Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 280851

Area Forecast Discussion
National Weather Service Pocatello ID
251 AM MDT WED SEP 28 2016

.SHORT TERM...Today through Fri night. Nearly clear skies will
last another period in southern Idaho before low pressure moves in
from the south. It doesn`t have a lot of moisture, but it should
generate light to moderate precipitation as it moves across from
south to north. For the overnight hours tonight, it will barely
move into the southern part of the forecast area during late
night. For Thu first the eastern third will have a threat of
precipitation, then it will spread westward during Thu afternoon.
Light rain will continue Thu night and Fri will be something of a
break. Temperatures for the coming week peak today, then cloud
cover will bring temperatures down on Thu, but not as strongly as
was being considered yesterday. The mild air associated with a low
coming from the south will keep temperatures mild both for the
overnight low and the afternoon high. Breezy conditions are
expected with this feature as it moves through Thu afternoon.
There is enough instability with this air to present a threat of
morning thunderstorms on Thu, besides the typical time of Thu
afternoon and evening. The thunderstorm threat continues on Fri
afternoon and evening.

.LONG TERM...Sat through Tue night. This appears to be generally a
wet pattern, but there is high uncertainty on how wet in the later
periods. There is little agreement between the ECMWF and the GFS
on the track of a low for the Sun night/Mon/Mon night periods. The
GFS has a more southerly track, with the low only giving us the
wrap-around moisture for part of the time, mainly Mon/Mon night.
The ECMWF brings the low directly through eastern Idaho, hitting
the entire forecast area pretty hard with rain and snow. Both have
shifted away from the solutions that were similar to each other
yesterday, but they are trending in opposite directions. Have
simply laid down a chance threat in hopes of seeing a resolution
to the now opposing scenarios. The approach of this low, from the
west, does mean it will have some colder air with it. Snow levels
could lower to 6500 feet elevation, perhaps even lower, but
towards the end there will be less precipitation threat. Since the
GFS solution is less of a flip-flop, have used it for
temperatures. It should also be a windy time, although by just how
much is not certain.


.AVIATION...Widespread VFR conditions at all TAF sites Wednesday
through 9/29 15Z. Showers develop at KBYI Thursday morning and
through the afternoon hours may affect all TAF sites. RS

.FIRE WEATHER...Sunny skies and light winds continue today and
Wednesday with valley temperatures warming into the middle and upper
70s. Late Wednesday night and early Thursday morning there will be a
developing disturbance near the Oregon coast. Moist unstable air
begins to advance through the Great Basin into the Caribou and South
Central Highlands to support isolated showers. The chance of showers
and isolated thunderstorms increases across southeast Idaho Thursday
afternoon/night. Cloud cover and additional moisture will result in
afternoon temperatures 5-10 degrees cooler with humidity in the 25-
45 percent range. The first wave of showers passes quickly by
Thursday night and the second arrives Saturday with a better chance
of wetting rains from showers and any embedded thunderstorms.
Temperatures continue to fall back to the 50s and 60s for the
weekend. Sunday should be between disturbances, another round of
showers follows on Monday of next week and again on Wednesday. RS

.PIH Watches/Warnings/Advisories...

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