922 FXUS65 KPIH 200731 AFDPIHArea Forecast Discussion National Weather Service Pocatello ID 131 AM MDT Sat Sep 20 2025
.KEY MESSAGES...
- Showers and Storms Over the Weekend, Especially Sunday
- Cooler than Normal Temps on Monday
- Above normal temps return Tuesday and into next weekend remaining mostly dry
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.SHORT TERM /THROUGH TONIGHT/... Issued at 129 AM MDT Sat Sep 20 2025
Early morning satellite imagery shows some mid/high level clouds in place across the region this morning and clouds, and precip, will be the main theme for the last weekend of summer. Monsoonal moisture continues to stream north into the region and today we should see some showers and thunderstorms develop across the area. The best chances today look to be primarily across the southern third of the region, namely across the south hills, into the Raft River region and maybe sneaking in to the southern Snake Plain. The atmosphere doesn`t appear to be overly conducive for any significant winds from these thunderstorms with HREF probabilities hovering around 10 percent or less for wind gusts greater than 30 kts. CAMs do show some potential for the precipitation to linger into the late evening and perhaps into the overnight hours of Sunday AM so the forecast does carry PoPs in spots accordingly. Temperatures tomorrow look to be very similar to Friday`s values although spots closer to the Utah border could end up a few degrees cooler with increased cloud cover. Overnight lows look to be very mild for this time of year, especially in the lower valleys with low to mid 50s, maybe even some upper 50s possible. Mountain locations will generally be in the 40s as we begin the day Sunday.
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.LONG TERM /SUNDAY THROUGH FRIDAY/... Issued at 105 PM MDT Fri Sep 19 2025
The best chance of showers and storms areawide will be Sunday, and eastern areas on Monday. There is better agreement today on what happens with the closed low early next week, which is to close it off east of the Divide. We will see a decent amount of moisture with the storm as it develops. Most of the precipitation falls in higher elevations with this storm. There is 15-35% chance of more than 0.25" in the central mountains and up to 50-60% in the eastern and southeast highlands. The potential for over 0.50" peaks between 20-50% along and east of I-15 through Monday morning. Those chances are in a given 12 hour period anywhere from 6am Sunday - 6am Monday. Showers and storms will linger east of I-15 Monday, but Tuesday and Wednesday looks dry as high pressure rebuilds for a short time over our area. The end of next week COULD be showery again. The Blend of Models follows the trend of the GFS and ECMWF, which brings a closed low far enough north to increase clouds and kick off some showers and storms. Temperatures are trending much cooler for Monday. Valley highs are now only expected to be in the mid to upper 60s, which is 5-10 degrees BELOW AVERAGE. We should rebound quickly next week and push back above average for the end of September.
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.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 927 PM MDT Fri Sep 19 2025
Low approaching from the south will bring on and off cirriform CIGs tonight, then in the morning a low to mid- level cloud deck should start moving in, first seen at KBYI and KPIH, then by mid-day at KIDA, KDIJ, and KSUN. TSRA and SHRA will develop during the afternoon or early evening, beginning at KBYI and KPIH. These are the only airdromes that appear to be threatened with thunder. KSUN and KDIJ have a threat of showers, with KSUN in the evening (due to the low) and KDIJ in the afternoon (due to afternoon heating). Only KIDA appears to avoid precipitation, at least in the afternoon and evening. No impact to VSBY is expected, and the risk of TSRA just barely rises to the PROB30 level.
Wind will not be as light, driven by slope-valley or just variable in direction. Only KSUN appears to have the slope- valley wind, and then just for the morning and early afternoon. A southerly component should kick in during the day on Sat for the other airports. Outside of TSRA, wind should not exceed 12KT. For thunderstorm outflow, there is not upper level support for any moderate to strong outflow, so have put in a minimum of 15G30KT.
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.FIRE WEATHER... Issued at 129 AM MDT Sat Sep 20 2025
Precipitation chances increase today for at least parts of the region becoming more widespread on Sunday as a surge of moisture moves in and a Pacific shortwave shifts inland. Sunday would be the day with better chances of measurable precipitation, with higher elevation regions seeing a 25-35% chance of a wetting rain. Those chances rise to 35-45% east of I-15 for Sunday evening and overnight as the frontal system associated with the low shifts through the region. Following the frontal system, temperatures will be below normal for Monday, with most lower elevation highs in the mid 60s- low 70s. A ridge of high pressure building into the region Monday through at least Wednesday should keep the region dry. There is quite a bit of uncertainty after midweek with respect to breaking down the ridge and allowing another system into the state, but for now any precipitation chances look isolated at best to round out the week.
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.PIH WATCHES/WARNINGS/ADVISORIES... None.
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SHORT TERM...McKaughan LONG TERM...Keyes AVIATION...Messick FIRE WEATHER...McKaughan
NWS PIH Office Area Forecast Discussion