textproduct: Great Falls

KEY MESSAGES

- Periods of gusty north to northwest winds and a few snow showers are expected Tuesday and Wednesday with passing weather disturbances.

- A period of colder temperatures is likely late this week into early this weekend, but the risk for very cold temperatures and widespread snowfall has decreased.

DISCUSSION

- Meteorological Overview:

A break in between weather disturbances will provide dry and less windy conditions to the area today before the next series of fast moving shortwaves in northerly flow aloft move across the area Tuesday and Wednesday. The first of these shortwave disturbances moves through Tuesday morning, shifting surface winds back to north/northwest as a weak surface low moves off to the southeast and high pressure builds south in its wake. The second shortwave looks to clip eastern MT Wednesday morning, followed by a renewed push of surface high pressure while the main push of colder air with both of these system remains well east of the area. The main impact from both of these waves will be a period of gusty north to northwest surface winds, primarily affecting the north-central MT plains. Some increase in moisture and shallow instability will support scattered snow showers with the wave passing Tuesday morning. The further east trajectory of Wednesday's disturbance is less favorable for snow showers, though a few flurries are possible.

Models continue to trend toward troughing across Canada remaining more consolidated and further east later this week, decreasing the risk for significant cold and snow across the area later this week into the weekend. There is still reasonable consensus for a period of colder temperatures as the trough elongates some and a cold 1050MB surface high slides south into the N-central US Thursday and Friday. Moisture however looks to be fairly limited with a much lower risk for widespread snowfall. Hoenisch

- Forecast Confidence & Scenarios:

Like previous clipper type systems, areas near the island mountain ranges of north-central MT are favored for locally stronger wind gusts Tuesday and Wednesday. Portions of Liberty, Hill, Blaine and Fergus counties are likely (>60% probability) to see a few gusts in excess of 45 mph, but the risk for strong gusts in excess of 55 mph remains low (<20%) and fairly isolated in coverage.

Northerly flow and marginal stability will favor a period of more persistent snow showers in the vicinity of the Little Belts and Snowies Tuesday, mainly in the morning. Accumulating snowfall is primarily limited to the mountains, but snow showers and gusty north winds may bring briefly reduce visibility across a wider portion of north-central MT Tuesday morning, even where little or no accumulation is expected. Hoenisch

AVIATION

19/06Z TAF Period

Low VFR/MVFR clouds and mountain obscuration will slowly thin and dissipate through 19/12Z. There may also be some isolated instances of patchy fog in places where partial clearing is observed and winds remain light. Another shortwave approaches the forecast area and initially brings increased higher level cloudiness and westerly breezes over the plains on Monday. MVFR clouds, mountain obscuration, and stronger northwesterly surface winds move in shortly beyond this TAF period. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 43 27 36 19 / 0 10 40 0 CTB 41 24 33 15 / 0 10 10 0 HLN 39 24 37 17 / 0 0 30 0 BZN 37 19 35 12 / 0 0 20 0 WYS 28 4 27 1 / 0 0 10 0 DLN 39 21 37 14 / 0 0 0 0 HVR 34 21 31 12 / 0 20 20 0 LWT 41 22 33 14 / 0 10 50 10

TFX WATCHES/WARNINGS/ADVISORIES

None.