textproduct: Great Falls

KEY MESSAGES

- Mild daytime and overnight temperatures will lead to rapid snowmelt across the plains today through Monday.

- Multiple periods of strong winds are expected this week with strongest winds likely late Monday through Monday night and again Tuesday night through Wednesday.

- A vigorous Pacific cold front on Wednesday may bring the strongest and most widespread period of wind along with the potential for locally intense snow showers.

DISCUSSION

- Meteorological Overview:

A mild Pacific airmass continues to overspread the region with shallow cold air mainly limited to areas below 3000ft along the Milk and Marias Rivers early this morning. Areas along the Milk River in Blaine county will likely be the latest to see the cold air erode by this afternoon. Flow over the upper level ridge compresses later today leading to increased mid-level westerly winds across the Rockies and this combined with surface troughing to the lee of the Rockies will support stronger winds developing today focused along the immediate east slopes of the Rocky Mtn Front where a High Wind Warning is in effect.

The pressure gradient across the Rockies relaxes some tonight with strong winds diminishing but overall mid-level flow continues to increase with breezy to locally windy conditions becoming more widespread across the rest of north-central MT. This sets the area up for relatively mild temperatures tonight, especially across the plains with even warmer temperatures across the area Monday. The first of two shortwaves tracks east along/north of the Canadian border Monday night, flattening the upper level ridge with a period of strong westerly midlevel flow developing across the region Monday and continuing through Wednesday with the passage of a stronger shortwave.

Strong winds initially redevelop Monday afternoon along the Rocky Mtn Front before spreading east across adjacent portions of north- central MT and peaking overnight Monday night as low pressure and the associated upper level wave track across AB/SK. Favorable conditions for mountain wave wind enhancement are expected late Monday/Monday night supporting the potential for strong winds further east to the I-15 corridor and east across Cascade and Judith Basin counties.

Wednesday still still holds the potential for a particularly widespread/higher end wind event for the area as mid-level flow increases to 60-80kts across much of the area with a fairly potent shortwave and associated Pacific cold front tracking across the region. Strong cooling aloft and afternoon timing of this wave would support deep mixing and transport of the stronger winds to the surface across much of the area while also bringing the potential for convective showers (changing to snow with the frontal passage). Expect more details to evolve this week.

Cooling behind the Wednesday system is brief with a colder airmass glancing portions of north-central MT Wednesday night. While cooler than early this week, temperatures look largely to remain above average into the weekend.

- Forecast Confidence & Scenarios:

Mild daytime and overnight temperatures will lead to rapid melting of the recent snow across eastern portions of north-central MT. With initially frozen ground, much of the snowmelt is likely to remain on the surface and may lead to standing water. While overall impact to creek/stream levels is low, most creeks are likely to be frozen with potential for water flow over the ice or potentially back up in some creek bottoms. Hoenisch

AVIATION

14/12Z TAF Period

VFR conditions prevail through the TAF period. Potential for mountain wave turbulence and instances of low level wind shear will develops later today and tonight as westerly flow aloft increases. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 49 39 55 43 / 0 0 0 0 CTB 44 32 50 35 / 0 0 0 10 HLN 48 30 53 39 / 0 0 0 20 BZN 53 27 54 37 / 0 0 0 0 WYS 43 13 39 24 / 0 0 0 10 DLN 53 29 52 37 / 0 0 0 0 HVR 39 29 47 32 / 0 0 10 0 LWT 47 34 50 36 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until 8 PM MST this evening for East Glacier Park Region-Northern High Plains.

High Wind Watch from Monday morning through Tuesday morning for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Eastern Toole and Liberty-Northern High Plains- Southern High Plains-Southern Rocky Mountain Front.

High Wind Watch from Monday afternoon through Tuesday morning for Cascade County below 5000ft-Judith Basin County and Judith Gap.