Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 162317

Area Forecast Discussion
National Weather Service Pocatello ID
517 PM MDT Mon Apr 16 2018


Radar shows batch of rain/snow mix moving out of the Magic Valley
into the Snake Plain. Evening rain/snow chances across the Snake
Plain look a little lower, so increased the threat. Not expecting
a significant impact although grassy surfaces in the lower valleys
and bench areas could pick up a light accumulation of snow. Some
slick roads may be possible tonight closer to pass level across
southeast Idaho with an inch or two possible.



.PREV DISCUSSION... /issued 208 PM MDT Mon Apr 16 2018/

SHORT TERM...Tonight through Wednesday night. Strong upper trough
slowly working across East Idaho. Surface cold front has passed
through most of the forecast area with the exception of the Bear
Lake region, where it is expected to pass through by evening. This
system has proven to be slightly stronger than expected. The band
of precipitation just ahead of the 700mb trough has produced light
amounts of snow today down to valley floors as much colder air has
followed the front. Winds have also been stronger just ahead of
and behind the front, but ahead of the precipitation band. Speeds
at times have bordered on advisory level, with pockets of blowing
dust creating mild travel concerns across the Arco Desert and
along I-15 north of Idaho Falls. Believe much of this impact will
dissipate next few hours as precipitation band continues to slowly
march east. Any snow that does reach valley floors with this band
likely to stay light and generally confined to grassy areas with
little accumulation on roadways. Precip band continues to shift
into highlands between I-15 and WY border overnight. There is weak
indication of potential for a convergence band late tonight, but
the signal is weak and short lived, and if it does manage to
occur, should be confined to regions near Idaho Falls. This leads
to second concern of the day, which is the winds on Tuesday.
Surface gradient is not as strong, but there is a more consistent
mid-level northwest flow aloft, and better chance at mixing
through the day as upper trough shifts east. GFS guidance, which
is turning out to be more reliable this spring for strong wind
events, pushes much of the southern half of the forecast area well
into advisory criteria very early in the day. For a brief period,
guidance puts Pocatello into High Wind range but the broad period
more likely to see advisory strength winds. Have decided to issue
a Wind Advisory for regions from Burley to Pocatello and south to
the UT line. Will stress potential for higher winds early in the
morning. Advisory will run through early evening to best match
combination of gradient strength and mixing past 700mb.
Fortunately, this takes us into a break. Upper ridge looks to
rebound Tuesday night through Wednesday. Next upper low shifts
into the western states late Wednesday into Wednesday night, but
main focus of upper low appears to be tracking toward central
Nevada. At this time, precipitation for Wednesday night appears to
be a glancing blow to the western-most portions of East Idaho. DMH

LONG TERM...Thursday through next Monday. Closed upper low to
meander south of Idaho Thursday, which will provide rain and snow
showers to our area. The amounts to which are a bit uncertain still
and will depend on where the low sets up and how much moisture there
will be to tap into. Activity is looking widely scattered at the
moment with overall rain amounts less than 1/4 of an inch. Not
enough to really cause any flooding concerns. Winds will be
increasing out of the north and northeast as well around 15 to 20
mph especially through the Snake River Plain. The low is expected to
track over southern Utah by early Friday and clear us out as high
pressure builds in. The weekend is still looking quite pleasant with
temperatures in the mid to upper 60s (and maybe some 70s in there!)
A new weather system, through weaker, tracks through on Monday
providing some showers to the area. NP/DMH

AVIATION...Low confidence in the TAF forecast this evening due to
slow moving progression of snow showers behind a frontal boundary.
These showers are lowering CIGS and VIS for many sites and bringing
snow to valley floors where it wasn`t previously expected.
Therefore, are including a mix of RA and/or SN at TAF sites for this
evening as the band moves through. For the most part, impacts at SUN
are through, however it won`t be impossible for additional showers
to pass through there as well. Windy conditions are also of concern
but should disappear as the moisture takes its influence. We are
already seeing improvements at BYI, but places like IDA and DIJ will
continue to be gusty this afternoon. Expect another round of windy
conditions tomorrow as well. NP/DMH


Wind Advisory from 8 AM to 9 PM MDT Tuesday for IDZ017-021>023.


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