Freeze Warning 2, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
231 AM MDT Wed May 6 2020

.SHORT TERM...Today through Friday night. Satellite imagery is
showing a strong shortwave making landfall this morning with low-
amplitude ridging downstream. Still expecting a strong, but
relatively dry, surface cold front to push through this afternoon.
Models are still pushing for a very tight gradient behind the
front. Winds remain the primary concern for this afternoon and
evening, though MOS guidance has dropped the overall wind forecast
slightly. We still anticipate seeing some areas of blowing dust
resulting from the strong winds, and this should be most
pronounced along Interstate 15 north of Idaho Falls and along
Interstate 86 around American Falls down to around the Raft River
area. Current headlines cover the wind and blowing dust fairly
well, and no changes are expected there. However, in the post-
frontal airmass, temperatures will cool late tonight/Thursday
morning and lows may drop below freezing in the Snake Plain for a
few hours. Fair weather is expected for most of the region
Thursday and Friday, though shortwaves embedded in a northwesterly
upper-level flow will clip the Island Park area, which may trigger
some showers in that area. Hinsberger

.LONG TERM...Sat through Tue night. Upper level ridge will keep the
weekend dry and clear with warming temperatures, but a big change
comes Mon morning and continues to the end of the period. A deep low
nearly stationary off the coast of OR brings up moisture that
interacts with some weak troughs that move through the northern
branch of the jet which sags into northern Montana. There is enough
moisture and enough heating despite the cloudiness that afternoon
instability will generate showers and thunderstorms, mainly over the
eastern highlands and central Idaho mountains. The upper level wind
supports Wind Advisory-level wind for Tue, and that is when the
strongest trough moves through southwest Montana, so showers and
thunderstorms have better coverage on Tue compared to Mon. With the
clouds, there is a cooling, with Tue night possibly being another
Frost or Freeze morning. Messick

&&

.AVIATION...No CIG or VSBY issues (broken high or mid-level clouds
only at worst) in spite of a front sweeping through today. The low
and associated cold front are so dry that SHRA and TSRA are limited
to the northern end of the central Idaho mountains (far from KSUN)
and along the ID-MT border and northern half of the ID-WY border
(including KDIJ). The big feature today is the wind expected with
the front. GFS MOS is going for an unprecedented 40KT sustained wind
for the mid and late afternoon at KPIH. The NAM MOS is not far
behind with 30KT. Both of those values are very rare this early in a
MOS forecast. So there could be some strong LLWS, mainly speed
shear, especially late morning to early afternoon. Wind of this
strength makes KSUN the most difficult forecast--will the strong
wind be able to surface in the Wood River canyon? The HRRR usually
underforecasts speed and it is showing wind in excess of 20KT, so
will have wind in that forecast. Since the feature is moving west to
east across the Gem State, expect wind to start first in KBYI/KSUN,
and last at KDIJ, with subsidence following a similar pattern.
Messick

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Blowing Dust Advisory from noon today to 10 PM MDT this evening
for IDZ053-054.

High Wind Warning from noon today to 10 PM MDT this evening for
IDZ051>055-057.

Wind Advisory from noon today to 10 PM MDT this evening for
IDZ056-058-059-062-067-068-070-075.

&&