Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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623 FXUS63 KBIS 200337 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1037 PM CDT Sun May 19 2024 .KEY MESSAGES... -Lows tonight in the far west are forecast in the mid-30s. - Expect below normal temperatures with daily chances for rain this coming week through the upcoming holiday weekend. && .UPDATE... Issued at 1030 PM CDT Sun May 19 2024 All severe storms are done. The Severe Thunderstorm Watch was cancelled at 03z, however a strong storm remains in northern Stutsman County. Small hail is possible with that as it moves north. Lows tonight are forecast to dip down into the mid-30s in the far west. Frost should not be a concern. UPDATE Issued at 716 PM CDT Sun May 19 2024 A Severe Thunderstorm Watch has been issued in the south central until 04z. The current storm is moving north into southern Morton County more may move into Emmons later. UPDATE Issued at 646 PM CDT Sun May 19 2024 Storms have fired in the southwest and south central. The strongest in the one entering Sioux County where 3000 J/kg of MUCAPE, 400 ms/s2 of effective helicity, and 70 kts of effective shear and 1000 J/kg of MLCAPE. The straight upper levels of the hodographs support splitting storms. This storm may or may already be in the process of splitting, and we would be dealing with the left mover, producing hail. The severe threat should only last until sunset, mainly in the south central. && .DISCUSSION... Issued at 340 PM CDT Sun May 19 2024 Western and central North Dakota currently sits under southwest flow aloft as a broad western US trough approaches. A surface low is currently located over eastern Wyoming and should move into western South Dakota by late afternoon and early evening. Precipitation chances will increase during this time frame from south to north along an inverted surface trough to the north of the low and an east to west oriented warm front near or just south of the South Dakota border. The highest rain chances will be across the south central and into portions of the James River Valley (60 to 90 percent) with low to medium chances further north and west (30 to 60 percent). As far as the severe weather potential goes, it does seem reasonable that we could see a fairly brief window for a strong to severe storm or two across southern portions of western and central North Dakota. However, the best chance for a severe storm or two is likely to be over the far south central, mainly over Sioux and Emmons counties. Confidence has decreased a bit regarding the severe weather potential as clouds have been stubborn to clear out in the most favored area for initiation per the latest CAMs. Thus far, the clouds have kept any appreciable instability south of the area with MUCAPE values only approaching 500 J/kg or so south of the I-94 corridor. MLCAPE values only max out in the 100 to 250 J/kg range across the south. That being said, RAP forecast soundings and SPC mesoanalysis trends suggest that we could see a small area of MLCAPE across portions of the far southwest and south central by 22z to 01z. Given the abundant cloud cover, this could be overdone a bit. One aspect that will not be lacking is shear with widespread effective shear forecast to be in the 50 to 65 knot range. This enhanced shear can also be gleaned from the widespread billow clouds on visible satellite imagery across south central North Dakota and north central South Dakota. Thus, if the warm front can lift north far enough and clear the far south central out it may not take a ton of instability for a strong to severe storm to pop. A quick glance at the latest CAMs suggests rapid convective initiation sometime in the 23z to 00z hour. The strongest updraft helicity tracks are generally confined to around the North Dakota/South Dakota border. Instability should wane rather quickly after 01z and thunderstorms will likely be in the weakening phase as they move into the James River Valley. A few storms could remain strong until around 03z before they move off into the Grand Forks forecast area. In a worst case scenario, storms across the far south central could see a brief window to produce damaging winds to 70 mph, hail to the size of ping pong balls, and a conditional risk for a brief tornado or two. Further north and west, isolated to scattered showers with a few embedded rumbles of thunder will be possible. Some showers may linger across the north late tonight into Monday morning as the shortwave moves off to the northeast. We will stay in southwest flow aloft through at least Tuesday as waves continue to rotate around the slow moving broad trough. The flow then flattens out and becomes nearly zonal midweek before the next potent trough approaches. Ensembles and global models continue to struggle with the evolution of the late week pattern regarding timing and track of this system. Either way, rain chances appear medium to high (40 to 70 percent) for most of western and central North Dakota Thursday into Friday. What is up in the air still is where the heaviest precipitation will fall and thunderstorm potential. Thus far, NBM is painting a picture of low to medium chances for thunderstorms (20 to 40 percent) during this same time frame. CIPS analogs still suggest some chances for severe weather towards the end of the week and into the holiday weekend but CSU Machine Learning guidance does not. Lows tonight may become fairly chilly across the southwest dipping into the mid to upper 30s. For now, frost is not expected but it will be something to watch. Lows will be in the 40s elsewhere. Highs will be in the 60s Monday through Wednesday and then we could see some 50s across the north on Thursday. Friday could be the coolest day of the week with NBM forecast highs in the lower 50s to lower 60s but the spread is rather large, likely due to model/ensemble uncertainty regarding the pattern. A warmup will then be possible over the holiday weekend. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 646 PM CDT Sun May 19 2024 VFR ceilings with scattered showers and thunderstorms. Winds could be breezy in the showers and will continue for the next few hours in the east. Monday morning ceilings look to lower below 1000kft in KJMS for a few hours, otherwise skies clearing in the west and scattered elsewhere. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Smith DISCUSSION...ZH AVIATION...Smith