textproduct: Great Falls

KEY MESSAGES

- There is a chance for scattered showers and thunderstorms through the evening hours across Southwest Montana.

- Cooler and wetter conditions return Monday and Tuesday with a chance for lower elevation rain and light mountain snow.

- Warmer temperatures return starting Wednesday and lasting through the rest of the week.

DISCUSSION

- Meteorological Overview:

Dry northwesterly flow aloft will bring one more day of mild and generally dry condtions before a stronger trough and attendant cold front dive southward tonight into Monday. The primary concern will be dry and breezy conditions over the plains and isolated shower and thunder activity over southwest MT.

The cold front will cross the Canadian border this evening, clear much of central MT by dawn, and then move into the southwest Monday morning. Winds will shift northerly behind the front and showers and higher mountain snow will increase in a north to south fashion. Colder air aloft moves in on Monday and will support widely scattered rain, snow, and graupel showers at all elevations, especially over central/north-central MT. A secondary shortwave dives southward on Tuesday and drops H700/H500 temperatures as low as -15C/-30C over the eastern portions of the forecast area. This will reinforce the well below average temperatures and offer additional snow shower activity.

This system moves out by the mid-week period with northwesterly flow aloft returning for much of the remainder of the week. Overall, this will bring drier and milder conditions; however, weak troughs will periodically pass through and bring scattered shower and thunderstorm activity, especially on Thursday. Ensembles remain in agreement with a broader trough moving in next weekend for cooling temperatures and increased rain/mountain snow. Similar to some of the previous storms this spring, lesser defined and smaller scale forcing within this trough add forecast uncertainty in terms of precipitation amounts and timing. - RCG

- Forecast Confidence & Scenarios:

There is still a 20-30% chance for scattered thunderstorms across southwest Montana through the evening. Widespread moisture is not expected from these showers but there is a chance for some gusty winds and small hail (generally pea-sized) out of the stronger storms that develop.

With the approaching cold front, expect another round of scattered showers primarily across central and north-central Montana. Lower elevations will generally see rain during the day on Monday with a chance for mixed precipitation starting late Monday and lasting through Tuesday morning. Snowfall accumulations at lower elevations is generally expected to be minimal with less than half an inch possible at best. The main concern will be impacts to roadways which may become slushy and slippery at times, especially Tuesday morning.

Light mountain snow will be possible Monday through Tuesday with snowfall accumulations generally expected to remain less than an inch for pass level and below. Up to 2 inches is possible at the highest elevations but significant impacts outside of winter driving conditions along mountain passes are not expected.

Starting on Wednesday temperatures will quickly rebound back into the 60s to low 70s. This pattern of warmer temperatures is expected to persist through at least Friday as upper level ridging persists over the western CONUS. With northwesterly flow aloft there will be daily chances for isolated to scattered thunderstorms across the region. In general, the region will stay dry through the second half of the week except for localized areas of precipitation that hinge completely on where convective initiation occurs. There is a chance for more widespread precipitation this weekend as the next trough is expected to move through the region. But with the amount of model disagreement remaining there is not enough confidence to determine how widespread the precipitation will be at this time. -thor

AVIATION

03/18Z TAF Period

VFR conditions will prevail at all but the KGTF, KCTB, and KLWT terminals during this TAF Period. For the last 12 hours of this TAF Period there will be low ceilings at all but the KEKS, and KWYS terminals. At the KWYS terminal there is a 15 - 20% chance for rain showers between 03/20Z and 03/24Z. At the KHLN terminals there is a 15 - 25% chance for rain showers between 04/14Z and 04/17Z. At the KGTF and KLWT terminals there is a 10 - 30% chance for rain showers between 04/06Z and 04/17Z. At the KCTB and KHVR terminals between 04/03Z and 04/10Z there is a 10 - 30% chance for rain showers. There will be mountain obscuration across much of Southwestern, Central, and North-central Montana during the duration of this TAF Period. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 43 56 34 54 / 30 20 10 20 CTB 40 55 30 54 / 20 10 0 10 HLN 42 58 33 54 / 10 20 10 20 BZN 39 58 29 52 / 10 20 10 20 WYS 31 59 27 49 / 10 20 10 20 DLN 39 63 31 57 / 0 10 10 0 HVR 41 57 28 54 / 30 10 0 10 LWT 38 52 28 48 / 30 30 10 40

TFX WATCHES/WARNINGS/ADVISORIES

None.