textproduct: Great Falls

KEY MESSAGES

- Well above normal to potentially record setting high temperatures are expected through the work week, with the hottest day occurring on Wednesday.

- Elevated Fire Weather conditions will exist on Monday for portions of Blaine and Fergus Counties, and for most of Southwest, Central, and North Central Montana on Wednesday.

- Showers and thunderstorms return for the second half of the work week.

UPDATE

No major updates were made to the forecast. A cold front pass overnight into Monday morning will bring low end chances for isolated showers across North-Central MT. Though, any precipitation that makes it to the ground will be light. -Wilson

DISCUSSION

/Issued 544 PM MDT Sun May 10 2026/

- Meteorological Overview:

Transient ridging over the Northern Rockies today will flatten through the overnight hours tonight as a fast moving shortwave begins to move from the Pacific Northwest this evening and over the region through Monday morning. At the surface a dry cold front will begin to advance southeast from Canada and across North Central through Southwest Montana from the late morning through early afternoon hours, with the primary impact from this front being a wind shift to the northwest and a period of breezy and gusty winds through the remainder of the daylight hours. High temperatures on Monday will be slightly cooler than that of Sunday, but still well above normal and in the 70s. Upper level ridging looks to build back in over the Northern Rockies on Tuesday, with temperatures rebounding 5 to 10 degrees and overall dry conditions persisting across Southwest through North Central Montana. - Moldan

As we head into Wednesday, a trough begins to work its way onshore the Western U.S. There is still model inconsistency in the exact timing and evolution of this trough moving across the region. However, models suggest that daily chances for precipitation returns Wednesday through the weekend. This model consistency affects the strength and timing of convection and winds. This trough will help cool temperatures down for the second half of the week, though temperatures will remain above normal. - Wilson

- Forecast Confidence & Scenarios:

Hot Temperatures on Wednesday...

Climate anomaly indicators such as the ECMWF EFIs and NAEFS support the potential for a climatologically unusual to very unusual day with respect to high temperatures, with numerous sites potentially setting records for May 13th. While the first day for high temperatures of 80 degrees generally occurs during the second and third weeks of May the fact that high temperatures could exceed 90 degrees is quite impressive considering that these temperatures do not typically occur until mid-June to late June. The primary limiting factor to these unusually warm temperatures from reaching their true potential will be upper level cloud cover.

The table below list the NBM5.0 probabilities for exceeding 85, 90, and 95 degrees (respectively) for select locations across North Central, Central, and Southwest Montana.

Probability of Maximum Temperatures Exceeding LOCATION 85 Degrees | 90 Degrees | 95 Degrees Browning 50% | <5% | 0% Cut Bank 90% | 40% | 5% Havre 95% | 85% | 40% Great Falls 95% | 85% | 25% Lewistown 90% | 20% | 0% Helena 95% | 70% | 10% White Sulphur Springs 90% | 5% | 0% Bozeman 90% | 40% | <5% Dillon 90% | 35% | <5% Ennis 95% | 35% | <5% West Yellowstone 40% | 0% | 20

-Moldan

Showers and Thunderstorms Returning Wednesday:

Although there remains inconsistencies in timing and evolutions of this trough returning mid week, ensembles agree that increasing southwest flow Wednesday will develop showers and thunderstorms to the region. CAPE varies from 500 to 1,500 j/kg with models. However, with deep inverted V soundings from a very dry surface layer will bring strong winds as the primary threat. Models also hint at strong synoptic winds increasing with the trough as well Thursday/Friday. Strength of the mid-level jet varies run to run, and the timing of the trough will also ultimately determine the strength and impact of these winds. - Wilson

AVIATION

11/00Z TAF Period

VFR conditions prevail this TAF period. Diurnal winds diminish around sunset ahead of a cold front Monday morning. Behind the front winds become gusty out of the west to northwest over the plains. An isolated shower is possible across the Hi-Line but there was not enough confidence to include it in the TAF. -AM/thor

FIRE WEATHER

Well above, to record or near record, high temperatures are expected across the Northern Rockies for the better part of the work week, with an increasing likelihood of record high temperatures being set across most of Southwest through North Central Montana on Wednesday as temperatures soar into the upper 80s to low 90s. Low afternoon relative humidity values will be observed each day with readings of between 15% to 25%, with dry conditions expected through Wednesday afternoon before showers and thunderstorms make a return for the second half of the work week. Breezy and gusty northwest winds will develop in wake of a cold front diving south from Canada on Monday, with gusts of between 35 to 45 mph occurring along and east of a Chinook, to Winifred, to Lewistown line. Elevated fire weather conditions will exist across eastern portions of Fire Weather Zones 113 and 115 due to the above normal temperatures, gusty northwest winds, and low relative humidity values; however, widespread critical fire weather conditions are not presently supported via the Hot-Dry-Windy Index (HDWI) on Monday as GEFS members remain largely in the 50-75Pct range. By Wednesday increasing south to west surface winds will push temperatures into the upper 80s to low 90s across all of Southwest through North Central Montana, with the strongest winds occurring along and south of the I-90 corridor in Southwest Montana and west of the I-15 corridor across Central and North Central Montana. Multiple GEFS members within the HDWI on Wednesday climb to between the 90-95Pct, with ERC values forecasted to climb to within the 80Pct of climatology. A Fire Weather Watch may be warranted on Wednesday for lower elevations, but for now we will holdoff given wind speeds and/or gusts will largely be marginally critical outside of shower/thunderstorm activity. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 52 75 40 78 / 10 0 0 0 CTB 49 69 36 76 / 10 0 10 0 HLN 49 77 39 81 / 10 0 0 0 BZN 46 78 36 80 / 0 0 0 0 WYS 38 75 33 80 / 0 20 20 0 DLN 46 79 37 85 / 0 0 0 0 HVR 52 74 34 78 / 30 10 0 0 LWT 48 72 36 73 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES