textproduct: Great Falls

KEY MESSAGES

- Showers and thunderstorms develop late tonight and persist through Thursday afternoon.

- Temperatures warm above normal on Friday, but cool back below normal over the weekend.

- Gusty winds develop on Friday and Saturday over Southwest Montana.

DISCUSSION

- Meteorological Overview:

Transient ridging will slide over the Northern Rockies this evening and through the early morning hours on Thursday ahead of a fast, compact shortwave and attendant Pacific front, which will then move over/across Southwest through North Central Montana through the mid- morning and afternoon hours on Thursday. Clear to partly clear skies late this afternoon and early this evening combined with light winds and recent precipitation may support the development of fog in the Milk River Valley of North Central Montana and the high, fog prone valleys in Southwest and Central Montana. As the aforementioned ridge begins to slide east of the region late this evening and through the early morning hours on Thursday cloud cover and chances for precipitation will begin to increase from west to east, with precipitation chances peaking between sunrise and the early afternoon hours on Thursday. The highest chances for showers and thunderstorms over this timeframe will exist along and south of the Montana Hwy 200 corridor and north of the I-90 corridor, with generally a 20-50% chance for showers and storms elsewhere. While a stronger thunderstorm or two can't be ruled out on Saturday, most notably over Fergus and Judith Basin Counties, the overall early nature of the Pacific front and preluding clouding conditions will help to limit instability across the area. Another period of transient ridging looks to move over the Northern Rockies during the overnight hours of Thursday, with increasing southwesterly flow then settling in on Friday over Southwest through North Central Montana. High temperatures look to climb above normal on Friday thanks to the the southwest flow aloft, with gusty south to west surface winds developing during the afternoon hours. Overall dry conditions can be expected on Friday, but an isolated afternoon/evening thunderstorm can't be ruled out over the Bears Paw/Little Rocky Mountain areas. - Moldan

For Saturday afternoon into early next week...an unstable southwesterly flow will develop over the CWA. This will result in daily chances for showers and thunderstorms to move through the CWA. At this time, most of the severe storms should be to our east, but an isolated strong/severe storm is possible. Overall, temperatures will be a bit above normal most days, except on Sunday, when temperatures are likely to be a few degrees below normal.

- Forecast Confidence & Scenarios: With warm air moving in aloft today, the forecast models want to keep the CWA dry. However, with recent moisture, the airmass is likely to become a bit unstable with any heating over North Central MT, thus kept low pops in the forecast, especially for areas along the Highway 2 corridor from Shelby to Harlem.

There is the potential that a few strong storms could develop over the eastern portions of the CWA on Saturday, but they should quickly move off to the northeast. Brusda

- Forecast Confidence & Scenarios:

Gusty Winds on Saturday...

H700-500 south to southwest flow will increase over Southwest Montana through the day, with values reaching 1 to 2 standard deviations above normal by the afternoon and evening hours. Deep mixing during this timeframe will help to transport the strong winds to the surface, most notably along and southeast of a Dillon, to Ennis, to Bozeman line where ECMWF EFIs of 0.6 to 0.75 indicate the potential for a climatologically unusual wind events. NBM5.0 probabilities for wind gusts of 40 mph or greater are in excess of a 70% chance along and south of a Dillon, to Ennis, to Big Sky line, with a 20-50% chance for gusts to exceed 55 mph across these same areas. Wind gusts exceeding 55 mph are entirely possible beneath decaying showers and thunderstorms, most notably in the Dillon and Ennis Areas. - Moldan

Strong Thunderstorms on Saturday...

There is the potential that a few strong storms could develop over the eastern portions of the CWA on Saturday, but they should quickly move off to the northeast. Brusda

AVIATION

03/18Z TAF Period

VFR conditons will prevail at all but the KGTF and KHVR terminals during this TAF Period. At the KGTF and KHVR terminals there will be MVFR-level ceilings for a few hours at the beginning of this TAF Period. After 04/00Z rain will begin to affect terminals beginning in Southwestern Montana and spreading up to North-central Montana by 04/12Z. During the beginning and end of this TAF Period there will be instances of mountain obscuration primarily across North-central Montana. -IG

HYDROLOGY

The latest hydrographs show river levels decreasing over the southwestern portions of Glacier County. This includes the Two Medicine River and Badger Creek. Thus if no new reports of flooding are received this morning, it is likely the flood advisory for southwestern Glacier County will expire at Noon today, or even be cancelled early. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 48 70 42 78 / 40 50 10 0 CTB 45 71 41 73 / 20 20 0 0 HLN 52 72 42 80 / 40 30 0 0 BZN 45 71 39 80 / 30 40 0 0 WYS 37 67 33 72 / 10 20 20 0 DLN 45 72 40 80 / 20 20 0 0 HVR 42 72 45 78 / 10 60 20 0 LWT 43 66 40 77 / 50 70 20 0

TFX WATCHES/WARNINGS/ADVISORIES

None.