491 
FXUS65 KPIH 030326
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
Issued by National Weather Service Boise ID
826 PM MST Tue Feb 2 2021

.DISCUSSION...Cold front and showers making steady eastward progress
across southern Idaho this evening.  At 800 PM MST the leading edge 
of showers was in Camas and Jerome Counties.  Expect brief wind 
gusts 30 to 40 mph and a wind shift to southwest or west as the cold 
front passes just before the showers begin.  The front and showers 
will reach the eastern Magic Valley by 900 PM and Pocatello around
1 AM. Showers will start as rain in the Magic Valley but change to 
snow shortly after midnight. Otherwise all snow is expected with 
light accumulations overnight in the Upper Snake Plain but several 
inches in the mountains. Precipitation should last 4 to 6 hours 
followed by partial clearing, breezy, and colder weather Thursday. 

LC

&&

.AVIATION...VFR becoming MVFR and locally IFR as cold front and 
showers approach from the west, reaching KBYI 04Z and KPIH 09Z,
then continuing east.  Mountains becoming obscured. Showers will
be initially rain at KBYI but will change to snow behind the cold 
front.  Elsewhere only snow.  Surface winds SW 15-25 kt becoming 
WSW 20-30 kt behind the front and during showers, then decreasing
to 15-25 kt. 

LC

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Thursday night...Upper trough has been 
slow to move inland. Precipitation has started to move into the 
Central Mountains per area web cams.  Frontal boundary still west of 
the state but precipitation starting to fill in ahead of the front 
per radar imagery. Aside from the slightly lower start, trough and 
precipitation progression appears to remain on track. Snow continues 
to target higher elevations primarily Central Mountains and Eastern 
Highlands. Warm southerly flow has induced very warm temperatures in 
lower elevations, especially along and south of I-86. Precip shifts 
into the Snake Plain and eastern highlands around/after midnight, 
and temperatures may be warm enough to the south for precipitation 
to at least start as rain. NAM soundings support burst of moderate 
snow along the front as it passes through Pocatello. Given the 
strong warming this afternoon, may be more difficult to lower 
temperatures enough to accumulate any meaningful snow in the 
Pocatello region before sunrise, but character should shift to all 
snow with frontal passage. Surface winds increase behind the front 
and will be quite breezy, but blowing snow may be minimized if the 
temperatures can stay warm enough. Upper trough shifts through 
during the afternoon.  This may not be well picked up with the short 
term ensembles yet, and will be feature to watch over the next 
forecast cycle or two. Otherwise will likely see additional light 
snow showers continue over higher elevations into late Wednesday. 
Cool northwest flow is in place for Wednesday night into late 
Thursday. Reinforcing shortwave arrives from the northwest Thursday 
night, producing upslope snows in portions of the central mountains 
and most of the eastern and southern highlands into Friday. DMH

LONG TERM...Friday through next Tuesday.  
The long term portion of the forecast will be characterized by 
persistent northwest flow, at least through Monday or so, as central 
and eastern Idaho will remain in between a ridge of high pressure 
across the eastern Pacific and a strengthening polar vortex near the 
Great Lakes and northern Great Plains. A disturbance embedded in the 
flow will pass through the region on Friday. Snow showers will be 
ongoing by daybreak Friday morning across the eastern highlands/WY 
border region and also across the central Idaho mountains. The 
western edge of the snow shower activity is a bit uncertain and will 
straddle the I-15 corridor, so it is possible that snow showers 
activity could extend west to the Pocatello to Idaho Falls corridor 
during the day Friday.  Snow shower activity should peak in coverage 
and intensity midday, then gradually wind down through Friday night. 
A second, weaker disturbance will briefly re-invigorate snow shower 
activity over the same locations late Friday through Saturday. A few 
inches of snow are expected across the eastern highlands during this 
period. From Saturday night through much of Monday, lingering 
moisture within the NW flow pattern will promote a continuation of 
occasional light snow showers over the same areas. WPC clusters 
generally indicate decent confidence in this pattern, with lesser 
likelihood for the ridge to take hold over the western U.S., as some 
earlier solutions were suggesting. One interesting trend to watch is 
there is a slight nod toward a trend indicating the southwest 
portion of the cold air associated with the above-mentioned polar 
vortex could reach farther west into Montana and Wyoming. This 
scenario could bring arctic air as far west as the Continental 
Divide, along with the potential for much colder temperatures than 
currently forecast across portions of east Idaho (particularly near 
the Montana border) from Sunday into early next week. This is 
something that will bear watching, but at this point the going 
forecast reflects the most likely scenario as it stands currently. 
The forecast becomes less certain at the end of the forecast period 
as it appears the upper pattern will begin to break down and evolve.

AD

&&

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

&&

$$