Marine Weather and Tide Forecast for South Hills, MT

DISCUSSION
/Issued 342 AM MDT Wed Apr 30 2025/

- Meteorological Overview:

Today through tonight...Moist, northwest flow in wake of an overnight shortwave will help to support showers across Southwest through North Central Montana through the late afternoon to evening hours, with highest areal coverage of showers being focused over the mountains in in northerly upslope areas. Additional precipitation amounts beneath any given shower will generally be light and less than 0.05"; however, a few of the stronger showers could produce localized amounts of 0.10" to nearly 0.25"

Thursday through Friday...A strong upper level ridge will build in over the Northern Rockies through the end of the work week. This upper level ridge will bring well above normal temperatures, with high temperatures by Friday of 10 to nearly 25 degrees above normal, and dry conditions to all locations.

Saturday through next Tuesday..Longwave troughing off of the Eastern Pacific will begin to dig towards the Great Basin and Desert Southwest through the weekend, with the upper level ridge axis sliding east of the Northern Rockies through the day on Saturday as southerly flow develops over Southwest through North Central Montana. Strong warm air advection within this southerly flow ahead of this longwave trough on Saturday will once again help to push high temperatures well above normal, with lower elevations peaking in the mid-70s to mid-80s. Increasing moisture within the southerly flow aloft will also bring a return chance for showers and thunderstorms on Saturday to most locations. Temperatures "cool" slightly through the second half of the weekend and first half of the upcoming work week as the longwave trough moves across the Western CONUS, with daily chances for precipitation. Precipitation chances, at this time, from Sunday through Tuesday will be highest along and south of the Montana Hwy 200 corridor - Moldan

- Forecast Confidence & Scenarios:

Climate anomaly indicators like the NAEFS and ECMWF EFIs continue to favor well above (10 to nearly 25 degrees) normal temperatures beneath an anomalously strong (for early May) upper level ridge on Friday and Saturday. Low (H850) to mid (H700)-level temperatures in the NAEFS continue to run 1 to 2 standard deviations above normal on both of these days over Southwest through North Central Montana, with temperatures at these levels approaching the 97.5thPct over the plains of North Central Montana. ECMWF EFI values of largely 0.5 to 0.8 support the idea that temperatures will be unusually warm over the timeframe, but from a climatological perspective not extreme outside of localized areas. Two localized areas that could see record high temperatures would be Cut Bank and Bozeman, mainly due to the fact that their record highs are "only" in the low 80s while most other locations are in the mid-80s to low 90s.

The following table indicates the probability of breaking the current record high temperature (listed after the probability value)
for each respective day.

LOCATION Friday Saturday Cut Bank 15% breaking 83 degrees | 93% breaking 81 degrees Havre 0% breaking 88 degrees | 1% breaking 90 degrees Great Falls 0% breaking 86 degrees | 7% breaking 86 degrees Lewistown 0% breaking 86 degrees | 1% breaking 82 degrees Helena 0% breaking 86 degrees | 19% breaking 84 degrees Bozeman 0% breaking 84 degrees | 80% breaking 80 degrees Dillon 0% breaking 85 degrees | 0% breaking 84 degrees

AVIATION
30/12Z TAF Period

The initial concern this TAF period will be for spotty low ceilings (Including mountain obscuration) and showers this morning. As daytime heating ensues and mixing occurs, ceilings will rise through the morning. This mixing will introduce opportunities for showers and perhaps a few thunderstorms as early as late morning, lasting into the late afternoon. Thereafter skies trend clearer heading into tonight. Areas that see precipitation later today will be candidates for patchy fog toward Thursday morning. -AM

Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information.

HYDROLOGY

Models are in good agreement that a strong upper level ridge will build across the Northwestern CONUS, which will result in some of the warmest weather so far this year across North Central and Southwestern Montana. Rivers will likely rise in response, as this will result in widespread melting of snowpack in the higher elevations. With that said, rivers still have plenty of capacity left to take on some additional snowmelt, so no major impacts are expected to arise as a direct result of the warmer temperatures at this time. - Ludwig

PRELIMINARY POINT TEMPS/POPS
GTF 59 35 66 39 / 50 20 10 0 CTB 58 34 66 34 / 30 10 10 0 HLN 59 36 68 38 / 50 20 0 0 BZN 55 31 63 31 / 50 20 10 0 WYS 51 22 58 21 / 40 20 10 0 DLN 56 29 63 33 / 30 20 0 0 HVR 61 36 67 34 / 60 20 10 0 LWT 52 34 60 34 / 70 30 10 0

TFX WATCHES/WARNINGS/ADVISORIES
None.