Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 181959

Area Forecast Discussion
National Weather Service Pocatello ID
159 PM MDT Sun Mar 18 2018

.SHORT TERM...Tonight through Tuesday night. Pockets of light snow
continue this afternoon across eastern Idaho, as the low across
the west slowly pushes east. Any real potential of snow will be in
the eastern highlands near the Wyoming Border and West Yellowstone
overnight. A few pockets of light snow could still linger across
the central mountains as well. As we try to clear out outside of
those locations, we are expecting stratus and/or fog to develop
late tonight and Monday morning. The fog is less certain but we
did see some in a couple of spots this morning, so am at least
confident enough to throw that in the forecast. This should be
mainly for the Snake Plain and valleys along either side of I-15
to the Utah border. High pressure tries to build over Idaho, but
1) it`s not very strong and 2) it`s not a "clean" ridge...meaning
there is moisture for clouds and some light precipitation. While a
few flurries or sprinkles are possible in the Snake Plain, the
best chance (and it`s not huge) will be in the central mountains
and from around Driggs to Island Park. Warmer weather will return
with an occasional breeze across our part of the state. This will
likely kick snow melt and runoff back in gear somewhat. Below
freezing temperatures overnight should mitigate that a bit,
although by Wednesday morning we are forecast some valley
locations remain in the mid 30s.  Keyes

.LONG TERM...Wed through next Sun night. 500mb long wave forecast is
for a trough to linger over the Pacific Northwest through the
period. It is stronger early, weakening a little by Thu afternoon.
This continues the potential for precipitation with mild
temperatures, at least for lows. Due to cloud cover and
precipitation, not sure if highs each day will be warmer than
normal. There is one major shortwave that blasts through the
forecast area, on Thu/Thu Night. Very high confidence on this
feature, which will be a warm storm with plenty of southerly airflow
prior to the front passing through Thu night. Snow levels even as
far north as Challis and Island Park will be nearly 7000 to 7500
feet elevation. This could generate some flooding with rain on snow,
especially the heavy snow of the last couple of weeks. Beyond the
Thu/Thu night storm, the guidance products suites start to diverge
in solutions. None of them are dry; but where the precipitation
drops is of a significant difference of opinion. Have broad-brushed
the Fri and upcoming weekend. For now, there is a threat of
precipitation, but just what kind and how much must be worked out.


.AVIATION...Marginal VFR developed this morning, along with a line
of weak showers that moved out of the central Idaho mountains and
into the Snake River plain. An increase in the wind this afternoon
should clear out the stratus, and not looking for a comeback except
possibly KIDA and KDIJ. Some brief showers expected at KDIJ, most of
the rest will showers in the vicinity, but with probabilities of
measurable below 25 percent in the other four airdromes, could not
continue the TEMPO groups. Messick



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