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

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

19/18Z TAF Period

Rain will continue to drift east across southwest MT through most of the TAF period. MVFR conditions are likely across terminals KWYS, KEKS, and KLWT with low ceilings being the primary risk as the showers shift eastward. Across Central and Northern MT, VFR conditions will prevail through the TAF period as cloud bases will remain above the minimums, though a spot shower cannot be ruled out especially for terminals KGTF and KHVR. As we move into the overnight hours, uncertainty is high on lingering cloud cover as the storm system exits east. Terminals KWYS, KBZN, and KEKS are of highest uncertainty as earlier departure of cloud cover could allow decreased visibility from fog particularly between 20/08z and 20/15z. Overall, cloud decks will improve towards the end of the TAF period moving from east to west giving way to VFR conditions. -JR

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