Area Forecast Discussion

KEY MESSAGES

- Rain will slowly end from west to east across Southwest and Central Montana through the overnight hours tonight.

- Drier and warmer weather pattern develops for the upcoming week.

DISCUSSION

/Issued 101 PM MDT Sat Sep 19 2026/

A vertically stacked mid-upper level low, centered over southern will slowly track east into Wyoming through tonight while gradually weakening. As the system continues eastward tonight, a few lingering showers remain possible across southwestern Montana into Sunday morning as moisture wraps around its backside. Clearing skies from the west overnight into Sunday morning may favor fog formation in southwestern Montana valleys. Upper-level ridging will then rebuild across Montana and the Northern Rockies by Sunday afternoon, returning predominantly sunny, warmer, and drier conditions to the area.

A dry weather pattern with above-normal temperatures is expected next week. Broad-scale ridging will attempt to build westward across the CONUS while troughing persists off the West Coast, maintaining upper-level heights above average under a southwesterly flow regime. High temperatures in the upper 70s to around 80 are anticipated, running roughly 10 degrees above early-autumn normals.

- Forecast Confidence & Scenarios:

Hi-Res Ensemble Forecast (HREF) guidance supports a 20-30% chance for reduced visibilities across Southwest and Central Montana where recent precipitation has fallen, which seems reasonable considering uncertainty with how fast skies clear tonight. Confidence is higher in fog development for areas west of the US Hwy 287 corridor where skies will clear well before sunrise on Sunday, with decreasing confidence east of this line. Where fog is able to develop there is the potential for locally dense fog given antecedent low level moisture and light winds. - Moldan

AVIATION

20/00Z TAF Period

Lingering showers and isolated thunderstorms will diminish over far southwest MT through 20/04Z, but light stratiform rain or rain showers may linger into the overnight hours over central/north- central areas east of I15. Once partial clearing begins to take place, areas of low stratus or fog will begin to develop over portions of central and southwest MT, most notably for areas of higher terrain/high valleys south of I90 between 20/09 and 20/18Z. KWYS will have the greatest categorical degradations, with less impact certainty (20% chance or less for visibility less than 1 mile) at KBZN, KEKS, and KHLN depending on how fast lower and mid- level clouds clear out tonight. - RCG

HYDROLOGY

The Flash Flood Watch and Flood Watch for portions of Southwest and Central Montana have been cancelled as precipitation rates have largely fallen below 0.1" per hour. While additional light rainfall will occur through the evening hours tonight the threat for flooding has diminished significantly. None-the-less, some areas that saw heavy rainfall from Friday evening/night through this morning may still see linger impacts like muddy roadways and ponding of water in low-lying areas. - Moldan

PRELIMINARY POINT TEMPS/POPS

TFX WATCHES / WARNINGS / ADVISORIES

None.