textproduct: Great Falls

KEY MESSAGES

- The beginning of the week will feature near normal high temperatures, with above normal temperatures pushing in Wednesday through Friday.

- Southwest flow will bring daily increased chances of precipitation during the afternoon hours Tuesday and Wednesday.

- Precipitation chances increase area wide towards the end of the work week with temperatures returning to near or slightly below normal.

DISCUSSION

- Meteorological Overview:

In the wake of Saturdays high wind event, a much calmer regime takes hold as upper-level ridging builds overhead. Generally calmer, light winds will take hold as near normal temperatures settle in across the area Sunday through Tuesday.

By midweek, split flow establishes over the western CONUS, leaving a cutoff low centered off the coast of California and allowing stronger ridging to expand westward across the northern Rockies and northern Plains. This pattern induces southwesterly flow aloft over Montana, driving a warming trend Wednesday through the end of the workweek. The southwesterly flow will also channel increased moisture into the area, resulting in the return of daily chances of afternoon showers largely focused across Southwest Montana Tuesday through Thursday.

Heading into next weekend, the cutoff low off the California coast begins to re-merge with the main jet stream thanks to a digging trough that originates from Alaska dips southward over the Pacific Northwest. Model consensus favors this feature transitioning into an open shortwave as it pushes east across the region. This progression will bring increased chances for more widespread precipitation alongside a drop in high temperature back down to near or slightly below seasonal averages. Winds through the entire forecast period are expected to remain generally light, with the exception of Wednesday which will see slightly breezier conditions as we advect warmer air in from the south/southeast.

-JR

-Forecast Confidence & Scenarios:

Confidence is high for light winds and near-normal temperatures through Tuesday under weak ridging, followed by above-normal temperatures Wednesday through Friday as the ridge axis expands further west. Confidence is also moderate to high for scattered, diurnally driven afternoon showers remaining largely confined to Southwest Montana Tuesday through Thursday.

Confidence is low regarding next weekends system due to divergence among both deterministic and ensemble guidance on how the cutoff low interacts with the broader jet:

-Scenario 1 (Open Progressive Shortwave - Favored): The cutoff low phases smoothly into the northern branch as an open wave, bringing a fairly quick round of more widespread precipitation and cooling temperatures back near or slightly below average.

-Scenario 2 (Slower/Deeper phasing): If the cutoff low lingers longer off the coast, or phases more aggressively with incoming norther-stream energy, precipitation timing could slow down, potentially prolonging moisture streaming from the southwest and bringing a sharper drop in temperatures once the eventual troughing pushes through.

-JR

AVIATION

18/06Z TAF Period

VFR conditions will prevail throughout the 1806/1906 TAF period, with periods of broken to scattered upper level cloudiness. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 60 38 71 41 / 0 0 0 0 CTB 57 32 61 36 / 0 0 0 0 HLN 62 34 67 38 / 0 0 0 0 BZN 60 31 66 34 / 0 0 0 0 WYS 57 23 59 25 / 0 0 0 0 DLN 60 32 63 34 / 0 0 0 0 HVR 62 35 66 36 / 0 0 0 0 LWT 58 35 71 40 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.