Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 221954

Area Forecast Discussion
National Weather Service Pocatello ID
154 PM MDT Sun Oct 22 2017

.SHORT TERM...Tonight through Wednesday. A strong moist west flow
was noted across the region early this afternoon as a Pacific short-
wave sheared east along the Canadian border. Areas of light rain
and/or snow were noted across the upslope regions of the CNTRL and
NE mountains and this will likely continue through the early part of
the evening as the aforementioned short-wave continues to shear east
along the Montana-Dakota highline. Strong gusty winds were also
noted across the INL and will likely persist until 8 or 9 PM when
the surface flow should decouple from the stronger but weakening
flow aloft. By midnight the short-wave will have moved far enough
east while the ridge over California expands northward resulting in
the loss of the direct moisture tap off the Pacific. As the storm
track lifts rapidly north into Canada late tonight and Monday
morning, drier conditions will overspread SE Idaho. The upper ridge
continues to amplify Monday afternoon and Tuesday before shifting
westward into the ERN Pacific Wednesday as a second short-wave tops
the ridge in NW Canada and digs SE toward Montana and the Dakota`s.
Much warmer daytime temperatures are expected under this flow
regime. Huston

.LONG TERM...Wednesday night through next Sunday night. Blocking
high on/just off the west coast will keep the storm track deep into
Canada as it reaches the North American coast, which will make it
difficult to get any shortwaves to get this far south until well
east of the Gem State. In fact by Fri it is a very traditional omega
block, and continues beyond the forecast period. Thus sunny and dry
should be the prevailing weather for this period, especially for the
weekend. Previous model runs have had a fairly strong short wave
come out of central Canada and move from north to south across
eastern Idaho; this morning`s trend in the GFS has been for this
feature to come in farther east and have less impact on the forecast
area.  However, the ECMWF solution has been about the same as
yesterday. So will not go a totally dry period, but will tone down
PoPs for the Wed night/Thu event. Otherwise, nearly clear skies with
the northerly flow keeping afternoon highs only slightly above
normal for the time of year. Messick

.AVIATION...Wind is peaking right now for most of the airdromes. The
precipitation development has been well under expectations, with the
exception of the Continental Divide. So have removed the
precipitation threat, even from KDIJ. Onset of the highest wind had
to be moved back, but it also appears as though those strong wind
should end during the early evening. The NAM time-heights indicate
abundant moisture in the low levels below 7000 ft MSL, however,
truth in the observations is that there isn`t that much. So have
disregarded the extreme low level moisture for tomorrow morning that
looks like it could contribute to a fog stratus problem, but have
indicated FEW-SCT coverage below 1000ft AGL. That is except for
KDIJ, which has a deep layer of moisture expected overnight tonight
in an upslope flow regime. However, have only gone with marginal VFR
conditions for the CIG there. Messick

.FIRE WEATHER...A storm system is moving through the region today.
Expect windy conditions today. Rain and snow is possible as well,
especially across the higher terrain. Lighter winds along with
drier, warmer weather will return to the region on Monday. Valle

Wind Advisory continues through 9 PM MDT this evening for IDZ020-021.

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