Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 262335
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
435 PM PDT Sun Mar 26 2017

.SYNOPSIS...
One storm system will bring light rain and mountain snow tonight
into Monday morning. Showery weather is expected through Tuesday
then a widespread moderate precipitation event will arrive on
Wednesday and Thursday. Friday will bring a dry break period
before more unsettled weather for next weekend.


&&

.DISCUSSION...

Tonight through Monday night: A moist frontal system will pass through
the region tonight and Monday delivering periods of light rain
and mountain snow. There is a decent moisture fetch tied to the
system however the dynamics will be weak and splitting with the
strongest lift tracking south into Oregon and most locations will
receive less than a quarter of an inch from this system. The
exception will be along the Cascade Crest, Blue Mtns, and into the
Camas Prairie where upward of half an inch will be possible.

As of 2PM...we were monitoring the first band of rain associated with
the warm front expanding into Ern WA and N ID. Rainfall amounts
have been light and on the order of a few hundredths or less.
Several runs of the HRRR indicate the potential for a brief break
in the rain behind the warm front however a cold front currently
on the WA Coast will limp through the region allowing a line of
precipitation to redevelop overnight. Satellite imagery also
indicates a strengthening jet digging down the backside of the
trof. Not only will this serve to split the energy south but also
slow the entire system down...thus the slow cold front passage.
The front will also loosen its thermal packing or frontal
structure, all factors contributing to a rather light
precipitation event.

The front will begin to clear east of the region Monday morning then
cooling aloft will aid to destabilization and likelihood for
convective showers. Just about all locations will have a chance
for an afternoon shower but westerly flow will keep the lee of the
Cascades at a slight risk and rising terrain of Ern WA and N ID,
greatest. There is a slim chance for an isolated t-storm as well
Monday afternoon but with marginal CAPE of 150-400 J/kg and 0-6km
shear less than 15 kts, felt the threat was too low to include in
the forecast at this time. SREF guidance did increase toward 20%
probability for a lightning strike across SE WA and NC ID but the
best sunshine may be in the southwestern Basin...so too early to
call where a rogue strike or two may actually occur.

Temperatures tonight will remain mild and generally above freezing
for most lowlands due to an abundance of cloud cover and light
rain. Highs on Monday will be warming into the upper 40s to 50s
just a few degrees shy of March 27th normal`s. Monday night will
feature a better chance for temperatures to dip in the lower 30s
coupled with patchy fog. /sb

Tuesday through Sunday...Models are in reasonably agreement in
depicting a continued active and progressive spring pattern
featuring at least one and maybe two more good atmospheric river
hosings punctuated by a brief dry interlude.

Tuesday will start out dry and seasonably cool...but the next feed
of deep moisture will become favorably oriented during the day
with an onset of light rain mainly over the mountains north of
the basin and possibly the Idaho Panhandle...but for the most part
Tuesday will be the increasingly cloudy moistening period before
the main event.

Tuesday night and Wednesday...the next atmospheric river will be
favorably directed into the forecast area and enhance into
universal light rain and high mountain snow through
Wednesday...first along a warm front and then along the trailing
cold front. At this time at appears the deep basin will pick up a
third of an inch of rain from this system with amounts increasing
as one moves east culminating in around three quarters of an inch
in the eastern basin zones and Idaho Panhandle valleys...with
around an inch in the mountains but much of this will fall as snow
above 4500 to 5000 feet. this will be good for building up late
season high elevation snowpack especially in the Cascades and
mountains along the Canadian Border.

This further shot of moderate to heavy widespread rain will
likely cause a response on area rivers draining eastern
Washington and north Idaho late this week...possibly delaying the
recession below flood stage on the St. Joe and quite possibly
promoting another minor flood spike on the Little Spokane by
Friday. Other mainstem rivers may rise but levels are now receding
to low enough to handle this storm without flooding. The areal
flood/small stream issues around the region will either be
aggravated somewhat or at least temporarily halted from improving
significantly.

Wednesday night and Thursday...The cold front passage of
Wednesday will herald the arrival of a cool upper level trough
depicted by all the latest model runs. This suggests continuing
showers driving into the Idaho Panhandle...and the possibility of
scattered showers over the eastern half of the forecast area with
a basically dry deep basin in a typical spring-time unsettled
and seasonably cool regime.

Friday and Friday night...The trough moves east and a quiet
upper level ridge takes over providing guarded confidence of a
much needed dry day on Friday.

Saturday through Sunday...Model agreement deteriorates this far
out with the GFS and Canadian models maintaining a flat ridge
over the region...but not the nice and quiet kind of dry ridge.
this will be a ridge which is welcoming another atmospheric river
into it`s westerly flow which implies another round of light
rain...largely skipping the deep basin but enhancing over the
eastern zones and focusing on the northeast and Idaho Panhandle
mountains. The ECMWF model brings a short wave disturbance through
the region. So which ever model is correct...increasing pops for
this period looks quite plausible.

Through the next week the flow regime will remain
progressive...with little opportunity for different transient air
masses to become established. Thus a temperature regime
characteristic of a polar maritime air mass is a safe
bet...warmer than normal low temperatures rarely and only locally
dipping below freezing and slightly cooler than normal high
temperatures impacted by the frequent presence and proximity of
rain or at least significant cloudiness. /Fugazzi


&&

.AVIATION...
00Z TAFs: A warm front followed by a cold front passage shorty
after tonight/tomorrow morning will allow for a prolonged interval
of generally light precipitation over the aviation area. MVFR
ceilings and visibilities associated with the precipitation
(lowland and valley rain with snow generally above 3500 feet MSL)
will linger at times with improvement most likely after 17Z
Monday. /Pelatti

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        38  50  34  49  39  50 /  80  40  20  40  60 100
Coeur d`Alene  37  48  34  46  37  49 /  80  70  30  40  50 100
Pullman        38  49  34  49  39  51 /  80  40  20  20  20 100
Lewiston       43  55  37  55  42  56 /  80  40  20  20  10  70
Colville       36  49  32  48  36  49 /  70  30  10  40  60 100
Sandpoint      34  45  33  45  34  46 /  80  60  20  50  50 100
Kellogg        35  45  33  44  34  46 /  90  90  40  40  40 100
Moses Lake     38  57  37  57  42  57 /  80  20  10  10  60 100
Wenatchee      37  54  36  53  38  54 /  70  20  10  20  70 100
Omak           36  53  33  51  38  53 /  90  20  10  30  70 100

&&

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

$$



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