textproduct: Great Falls

KEY MESSAGES

- It will be windy across North-central, Central, and Southwestern Montana this afternoon through Friday.

- Severe thunderstorms will continue through this evening with wind gusts in excess of 60 mph.

- It will cool off through this weekend with showers and thunderstorms Friday through Sunday.

DISCUSSION

- Meteorological Overview:

This afternoon there is an an upper-level trough moving over North- central, Central, and Southwestern Montana. This will allow temperatures to cool down slightly with showers and thunderstorms across the area. Due to strong southerly flow aloft and strong low- level winds it will be windy across North-central, Central, and Southwestern Montana on Wednesday with the strongest winds along the Rocky Mountain Front and in north-south orientated valleys. On Thursday the upper-level trough remains over North-central, Central, and Southwestern Montana. This combined with strong southerly flow aloft and strong low-level winds will bring another day of windy conditions to the area. On Thursday it will be mostly dry.

On Friday a closed upper-level low is over Washington and Oregon with southwest flow over North-central, Central, and Southwestern Montana. This will allow temperatures to be around seasonal averages with another day of showers and thunderstorms and breezy conditions. On Saturday and Sunday the closed upper-level low remains over Washington and Oregon with southwest flow over North- central, Central, and Southwestern Montana. This will bring another day with about seasonal averages for temperatures and showers and thunderstorms around each day this weekend. -IG

- Forecast Confidence & Scenarios:

On Thursday there is a 40 - 60% chance for wind gusts of 45 mph or greater across Southwestern Montana. On Thursday there is a 30 - 60% chance for wind gusts of 35 mph or greater across North-central Montana. On Friday there is a 40 - 80% chance for wind gusts of 30 mph or greater across North-central, Central, and Southwestern Montana with the greatest probability in Southwestern Montana.

Today the Storm Prediction Center (SPC) issued a slight risk (15% chance for wind gusts of 58 mph or greater within 25 miles of a point) for severe thunderstorms for most of North-central Montana. Today the SPC issued a marginal risk (5% chance for wind gusts of 58 mph or greater within 25 miles of a point) across most of the rest of Central and Southwestern Montana. On Saturday there is a 15 - 30% chance for thunderstorms across Central and Southwestern Montana. On Sunday there is a 15 - 30% chance for thunderstorms across North-central, Central, and Southwestern Montana. -IG

Fire Weather: Medium Confidence (50%) in critical conditions on today and Thursday. Winds are the highest source of confidence, humidity is our lowest with values borderline. However, deep mixing advertised by the models does support values approaching critical values.

Extended Regime: Low Confidence (30%) in the overall changes in the upper-level pattern. Cut off lows are notoriously difficult to pin point in the long range as are the resulting impacts. -JR

AVIATION

02/18Z TAF Period

VFR conditions will prevail at all terminals during this TAF Period outside of during any thunderstorms. During the beginning of this TAF Period thunderstorms will affect the KHLN, KGTF, KCTB, and KHVR terminals. During any thunderstorms there will be gusty, erratic winds, lightning, and a brief heavy downpour. The heavy downpour could briefly cause mountain obscuration and a reduction in visibility to MVFR-levels. Isolated thunderstorms will produce wind gusts in excess of 50 kts. Isolated thunderstorms have a low chance to kick up enough dust to reduce visibility to MVFR-levels or lower. During the duration of this TAF Period there will be isolated instances of low-level wind shear. At the KEKS terminal for the first 9 hours of this TAF Period there will be sustained winds in excess of 30 kts. During this TAF Period smoke from wildfires will reduce slantwise visibility across all terminals. -IG

For KGTF: Winds will quickly pick up out of the south/southwest this afternoon. There is a 20% chance for exceeding a 15kt crosswind between 02/18Z and 02/21Z. Between 21Z and 23Z a line of thunderstorms will approach KGTF. The thunderstorms will produce wind gusts in excess of 50 kts with a low chance for a wind gust exceeding 60 kts. Additionally there is an expected wind shift with this line from a more south/southwest direction to the west behind the line of thunderstorms. Gusty winds will continue through at least 03/04Z before slowly tapering off as the night continues. The threat for crosswinds will be low but the headwinds may be above 15kts through at least 03/03Z. -thor/IG

PRELIMINARY POINT TEMPS/POPS

GTF 50 76 49 74 / 10 0 10 10 CTB 46 66 45 66 / 50 0 30 10 HLN 46 75 47 74 / 10 0 10 30 BZN 47 76 45 79 / 0 0 0 0 WYS 33 64 36 68 / 0 0 0 0 DLN 42 72 41 74 / 10 0 10 20 HVR 50 80 51 81 / 50 0 0 0 LWT 49 77 52 80 / 20 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until 9 PM MDT this evening for Madison River Valley.

High Wind Watch from 9 PM MDT this evening through Thursday evening for Madison River Valley.