textproduct: Great Falls

KEY MESSAGES

- Cold night tonight, with most, if not all locations dipping well into the 20s or colder.

- Temperatures trend closer to average after today.

- Intermittent stretches of showers and a few thunderstorms through the week.

DISCUSSION

- Meteorological Overview:

Cyclonic northerly to northwesterly flow aloft continues through the remainder of the afternoon and early evening, fostering showers and snow showers through sunset. Flow aloft trends more anticyclonic tonight, which will aid in clearing skies by daybreak Wednesday. Given the clearing skies and an already cool airmass in place, overnight lows tonight look to fall well into the 20s, and well into the teens or colder in cold prone locations. Some patchy fog cannot be ruled out tonight, particularly in areas that see more than a few hundreths of an inch of precipitation through the remainder of the day today.

Temperatures trend a bit warmer for Wednesday, but the cold start will limit the overall magnitude of warming in a few areas. A weak wave progressing through the northwesterly flow Wednesday night will result in showers and perhaps a thunderstorm or two, which linger through much of Thursday.

Another brief stretch of more benign weather early Friday quickly diminishes as another wave aloft moves through late Friday into Saturday. Uncertainty is higher with this system, largely related to magnitude and location of the upper wave. The main takeaway for Saturday will be for cooler temperatures with opportunities for precipitation through much of the day. Ensemble averages/cluster guidance favors ridging Sunday into the first half of next week, which would largely promote a warmer/drier stretch. -AM

- Forecast Confidence & Scenarios:

Cold temperatures tonight:

Only a few areas across the region have more than a 10% probability for a low temperature tonight that is warmer than 30 F. Additionally, a few areas will challenge record lows for the calendar day Wednesday. Protective measures may need to be taken for sensitive vegetation through the morning Wednesday. -AM

Precipitation Saturday:

Uncertainty related to the position and strength of the upper level system late Friday into Saturday is resulting in a large range of scenarios for any given location. 10th to 90th percentile precipitation amounts over the Golden Triangle are a trace to a half inch respectively, indicating lower confidence in specifics at this range. -AM

AVIATION

05/18Z TAF Period

VFR conditions will prevail at all terminals except for the KGTF and KCTB terminals during this TAF Period. For the first 6 hours of this TAF Period there will be low ceilings at all terminals (VFR for all but the KGTF and KCTB terminals). At the KLWT, KGTF, KHLN, KBZN, and KEKS terminals there is a 10 - 20% chance for rain/snow showers between now and 06/02Z. Any heavy snow/rain shower will briefly reduce visibility to MVFR-levels. There will be mountain obscuration across all of Southwestern, Central, and North-central Montana during first 6 hours of this TAF Period. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 25 70 48 66 / 10 0 30 70 CTB 22 69 45 67 / 10 0 20 40 HLN 26 68 48 70 / 20 0 20 60 BZN 21 64 41 69 / 10 0 20 60 WYS 15 55 32 62 / 10 0 20 60 DLN 22 65 42 70 / 10 0 10 10 HVR 21 67 40 72 / 10 0 10 40 LWT 21 60 41 62 / 10 0 20 80

TFX WATCHES/WARNINGS/ADVISORIES

None.