817
FXUS65 KPIH 082048
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
248 PM MDT Wed May 8 2024

.SHORT TERM...Tonight through Thursday night. Remnants of the deep
upper low refuse to give up impacting East Idaho with trough
draped east-west across the state this afternoon. Mainly isolated
showers remain possible through early evening as moisture works
around the low and drops into East Idaho from Montana. Gusty
northerly downslope winds are draining out of the Central
Mountains and off the Divide, supporting slightly warmer but
breezy conditions continuing tonight. Elsewhere through the Snake
Plain, the downslope conditions are not quite as strong, so
temperatures around/less than 36F are expected, supporting another
night of Frost Advisory. Models support the trough dropping into
Utah and briefly closing off over the Great Basin Tuesday,
allowing the wrap around moisture to shift across mainly the
southern highlands during the day. Thus showers and isolated
thunderstorms will be possible mainly across the southern and
southeast highlands in the afternoon. The gusty northeast gradient
will continue, with the strongest winds centered across the Arco
Desert region. Wind speeds may be marginal for Wind Advisory but
hoisted the headline anyway as the northeasterly direction may
catch drivers off guard along US-20 and US-26, especially those
that commute those routes routinely. Northeasterly gradient
continues into Thursday night, but slackens considerably. Strong
possibility that one more Frost Advisory will be needed,
particularly along zones containing the I-15 growing corridor.
Could see a few pockets of fog in protected valley regions, and
have retained the previous forecast. DMH

.LONG TERM...FRIDAY THROUGH NEXT WEDNESDAY...
This portion of the forecast continues to resemble a lunchmeat
sandwich as an elongated W-E zone of low pressure...the leftovers of
the active wx we`ve been munching on for days...sinks southward
across the Four Corners region to central Plains, and a "tongue" of
high pressure noses in on top of it eastward across the nrn Rockies
from the Pacific. This overall synoptic configuration should whet
our appetites for spring w/ drier conditions and a strong warming
trend Fri-Sat-Sun with highs by Sun ranging from about 70 to 80 degF
for most lower elevation population centers, but the proximity of
low pressure to our south is close enough that we can`t completely
rule out some limited coverage of at least isolated afternoon
shower/t-storm activity down across some of our SE highlands into
Bear Lake, as reflected by light PoPs carried in our forecast
courtesy of the NBM. Confidence in coverage of any precip is low,
whereas confidence in dry conditions for MOST of the CWA is higher.
Compared to this time yesterday, both long-range deterministic model
solutions and resultant 500mb height cluster analysis are now a bit
more progressive with trying to kick this low pressure zone out to
the east by Sun-Mon, with perhaps some trend toward opening up the
NW flow storm track and allowing fresh disturbances to take aim at
our region during the Mon-Tue-Wed period next week. The strength of
Pacific ridging will in part govern whether this storm track will be
held further to our N/NE (keeping us dry) or will take better aim at
SE Idaho , with the NBM for now brushing our ern highlands and Upper
Snake Highlands with light PoPs from time to time and no significant
reduction in overall temps. Height clusters are split on this as
well. A tightening pressure gradient between the Pacific ridge and
this storm track may tend to increase winds over these days, most
notable diurnally during the afternoons. For now, no major airmass
changes or significant precip events are expected, and we`ll need to
watch the impact warmer temps will have on mid-high elevation
snowmelt and resultant river responses. - KSmith


&&

.AVIATION...
The world of aviation is SLOWLY trending less impactful as low
pressure just to our east sinks southward and increasingly
surrenders synoptic control to a tongue of high pressure nosing in
eastward across the nrn Rockies off the Pacific. Showers at KDIJ and
VCSH elsewhere continue, but will trend down this eve and end for
the night by 02-05z/8-11pm depending on the terminal. Clouds are
still widespread but are now VFR everywhere except KDIJ and will
slowly rise/thin out as we head into tonight, reaching at least SCT
coverage if not FEW. Winds remain breezy but generally not as strong
as yesterday, and will relax slightly for the overnight. Biggest
challenge through this eve is really to capture the timing as winds
evolve from WSW to NNE everywhere but KSUN (which will be a runway
crosswind at many airports)...current TAF thinking for this timing
is based on a blend of MOS guidance and the latest hourly HRRR, with
moderate confidence. Otherwise, main impacts will be occasionally
MVFR cigs/vsbys continuing at KDIJ through about 00-01z/6-7pm when
most rain/snow showers finally end, and the potential for criteria-
borderline LLWS developing at KPIH after about 05z/11pm as sfc winds
relax and decouple. This will be almost entirely speed shear as
winds should be roughly out of the NE throughout the column. LLWS
criteria are not currently expected to be met elsewhere across the
forecast area, but this will be monitored. Heading into Thu, still
can`t rule out a few afternoon showers or even VCTS as departing low
pressure is still too close for comfort, but with winds continuing
to slowly relax day by day and a continued overall trend toward
drier, calmer VFR wx as we round out the week and head into the
weekend. - KSmith

&&

.HYDROLOGY...
Recent precipitation and warming temperatures are expected to
influence East Idaho waterways in the coming days. Whatever
snowfall was realized recently at mid-slope is likely to melt off,
and temperature profiles support some snow melt at higher
elevations. Flood Warnings remain in place for the Blackfoot and
Portneuf rivers. High, fast, and cold flows are expected to
continue and/or increase on other waterways. As the conditions
turn warmer and drier, people recreating on/near East Idaho
rivers and streams are urged to remain cautious, and keep children
and pets away from the water. DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 3 AM to 9 AM MDT Thursday for IDZ051-053-055.

Wind Advisory from 10 AM to 7 PM MDT Thursday for IDZ052.

&&

$$