High Wind in Idaho, March 6, 2021

Area Forecast Discussion
National Weather Service Pocatello ID
251 AM MST Sat Mar 6 2021

.SHORT TERM...Today through Monday.

A weak cold front will pass through central and east
Idaho this afternoon. This will produce some light snow
accumulations for the mountains and eastern highlands with most
accumulations under an inch or so. Gusty winds will accompany the
cold front this afternoon, but expect those winds to remain under
advisory levels. In areas where the snow has receded, there could be
a brief period of fire danger associated with grass and brush
fires with the winds since green-out hasn't occurred yet.

This system will quickly exit tonight leaving dry weather for Sunday
with slightly cooler temperatures. A broad trough will work into the
Pacific Northwest next week. We'll see the first round of
precipitation associated with that trough arrive Monday. Snow levels
look warm above 5500-6000 feet on Monday. Precipitation amounts with
this initial round of moisture look light on Monday with snowfall
amounts expected to be around an inch or less.

13

.LONG TERM...Tuesday through next Saturday night. Deterministic and
ensemble model guidance remains in fairly good agreement through
midweek before agreement and predictability falters a bit by week's-
end. A broad area of low pressure off of the California coast will
evolve into a SW-NE oriented low pressure trough which will be
firmly entrenched across the region through midweek. How these two
features evolve has come somewhat into question, as scenarios range
from the ECMWF/Canadian idea of taking the broad California coast
low eastward across the Great Basin through next weekend with little
weakening. The GFS camp resembles the scenarios from the past two
days, which allows the flow to transition to northwest before a
ridge of high pressure builds across the region next weekend. While
WPC cluster analysis reveals weight to either scenario, the most
likely case at this point appears to be somewhere in between. Either
way, central and eastern Idaho will miss most of the action, with
the most likely scenario panting a relatively cool, quiet week. The
best chance for precipitation remains on Tuesday, when the broad low
will be close enough to exert some influence. While showers are
possible area-wide, the best chance will be across the south hills
and eastern highlands. Precipiation type will be mostly snow, with
a rain/snow mix possible at lower elevations. Steep lapse rates
reveal some diurnal convective enhancement, so some graupel showers
will be possible as well. 1-2" of snow in the Island Park area
appears to be the most we can squeeze out of this system. Shower
chances dwindle on Wednesday, with the heat of the day being the
best chance for some shower activity mainly in higher terrain areas -
- eastern highlands favored. Shower chances continue to decrease
Thursday and Friday with the same areas favored. Tuesday will be the
coolest day, with a modest temperature rebound back to near seasonal
normals for the rest of the period.

AD

&&

.AVIATION...Low pressure trough and associated weak cold front will
traverse eastward across the area this afternoon. South-southwest
winds will increase to 30-40kts in the 1-2kft layer this morning for
all but KSUN (winds will be closer to 20kt in this layer here -- but
brief wind shear is likely with the frontal passage around 20Z ) so
wind shear will continue in the TAFs until these winds reach the
surface. Odds favor this occurring at KBYI and PIH around 15Z, IDA
around 18Z and DIJ between 17-20Z. Models usually struggle with this
timing so confidence is medium. VFR conditions are expected with the
exception of two terminals, KSUN and KDIJ. Rain and snow showers
will be possible at KSUN between roughly 20-00Z, and brief
reductions to MVFR. The chances for MVFR conditions in snow showers
is slightly higher at KDIJ, mainly between 00-03Z. Surface winds
will become increasingly southwesterly in the afternoon for KBYI,
KPIH and KIDA along and behind the frontal boundary, with 15-25kt
winds expected along with briefly higher gusts in the afternoon.
KDIJ and KSUN may also experience briefly gusty SW surface winds
along/behind the boundary's passage in the late afternoon hours.
Fog/stratus potential looks limited behind this system, with only a
modest chance at KDIJ between 03-06Z. Surface winds will calm down
into the 5-15kt range for KBYI, KPIH and KIDA after sunset.

AD

&&

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