Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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661 FXUS65 KTFX 192011 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 211 PM MDT Sun May 19 2024 .SYNOPSIS... Showers, thunderstorms, small hail and snow will all decrease over the area tonight, as drier air moves in for a few hours. However, expect showers and thunderstorms to redevelop over Southwest MT on Monday, with the showers becoming more widespread on Tuesday. A spring storm will affect much of the area Wed and Thu, with periods of heavy rain and mountain snow expected. Generally, below normal temperatures are expected for most areas this week. && .DISCUSSION... Tonight through Tuesday...Expect a variety of weather conditions over the CWA tonight, with rain, snow, thunderstorms and small hail all diminishing this evening, as the main upper level trof moves off to our east. No significant impacts are expected from the weather this evening. Most snow or small hail accumulations will only occur on grassy areas. Much of the area starts out dry tomorrow morning, but a slow moving upper level disturbance moves into Southwest MT by mid day, producing scattered showers/thunderstorms by late morning and then continuing into Tuesday. Again, this thunderstorm activity is expected to be on the light side for most storms. Afternoon temperatures will warm up a bit for Monday and Tuesday, with near normal afternoon temperatures expected on Tuesday. Wednesday into Friday...A spring storm is expected to affect much of the CWA for the middle portion of the week. There is a 50 percent chance of 0.25 to 0.75 inches of liquid at lower elevations and 1 to 1.50 inches in the mountains. There is less than a 10 percent chance of getting over 2 inches of liquid in the mountains at this time. The heavy rain could cause some impacts in the Monarch and Neihart areas. Additionally, snow levels look to be around 7000 feet. There is a 50 percent chance of over 8 inches of snow in the mountains of Northwest Beaverhead County and the Tobacco Root Mountains, and about a 30 percent chance over the Rocky Mountain Front and the Kings Hill area. Thus winter statements are likely for portions of the CWA for this event. This system is slow, and it will take almost 2 days to move through the CWA. Below normal temperatures are expected during this time. There is also a small concern that snow levels could lower to near valley floors during the morning hours on Thurs/Fri, which could impact some bigger lower elevation cities. Saturday and Sunday...Some forecast models show the potential for a 2nd spring storm to move through the CWA, while other models have lighter precipitation. Never the less, below normal temperatures and the chance for precipitation is looking likely for most areas at this time next weekend. Brusda && .AVIATION... 19/18Z TAF Period For all but the KBZN and KLWT terminals VFR conditions will prevail during this TAF period. At the KBZN and KLWT terminals rain is reducing ceilings to MVFR levels and will continue to do so for the first few hours of this TAF period. At the KCTB, KGTF, and KHLN terminals this afternoon and early evening there will be isolated thunderstorms. At the KBZN, KEKS, KLWT, KHVR, and KWYS terminals this afternoon and evening there is a slight chance (%20) for a thunderstorm or two but there wasn`t enough probabilistic support to include it in those TAFs. For all terminals light rain showers will continue through this afternoon into the early evening with minimal impacts to aviation operations. For the KBZN, KEKS, and KHLN there is a 40% chance of rain/snow Monday morning which could reduce visibility and ceilings to MVFR levels and so a PROB30 group was included for those terminals. Tonight there is a 50% chance of rain/snow reducing visibility and ceilings to MVFR levels at the KWYS terminal and so a PROB30 group was included for it. For the KLWT and KGTF terminals there is a 20% chance of rain on Monday morning but there wasn`t enough probabilistic support to include a PROB30 group for it. This afternoon and Monday morning there will be mountain obscuration across Southwestern Montana. This afternoon and early evening there will be instances of mountain wave turbulence. - IG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... A flood watch has been issued for the Kings Hill, Monarch and Neihart areas from Wednesday night into Friday. There is a 50 percent chance of 1 inch of liquid from this event in this area. There is a 10 percent chance of 2 inches of liquid. Some of the precipitation will fall as snow, especially for elevations above 7000 feet, which will help, but for areas lower than 7000 feet, impacts could develop fairly quickly given how saturated the soil is and how full the creeks/streams are currently in this region. At this time, other areas of North Central and Southwest MT should be able to handle the expected rainfall, but there is the potential that additional flood statements might be needed. Brusda && .PRELIMINARY POINT TEMPS/POPS... GTF 33 59 36 65 / 20 50 20 30 CTB 33 57 34 63 / 30 60 10 20 HLN 36 61 38 66 / 20 60 20 30 BZN 31 56 32 62 / 20 70 40 40 WYS 26 50 28 52 / 30 70 60 60 DLN 34 54 31 59 / 40 60 30 20 HVR 35 61 37 66 / 30 40 10 20 LWT 31 54 33 59 / 20 60 20 40 && .TFX WATCHES/WARNINGS/ADVISORIES... Flood Watch from Wednesday evening through Friday morning for Little Belt and Highwood Mountains. && $$ http://www.weather.gov/greatfalls