textproduct: Great Falls

KEY MESSAGES

- It will be cold this afternoon through Tuesday morning.

- Isolated rain and snow showers will affect North-central, Central, and Southwestern Montana this afternoon through Friday with the heaviest and most widespread precipitation Wednesday through Thursday.

- It will gradually warm up Tuesday afternoon through the weekend.

DISCUSSION

- Meteorological Overview:

This afternoon an upper-level trough remains over North-central, Central, and Southwestern Montana. As a result rain/snow showers and cold temperatures (well-below) seasonal averages will linger across the area. This afternoon rain/snow showers will primarily be confined to the Continental Divide with a few isolated rain showers spreading eastward to the plains of North-central Montana. On Tuesday the upper-level trough remains over North-central, Central, and Southwestern Montana in the morning before northwest flow aloft moves over the area by the afternooon. This will keep cold temperatures across North-central, Central, and Southwestern Montana Tuesday morning before they gradually warm up by Tuesday afternoon. Tuesday afternoon there will be isolated lower-elevation rain showers and mountain snow showers due to the northwest flow aloft. Additionally there will be enough instability around in the afternoon that there is the potential for a few rumbles of thunder.

On Wednesday an upper-level trough, associated with a Canadian Cold Front, moves over North-central, Central, and Southwestern Montana. This will bring rain to lower-elevations and snow to mountain locations on Wednesday. On Wednesday temperatures will cool down to slightly below seasonal averages. Wednesday afternoon some instability will build and allow a few rumbles of thunder to occur across North-central, Central, and Southwestern Montana. On Thursday the upper-level trough remains over North-central, Central, and Southwestern Montana. This will allow cooler temperatures with widespread precipitation to linger over the area on Thursday. On Friday northwest flow aloft moves over North-central, Central, and Southwestern Montana. This will allow temperatures to warm up to near seasonal averages with isolated showers and thunderstorms Friday afternoon. On Saturday and Sunday an upper-level ridge/zonal flow builds in over North-central, Central, and Southwestern Montana. This will bring warm, mostly dry, and windy weather to the area for Memorial Day weekend. -IG

- Forecast Confidence & Scenarios:

On Tuesday morning there is a 30 - 70% chance for low temperatures of 28 degrees or colder across the lower-elevations of North- central, Central, and Southwestern Montana. On Tuesday there is a 20% chance for thunder across North-central Montana. On Wednesday there is a 15 - 30% chance for thunder across North-central, Central, and Southwestern Montana. On Wednesday along the Rocky Mountain Front there is greater than a 50 - 70% chance for a half inch of liquid precipitation. On Wednesday along the Highway 200 Corridor between Great Falls and Lewistown there is 25 - 40% chance for a half inch of liquid precipitation or greater. Elsewhere across North-central, Central, and Southwestern Montana there is a 10 - 40% chance for a quarter inch of liquid precipitation or greater on Wednesday. Wednesday through Thursday there is greater than a 50% chance for 2 inches of snow or greater across the mountains of North-central, Central, and Southwestern Montana. On Saturday and Sunday there is a 20 - 50% chance for wind gusts of 40 mph or greater. -IG

AVIATION

18/18Z TAF Period

Primary concern this TAF period will be for low-VFR or MVFR ceilings at times through the afternoon. Additionally, numerous showers look to develop this afternoon, mostly near terrain, which will be capable of brief cig/vis reductions and briefly gusty winds at terminals in close proximity to mountains. Mountains will be obscured at times through the evening where showers form.

Clouds begin to clear tonight, which paired light winds, will yield an opportunity for fog by Tuesday morning. Confidence in this fog developing at any specific terminal was too low to warrant mention in TAFs at this time, however. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 30 64 40 56 / 0 40 20 70 CTB 29 63 37 53 / 30 20 30 90 HLN 30 65 38 60 / 10 30 30 40 BZN 24 62 33 60 / 0 0 30 20 WYS 15 54 25 54 / 0 10 20 20 DLN 25 61 33 61 / 0 10 20 10 HVR 28 68 40 60 / 0 40 60 50 LWT 26 60 36 56 / 0 20 30 70

TFX WATCHES/WARNINGS/ADVISORIES

None.