Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 172015

Area Forecast Discussion
National Weather Service Pocatello ID
115 PM MST Fri Feb 17 2017

.SHORT TERM...Tonight through Sunday night. A large Pac storm
system over CA will gradually move northeast into the Great Basin
on Sat. The first wave of precip is already showing up in northern
NV/UT and southern ID. Precip will become widespread by Sat morn.
Strong southerly flow ahead of the system will maximize precip
over the southern portion of the central mtns...extending eastward
along the Divide due to upslope. This will be in the form of heavy
snow mainly above 6500 ft. Heavier precip will also extend into
the northern portion of the Snake River Plain...although most of
this should be rain. The rest of the area should see much lighter
precip...especially along the I-86/I-15 corridor from Burley to
Blackfoot due to strong downslope flow. This will be rain and some
high elevation snow. This will be the situation into Sat night. As
a cold front moves thru early Sun morn...the flow will turn more
westerly. This will allow precip to become heavier over the
previously downsloped areas. Precip finally tapers off Sun
night...for this storm.

Snowfall amounts are expected to range from 12 to 18 inches in the
central mtns...and 8 to 12 inches in the upper Snake Highlands.
Snowfall in the eastern and southern highlands should only be a
few inches at higher elevations. Southerly winds are expected to
pick up strength tonight and continue thru Sat. Rainfall amounts
are expected to range from 0.5 to 0.75 inch. Hedges

.LONG TERM...Monday through Friday. Nose of advancing atmospheric
river will be at our doorstep Monday morning. This will herald the
return of moderate to heavy rain/mountain snow to begin the work
week. The moisture transport will likely be sustained through
Tuesday with the Central Mountains likely getting moderate to heavy
snowfall through Tuesday afternoon. We may possibly get a brief
break from precip Tuesday night, but a more dynamic system will
approach from the west Wednesday morning and will impact the
forecast area through Friday. This system is more pronounced in the
12Z GFS run than the ECMWF, which supports a broader upper trough,
but is still a widespread precipitation producer. Snow levels drop
as the system shifts eastward, and will finally reach the valley
floors Wednesday afternoon. Temperatures and rainfall will continue
to erode the lower level snowpack leading to more runoff and will
likely extend flood risks through Friday. Hinsberger


.AVIATION...Another dry and stable afternoon will give way to
another wet and unsettled evening. A vigorous shortwave will lift
out of a low positioned off the California coast with the leading
edge of precipitation reaching the TAF sites by 00Z to 02Z. KBYI
should remain VFR, but could see brief periods of MVFR. Models are
suggesting predominant precip type will be snow at KSUN and KDIJ,
but forecast soundings favor rain or a rain/snow mix. Have opted for
-RASN at KSUN and -RASN changing over to -SN at KDIJ in the early
morning hours. Forecast soundings also show increasing boundary-
layer winds overnight which suggests the potential for low-
level wind shear.  Hinsberger


.HYDROLOGY...Widespread rain will dominate the weather over the
weekend. Over the southern part of the fcst area...precip will be
generally lighter...but become heavier by Sun morn. This will
likely result in worsening flooding conditions. Another storm
system is due to hit on Mon. Hedges


Winter Storm Warning from 8 PM this evening to 5 PM MST Sunday
for IDZ018-019-031-032.


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