textproduct: Great Falls

KEY MESSAGES

- Showers and thunderstorms are expected each afternoon through Friday.

- Temperatures will gradually warm up through this weekend.

- It will be breezy across portions of North-central Montana for the 4th of July.

DISCUSSION

- Meteorological Overview:

This afternoon a weak upper-level shortwave ridge moves over North- central, Central, and Southwestern Montana. This will allow temperatures to warm up. Due to lingering instability there will be scattered showers and thunderstorms this afternoon and evening. However, due to limited wind shear, thunderstorms will stay on the weaker side and only produce lightning, heavy rain, and gusty winds. On Wednesday the weak upper-level ridge remains over North-central, Central, and Southwestern Montana. Wednesday afternoon an upper- level shortwave will move through and bring another round of showers and thunderstorms to most of the area Wednesday afternoon/evening. Due to increasing wind shear from the shortwave there will be isolated stronger thunderstorms that have the potential to produce some strong wind gusts. See the Forecast Confidence & Scenarios section for details.

On Thursday the upper-level ridge slides slightly to the east and gives North-central, Central, and Southwestern Montana southwest flow aloft. This will allow warm temperatures to continue with another day of showers and thunderstorms. On Friday the southwest flow transitions to more zonal (west to east) flow. This will keep temperatures status quo. Friday afternoon there will be isolated showers and thunderstorms. Saturday through Monday there will be zonal flow over North-central, Central, and Southwestern Montana. This keeps mostly dry weather with warm temperatures around for Saturday through Monday. On Saturday strong mid and low-level winds will bring windy conditions to portions of North- central Montana. -IG

- Forecast Confidence & Scenarios:

On Wednesday there is a 30 - 50% chance for thunderstorms across most of Southwestern, Central, and North-central Montana excluding Glacier County. On Wednesday the Storm Prediction Center has issued a Marginal Risk (5% chance for wind gusts of 58 mph or greater within 25 miles of a point) for most of North-central, Central, and Southwestern Montana excluding Glacier County. On Wednesday there is enough instability for severe thunderstorms but the limiting factor is wind shear. Some wind shear is being provided by an upper-level shortwave that is moving through. The timing of the shortwave will affect how much shear will be available to support severe thunderstorms. The most likely scenario is that there will be a few strong to severe thunderstorms that produce strong winds.

On Thursday there is a 15 - 30% chance for thunderstorms across most of Southwestern, Central, and North-central Montana excluding Glacier County. On Friday there is a 30 - 45% chance for thunderstorms across most of Southwestern, Central, and North- central Montana excluding Glacier County. On Thursday and Friday there is enough instability for strong thunderstorms but currently hi-res models have too low of wind shear to support strong thunderstorms. -IG

AVIATION

30/18Z TAF Period

Scattered showers and thunderstorms are possible through the afternoon but confidence in impacts to any one terminal remains on the lower side. VFR conditions are expected to prevail through the period but there may be some periods of mountain obscuration, especially around any showers and thunderstorms that develop. Generally calm conditions will continue through Wednesday morning with another chance for showers and thunderstorms possible in the afternoon. -thor

HYDROLOGY

A Flood Warning remains in effect for a portion of western Glacier County through this evening. Scattered showers/thunderstorms are expected over the next few days. Minor flooding is expected to linger at least through this evening. As a result the Flood Warnings have been extended through this evening. IG/Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 50 75 50 77 / 20 30 20 10 CTB 48 72 47 73 / 10 0 0 0 HLN 51 73 50 76 / 60 70 70 30 BZN 44 74 46 76 / 30 70 50 10 WYS 33 70 36 72 / 20 10 10 0 DLN 43 71 44 75 / 60 70 40 0 HVR 50 79 51 80 / 10 10 40 20 LWT 45 73 46 75 / 10 60 60 40

TFX WATCHES/WARNINGS/ADVISORIES

None.