textproduct: Pocatello

KEY MESSAGES

- A very chilly overnight tonight in the Snake River plain and eastern Magic Valley. Frost and Freeze bulletins have been issued.

- Some precipitation, including Thursday afternoon thunderstorms, is possible starting Tue evening and continuing through Thu afternoon.

- Weaker wind until the weekend.

DISCUSSION

Issued at 143 PM MDT Mon May 18 2026

Tonight through Thu afternoon...Save for some showers in the extreme southeast corner of the forecast area, the next 24 hours will continue to be dry, cool to cold, and windy. This is due to an upper level trough currently in WY still pushing slowly eastward. The clear skies and continued northerly airflow means a quite cold overnight tonight, with 20 to 30 degrees expected in the Snake River plain. With the northerly flow not as strong in the eastern Magic Valley, temperatures are only expected to bottom out tonight in the middle 30s. These two reasons are why a Frost Advisory has been issued for the two Magic Valley zones and a Freeze Warning once again for all zones in the Snake River plain. The start time was mostly based on when the affected zones finally lose this strong wind tonight, which is still actually fairly late. By 19/15Z 19/0900MDT the temperatures should surge back above Freeze and Frost thresholds.

The north wind is expected to shift to a southwest wind and not be as problematic for the Snake River plain for Tue. The light northerly wind in the morning will shift to a south to southwest wind for the afternoon, ending the need for a Lake Wind Advisory on Tue. This lighter south to west wind continues Wed, then a northerly wind returns for Thu. It doesn't take much for a Lake Wind Advisory to be needed in the north flow regime, so it may return.

Finally, impulses moving through the northwest to west upper air flow will return on Tue night. This will mean showers over the north end of the forecast area that night, then a further digging southward will spread precipitation from a close low in central MT for heavier rainfall on Wed night and Thu morning. The precipitation will be mainly focused on the central Idaho mountains and the southern and eastern highlands, with the northern end of the Snake River plain most likely to see precipitation in the lower elevations. While isolated thunderstorms are possible Tue and Wed, Thu includes the associated cold front with this MT low actually coming through and generating high chance of thunderstorms. Since the afternoon has more unstable air, the best threat is in the eastern third of the forecast area.

Thu night through next Mon...The low clears out early enough on Thu that while it is colder, the sunny skies of Fri should allow a warming trend to develop quickly. By Sat afternoon temperatures should soar above normal after a near normal Fri afternoon. A gradual warming trend continues at least into Mon, for both highs and lows. Weak troughing gets replaced by weak upper level ridging, which will allow some breezy westerly wind, but doesn't appear to bring an significant precipitation. It appears to be fairly limited to higher elevations that can provide lifting with west-facing slopes in the zonal flow, especially Fri and Sat. Only a minority of the solutions cluster around a wet scenario for eastern Idaho. This accounts for the warming trend. The zonal flow tightens starting Sat, so it will likely be breezy to windy for Sat/Sun/Mon, at least in the afternoon.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 346 PM MDT Mon May 18 2026

VFR conditions are expected through the forecast period. Gusty N/NE winds remain in place for the Snake Plain/Teton Valley terminals and these will continue into the early evening before beginning to taper off, becoming more light and variable overnight and into Tuesday morning. KSUN will see more of a northwesterly wind component this afternoon and continuing into the evening. KBYI will see a more westerly wind component this afternoon and early evening and not nearly as breezy as the other locations. Not expecting any precip at terminals through the period with skies becoming more clear into Tuesday morning. By Tuesday afternoon overall light southwest winds return and Mid-level SCT to BKN clouds return.|

PIH WATCHES/WARNINGS/ADVISORIES

Frost Advisory from 3 AM to 9 AM MDT Tuesday for IDZ051-055. Freeze Warning from midnight tonight to 9 AM MDT Tuesday for IDZ052>054.