Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 202000

Area Forecast Discussion
National Weather Service Pocatello ID
200 PM MDT TUE SEP 20 2016

.DISCUSSION...The latest satellite imagery was showing a low
pressure trough building SE across Vancouver Is. early this
afternoon with a modest connection to sub-tropical moisture
extending as far west as Hawaii. The models continue to develop the
trough southward along the coast tonight and Wednesday resulting in
increasing moisture and precipitation developing across SRN Idaho
Wednesday afternoon. The low begins to migrate slowly inland
Wednesday night through Friday night eventually exiting east of the
divide sometime Saturday afternoon. An extended period of moderate
to heavy rainfall is anticipated across the region over the 3-day
period with upwards of 1.50 to 3.00 inches of liquid precipitation
and accumulating snow primarily above 8000 MSL in the Central
Mountains. Outdoor enthusiasts recreating or hunting above 8000 MSL
should be prepared for periods of winter-like conditions. Also,
those living or recreating in water-sheds below recent fire activity
should be prepared for debris flows and/or accentuated runoff. A
ridge of high pressure is expected to rebound across the region
Saturday evening behind the exiting low providing dry and clear
conditions through mid-week. Look for cooler daytime highs as the
storm system moves into the region, bottoming out on Friday about 15
deg below normal and then slowly rebounding to normal early next
week. We may see freezing temperatures in the Snake River Plain
Sunday morning under clearing skies behind the exiting low. Huston

.AVIATION...Mid-level CIGs should develop tonight, but very little
precipitation until Wed night. Extremely dry air below 700mb
continues until then. Some gusty wind possible this afternoon and
evening as a frontal system moves in from the northwest. Messick

.FIRE WEATHER...A season-ending event is fast approaching. Deep
low pressure is moving in from the northwest. It is entraining moist
and unstable air from the subtropics. The first thing to happen will
be extensive cloud cover developing overnight and continuing to
lower and produce some light showers on Wed. By Wed night, light to
moderate rain will develop, changing over to moderate to heavy rain
for all of Thu and most of Fri. Sat will see clearing from west to
east across Idaho. Wind will be strong with the front, but humidity
should remain high with the precipitation and nature of the air mass
moving in. Widespread 1 to 2 inches of rain is expected over the Wed
night to Sat afternoon time period. Messick

.PIH Watches/Warnings/Advisories...

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