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000
FXUS65 KPIH 122037
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
237 PM MDT Fri Apr 12 2024

.KEY MESSAGES...

* Isolated thunderstorms will be possible Friday afternoon and
  evening with a 5-14% chance of severe thunderstorms in and
  around the CNTRL Mountains

* Seasonably warm temperatures will continue through the weekend
  with highs in the 60s/70s each day

* Breezy winds are expected each day through early next week with
  stronger winds favored on Monday as a cold front moves through
  supporting a cooldown towards midweek

.SHORT TERM...Today through Saturday Night.
Early afternoon satellite imagery shows mostly sunny skies and
isolated showers across CNTRL/ERN Idaho as a H5 shortwave trough
lifts north out of the Great Basin. The storm environment this
afternoon and evening remains unchanged, still being conducive for
isolated thunderstorm development beginning between 3-6 PM and
continuing through around midnight tonight. The only changes have
been trimming down the areal coverage of thunderstorms to exclude
areas south and east of the Shoshone/Arco/Mud Lake Desert with
around a 10-40% chance probability of thunder on the HREF model
further NW into the CNTRL Mountains. We may see some isolated
storms outside this area but the focus will remain further north
and west.

The HREF model ensemble SBCAPE between 300-700 J/kg and around
25-35 ts of 0-6 km shear will support any organized cells or lines
to potentially develop into stronger storms with an emphasis on
these storms in the Magic Valley and CNTRL Mountains. The SPC has
expanded their marginal risk (5-14% chance of severe
thunderstorms) further east and now includes all of Custer County
and portions of Lincoln and Blaine Counties. The HRRR and NAM show
storms initially beginning in and around the Magic Valley before
lifting north into the Magic Valley with the HRRR showing
thunderstorm outflow gusts in excess of 40 mph and hail up to
around quarter size. Any convection will subside overnight with
dry conditions back for tomorrow outside of a slight chance for
isolated mountain showers.

Given it is currently 72 degrees early this afternoon at the
Pocatello Airport, today officially marks the warmest day in our
region so far this year with widespread 60s/70s across the area.
While staying below any record levels, this is the first time
Pocatello has gotten above 70 degrees since October 22nd 2023 or
173 days. Normal highs for this time of year are mostly in the 50s
making this stretch of mild weather about 10 to 15 degrees above
normal. As Friday`s H5 shortwave departs north into Montana for
Saturday, high pressure and southerly flow will remain in place
supporting highs in the 60s/70s with breezy winds out of the
south. MacKay

.LONG TERM...Sunday through next Friday.
The risk of showers and perhaps a t-storm will return Sun
afternoon as low pressure along the Pacific coast finally ejects
inland, but it`s posture still to the SW of our CWA will maintain
southerly flow and another decently mild day (highs in the upper
50s to upper 60s). A noticeable cooling trend finally kicks off
Mon and beyond as this initial low tracks east, and now-westerly
winds Mon afternoon may approach Wind Advisory criteria over the
ern Magic Valley and Raft River region. This is where everything
falls apart...we`ve been advertising a much cooler and wetter
pattern dominating the region for much of next week, but today`s
deterministic models look wildly different from yesterday`s runs
and offer a wide variety of different solutions. For example, the
GFS still favors another closed low dropping into Idaho from
Canada Tue, but the Canadian now keeps this system entirely up in
Canada, and this model and the ECMWF even show increasing
influence from at least "dirty" ridging now arriving as early as
Wed and Thu. Model agreement is non- existent regarding the
potential for additional low pressure features by the end of the
week as well. With the high degree of uncertainty, did not stray
from the NBM which has backed off on breezy conditions from Wed
onward and also isn`t advertising quite as much cooling (for
example, highs Wed in the 40s and 50s instead of 30s and 40s), but
still broadbrushes light PoPs across SE Idaho for much of the
week. WPC QPF remains VERY modest throughout the week (less than
0.50" even in the mntns). Even 500mb height cluster analysis
advertises about a 40% chance of increasing ridging Wed/Thu and a
60% chance of troughing remaining in place. In any case, the
sooner we can get the troughing out of here, the sooner we can
feel spring again. - KSmith

&&

.AVIATION...For the 18Z TAFS through 18Z Friday.
At least weak ascent from sfc heating, mid-level warm air
advection, and the overall approach of a weak, negatively-tilted
shortwave trough supports our continued expectation of at least
isolated showers and t-storms this afternoon and eve, especially
between 21z/3pm and 03z/9pm. The latest HREF suite of high-res,
hourly CAMs continues to favor the wrn corridor from SW Idaho NE
across portions of the Magic Valley into the Central Mntns with
best consensus for storms (maybe more sct coverage), thus we
maintain VCTS at KBYI and KSUN with slight tweaks to forecast
start/end timing. Further east, one or two models hint at some
potential for a shower or two, but with overall less coverage, we
cautiously have removed VCSH from the rest of our TAF terminals.
Dry-leaning low-levels will keep cloud bases pretty high, but IF a
t-storm were to make a direct hit on an airport, a very brief
period of MVFR cigs/vsbys can`t be ruled out, but with no
confidence in occurrence at this juncture. We`ll be closely
monitoring radar and satellite trends this afternoon. A couple
storm cells could produce small hail and gusty outflow winds in
excess of 50 MPH (and evidence of this is seen in the HREF wind
gust max as well as the last several HRRR runs). Model guidance
for wind is frankly very messy both this afternoon and most of
tonight, leading to pretty low confidence especially on direction
(and tossing a t-storm outflow or two into the mix could wreak
additional havoc). Broadly speaking, a SSW flow is expected to
dominate everywhere but KSUN (preceded by easterly winds at KBYI),
with some gusts as high as about 20kts away from any t-storms.
Skies may trend toward SKC again by late tonight and Sat, with
another breezy but drier day expected Sat afternoon. - KSmith

&&

.HYDROLOGY...
Water levels remain elevated on the Portneuf River in Pocatello
and Topaz where River Flood Warnings and an advisory,
respectively, remain in place. With warm temps continuing for a
few more days, expecting continued mid/high elevation snowmelt
which should lead to rises at both gauges over the days ahead.
Stay tuned for further updates over the days ahead.
McKaughan/MacKay

&&

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

&&

$$