textproduct: Great Falls

KEY MESSAGES

- Scattered areas of light rain and snow continue through this afternoon, mostly over southwest Montana and along the Continental Divide.

- An active jet stream will bring breezy to windy conditions and periods of mountain snow this weekend.

- Colder temperatures and periods of light snow are expected heading into Thanksgiving.

DISCUSSION

- Meteorological Overview:

Meteorological Overview:

Patchy fog over the Milk River Valley area is slowly dissipating, but low stratus looks to stick around for much of the morning. A weak Pacific trough passes through the Northern Rockies today and will bring scattered areas of light rain and snow through this afternoon. Most of this activity will be focused over central/southwest MT and along the Continental Divide. H700 temperatures fall to the -5 to -10C range this morning, lowest over north-central MT. This should lower snow levels down to the plains and valleys, but accumulating snow should be minimal with negligible precipitation amounts. Todays high temperatures will cool closer to average in response to the frontal passage.

Weak ridging aloft will bring dry and mild conditions for the second half of the work week while the northern jet stream stays in Canada and a closed low slides down the California coast. The upper level jet sags southward into the Northern Rockies this weekend and brings periods breezy to windy conditions and some mountain snow. A northwesterly flow aloft develops and sends a series of colder troughs through the state heading into the Thanksgiving holiday. This looks to bring a period of strong, gusty winds followed by occasional mostly light snow and the coldest temperatures of the season so far. -RCG

- Forecast Confidence & Scenarios:

Forecast Confidence & Scenarios:

Scattered areas of light rain and snow today...

Colder west to northwesterly flow should lower snow levels to the valleys and plains, at least briefly. Accumulations, if any, will be minimal with probabilities for one inch of snow or more around 20% over the higher terrain of central and southwest MT, dropping to near zero for other areas.

Increasing winds and light mountain snow this weekend..

A tightening surface pressure gradient will bring an initial wave of windy conditions to the Rocky Mountain Front Friday into Saturday. Probabilities for 55 mph+ gusts increase to around 80% over the eastern foothills of the Rocky Mountain Front eastward to the Browning area. Despite a tightening surface pressure gradient, H700 winds will mostly be less than 50 kts and will have a northwesterly trajectory. This situation will continue to be monitored over the next day or so for increased winds due to mountain wave activity. Winds will also be on the increase in other areas throughout the weekend with many central and north- central locations seeing gusts in the 30 to 50 mph range. Mountain snow looks to be on the lighter side and mostly confined to the higher terrain of the Rocky Mountain Front.

Colder temperatures and some snow heading into Thanksgiving

Ensembles are still highlighting a strong trough and attendant cold front to surge through the Northern Rockies sometime Monday into Tuesday. The dynamics look supportive for a period of widespread strong, gusty winds and locally intense snow showers. The NBM probabilistic guidance hasn't really caught on to this with meager chances for 55 mph gusts less than 50% for nearly all locations, but the ECMWF Extreme Forecast Index and Shift of Tails is starting to catch onto the stronger winds. The timing of the front will play a significant role in whether the strongest 60 to 70 kt H700 winds transfer to the surface. This front will usher in a more active and colder pattern, though recent ensembles have decreased the amplitude of the troughs passing through the Northern Rockies. Overall, there's an expectation for the coldest temperatures of the season heading into Thanksgiving. - RCG

AVIATION

19/06Z TAF Period

VFR conditions will prevail across the KEKS, KHLN, and KCTB terminal. At KLWT, KGTF, and KBZN terminals there will be a brief period of MVFR level ceilings between about 19/14Z and 19/20Z. Fog is reducing visibility to a half mile or less intermittently at the KHVR terminal and is expected to continue doing so until 19/10Z. At the KBZN, KEKS, and KHLN terminals between now and 19/20Z there is a 10 - 30% chance for a rain/snow mix. During the majority of this TAF Period there will be periodic mountain obscuration across Southwestern Montana. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 43 26 53 33 / 20 0 0 0 CTB 45 22 50 30 / 10 0 0 0 HLN 43 27 49 28 / 20 0 0 0 BZN 48 24 50 24 / 30 0 0 0 WYS 43 24 45 18 / 30 20 10 0 DLN 47 27 47 24 / 10 10 0 0 HVR 44 19 46 26 / 20 0 0 0 LWT 42 24 53 29 / 20 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.