textproduct: Great Falls

KEY MESSAGES

- Tranquil weather today with mostly sunny skies and near to above average temperatures. - A cold front pushes through the area on Saturday, bringing showers and thunderstorms, some of which may bring some heavy rainfall. - Closer to average to start next week, but afternoon showers and thunderstorms will remain common. - Potential warm spell later next week.

DISCUSSION

- Meteorological Overview:

Today will be a noticeably drier day across North Central and Southwestern Montana today as a weak upper level ridge slides overhead. Satellite is showing some mid and upper level clouds across Southwestern Montana early this afternoon, which will gradually slide northward and thicken as the afternoon progresses into the evening. While these clouds will filter the sunlight a bit, they wont produce any precipitation as they lift through the area.

A cold front will push through the area tomorrow, bringing with it a round of showers and thunderstorms as it pushes through the area. With this forcing mechanism in place, along with some better atmospheric dynamics and more moisture, the showers and storms could be a bit more organized and stronger. Right now, it seems that the largest concern will be some heavy rainfall from the storms, though some gusty winds and hail will also be possible.

As we head into next week, northwesterly flow aloft will keep our temperatures near average with a few pop up afternoon showers and thunderstorms, particularly Sunday and Monday. Upper level ridging will nudge back into the area Tuesday and Wednesday as the summertime ridge begins to build into the Western US, though there will still be a few opportunities for weak systems to ride on the north side of the ridge and bring us some more showers and storms through the second half of the week. Even with these systems, temperatures look to begin to nudge warmer, with well above average temperatures possible Thursday and Friday.

- Forecast Confidence & Scenarios:

Saturday Thunderstorms: A cold front moving through the northwestern US on Saturday will bring a round of showers and thunderstorms to the area as it pushes through. While a widespread severe outbreak is not expected at this time, the presence of a forcing mechanism (the front), modest instability, and modest shear profiles indicate there is some potential for the storms to be a bit better organized than storms we have had recently. Given this, I cant rule out the possibility of a stronger storm or two that would be able to produce some sub-severe wind or hail (58 mph gusts or 1 inch diameter hail) ahead of the front. The larger concern, however, will be the possibility of some heavier, torrential downpours with a few of the thunderstorms. Burn scars, such as the Horse Gulch, will be the main concern, but some ponding in low lying areas is also possible.

Warmth next week: There seems to be decent agreement in the synoptic models that our upper level ridge will become notably stronger than average late next week. Looking at the WPC Cluster Analysis tool, we can see that, at least for Thursday, around 75% of the ensemble members (this tool looks at the Canadian, GFS, and ECMWF ensemble members) are showing above average 500 mb heights, which generally lead to warmer than average temperatures under the higher heights. An approaching upper level low makes things a little less certain for next Friday, as the percent of models forecasting a general ridge pattern drops to around 60% of the ensemble space, with the other 40% showing our area starting to possibly cool down as the upper level system moves ashore the North American continent. Of course, the exact position/timing/strength of this system are yet to be resolved, so there is lots that can change over the coming days. Ludwig

AVIATION

19/18Z TAF Period

Generally quiet weather conditions expected over the CWA through 12z Sat, other than some passing mid/high level clouds. Showers/thunderstorms develop over Southwest MT on Sat morning, then move northeastward towards Central MT on Sat afternoon. Mountains/passes could become obscured after 15z by clouds/precip. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 46 81 50 72 / 0 10 20 20 CTB 44 80 46 65 / 0 10 10 50 HLN 49 82 51 77 / 0 30 20 0 BZN 46 76 47 77 / 0 60 60 10 WYS 42 70 39 69 / 0 80 80 40 DLN 48 74 45 77 / 0 80 70 0 HVR 48 82 50 73 / 0 10 40 10 LWT 44 77 47 69 / 0 30 40 10

TFX WATCHES/WARNINGS/ADVISORIES

None.