000
FXUS66 KOTX 210538
AFDOTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
1040 PM PDT Mon May 20 2013

.SYNOPSIS...
The mild spring weather will come to an end. A strong cold front will
sweep through the region Tuesday with showers likely, a chance of
thunderstorms, breezy winds and cooler temperatures. Cool and
showery conditions will prevail through much of the week, but will
some improvements for the holiday weekend.


&&

.DISCUSSION...

Evening update: Just minor tweeks to the sky grids for this
evening as the forecast looks decent for the remainder of tonight.
The main focus will be a deep area of low pressure which continues
to barrel toward the WA Coast this evening and will bring a wide
array of weather to the Inland NW on Tuesday.

Rain has already spread on the WA Coast and this moisture will
begin to increase along and just east of the Cascades overnight.
Showers are expected to materialize after 12z (5AM) in these
areas and as the upper-level front approaches...there may be
enough midlevel instability to squeeze out an elevated
thunderstorm before 9AM.

The main thunderstorm threat will come mid to late afternoon and
continue into the early evening. 00Z NAM continues to advertise
upwards of 1000 J/kg of surface based CAPE across portions of NE
WA and Nrn ID Panhandle. GFS is lower but also carries a drier
boundary layer. Based on what happened today in conjunction with
MOS guidance...somewhere in between appears and decent forecast
for surface moisture. As for surface warming...models tend to
agree that the northeastern quadrant of my CWA will be prime
real estate for sunshine allowing sufficient surface warming
and temperatures in the 70`s. Remarkably, guidance is in good
agreement with the timing and placement of the sfc-800mb cold
front which will take on a negative tilt and punch across Ern WA
between 20-00z...and extend from Republic...Deer Park...St
Maries...to Kamiah by roughly 00z and continue east and north btwn
00-03z (5PM-8PM). 0-6km wind shear will be increasing near 40kts
or so and will also contain modest veering with height.

If all things come together as modeled...there is a good
possibility that thunderstorms will fire along the cold front and
potentially become strong to severe late across portions of
northeastern WA and the Northern Idaho Panhandle. We have issued a
weather story to address the locations which are most favored. At
this time, appears large hail will be the foremost threat but
damaging winds cannot be ruled out.

Something else which will need further addressing is the
precipitation threat behind the sfc-800mb cold front. The first
front will be the focus for thunderstorms but the secondary
mid and upper-level front will be the focus for heavier
precipitation with upwards of a quarter of an inch possible. There
may be enough midlevel instability to warrant mention of elevated
thunder briefly in the 3-6z period...focusing on the sw basin and
expanding NE overnight. This will mark the period when the cooler
air really arrives and snow levels will plummet. Bufkit data from
Pullman suggest precipitation will switch over to snow some point
in the middle of the night which appears plausible given strong
model agreement of 850mb temperatures near -1C so locations
generally above 2500 feet in the lower ID Panhandle and Cascades
could wake up to some wet snow falling. It is advertised to check
on pass conditions if traveling across the mountains Tuesday night
and Wednesday.  /sb

&&

.AVIATION...
06Z TAFS: A deep area of low pressure will track into the region
during the next 24 hrs.  Mid and high clouds will be on the increase
tonight and showers are expected to develop btwn KEAT-KOMK
during the early morning hrs with the slight potential for an
elevated t-storm. More alarming to the aviation community will
be the passage of a strong cold front through the region through
the aftn hrs.  The front is expected to cross through KEAT/KMWH
arnd 18z and KGEG-KCOE-KPUW-KLWS near 21z.  There is a decent
potential that showers will occur along the front and thunderstorms
will develop upon reaching the WA/ID border...some which may become
strong or severe over extreme NE WA and Nrn ID.  The frnt will also
bring a wind shift to the W/SW and be breezy.  A secondary front
will arrive  btwn 00-06 focusing light to moderate pcpn and potential
for MVFR cigs frm KGEG-KCOE south to KPUW.  Pcpn may switch to snow at
times Wednesday morning at KPUW. /sb


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        51  75  41  52  36  60 /   0  20  90  90  40  40
Coeur d`Alene  46  77  42  49  36  59 /   0  30  90  90  50  40
Pullman        48  73  39  51  35  60 /   0  10  80  80  30  40
Lewiston       52  81  45  59  40  67 /   0  10  80  70  30  40
Colville       45  78  43  55  37  64 /   0  50  90  80  60  50
Sandpoint      44  76  43  51  36  58 /   0  30  90  90  80  50
Kellogg        50  76  41  45  34  54 /   0  30  90  90  70  60
Moses Lake     51  73  43  63  40  68 /   0  50  50  30  30  30
Wenatchee      53  66  43  59  43  64 /   0  60  50  40  40  40
Omak           48  71  42  60  38  65 /   0  80  80  70  50  50

&&

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

$$