwave disturbance will push through tonight.
Models show enough mid level instability that I decided to add a
slight chance for thunderstorms tonight into Saturday morning.
Nocturnal convection will be possible east of a line from Omak to
Wenatchee with the best chances expected across the eastern half
of the forecast area. P-wats look to increase to as high as an
inch. This would be up around our peak of what is expected for
late May and would result in very wet showers and thunderstorms
through the night. /SVH

Sat through Fri: We still have two main areas of focus. The first
is the initial warm and potentially thundery conditions in the
thermal ridge ahead of the mid to late week strong cyclone. The
second is the return to showery/thundery/cooler wx Tue through
Thur under this cyclone. We have showers (and some isolated
thunder) in the fcst every afternoon for at least a part of Ern
Wa and N Idaho, especially when the upper low translates over the
region beginning Mon Nt. This Tues through Fri period will
resemble closely the wx regime we just went through...with a
resurgence of showers and thunder every afternoon where it`s not
already showering. There`s no way we can get around broad-brushing
this type of regime given the high level of confidence we have
that pattern recognition supports the heaviest showers every
afternoon. Monday will be the big wx day as a surge of high
theta-e air (warm/moist) ahead of the ejecting vort max provides
at least two major ingredients for an outbreak of potentially
strong thunderstorms that will expand NE through Ern Oregon and
into N Idaho. Monday will be the best chance of thunder, with
uncapped CAPE of 500-750 j/kg combining with only modest 20-30kts
of deep layer shear. Tues, however, will be a tougher thunder fcst
as most model guidance brings the low far enough inland that the
subsidence within the rather wide dry slot shunts the deepest
instability quickly into Wrn


.AVIATION...06Z TAFS: General low pressure with weak weather
disturbances moving through it keep scattered showers and
thunderstorms in the aviation area tonight and again tomorrow.


Spokane        82  60  83  59  80  58 /  10  30  30  10  10  20
Coeur d`Alene  82  58  82  56  80  56 /  10  30  30  10  10  20
Pullman        81  58  79  57  79  55 /  10  30  30  10  20  40
Lewiston       88  63  86  62  87  61 /  10  40  30  20  30  30
Colville       83  55  84  54  83  55 /  50  40  30  20  10  10
Sandpoint      81  53  81  53  78  53 /  30  30  30  20  10  20
Kellogg        81  55  80  54  81  53 /  20  30  40  20  20  30
Moses Lake     89  59  89  58  86  61 /  10  20  10   0  10  20
Wenatchee      89  62  89  60  84  62 /  20  10  10   0  10  20
Omak           87  57  89  53  85  56 /  40  20  20  10  10  10



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