Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
517 FXUS65 KTFX 190600 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1200 AM MDT Thu Sep 19 2024 Aviation Section Updated .SYNOPSIS... This afternoon through tonight there will be rain showers across most of North-central, Central, and Southwestern Montana. The rain showers will end in Southwestern Montana this evening and from west to east across North-central and Central Montana by Thursday morning. Thursday it will warm up and be dry during most of the day. Unsettled weather returns to close out the work week continuing through the weekend. Early next week widespread precipitation looks to return to North-central, Central, and Southwestern Montana. && .UPDATE... Adjustments were made to the precipitation chances to reflect current conditions and the latest model guidance. Rain will continue to slowly migrate to the east as the low moves further into North Dakota. For the most part, showers will taper off for locations in Hill, Blaine, and Fergus counties by midnight. Thursday is still on track to be dry which will allow locations currently under the Flood Advisory to experience some relief. Wind speeds have diminished considerably over the past couple hours leading to an early cancellation of the high wind warning. Some gusty winds are still possible around the Lewistown Divide and into the higher elevations of Fergus county, however, no significant impacts are expected from here on out. Looking to the overnight hours, there are increasing chances for fog development along the valleys of southwestern Montana. Widespread impacts are not expected at this time, however, there is around a 40-60% chance for localized dense fog developing in and around West Yellowstone tonight. -thor && .AVIATION... 19/06Z TAF Period A few lingering light showers are possible for the next few hours across North Central MT. There`s a 40% for dense fog (1/2SM or less) at the KWYS terminal starting around 12z. However, there`s a chance cloud cover limits fog development. Due to the uncertainty, I`ve kept a TEMPO for LIFR conditions at KWYS this morning. Other terminals have a low fog potential due to the cloud cover. Otherwise, VFR conditions are expected through the TAF period. Cloud cover clears moderately around 12z. Lower clouds along the mountains will keep mountains obscured through 12z. -Wilson Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... Heavy rainfall continues to affect portions of Central MT as of 7 PM Wednesday evening. Rainfall reports of 4 to 6 inches are common from Belt to Lewistown today. An additional 1 to 2 inches of rainfall is possible in this area. A very good rainfall also extends further northward up into the Bears Paw Mountains. Thus this entire area is now under a flood advisory until Noon on Thursday, as minor flood impacts are possible. There is the potential that flood warnings might need to be issued for portions of the Lewistown area should more significant flooding impacts develop because of the additional expected rainfall this evening. The area flood watch has been cancelled, as a flood advisory is now in effect. The flash flood watch for the burn scar of Horse Gulch has been cancelled. Brusda && .PREV DISCUSSION... /ISSUED 700 PM MDT Wed Sep 18 2024/ Rest of Today... There is a surface low over Petroleum County that will track east this afternoon before moving north out of Montana by midnight tonight. This is bringing precipitation to much of North- central, Central, and Southwestern Montana this afternoon. The heaviest precipitation will be in Hill, Blaine, Choteau, Fergus, and Judith Basin Counties. The precipitation will end by early Thursday morning from west to east across North-central and Central Montana. The precipitation will end in Southwestern Montana by 6 pm tonight. There is a 40 - 80% chance for greater than a half inch of rain in Hill, Blaine, Choteau, Judith Basin, and Fergus Counties through midnight tonight. There is a 50% chance for an inch of rain or greater through midnight tonight from Havre to Fort Benton to southern Fergus County to northeastern Blaine County. For the other areas that are east of the I-15 Corridor there is a 20 - 50% chance for a tenth of an inch of rain or greater through midnight tonight. For more hydrology information see the HYDROLOGY section below. Due to the rain and clouds temperatures across North-central, Central, and Southwestern Montana will struggle to get to 60 degrees this afternoon. Due to a strong surface pressure gradient and an upper- level jet it will be windy across the plains of North-central Montana this afternoon through tonight. There is a 90% chance for wind gusts of 55 mph or greater in Fergus and Judith Basin Counties through midnight tonight. There is also a 70% chance for sustained winds of 40 mph or greater in Fergus and Judith Basin Counties through midnight tonight. As a result a High Wind Warning remains in effect for Fergus County and Judith Basin County below 5000 feet through midnight tonight. Thursday through Saturday... On Thursday an upper-level ridge moves over North-central, Central, and Southwestern Montana. As result due to clearing skies, thursday morning there is a 50% chance for fog to form in the West Yellowstone area. The upper-level ridge will warm up temperatures to around seasonal averages and bring dry conditions to the area for the day on Thursday. Between midnight and 6 AM Thursday there is 30 - 60% chance for a quarter inch of rain in Hill, Blaine, Choteau, Judith Basin, and Fergus Counties. On Friday a weak upper-level trough moves above North-central, Central, and Southwestern Montana. This will bring isolated showers to the area with slightly cooler temperatures. On Friday there is a 5 to 30% chance for a tenth of an inch of rain or greater across North- central, Central, and Southwestern Montana. On Saturday the upper- level trough remains over North-central, Central, and Southwestern Montana. This will cool temperatures down to a few degrees below seasonal averages. There will also be an isolated rain shower across North-central, Central, and Southwestern Montana. On Saturday there is a 5 - 10% chance for a tenth of an inch of rain or greater across the area. Sunday through next Wednesday... On Sunday an upper-level ridge moves over North-central, Central, and Southwestern Montana. Then an upper-level shortwave will move through the flow. This will bring a 5 - 10% chance for rain to North-central, Central, and Southwestern Montana. On Monday clusters indicate that there will be zonal flow over North-central, Central, and Southwestern Montana. This will keep unsettled weather in place for the area. On Tuesday and next Wednesday ensemble clusters and deterministic models begin to diverge. One scenario is for zonal flow to remain over North- central, Central, and Southwestern Montana. This keeps the unsettled weather in place for the area. Another scenario is for an upper- level ridge to move over North-central, Central, and Southwestern Montana. This would warm up temperatures and bring dry and calm conditions to the area. The third and final scenario is for an upper-level trough to begin to move over North-central, Central, and Southwestern Montana. This would bring cooler temperatures and widespread precipitation to the area. -IG && .PRELIMINARY POINT TEMPS/POPS... GTF 47 73 48 70 / 30 0 0 0 CTB 46 71 45 64 / 10 0 0 30 HLN 48 74 48 73 / 10 0 0 0 BZN 41 71 42 73 / 30 0 0 10 WYS 32 60 31 64 / 40 10 0 10 DLN 39 68 41 69 / 10 0 0 0 HVR 48 71 47 67 / 100 0 0 10 LWT 46 66 45 67 / 100 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls