textproduct: Great Falls

KEY MESSAGES

- It will be windy Saturday through Sunday across North-central Montana with very strong winds spreading down to the I-90 Corridor on Sunday.

- Saturday and Sunday there will be light mountain snow.

- Sunday evening through Monday there will be light snow across North-central Montana.

- Next week there will be several rounds of precipitation with breezy conditions at times.

DISCUSSION

- Meteorological Overview:

On Saturday an upper-level ridge begins to move over North-central, Central, and Southwestern Montana. On Saturday it will be dry and warm across the lower-elevations. On Saturday there will be light snow across the mountains of North-central, Central, and Southwestern Montana. Due to an increasing pressure gradient on Saturday it will be windy across North-central Montana with the strongest winds along the Rocky Mountain Front. On Sunday the upper-level ridge begins to flatten out. This combined with strong low-level and upper-level winds and a strong pressure gradient will bring strong winds to North-central Montana down to the I-90 corridor with the strongest winds in North-central Montana. On Sunday there will be light snow along the Rocky Mountain Front and Gallatin and Madison ranges. Sunday evening an upper-level shortwave trough will move through the upper-level flow and bring precipitation to North-central, Central, and Southwestern Montana. The shortwave has the potential to stop the strong winds along the Hi-Line earlier than the rest of North- central, Central, and Southwestern Montana. On Sunday the strong winds will lead to blowing dust at times across portions of North- central Montana.

On Monday and Tuesday there will be upper-level zonal flow over North-central, Central, and Southwestern Montana. This will allow temperatures to cool off with precipitation across the area on Monday. On Wednesday an upper-level ridge briefly builds back in over the area. This will warm temperatures up with mostly dry weather. Wednesday night into Thursday an upper-level shortwave will move over North-central, Central, and Southwestern Montana. This will bring another round of precipitation to the mountains with warm temperatures for the lower-elevations on Thursday. Wednesday night into Thursday due to a strong surface pressure gradient and strong low-level and mid-level winds it will be windy across North-central, Central, and Southwestern Montana. On Friday there will be upper- level zonal flow over North-central, Central, and Southwestern Montana. This will allow temperatures to cool down with mostly dry weather for the lower-elevations with mountain snow. -IG

- Forecast Confidence & Scenarios:

On Saturday there is a 60 - 80% chance for wind gusts of 75 mph or greater along the Rocky Mountain Front. On Saturday across the rest of North-central Montana there is a 20 - 60% chance for wind gusts in excess of 55 mph. As a result across a High Wind Warning is in effect for the lower-elevations of Judith Basin County from Saturday morning through midnight Sunday. On Sunday there is a 70 - 90% chance for wind gusts of 75 mph or greater along the Rocky Mountain Front and plains west of I-15. As a result a High Wind Warning was issued for the Rocky Mountain Front and plains west of I-15 from 2 AM Saturday morning through midnight Sunday. On Sunday there is 40 - 80% chance for wind gusts in excess of 90 mph along the Rocky Mountain Front. On Sunday along the immediate eastern slopes of the Rocky Mountain Rocky Front there is a 50% chance for wind gusts in excess of 100 mph. On Sunday across the plains of North-central Montana down to the I-90 corridor there is a 50 - 80% chance for wind gusts of 55 mph or greater. As a result a High Wind Warning was issued for North-central Montana down to Helena from early Sunday morning to midnight Sunday. A High Wind Watch remains in effect from Helena down to the I-90 corridor from early Sunday morning to midnight on Sunday. See the Watches section below for details.

For snow Saturday through Sunday there is a 50 - 80% chance for 4 inches of snow or greater along the Northern Rocky Mountain Front. Since most of this snow will fall above pass-level no products are needed for it. For snow Sunday night through Monday there is a 30 - 60% chance for one inch of snow or greater along the Hi-Line. Across the mountains of North-central, Central, and Southwestern Montana there is a 30 - 60% chance for 2 inches of snow on Monday. From Tuesday through Thursday across the mountains of North-central, Central, and Southwestern Montana there is greater than a 50% chance for 6 inches of snow or greater. -IG

AVIATION

07/06Z TAF Period

Pacific moisture within increasing westerly flow aloft will lead to mountain obscuration and low-VFR CIGS throughout for much of the 0706/0806 TAF period. A stay rain and/snow shower can't be ruled out along and southwest of KHLN to KBZN line between 12-18z, which thereafter much of the precipitation will be confined to the Continental Divide. Surface winds will also be on the increase through the TAF period, especially over the plains of Central and North Central Montana beyond 09-15z Saturday. Instance of low level wind shear and mountain wave turbulence will increase over this timeframe, especially along the Rocky Mountain Front. - Moldan

FIRE WEATHER

There will be elevated fire weather concerns for grassland areas this weekend. Particularly for areas that received little to no precipitation yesterday and today. Strong winds, gusting over 60 mph at times, combined with high temperatures in the upper 50s and 60s and minimum relative humidity values in the 20s and 30s may make it difficult to contain any existing or new fire starts. The worst conditions look to occur on Sunday when the winds will be strongest and most widespread. - RCG/IG

PRELIMINARY POINT TEMPS/POPS

GTF 49 33 59 47 / 40 0 10 10 CTB 45 32 55 43 / 0 0 10 0 HLN 46 30 55 39 / 10 10 30 10 BZN 43 23 52 33 / 30 0 20 10 WYS 37 12 36 27 / 20 0 60 30 DLN 42 24 51 32 / 10 0 20 0 HVR 51 30 63 41 / 10 0 10 10 LWT 43 27 55 39 / 20 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until midnight MST Sunday night for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains-Southern High Plains-Southern Rocky Mountain Front.

High Wind Warning from 3 AM Sunday to midnight MST Sunday night for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Fergus County below 4500ft-Gates of the Mountains-Helena Valley-Hill County-Little Belt and Highwood Mountains-Northern Blaine County-Snowy and Judith Mountains-Upper Blackfoot and MacDonald Pass-Western and Central Chouteau County.

High Wind Watch from late Saturday night through Sunday evening for Big Belt, Bridger and Castle Mountains-Canyon Ferry Area- Elkhorn and Boulder Mountains-Gallatin Valley-Meagher County Valleys-Missouri Headwaters.

High Wind Warning from 8 AM Saturday to midnight MST Sunday night for Judith Basin County and Judith Gap.