Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 200924

Area Forecast Discussion
National Weather Service Pocatello ID
324 AM MDT Tue Mar 20 2018

.SHORT TERM...Today through Thursday night.  Expect weak high
pressure ridging today bringing weak west northwest flow over the
area. A weak wave will move through the ridge bringing light,
mostly mountain snow showers in northwest flow impacting mainly
the northern central mountains as well as the southern and eastern
highlands. Tuesday night into Wednesday morning high pressure
ridging moves east allowing for southwest flow across the area.
Moisture starts to move into the area in southwest flow bringing
mostly light valley rain and light mountain snow showers across
the area on Wednesday. With Southwest flow expect breezy winds and
above normal temperatures Wednesday. By early Thursday morning
expect widespread precipitation, warmer temperatures, and breezy
winds with snow levels rising to 7000 ft, possibly higher. Expect,
in general, 0.50 to 1 inch of precipitation Thursday into Friday
morning. Look for 5 to 10 inches of snow with locally higher
amounts mainly above 7000 ft. With higher snow levels and warmer
temperatures expect rain on snow in some areas. Warmer temperatures,
breezy winds, and rain on snow will bring back snow melt and
higher runoffs. Wyatt

.LONG TERM...Friday through next Tuesday. Both the GFS and ECMWF are
in good agreement that additional precipitation will fall across SE
Idaho Friday night as ejecting energy from the low pressure center
off the Oregon coast shears through the region. The remainder of the
weakened low follows Sunday with accompanying showers overspreading
SE Idaho once again. By Monday, the operational GFS and ECMWF begin
to show notable differences between their solutions as the GFS
favors a series of progressive disturbances embedded in the NW flow
shearing SE through the NRN Rockies whereas the ECMWF is a little
slower and further north with the passing disturbances as a more
amplified ridge builds along the NW coast. Mainly tried to split the
difference in the models maintaining some mention of precipitation
along the Montana and Wyoming borders through early next week. Have
not strayed too far from statistical guidance which is indicating
warm temps Friday which cool over the weekend and then warm once
again early next week. Huston


.AVIATION...A flat upper ridge was positioned over the region early
this morning as mid-level CIGS advanced through SE Idaho. Numerical
models suggest that a weak low over Oregon will shear east through
the region this afternoon helping to support showers. Main impacts
will likely be seen at KSUN and KDIJ where TEMPO MVFR CIGS in
showers are possible while the valley terminals may see low VFR CIGS
with any passing VCTY shower. Improving conditions are anticipated
after about 03z. Huston


.HYDROLOGY...As warmer weather returns along with gusty winds through
Thursday, snowmelt is expected to pick up across eastern Idaho.
This should increase runoff on multiple rivers and streams,
although river and stream flooding is not forecast at this time.
In areas where the ground is still frozen with existing snow
cover, sheet flooding is possible. The risk for both increases
Wednesday and especially Thursday as one or more rounds of rain
and snow are anticipated. Snow levels will be quite high, rain on
top of snow could seen above 7000 feet if not closer to 8000 feet
by Thursday. While details are still left to be worked out,
including precipitation amounts, it does look to be quite wet in a
24 to 48 hour period. If models continue the warm and wet trends,
expect an areal flood watch by Wednesday highlighting the sheet
flood potential areas for mainly Thursday. Wyatt



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