Area Forecast Discussion
Issued by NWS Pocatello, ID

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531
FXUS65 KPIH 192028
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
228 PM MDT Wed Sep 19 2018

.SHORT TERM...Tonight through Friday night
A cold front tonight will bring scattered showers to central Idaho
with only isolated activity elsewhere. The driving shortwave
trough axis approaching western Idaho will push through the region
tonight dragging a relatively dry cold front with it. The dry air
is evident on the multi-layered water vapor imagery this
afternoon, pushing through central NV into southeast ID. Winds
will pick up in the cold advection behind the front tonight, but
model trends have favored a weaker trough, and thus weaker mixing
of surface winds.

A return to dry conditions is expected for Thursday, save for our
extreme northeastern zone near Island Park. A few lingering
showers and clouds are possible here through about midday. Dry
zonal flow will clear skies across the region, and moderate
temperatures heading into the early weekend.
TAX

.LONG TERM...Saturday through Wednesday
Dry weather is expected through much of the weekend, although the
next cold front is poised to move into our northwest by Sunday
afternoon. The upper-level flow amplifies Saturday allowing
heights to build through the region. For this reason, the forecast
has been trended towards the bullishly warm MEX guidance,
especially in the favored downslope areas of the Snake Plain.
Sunday temperatures and resulting RH values will be tricky,
depending ultimately on the timing of the front.

Confidence in the overall pattern next week is waning. Guidance
remains fairly consistent on digging a deep trough into the
western US after Sunday`s cold front. The problem has been the
placement of the trough and resultant weather it sets up for us.
There will be a cool down for Monday and perhaps Tuesday, but the
big pattern shift that was discussed 24-48 hrs ago appears fairly
transient with cool and dry weather giving way to another warmup
towards the middle of next week. How strong of a warmup remains to
be seen.
TAX


&&

.AVIATION...A Cold Front is forecast to cross SE Idaho this evening,
reaching a BYI-SUN line around 00Z, PIH to IDA between 00-01Z and
DIJ by 03Z. This will cause a wind shift to the SW at KSUN and DIJ,
and simply an increase in winds at BYI, IDA, PIH and DIJ, with gusts
in the 20-30KT range possible along and behind the front, before
winds begin to subside towards 06Z. Am carrying VCSH at all TAF
sites, but this should be mainly Virga or sprinkles accompanied by a
VFR mid deck. HRRR paints the potential for MVFR Stratus from 12-15Z
Thu at IDA but have disregarded this potential ATTM due to the
forecast dry nature of the boundary layer. Gusty Afternoon SW winds
in the 10-20 kt with occasional higher gusts expected at BYI, PIH,
IDA and DIJ between mainly 19-00Z tomorrow afternoon. AD/TAX


&&

.FIRE WEATHER...Combination of wind gusts and low humidity will be
near critical levels for the remainder of the afternoon and early
evening hours. A relatively dry surface cold front will push in from
the west, bringing some stronger wind gusts to Fire Weather Zones
410, 413, and 425 this evening as humidity begins to recover.
Despite the absence of fire weather headlines today, there is
potential for rapid fire spread given the near record low ERC
values. Isolated dry thunderstorms will also be a threat this
afternoon and evening, mainly along the Utah border and across the
Salmon-Challis, however the threat is low. Any activity should taper
off late tonight. Fire Weather Headlines were also considered for
Thursday Afternoon for zones 425 and 410 due to the expected
combination of critical RH and Wind Gusts in the Craters of the Moon
vicinity. Due to the combination of only a small portion of both
zones predicted to exceed critical thresholds and after coordination
with local fire dispatch centers, we opted against a fire weather
headline. The next period of impactful fire weather is expected
Saturday as another mainly dry cold front is forecast to swing
through the region. The combination of gusty winds and low relative
humidity will again combine to elevate fire weather concerns.
Otherwise, seasonable Temperatures and continued dry weather is
currently anticipated to continue into at least early next week.
AD/TAX


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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