textproduct: Great Falls

KEY MESSAGES

- It will be windy across North-central, Central, and Southwestern Montana this afternoon with isolated showers and thunderstorms.

- Widespread showers and isolated thunderstorms will affect North-central, Central, and Southwestern Montana Sunday through early next week.

- It will cool off this weekend though early next week.

DISCUSSION

- Meteorological Overview:

This afternoon an upper-level closed low is over Washington and Oregon with southerly flow over North-central, Central, and Southwestern Montana. This will bring breezy winds to the area with the strongest winds in north-south orientated valleys in Southwestern Montana. There will be isolated showers and thunderstorms primarily confined along the Continental Divide this afternoon/evening. Some of these showers and thunderstorms could make it as far the I-15 corridor by this evening. It will be around seasonal averages today. On Saturday the upper-level closed low remains over Washington and Oregon with southerly flow aloft. It will remain warm and breezy on Saturday with showers and thunderstorms primarily confined to the continental divide.

On Sunday the upper-level closed low remains over Washington and Oregon with southerly flow aloft. As the upper-level low weakens and begins to slide east a shortwave moves through the upper-level trough. This will bring showers and thunderstorms to North-central Montana with stronger thunderstorms expected in Blaine and Fergus County. See the Forecast Confidence & Scenarios Section for details. On Monday the upper-level trough moves over North- central, Central, and Southwestern Montana. This will bring cooler temperatures and widespread showers and thunderstorms to the area on Monday. On Tuesday the upper-level trough begins to exit North-central, Central, and Southwestern Montana. This will allow temperatures to gradually warm up but remain below seasonal averages across the area. Rain showers will linger through the day on Tuesday. On Wednesday and Thursday an upper-level ridge builds back in over North-central, Central, and Southwestern Montana. This will allow temperatures to warm up with mostly dry weather. -IG

- Forecast Confidence & Scenarios:

On Sunday there is a 30 - 40% chance for thunderstorms along and east of a Cut Bank to Great Falls line. For Sunday the Storm Prediction Center has issued a marginal risk (5% chance for 58 mph wind gusts or greater and/or a 5% chance for hail 1 inch in diameter or greater) for severe thunderstorms northeast of a Cut Bank to Great Falls to Judith Gap line. On Monday there is a 25 - 40% chance for thunderstorms across North-central, Central, and Southwestern Montana.

From 6 am Sunday through 6 am Tuesday there is greater than a 60% chance for 2 inches of rain or greater along the Hi-Line. From 6 am Sunday through 6 am Tuesday there is a 60 - 80% chance for 1 inch of rainfall or greater across North-central Montana. From 6 am Sunday through 6 am Tuesday there is a 30 - 60% chance for half an inch of rain or greater across Central and Southwestern Montana. Deterministic models are still flip-floping with respect to where the heaviest precipitation amounts will be. -IG

AVIATION

04/18Z TAF Period

VFR conditions will prevail throughout this TAF period for most terminals. KCTB is the exception, as light showers beginning around 02Z and continuing through the TAF period will lower ceilings to MVFR conditions by around 14Z. KHLN and KGTF will see chances for showers this afternoon into the evening. There is a small, but non-zero, chance that KGTF will see some weak thunderstorms between 22Z and 04Z.

For KGTF: VFR conditions will prevail throughout this TAF period, with MVFR conditions possible due to a passing thunderstorm. There is a small, but non-zero, chance of weak thunderstorm development between 22Z and 04Z. Winds will become light and variable by around 05Z. Outside of any thunderstorm that develops, there is a less than 10% chance of a cross-wind exceeding 15 kts. -Dzomba

PRELIMINARY POINT TEMPS/POPS

GTF 49 75 50 75 / 40 10 30 10 CTB 46 67 48 64 / 70 70 70 70 HLN 49 77 49 78 / 20 20 30 10 BZN 46 81 46 82 / 0 0 0 0 WYS 39 72 38 75 / 0 0 0 0 DLN 45 79 44 81 / 10 0 0 0 HVR 50 81 55 80 / 0 10 30 60 LWT 48 78 50 78 / 0 0 10 30

TFX WATCHES/WARNINGS/ADVISORIES

None.