Severe Thunderstorm Warning 4, NWS Boise, ID

Area Forecast Discussion
National Weather Service Boise ID
240 PM MDT Fri May 5 2017

.SHORT TERM...Tonight through Sunday...Convection has been trying
to get established this afternoon, however, mid and high
cloudiness is limiting heating and making sustained updrafts
difficult. The showers and isolated thunderstorms that have
developed thus far have generally been short lived with little in
the way of impacts. A short-wave, visible on water vapor imagery,
still remains poised to slide northward into the Pacific Northwest
this evening and overnight. Models are hinting that this feature
will interact with the broad swath of moist air streaming overhead
to generate a more significant round of showers/thunderstorms.
Model soundings are indicating that dry low level air will be in
place through the evening, which may inhibit storm generation. On
the other hand, storms that do develop will have the potential to
generate strong gusty winds, and perhaps small hail.

Closer to the surface, a cold front is tracking eastward across
Washington and Oregon. Currently the front is draped nearly
halfway across those states. The front will slide eastward this
evening and overnight, eventually surging through eastern Oregon
and southwest idaho by early morning. This front will cool the
atmosphere as well as usher in gusty northwest winds. Models are
indicating that the front will track slowly east across Idaho
Saturday and will serve as the focal point for another round of
showers/thunderstorms Saturday afternoon and evening.

The region will be slowly drying out Saturday Night into Sunday as
low pressure, currently along the Pacific Northwest coast, dives
southward into California and southern Nevada. This will allow for
weak high pressure to prevail over eastern Oregon and Idaho.
Lingering moisture in the mid/upper levels of the atmosphere
combined with heating and terrain will generate showers and
perhaps a few thunderstorms near higher terrain Sunday.

Temperatures will cool significantly behind the front with below
normal readings expected in most locations Saturday. Normal to
slightly above normal temperatures will return for Sunday.

.LONG TERM...Sunday night through Wednesday...A split flow and weak
upper level ridge will keep most of our area dry through Wednesday.
The closed upper level low will remain centered over Arizona through
Tuesday, then drift slowly northeast over the four corners on
Wednesday. Models show that most of the precipitation associated
with this system will stay south of our CWA, but the central Idaho
mountains and southern Twin Falls County could still see a few
showers. Temperatures will be near normal on Monday, then warm to 5-
10 degrees above normal by Wednesday.

Wednesday night through Friday...The main player for the long term
forecast is an upper level low sitting off the Canadian coastline
Wednesday night. This low slowly starts to track its way southeast
through the period. The forecast remains mostly dry for the CWA
through at least Friday afternoon with some slight chances of higher
elevation showers earlier in the period in Baker County and the West
Central Mountains. By Friday night differences in what to do with
the low start to become evident. A slight chance of showers remains
for the higher elevations through the remainder of the period.
Temperatures will begin Thursday above normal then drop to a few
degrees below normal Friday as the upper low starts to track
southeast.

&&

.AVIATION...Mainly VFR. Expect isolated showers and thunderstorms
this afternoon, then widespread showers and scattered thunderstorms
this evening. Gusty winds, reduced visibilities in blowing dust, and
small hail are possible near thunderstorms. Scattered showers, with
more numerous showers and isolated thunderstorms over the higher
terrain, will continue through Saturday evening. Showers will
decrease in coverage late Saturday night, and be confined mainly
over the higher terrain on Sunday. Surface winds will be southeast
to southwest 10 to 20 kts, then become west to northwest following a
cold front tonight. Winds aloft will be southwest 20-30 kts.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.

&&

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SHORT TERM...MC
LONG TERM....JT/JC
AVIATION.....JT