textproduct: Great Falls

KEY MESSAGES

- An early summer storm will affect the entire CWA over the next few days with a combination of thunderstorms and widespread rain.

- Below normal temperatures the next few days, before warmer air returns by the middle of next week.

- Daily chances for afternoon thunderstorms expected for the 2nd half of next week.

DISCUSSION

- Meteorological Overview: A summer storm will affect the CWA over the next few days, with a variety of different weather conditions. Expect showers/thunderstorms today, with the strongest storms likely over the eastern portions of the CWA. Large hail would be the main impact from any severe storms today. Afternoon temperatures will be below normal across the CWA today, with Southwest MT being the coolest area. Expect widespread precipitation to develop over Southwest MT this morning and spread northward into Central MT by evening. All of this precipitation is a result of a slow moving upper level low that will move from the Pacific Northwest, southeastward towards the West Yellowstone area. This upper level low will then swing northward Sun into Monday, slowly, resulting in a few days of widespread precipitation, especially over North Central MT. Much below normal temperatures are expected underneath this upper level low. For elevations above 6500 feet, the temperature will be cold enough for snow to fall, especially in Southwest MT. Thus the winter weather advisory will continue for the Southwest, with the mountains in Jefferson County added to the advisory area.

The precipitation will diminish on Tuesday, with a widespread rainfall of 1 to 3 inches for most areas, along with higher amounts on the east side of Glacier National Park.

For Wednesday through the 4th of July, expect a rather unstable southwesterly flow aloft pattern to set up over our CWA. An upper level low will be over the Pacific Northwest for all late next week, resulting in warmer air moving back into the CWA, but also for daily chances for showers/thunderstorms. Some storms could be on the strong side later next week as the airmass will remain unstable, especially during the late afternoon/evening hours.

- Forecast Confidence & Scenarios: A marginal risk for severe storms continues today over the eastern portions of the CWA. Large hail would be the main severe weather impact today.

A winter weather advisory continues for the mountain areas of Southwest MT, with a 3 to 6 inch snowfall likely for elevations above 6500 feet. Some ridge tops could exceed 8 inches, especially those ridge tops that are near/above 9000 feet.

A flood watch was issued for the Glacier Park region, as this area has the potential to get around 4 inches of rainfall. This rainfall, combined with high elevation snowmelt could result in some flooding issues on the east side of Glacier National Park by late Sunday or Monday. Additional flood statements might be needed for areas that receive over 3 inches of rainfall over the remainder of the CWA. Brusda

AVIATION

27/12Z TAF Period

Scattered showers and thunderstorms will affect the CWA throughout the period. Expect the precipitation to become more widespread over Central and Southwest MT by this evening. Some of the stronger storms could also produce small hail. Any morning fog should burn off by 15z today. Mountains/passes will be obscured at times across the CWA by clouds/precip. Brusda

HYDROLOGY

Periods of rain will affect the CWA from today through Monday. Widespread rainfall amounts of 1 to 3 inches are expected across the CWA over the next 3 days.

In the Glacier Park region, rainfall could be a bit heavier, possibly up to 4 inches. Additionally, with some high elevation snow still left, the combination of rainfall/snowmelt could lead to some flooding on the east side of Glacier National Park. Thus a flood watch has been issued for this region starting on Sunday.

Additional flood statement might be needed if rainfall amounts start to exceed 3 inches elsewhere across the CWA. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 70 48 57 45 / 50 90 90 90 CTB 69 48 61 47 / 30 70 80 100 HLN 66 46 54 45 / 90 90 100 90 BZN 63 41 54 39 / 90 80 80 80 WYS 55 32 49 29 / 90 90 70 70 DLN 59 38 52 37 / 100 90 70 90 HVR 75 50 66 47 / 30 80 80 80 LWT 66 44 56 41 / 90 80 80 70

TFX WATCHES/WARNINGS/ADVISORIES

Flood Watch from Sunday evening through Tuesday morning for East Glacier Park Region.

Winter Weather Advisory from 6 PM this evening to noon MDT Monday for Elkhorn and Boulder Mountains-Gallatin and Madison County Mountains and Centennial Mountains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains.