textproduct: Great Falls

KEY MESSAGES

- Rain and cool temperatures will continue to affect North Central MT through Wednesday.

- It turns warmer for most areas by Thursday, but also expect a return of more thunderstorm activity.

DISCUSSION

- Meteorological Overview: A cut off upper level low is currently spinning over eastern MT. This cut off low will slowly drift northward into southern Canada by Wednesday. This means periods of rain/showers are likely to continue over North Central MT into Wed. The heaviest precipitation is likely to fall today, with the northern Rockies seeing the heaviest amounts. This upper level low is far enough north, that Southwest MT will have little/minor impacts from this system. Do expect afternoon temperatures to be quite a bit below normal through Wednesday over North Central MT, while seasonable temperatures can be expected over the Southwest after today.

The cut off upper level low should move out Wed, because the next upper level trof will approach the area from the Pacific Northwest by Thursday. There is a good chance for showers/thunderstorms with this trof, as a moist southwesterly flow aloft develops ahead of this system.

The flow aloft remain out of the southwest for the weekend, resulting in above normal temperatures for most areas on Saturday, but then falling a bit below normal on Sunday. Weak weather disturbances will move through the area Fri/Sat, allowing for a chance for storms, but a stronger upper level trof should move through on Sunday, resulting in a bit more widespread precipitation, along with cooler temperatures.

Next Monday, it tries to dry out/warm out as the CWA will be in between weather systems.

- Forecast Confidence & Scenarios: Another 0.50 to 1.25 inches of precipitation is expected over the northern Rockies today, generally around Glacier Park. Snow levels have lowered to around 6000 feet, but with the Going to the Sun Road still closed, and still a good snowpack on the ground at higher elevations, no winter weather advisory issued at this time. An SPS was issued though to highlight the snowfall potential.

Precipitable water remains fairly high on Thursday, up to an inch over portions of North Central MT, that some storms on Thu could produce heavy rainfall.

AVIATION

01/12Z TAF Period

North Central MT will have the higher impacts during this period, with widespread rain/mountain snow at times. Expect low ceilings throughout the period, along with mountains obscured.

For Southwest MT, it will not be as bad. Expect some clearing near the MT/ID border, with a few passing showers as you move northward towards Central MT. Some mountains/passes could be obscured at times, especially as you go north towards Central MT. Brusda

HYDROLOGY

At this time, no areal flooding is expected across the CWA. The main concern is the St. Mary River and Badger Creek. Both streams are just below flood stage. With snow falling in the mountains today, this should slow river rises a bit, even with the lower elevation rains. That being said, it is possible that a flood statement might be need later today, or even later this week, should the streams start to go above flood stage.

Note, impacts are minor on both streams if the rivers do go just above flood stage. It is not until the streams are a few feet above stage that impacts start to become more impactful. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 52 42 57 42 / 100 80 70 10 CTB 45 37 51 38 / 100 90 80 20 HLN 60 42 64 44 / 70 10 30 10 BZN 63 37 67 39 / 10 40 10 0 WYS 62 30 66 32 / 10 10 0 0 DLN 64 38 69 39 / 10 30 0 0 HVR 52 40 58 41 / 100 90 80 30 LWT 53 37 59 39 / 60 30 60 10

TFX WATCHES/WARNINGS/ADVISORIES

None.