FXUS63 KBIS 020300 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1000 PM CDT Sat Jun 1 2024 .KEY MESSAGES... - Scattered severe thunderstorms will be possible Sunday afternoon and evening. Threats include large hail up to the size of golf balls, damaging winds up to 60 mph, and a tornado or two possible. - Chances for showers and thunderstorms begin late tonight and continue through the first half of next week. Temperatures will be near to slightly above average, with highs in the lower 70s to lower 80s through much of the work week. - Strong west to northwest winds are possible Tuesday through Thursday. && .UPDATE... Issued at 956 PM CDT Sat Jun 1 2024 Going forecast remains in good shape. Only eye-catcher for this update is there is a northward moving boundary noticeable on KABR radar that is just to the south of the Highway 12 corridor in the Aberdeen area. If this boundary holds together, it will cross the state line a little after midnight, right around when the modest low level jet starts to perk up. Not sure if this will add any influence at all on any possible convective development, but will keep an eye on it just in case. UPDATE Issued at 725 PM CDT Sat Jun 1 2024 For early evening update, main change was adjusting low thunderstorm chances for overnight. A look at latest RAP soundings shows a modest but still relevant low level jet developing over the James River Valley into parts of central North Dakota late tonight through the overnight hours. Therefore, have broadened out the low chances for thunderstorms a bit. Also increased cloud cover over most locations on Sunday afternoon given the expected convection. && .DISCUSSION... Issued at 318 PM CDT Sat Jun 1 2024 This afternoon, a weak surface high pressure was centered over south central North Dakota, underneath cyclonic flow aloft from a strong closed low over the northern Canadian Prairies. Skies across the forecast area were mostly sunny, aside from some fair weather cu across our northern tier of counties. A westerly breeze continued up north as well from a marginal surface pressure gradient, with highs this afternoon in the 70s across the area. Just upstream over Montana, an embedded shortwave in quasi-zonal flow aloft was moving east, with an associated expansive cirrus field. A surface low is expected to deepen in southern Montana attendant to this wave, and move east into the Dakotas on Sunday. Ahead of this surface low, a warm front will lift north late tonight Sunday morning, likely triggering convection across north central North Dakota through the morning. The surface low and attendant cold front are also expected to cross into western North Dakota sometime in the early morning hours as well, bringing additional precipitation. At this point, we aren't expecting any severe weather in the morning either in north central or in western North Dakota, with southeast return flow still increasing and bringing in additional instability. Midlevel height falls will move into central North Dakota in the early afternoon, which is when the potential severe thunderstorm window opens. There is still a moderate amount of uncertainty regarding the evolution of the severe threat considering the timing and placement of the two different fronts, as well as if earlier convection doesn't progress as expected. The 12Z HREF paints max UH tracks both in north central North Dakota earlier in the afternoon, where there is less confidence in any storms becoming severe, and then in the south central and James River Valley in the late afternoon and early evening, where confidence is a bit higher. Forecast MLCAPE values range from ~1000 J/kg in the north to up to 2000 J/kg across the south, with bulk shear from 30 to 40 knots and modest low- and mid- level lapse rates. Of note, guidance is advertising storm relative helicity values up to 200 m2/s2 in the southern James River Valley, which aids in tornado potential. Recent CAMs agree the most on convection spreading south and east through the afternoon, overcoming a weak cap that is forecast across the south central/east. The general expectation is for convection to become cluster/linear as it moves through the James River Valley and then into eastern North Dakota, which makes sense based on storm relative flow being more parallel than perpendicular to the front, although this will depend on the timing of the front. If we were to have any cells stay discrete in the James River Valley tomorrow afternoon and evening (potentially ahead of the front), these would have the highest threat ceiling given the forecast environment, so something to keep an eye on. If we do end up with a primarily linear storm mode, it would favor mostly a wind threat, although we could not rule out a quick spin up tornado along the leading edge of convection. We do still have a Slight Risk (Level 2 out of 5) that was expanded slightly to the west with the midday update from SPC. Potential hazards continue to be hail up to the size of golf balls, damaging wind gusts up to 60 mph, and a tornado or two. Latest estimated timing has severe storm potential from 12 PM to 8 PM CDT. With the expected progressiveness to this system, it is likely that storms will be east of the forecast area by the late evening. A shallow ridge builds in on Monday for a quick warmup and the warmest day of the period, with forecast highs in the mid 70s to lower 80s. The break from precipitation will be short-lived as another quick-moving wave moves west to east, with showers and thunderstorms likely Monday evening, through the night, and through much of Tuesday before tapering off. The timing of the front does not seem favorable in guidance for much severe potential, although a low-level jet kicking in late Monday could keep convection strong into the morning hours. The latest CSU machine learning probabilities are now showing a low potential for severe weather on Monday. We then transition to a very broadly northwest flow pattern, with near-normal temperatures most of the work week. The ECMWF EFI is signaling the potential for strong winds across the area Tuesday through Thursday, with the highest likelihood on Wednesday. Late in the week, there is increasing confidence in a stout upper ridge building in over the western half of the CONUS. The eastern extent of the ridge will influence how warm temperatures get, but for now there is moderate confidence in widespread highs in the 70s to end the work week, with temperatures warmer in western North Dakota and cooler in the east. Precipitation chances drop off substantially under this pattern, although this will also be influenced by the location of the ridge axis, and if any embedded shortwaves move through. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 725 PM CDT Sat Jun 1 2024 VFR conditions through this evening. Late tonight into the overnight hours, isolated thunderstorms will be possible over central and eastern North Dakota as a low level jet develops. Numerous showers and thunderstorms will develop over western North Dakota Sunday morning, spreading east. Some storms may become severe Sunday afternoon, mainly over central and eastern North Dakota. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...JJS DISCUSSION...Jones AVIATION...JJS