Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 170428

Area Forecast Discussion
National Weather Service Pocatello ID
928 PM MST Fri Nov 16 2018


Updated forecast to increase snow chances across the Snake Plain
for the overnight period. Radar trends have been showing snow
increasing across the upper Snake Plain with most high-res models
showing snow moving down the Snake Plain in the next couple of
hours. Increased snow amounts slightly, with many areas receiving
around an inch, slight increase from half an inch. Not seeing a
ton of impacts so far. Roads are warm this evening and seeing much
of the snow in the upper valley melting. Am concerned about wet
roads freezing overnight with snow possibly accumulating on road
surfaces. Not confident enough in hazardous conditions developing
at this time to issue advisories, but will continue to monitor the



.PREV DISCUSSION... /issued 105 PM MST Fri Nov 16 2018/

SHORT TERM...Tonight through Monday. Focus in the short-term
periods will be a mid-level shortwave embedded in the
northwesterly flow. Models begin precipitation late this afternoon
from around Challis to Island Park. Rain will begin in the Snake
Plain this evening but should chance over to snow before midnight.
NAMNest and GFS expand the precip field well into the Twin Falls
area to our west overnight. Overall, the Caribou Highlands may see
about 3 to 5 inches in the higher elevations, 1 to 3 inches in the
lower elevations. Snow accumulation should taper off gradually
westward with a trace to half an inch expected in the Snake Plain.
As the upper dynamics shifts to the south and east late tomorrow
morning, the PoPs should fall to near zero, but some upslope
around Bear Lake could sustain some precip through tomorrow
afternoon. With clearing skies behind the system tomorrow night,
min temperatures could drop 10 to 15 degrees over tonight`s lows.
High pressure will move back into the region Sunday leading to
clear and dry conditions with no significant impacts expected.

LONG TERM...Monday evening through next Friday. A high pressure
ridge will be in control of the weather pattern early next week;
with slightly above normal to normal temperatures. The ridge will
break down mid-week with the arrival of a trough or closed-upper low
from the west. There are differences between long-range model
solutions where the GFS and ECMWF has been switching places in their
thoughts between runs. At the moment, GFS model is wetter for the
upcoming early travel period for the Thanksgiving holiday
(Wednesday); while yesterday the ECMWF was wetter. On Thanksgiving
itself, remnant moisture would remain in place if you believe the
current ECMWF solution or it will be dry believing the GFS under
building high pressure. Each model depicts a new closed upper low
offshore WA allowing for incoming moisture during the Friday
through Sunday timeframe. How the low reacts during this time
frame will drive our forecast (ie/deepen, or dig into a deep wave
trough, or stream mass amounts of moisture into our area, etc)
Models are depicting a long wave trough with with significant
amounts of moisture encompassing ID. This actually appears more
confident than the Wed-Thurs solutions, which is odd. What that
means though, is that post holiday travel will be more impacted
than early holiday travel. NP/JH

AVIATION...TAFs will be in VFR status until late this evening.
Expect CIG and VIS to drop at DIJ and IDA after 02z, followed by
PIH. Conditions are currently forecast to drop to MVFR conditions
but may very well drop to IFR for a period during the overnight
hours. Improvement is forecast by mid-morning at IDA and DIJ and
late morning at PIH. Impacts will be less at SUN and BYI with snow
still forecast but not currently dropping below VFR. NP/JH



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