textproduct: Great Falls

KEY MESSAGES

-Generally milder and drier conditions prevail for much of the workweek, but a weak front will bring slightly cooler temperatures on Wednesday.

-Patchy fog development will increase over the next couple of nights over the plains and southwest valleys.

-Passing weather systems will bring periods of breezy to windy conditions heading into the weekend and early next week.

DISCUSSION

- Meteorological Overview:

Ridging aloft looks to bring general mild and dry conditions for much of the upcoming workweek; however, there will be a weak frontal passage that brings a cooler low level easterly flow tonight into Wednesday. The effects of this will be mostly felt over the plains where there looks to be some nighttime and early morning patchy fog development and a slight cooldown. There will also be some patchy fog over some of the southwest valleys during this time, especially the colder high valleys along the MT/ID/WY borders. Otherwise, temperatures will mostly run a few degrees above average for most locations and there will be localized breeziness.

Strong westerly flow aloft becomes established over the Northern Rockies during the second half of the week. The first of a series of fast moving zonal shortwaves will bring an initial round of breezy to windy conditions Thursday into Friday. This will be followed by additional systems parading through the forecast area during the weekend. Ensembles are having some difficulty resolving the timing and strength of each system, but they do agree that the Rocky Mountain Front and plains will be the recipients of the strongest winds. With ridging generally remaining the most influential weather feature, despite the elevated westerly flow and shortwave passages, temperatures look to remain above average and precipitation will generally be spotty and confined to mountain areas. - RCG

- Forecast Confidence & Scenarios:

Patchy Fog Wednesday morning

Latest Hi-Res Ensemble Forecast (HREF) guidance supports a low, 10-30%, chance for visibilities to fall below one quarter of a mile along the Hi-Line from Cut Bank points east through Blaine County from midnight tonight through late Wednesday morning. The probabilities are highest in the Milk River Valley from Fresno Reservoir points northwest into southern Alberta. BUFKIT soundings for locations along the Hi-Line do support the potential for fog given very dry air just above the boundary layer and light winds within the boundary layer; however, current thinking is that fog will be patchy in nature, with the densest fog being located near local waterways (i.e. Milk River, Marias River, Fresno Reservoir, Lake Elwell). Given the expected patchy nature of the densest fog we are currently not anticipating the need for any Dense Fog Advisories, but will continue to monitor the situation. - Moldan

High Winds Possible at Times from Thursday Through the Weekend Uncertainty still exists with the timing of individual waves and where the core of strongest mid-level winds will be throughout the timeframe, with a significant spread in wind gusts between the ensemble members of the GFS (stronger) and ECMWF (weaker). With that being said, NBM probabilities continue to support the periods from Thursday evening through Friday evening and then from Sunday morning through Sunday evening for the potential of high winds, most notably along the Rocky Mountain Front.

AVIATION

3/18Z TAF Period

Excluding a few exceptions, VFR conditions will generally prevail for much of the TAF period. The low-level clouds at KWYS are expected to lift with ceilings around 5000ft by 18Z, allowing for the return of VFR conditions. The other concern will be patchy low- level clouds and or mist potentially developing after 04/04Z for KHLN, KWYS, KBZN, and KHVR, which could result in a period of MVFR/IFR conditions. Any low-level clouds and or mist are expected to clear or lift by 04/16Z.

PRELIMINARY POINT TEMPS/POPS

GTF 29 48 31 55 / 0 0 0 0 CTB 27 48 28 51 / 0 0 0 0 HLN 27 48 27 50 / 0 0 0 0 BZN 26 43 26 47 / 0 0 0 0 WYS 19 50 19 42 / 0 0 0 0 DLN 25 45 25 45 / 0 0 0 0 HVR 28 43 27 51 / 0 0 0 0 LWT 30 46 29 54 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.