textproduct: Great Falls

KEY MESSAGES

- Daily rounds of scattered showers and thunderstorms continue through at least Friday, most widespread this afternoon and evening.

- Drier, warmer, and breezy to windy conditions move in for the holiday weekend.

- Temperatures warm further heading into early next week, although shower and thunderstorm activity looks to ramp up.

DISCUSSION

- Meteorological Overview:

An initial wave of showers and thunderstorms moving through central MT this morning will slowly diminish and end around dawn. There is also some lingering smoke and haze from Canadian wildfires that will be clearing out this morning as the general flow aloft becomes west and eventually southwesterly. A shortwave will move through this increasingly unstable southwesterly flow and bring scattered to numerous showers and thunderstorms this afternoon and evening. ML CAPE values will be running roughly between 600 and 1100 J/kg over southwest MT and central/north- central areas east of I15/highway 87. The combination of this instability with bulk shear running above 30 kts will be sufficient to produce a few strong to severe storms in these areas with strong, gusty winds, hail, and heavy downpours being the primary hazards in addition to cloud to ground lightning.

Similar conditions prevail on Thursday and Friday with widely scattered showers and thunderstorms, but there will be a lack of a defined shortwave and shear on Thursday and on Friday the shortwave positioning looks to be a little too far east for widespread activity. Flat ridging starts to build in and bring warmer temperatures and drier conditions for the holiday weekend; however, a mid-level trough passing north of the Canadian border looks strengthen the westerly flow aloft and combine with deep layer mixing for breezy to windy conditions. Saturday, Independence Day, will be the windiest day with the highest probabilities for 40 mph wind gusts or higher along the Rocky Mountain Front. The greatest impacts from the winds will be for holiday related activities and for outdoor recreation. Recent rainfall and surface greening should preclude fire weather concerns despite the low afternoon humidities.

Mid-level heights continue to rise and bring summerlike temperatures early next week. The only caveat will be a southwesterly flow aloft developing again in response to a trough moving onto the PAcific NW coast. Shortwaves look to interact with building instability for increased shower and thunderstorm activity next Monday and Tuesday. The ECMWF Extreme Forecast Index (EFI) is already beginning to highlight unusually high CAPE and shear availability for strong to severe storms for these days should this pattern come to fruition. - RCG

AVIATION

01/06Z TAF Period

A few scattered showers/thunderstorms will affect the CWA before 12z Wed. A short break in the precip will occur on Wed morning, before another round of showers/thunderstorms affects Southwest and Central MT on Wed afternoon/evening. Some storms could produce gusty winds on Wed afternoon. Smoke from distant fires is now affecting much of the CWA for distant visibility. Distant visibility is now less than 20 miles in some areas. Expect distant visibility to be affected across the CWA by clouds/precip/smoke through the period. Brusda

HYDROLOGY

Ongoing flooding continues to be reported along Swift Creek in the Many Glacier area, so the Flood Warning for that area was extended through 430 pm MDT Wednesday. All other flood products were lifted per receding waters and no significant rains expected in the near term. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 75 51 77 52 / 30 30 0 10 CTB 72 48 73 48 / 20 20 0 0 HLN 73 50 76 51 / 70 60 30 10 BZN 74 46 76 48 / 70 40 10 20 WYS 70 37 72 39 / 10 20 10 0 DLN 71 44 75 46 / 70 40 10 10 HVR 79 53 80 52 / 20 40 10 10 LWT 74 47 74 48 / 50 60 40 10

TFX WATCHES/WARNINGS/ADVISORIES

None.