Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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246 FXUS63 KBIS 151945 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 245 PM CDT Sun Sep 15 2024 .KEY MESSAGES... - Warm and dry today with temperatures mainly in the 80s. - Thunderstorm chances return tonight through Monday night with some strong to severe storms possible along with locally heavy rain. - An active pattern continues through the week, with strong to severe storms again possible on Tuesday, along with a general cooling trend from mid to late week. && .DISCUSSION... Issued at 245 PM CDT Sun Sep 15 2024 A weak surface cold front is pushing across the northern Plains this afternoon, promoting a reorganization of the previously variable winds to become east east southeasterly wind with sustained speeds from around 10 to 15 mph. The passage of this cold front, along with the high pressure building in behind it, has promoted the generally dry conditions found today, along with high temperatures generally in the 80s this afternoon. The northern Plains is set to see a fairly active upper level pattern through the short term as an obstinate upper level low parked over the eastern CONUS will, in turn, promote the development of upper level troughing over the western CONUS. With southwesterly flow thus found over much of the northern Plains, periodic shortwaves ejecting out of this trough will promote near daily chances for showers and thunderstorms over western and central North Dakota through much of the coming workweek. This first of these chances will develop this evening as a shortwave and associated surface low center over northern Wyoming will hijack the previously mentioned weak cold front, bringing it slowly back north as a warm front. Conditions near the surface are expected to remain fairly stable though with a low level jet draped across the south central, increasing moisture behind the front promoting increased instability - with models MUCAPE values progged from 1500 to 2000 J/KG - and at least sufficient shear could allow a few stronger and maybe a marginally severe storm to organize across the southwest and south central late this evening and overnight into Monday morning. The hazards associated with any severe thunderstorms that do develop this evening and overnight would mainly be winds up to 60 mph and some large up hail up to quarters in size. In their most recent update, SPC has included portions of southwestern and much of central North Dakota into a Marginal (level 1 of 5) risk for severe thunderstorms for today. Ongoing showers and thunderstorms trailing behind the warm front are expected to persist and move across central North Dakota overnight through Monday, along with persistant moisture transport driving dewpoint temperatures into the upper 60s and lower 70s across this after by Monday afternoon. With instability maximized by this period, with model MUCAPE values falling into the 1500-2500 J/KG range, the potential for severe thunderstorm is somewhat higher on Monday than it today. The fly in the ointment is again the available shear across the forecast are during this period that, while still sufficient for severe thunderstorm development, is stymied by poor mid level flow. As such, the main hazards associated with any severe storms that do develop across central North Dakota on Monday would be hail to the size of quarters and winds up to 60 mph. There also is some potential for an isolated tornado, with a decent veering wind profile and low LCLs across the James River Valley. Current, the SPC has placed much of central North Dakota into a Marginal (level 1 of 5) risk for severe thunderstorms on Monday. With redeveloping convection along the slow moving warm front and PWATs exceeding 1.5, some areas could see locally heavy rainfall. Otherwise on Monday, south southeasterly winds will strengthen behind the warm front, with sustained speeds from 15 to 20 mph and gusts from 25 to 30 mph generally expected, with the highest speeds across the south central, south of the I94 corridor. Seasonable warm temperatures, with highs generally in the 80s, also continue on Monday, though portions of the north central ahead of the warm front will only reach the mid to upper 70s. Monday night into Tuesday morning, the upper level trough will close off as it tracks over the Rockies, promoting a transient upper level ridge that will help clear out any lingering showers and thunderstorm over the forecast area during the early morning hours. Late Tuesday afternoon and Tuesday evening, another cold front will be dragged through the northern Plains as the previously mentioned surface low begins to move northward into Canada. Another round of showers and thunderstorms are anticipated to develop along and behind this front Tuesday evening, with some potential for severe weather shifting in out of eastern Montana and over the western Dakotas. As it stands, the SPC has placed much of western and portions of south central North Dakota into a Marginal (level 1 of 5) risk for severe thunderstorms on Tuesday. High temperatures will also peak ahead of the cold front on Tuesday, forecast from around 80 in the north central to the lower 90s in the southwest. As the the inciting upper level low begins to shift northward into the Canadian Prairies Wednesday, the another upper level low will dig into the western CONUS and sustain the active weather pattern through at least the end of the workweek. The potential for, the timing of, and the strength of any showers and thunderstorms become increasingly uncertain this far out, however, especially as the better moisture returns from the golf experienced earlier in the week is expected to be cut off in the later half. There is better agreement for a cooling trend through the end of and into next week, as NBM forecast highs drop broadly into the 60s by the coming weekend and into next week. Individual ensemble members remain fairly discordant to the degree of cooling however, with a 5 to 10 Fahrenheit spread between clusters depending on the relative speed and strength of the second low passing through the northern Plains by the end of the forecast period. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 1245 PM CDT Sun Sep 15 2024 Mainly VFR ceilings and visibility are anticipated at all TAF sites throughout the 18Z TAF period. Overnight into Tuesday, showers and thunderstorms are expected to develop over portions of southwestern and central North Dakota, with convection being possible over the terminals KBIS and then KMOT during this period. As such, we have included VCTS and -SHRA at those terminals for this update. Chances for showers will also be found at KDIK and KJMS, though confidence is lower at this time. As such, VCSH have been added to those terminals. Where showers or thunderstorms do develop, MVFR ceilings and variable winds are possible. Otherwise, variable winds will organize behind a weak cold front moving through western and central North Dakota today, becoming south southeasterly this afternoon with speeds from 10 to 15 mph, before generally diminishing overnight through the end of the TAF period. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Adam AVIATION...Adam