####018002496#### FXUS63 KUNR 041021 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 421 AM MDT Sat May 4 2024 .KEY MESSAGES... - Warmer and windy this weekend - Strong Storm lifts into Northern Plains Monday/Tuesday; Thunderstorms late Sunday/Monday, high winds Tuesday/Wednesday, some snow for the Black Hills Tuesday/Wednesday. && .DISCUSSION...(Today Through Friday) Issued at 230 AM MDT Sat May 4 2024 Current surface map places high across eastern Montana into the western Dakotas. Skies are mostly clear with temperatures in the 20s to mid 30s. Surface high slides into the eastern Dakotas this afternoon with southerly winds increasing across northeastern Wyoming and western South Dakota. Highs mainly in the 60s today. Upper low tracks through the Great Basin Sunday and swings through western South Dakota Monday before stalling out along the northern Montana/North Dakota border early Tuesday. Tight pressure gradient on Sunday will promote gusty south winds, with the strongest winds on the plains east of the Black Hills. A few thunderstorms possible over northeastern Wyoming and Black Hills Sunday afternoon with narrow axis of buoyancy. An uptick in thunderstorm activity is expected Sunday night/early Monday with strong QG forcing. Buoyancy/shear favorable for a few strong/severe storms along dryline surge Monday over south central South Dakota. Widespread rains with deformation zone will set up northwest of the forecast area on Tuesday, with shower activity mainly limited to parts of northeastern Wyoming into northwestern South Dakota. Strong westerly winds expected on Tuesday, with the strongest winds on the plains north of the Black Hills. As the low weakens and slowly drifts southeast Wednesday, showers will spread southward across the forecast area. Thermal profiles support some snow for the higher elevations of the Black Hills late Tuesday into Wednesday with minor accumulations possible. && .AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning) Issued At 420 AM MDT Sat May 4 2024 VFR conditions are expected through the TAF period. Some low- level wind shear may develop after 06Z Sunday, especially over the western SD plains. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...7 AVIATION...Pojorlie ####018005876#### FXUS65 KTFX 041022 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 422 AM MDT Sat May 4 2024 .SYNOPSIS... Weak high pressure will keep North Central, Central, and Southwest Montana dry and a bit warmer than normal through tonight with gusty southeasterly winds. However, a Pacific weather system will first bring an increasing chance for showers and thunderstorms to the area on Sunday, then more widespread mountain snow and low elevation rain with cooler than normal temperatures Monday through Thursday. Warmer and drier conditions should then move in to end the week. && .DISCUSSION... Today and Tonight... High pressure aloft will keep this period dry and a bit warmer than normal across North Central, Central, and Southwest Montana. However, a cold front approaching Montana from the west ahead of a Pacific low pressure system will combine with an exiting area of surface high pressure to strengthen the surface pressure gradient over the area. This is forecast to bring southerly winds gusting in excess of 30 mph at times today across the area, with the winds shifting more easterly tonight and remaining gusty. Sunday through Sunday Night... The Pacific system is forecast to move east across the Great Basin on Sunday, which put the area under an increasingly moist and unstable southerly flow aloft as the Pacific cold front moves across the area. This should spread showers over most of the area Sunday into Sunday evening with a few embedded thunderstorms. The main threats from these storms will be isolated lightning strikes, brief heavy rain showers, and gusty winds, but some small hail is also possible. The main threat for thunderstorms will diminish during the evening, but snow levels will start to lower from the southwest overnight as the low pressure area is forecast to move northeast into Southwest Montana. This will likely result in at least some light accumulations of wet snow above 6000 feet, which may cause some travel problems over mountain passes, so some winter weather highlights may be needed starting Sunday night in Southwest Montana. Monday through Thursday... This is forecast to be coolest, wettest, and windiest period of the upcoming week. The low pressure center is predicted to continue moving northeast to around the Montana/North Dakota border Monday into Monday night, where it seems to deepen and cut off from its main trough, causing it to remain there into Wednesday. This will result in deep moisture wrapping around the low and bringing widespread mountain snow and low elevation rain to the forecast area, as temperatures cool back below normal. The heaviest precipitation amounts are forecast to be closest to the low pressure center, which includes the plains of North Central Montana; probabilistic guidance gives a 50 to 70 percent chance of at least 1 inch of precipitation there for Monday through Wednesday night, with a 40 to 50 percent chance of 2 inches of precipitation across Hill, Blaine, and Chouteau Counties. However, this same guidance gives at least a 50 percent chance of 12 inches or more of snow to the mountains of the Rocky Mountain Front, the Little and Big Belt mountains of Central Montana, and the mountains of Gallatin and Madison Counties; in fact, there is a 70+ percent chance of 24 inches or more of snow in the Little Belts. In addition, models are forecasting that northwest winds moving around the low pressure area at the mid levels of the atmosphere could exceed 60 mph on Tuesday, which may translate down into at least the mountains, if not the plains of North Central Montana, mainly on Tuesday. Overall, confidence is increasing in the potential need for winter weather highlights in the mountains and wind highlights on the plains. However, run-to- run model inconsistency adds uncertainty to timing and location for such highlights, so will hold off for now. Overall, though, the system should start exiting the area on Thursday. Friday through next Saturday... Ensemble model clusters are in good agreement with bringing high pressure into Montana late in the week, but just how strong it will be, and just how warm the temperatures will be, remains uncertain. Regardless, this should bring drying conditions to the area with a return to warmer than normal temperatures. -Coulston && .AVIATION... 1143 PM MDT Fri May 3 2024 (04/06Z TAF Period) Lingering clouds from isolated shower activity earlier this evening are quickly giving away to mostly clear skies. Aside from some isolated fog patches later tonight/early Saturday over the far southwest valleys and portions of the plains, VFR conditions associated with high pressure over the Northern Rockies are expected for most if not all of the 04/06Z to 05/06Z TAF period. However, keep in mid that higher clouds do increase later tonight into Saturday, and a few light showers may lift northward into far Southwest Montana around 04/00Z and beyond. Light east to southeasterly surface winds increase on Saturday and may gust up to 25 mph at times. - RCG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 63 42 64 42 / 0 10 30 90 CTB 58 37 59 40 / 0 10 20 30 HLN 67 44 68 43 / 10 10 60 80 BZN 65 41 66 36 / 0 10 70 80 WYS 59 36 53 28 / 0 30 90 90 DLN 64 44 60 36 / 0 20 70 90 HVR 63 39 70 43 / 0 0 10 80 LWT 58 36 66 39 / 0 0 20 80 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls