Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 232013

Area Forecast Discussion
National Weather Service Pocatello ID
213 PM MDT Fri Mar 23 2018

.SHORT TERM...Tonight through Sunday night. Deep low remains
centered off PacNW coast, but will shift inland. Weekend forecast
best characterized by series of shortwaves ejecting out ahead of
the low as the low opens and shifts inland through Sunday night.
First shortwave ejects through OR across ID panhandle tonight
associated with upper jet and weakly negative tilt. Bulk of energy
too far west but region in favorable jet dynamics for formation of
band of showers overnight through mid day Saturday. Cold front
accompanies this feature. Snow levels ahead of front stay mild
enough to keep precip mix of rain/snow even after midnight
tonight. Temps drop far enough around or just after sunrise for
snow levels to fall to valley floors, and they should stay cold
enough to support snow or a rain/snow mix even through the
afternoon. Pacific low opens overnight Sat night and begins
shifting inland. Next shortwave shifts across NV/UT Sat night into
Sunday. NAM develops region of showers associated with this
feature, impacting primarily southern highlands Sat night.
Shortwave pushes northeast through the remainder of the region
during the day Sunday and into Sunday night as main trough axis
slides across the region. Wrap around precipitation continues
Sunday night mainly over northern Snake Plain and northeast corner
of the region. Total QPF values tonight through Sat night
generally less than one-quarter inch most locations, though some
higher elevations east of I-15 could peak out closer to one-half
inch. Liquid values are even less for Sunday and Sunday night. DMH

.LONG TERM...Monday through next Friday. Fair agreement among long-
term models as relatively dry and stable conditions prevail through
most of the week. There will likely be some lingering showers over
the Eastern Highlands through Monday night. We may also see some
showers develop along the southern periphery of a short wave
embedded in a northwesterly flow on Wednesday, but the main energy
along that will be over MT/WY. The general trend in the long-term is
the re-development of upper ridging off the Pacific Coast, and
high temperatures to come back into the 50s. Hinsberger


.AVIATION...Dry air is moving back into the region in the wake of
yesterday`s weather system. Thus, we have VFR conditions expected
throughout the day today. Things change tonight as a wave lifts out
of the Pacific trough and, with associated surface frontogenesis,
triggers rain/snow over the forecast area. Models are timing the
band of precip just after midnight tonight, and as late as 11Z at
KDIJ. KIDA and KDIJ may be the hardest hit with IFR conditions
through the 4- to 6-hour event. A few degrees cooler, and KBYI and
KPIH may get snow rather than rain, and this would likely take those
terminals below VFR as well. Hinsberger


.HYDROLOGY...Snowmelt and rainfall runoff continues across much of
the forecast area, but impacts remain over Clark, Fremont, and
Madison counties as well as the Big Wood River Valley around Ketchum
and Hailey. Most hydrographs are at or just coming down from their
crests with minor flooding ongoing at Topaz. That water is making
its way to the Portneuf River in Pocatello, which is beginning to
respond to the increased flow from Topaz and Marsh Creek. A weather
system will develop in the overnight hours, adding a bit more precip
to the scale, but some of this may actually be snow. Expect to see
water continue to flow downstream and flood waters recede.



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