textproduct: Great Falls

KEY MESSAGES

- Warm and dry conditions will prevail throughout this work week.

- A cooler and wetter system is expected this weekend.

- There is the potential for snow levels to drop low enough for lower elevation snow Sunday and Monday.

DISCUSSION

- Meteorological Overview:

The ridge continues to flatten today, causing increased westerly flow aloft. These winds have been mixing down to the surface, causing breezy conditions, which are expected to dissipate this evening. Today will be the warmest day of the forecast period, with multiple locations seeing forecasted highs in the low to mid 80s. Tomorrow upper level ridging once again forms, with the axis of the ridge centered off to the west. This will cause northwesterly flow aloft, and continue to support warm and dry conditions through the rest of the work week.

Confidence is increasing in a pattern change beginning on Saturday, with a large upper level trough digging southwest from the Olympic Peninsula. This will bring in much colder air and increased moisture. The combination of the colder temperatures and increased moisture will create the possibility of snow. Subsequently, snow levels will decrease, and there is the potential for the snow to reach the lower elevations. However, there is still a great deal of uncertainty with this system and how the snowfall potential will play out. See the Forecast Confidence & Scenarios section for more details.

- Forecast Confidence & Scenarios:

Consistency between models regarding a pattern change have increased, therefore increasing confidence that colder temperatures and snowfall will occur. However, there is still a large amount of uncertainty in how cold it gets and how much snow falls. Models are still divided on the position and timing of the trough, which is where the main source of the uncertainty lies. As of the issuance of this AFD, there is now a 60-75% chance of 1" of snow across lower elevations and a 40-60% chance of 3" of snow across lower elevations. Currently, the models are showing Central MT receiving the most lower elevation snow. -Dzomba

AVIATION

05/18Z TAF Period.

VFR conditions will prevail through the 0518/0618 TAF period, with scattered to at times broken upper level cloudiness. Breezy and gusty southwest to west winds will persist through 00-03z Tuesday, with the strongest winds approaching 35kts occurring over the plains of Central and North Central Montana. Some mountain wave turbulence can't be ruled out in lee of the Continental Divide, especially between the KCTB and KGTF terminals through the evening hours tonight. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 50 80 46 73 / 0 0 0 0 CTB 44 75 42 68 / 0 0 0 0 HLN 48 80 44 77 / 0 0 0 0 BZN 47 78 43 75 / 0 0 0 0 WYS 37 74 34 73 / 0 0 0 0 DLN 46 79 42 77 / 0 0 0 0 HVR 46 76 42 72 / 0 0 0 0 LWT 51 77 46 73 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES