Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 191016

Area Forecast Discussion
National Weather Service Pocatello ID
316 AM MST Fri Jan 19 2018

.SHORT TERM...Today through Sunday. Our latest rain and snow storm
continues to push slowly east today. We had some very strong
southerly winds especially with gap winds along the 84/86 corridor
earlier this morning. However, the cold front has pushed to
along/just east of the I-15 corridor and will keep sweeping east.
Winds have died down a bit in its wake. The precipitation and
stronger push of colder air is lagging just a bit behind the
front, as the main low is still to our west. As we go through this
morning and afternoon, the bulk of precipitation will push to the
southern and eastern highlands. There will likely be some
lingering showers across portions of the central mountains, but we
should be mostly dry with winds picking back up across the Snake
Plain. Snow levels will eventually fall to valley floors the rest
of the day. Most of the snow across the southern and eastern
highlands will be above 6500ft, as those areas will take a bit
longer for snow levels to really drop. Look for 2-6" above that
elevation with locally higher amounts to 9" across the Bear River
Range and adjacent to the Tetons and Yellowstone. Below 6500ft,
snowfall will be limited to around an inch or even less. Gusty
winds will likely create a few pockets of blowing/drifting snow
but impacts should not be widespread since this is a wet snowfall.
That said, there will likely be some slick roadways in places up
in the mountains. Snow should continue to wind down after sunrise
in the central mountains with an additional inch or two for the
rest of the day. We left the WINTER WEATHER ADVISORY for the
Sawtooths going for now since it`s still snowing. Snowfall for the
Snake Plain will be minimal, and if it does accumulate it will be
mostly on grassy surfaces. There COULD be some slick spots at
times but nothing that would be of substantial impact. By sunrise
Saturday, most of the snow should be focused in two areas. As the
storm is still splitting, this will allow moisture to still push
north into the southeast highlands. This will keep snow going
around Bear Lake. Another area will be more associated with a
combination convergence/upslope band along/east of the I-15
corridor from Pocatello north to Idaho Falls, north and east from
there to around Driggs and Island Park. Most of the Snake Plain
will less than an inch although higher bench areas could see 1-2"
around Idaho Falls and Rexburg. This trend extends northeast
toward along US-20 toward Ashton Hill. For Saturday, as the storm
is still slow to clear, lingering light snow is possible southeast
of a Ashton to Malta line with the best chance still around Bear
Lake. A few showers are possible south of Burley as well as the
central mountains. Sunday should be dry, but the break won`t last
long as the next storm arrives Sunday night. Keyes

.LONG TERM...Sunday night through Friday. Monday system still
appears to be on track, but have trimmed precipitation back somewhat
Sunday in eastern portions of region to better match latest model
trends. Once Monday system passes, flat dirty ridge left in place so
kept weak low confidence pops Monday night into Tuesday. Models
struggling a little bit with timing and depth of Wednesday through
Friday system thus confidence much lower for latter portions of the
forecast. ECMWF appears to be slightly slower and stronger than the
GFS. Ensembles having a difficult time as well with high spread on
precip chances. Kept with blend towards mean with little change from
previous forecast. Highest chances thus fall in the
Wednesday/Thursday time frame with trend toward drier conditions
Friday as main trough axis shifts east, either as broad closed low
via ECMWF or open trough via GFS/GFES. Temperatures cold enough to
support snow throughout.  DMH


.AVIATION...Cold front shifting through early this morning with wind
shifts across the region. As winds shift more westerly at surface,
believe threat for LLWS primarily over, though much stronger winds
aloft could produce enough shear to approach 20kt forecast
threshold. Temperatures falling through the day apt to produce rain
at terminals this morning, mixing with and changing to snow later
today, though timing for this also coincident with precip ending and
ceilings improving at KSUN/KBYI. Winds at KBYI/KPIH/KIDA stay
elevated around the 15-20kt range through the day, decreasing after
sunset. Snow expected to continue overnight at KDIJ, and potential
as well at KIDA/KPIH with some hint of development of convergence
band of precip overnight. DMH


Winter Weather Advisory until 11 AM MST this morning for IDZ018.


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