644
FXUS65 KPIH 012122
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
322 PM MDT Sat Jun 1 2024

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT...
A weak shortwave trough crossing the region today and tonight might
be able to spark off at least isolated showers and a couple t-storms
(meaning most areas will hold dry for most of the period). Forecast
soundings this afternoon suggest a gusty wind environment supported
by inverted-V profiles, steep low-level lapse rates, and DCAPE over
1,000 J/kg, with the best overlap of instability (400-800 J/kg
SBCAPE) and HREF simulated reflectivity down across the srn
highlands and UT border areas. (Best chance for a few light showers
in the Snake Plain is likely during the overnight hours tonight).
The NBM continues to run too dry compared to a consensus of the HREF
members, so manually increased and broadbrushed 10-30% PoPs across
wider swaths of the forecast area today and tonight to cover
whatever does manage to develop (leaning a bit on the NamNEST for
our edits). Certainly not a washout for anyone! Zonal flow with some
general troughiness continues Sun with best chance for additional
showers/t-storms across the ern highlands, and mostly dry elsewhere.
Winds will also start to increase Sun and may be near advisory
criteria across the Arco Desert region, but given the marginal
setup, the fact that this area is normally the windiest in our CWA
anyway, and the fact that winds will be stronger Mon in comparison,
have decided not to issue a WIND ADVISORY at this time. Further
south, NBM4.2 blended guidance suggests winds will be very close to
LAKE WIND ADVISORY thresholds over American Falls Reservoir, but the
HREF and traditional MOS-based rules-of-thumb come in lower, thus we
have not issued any alerts here either. Again, looking at the
forecast wholistically, Mon looks like the more favorable day where
we`ll be messaging at least some advisory-level wind impacts. Rain
will also start moving into the Central Mntns Sun eve, but we`ll
discuss this next storm in more detail below. 01

.LONG TERM...MONDAY THROUGH NEXT SATURDAY...
Main focus of the long-term is on Monday, as an atmospheric river of
moisture pounds portions of our Central Mntns (especially the
Sawtooths) with rain over about a 24 hour period. On the one hand,
the overall duration of this event is somewhat limited, mainstem
rivers are not forecast to reach flood stage, temps are not
excessively warm as far as how much high-elevation snowmelt they
will support, and the heaviest QPF is likely to fall just north and
west of our CWA (as a westerly flow does impact at least the wrn
slopes and spine of the Sawtooths and adjacent mntn ranges from west
of Ketchum up to Stanley), with less certainly regarding how much
heavy rain might spill over east of ID-75. On the other hand, WPC is
leaning into the 90-95th percentile of the NBM with their
recommended QPF which we are using for our forecast yielding 1.00 to
2.00 inches west of Clayton and Ketchum and overnight lows may hold
above freezing Sun night/Mon AM even at high elevations, so this is
technically a rain-on-snow event with overnight lows above freezing
and QPF over 1 inch, which is always something we approach with
caution. The National Water Center is modeling as much as 1-2" of
SWE melt to go along with 1-2" of QPF...overall quite a bit of water
might be at play here, although again not all of it within our CWA
border. Following a coordination call today, an upgrade to a SLIGHT
RISK of Excessive Rainfall was introduced for the Stanley to Galena
Summit corridor. A FLOOD WATCH was also discussed with neighboring
WFOs, and for now we have opted to hold off given some of the mixed
signals noted above and relatively low confidence on how this pans
out for our area. Stay tuned. The potential certainly exists for
impacts from small stream/creek flooding, runoff, and backcountry
road erosion from late Sun night through Mon eve. Elsewhere across
the rest of the CWA, showers and t-storms are expected Mon as well
with lighter QPF amounts of 0.10 to 0.50 inches, and best
instability during the afternoon. Expect cooler high temps generally
holding in the upper 50s to upper 60s Mon as well. We already
alluded to some wind...SW winds of 25-35 MPH with gusts over 50 MPH
are currently forecast across the Arco Desert, Mud Lake, and upper
Snake Plain region Mon afternoon, lower but still breezy elsewhere,
so a WIND ADVISORY is looking likely. Beyond Mon, drier wx and a
strong warming trend resume, with lower elevation high temps
potentially approaching 90 by Thu and Fri. Next chance of a shower
or t-storm returning to the mix is Thu eve. 01

&&

.AVIATION...
A weak shortwave feature moving through the region today will
provide for a few isolated thunderstorms this afternoon into
evening, then a higher probability of more organized showers
working across the region overnight. The thunderstorm threat today
works mainly across higher elevations closer to the Montana and
Utah borders, staying away from the terminals. PIH and SUN and DIJ
might be the closest sites to potential threat, but not enough
confidence to include even VCTS at this time. Afternoon convective
build-ups are likely, however. Gusty outflows 35-40kts would be
possible, especially to the south. VFR -SHRA work through mainly
evening and overnight, with clearing expected around or after
sunrise. DMH

&&

.FIRE WEATHER...
A weak shortwave passing through the area will bring a 10 to 30
percent chance for mostly dry thunderstorms, particularly in the
southern half of the Eastern Highlands. While there is a slightly
better chance for a few showers overnight into Sunday (20 to 40
percent chance), any QPF looks to remain light, less than a tenth
of an inch. Highs today will be in the 60s and 70s again for most,
though parts of the eastern Magic Valley and lower Snake Plain
will warm to near 80 degrees F. Winds will gusts around 20 to 30
mph for most this afternoon with gusts near 35 mph in the Mud Lake
area. Winds will back off tonight, but pick up once again for
Sunday, Monday, and Tuesday afternoons with the strongest gusts up
to 45 mph in the Mud Lake/Arco Desert area and gusts 30 to 40 mph
elsewhere. A few showers linger around the Wyoming border Sunday
morning, but our next system moves in Sunday PM through Monday and
will bring measurable rain to almost everyone in eastern Idaho.
The highest rain totals will be up in the Sawtooths/Stanley area
where there is a 50 to 70 percent chance of at least a half inch
of QPF on Monday. After Monday, we`ll dry out and warm up through
the rest of the week. AMM

&&

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

&&

$$