251 FXUS65 KPIH 151915 AFDPIHArea Forecast Discussion National Weather Service Pocatello ID 115 PM MDT Mon Sep 15 2025
.KEY MESSAGES...
- Shower and thunderstorm potential decreasing through Tuesday evening
- Dry weather for midweek until the weekend
- Warmer afternoon temperatures return under high pressure
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.SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 103 PM MDT Mon Sep 15 2025
As low pressure slowly departs to the northeast in the next 24 hours, pockets of showers and isolated storms will persist...especially into tonight. The best chances will remain across portions of the central mountains, upper end of the Snake Plain and eastern highlands. A brief burst of rain is possible. Right now, any risk of small hail and stronger wind is slim to none. Coverage dwindles from southwest to northeast. We may see an additional band develop along a windshift dropping southwest across our area overnight. On Tuesday, some wraparound showers with a rumble of thunder possible are expected along the Montana and Wyoming borders. That will quickly end tomorrow evening. Temperatures will be at to just below average both in the morning and afternoon.
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.LONG TERM /WEDNESDAY THROUGH SUNDAY/... Issued at 103 PM MDT Mon Sep 15 2025
Wed through next Mon night. The upper level pattern is very weak through Sat in the western states, with the ridge sitting over the Great Basin. This should allow a warming with a dry pattern through that period. Afternoon temperatures continue to be above climatic normals for this time of year. The weak pattern means little to no wind with no feature moving through. The only fly in the ointment is that such a weak pattern could allow moist and unstable air from the Gulf of California to make its way into southern Idaho. However, the NBM is indicating precipitation probabilities at 10 percent of below for the moment.
On Sun, a very weak upper level trough moves through southern Canada for two clusters making up 49 percent of the solutions with 26 percent having this trough dig far enough south to perhaps bring clouds, precipitation, and unstable air. For Mon, about 40 percent of the solutions continue to have low pressure over some part of southern Canada. The end of this period has a much faster and more zonal flow that the weak flow of the first half. Thus the weather at the end may be more determined by the progression of shortwaves through this mean flow, and makes the forecast more uncertain for Sun and Mon. This risk falls out in the 10 to 25 percent range of probability, so the slight chance risk appears validated for now.
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.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1046 AM MDT Mon Sep 15 2025
The potential for showers and a few storms remains through this evening at SUN, IDA and DIJ. Due to somewhat higher confidence, we only included PROB30 at DIJ. We will just need to see how things progress to see when and where we need to adjust things. We eventually see a full shift to northerly flow this evening and tonight on the back side of the low over us today. We COULD see some wraparound showers tomorrow, but confidence is way too low at the moment to put any mention in the TAFs.
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.FIRE WEATHER... Issued at 103 PM MDT Mon Sep 15 2025
Warming and drying will return to the forecast area as high pressure moves in behind the low that generated showers and thunderstorms this previous weekend. High pressure remains through Sat afternoon, allowing temperatures to continue above climatic normals and for humidity to be lower than usual, with some lower elevation humidity lowering below 15 percent by Fri. The warmer conditions will be offset by the stabilizing high pressure for instabilities to remain about the same every afternoon. The very weak high pressure pattern after today should keep wind away from critical thresholds and the sunshine produce normal slope-valley interactions. The next risk of precipitation and convection is not really until Sun at the earliest.
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.PIH WATCHES/WARNINGS/ADVISORIES... None.
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SHORT TERM...Keyes LONG TERM...Messick AVIATION...Keyes FIRE WEATHER...Messick
NWS PIH Office Area Forecast Discussion