Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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918 FXUS63 KBIS 010551 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1251 AM CDT Mon Jul 1 2024 .KEY MESSAGES... - Isolated to scattered strong to severe thunderstorms are possible tonight, with up to a Level 2 of 5 risk in portions of the far west and a level 1 of 5 risk over the rest of the area. The main hazards are hail up to quarter size, and wind gusts up to 60 mph. - Breezy conditions are expected tonight. - There is a Level 2 of 5 risk for severe thunderstorms Monday in southern North Dakota, and a Level 1 of 5 risk for much of the rest of the area. The main hazards are hail up to ping pong ball size and wind gusts up to 60 mph. - The chance for showers and thunderstorms on Independence Day is 60 to 80 percent across all of western and central North Dakota. && .UPDATE... Issued at 1250 AM CDT Mon Jul 1 2024 Thunderstorms across eastern Montana have begun to move into northwestern North Dakota, mostly as a large, messy cluster. These storms are not severe, but have had quite a bit of lightning associated with them. Hail doesn`t appear to be a concern with these, and likely won`t be a concern over the next few hours as well. The low level jet intensifying could potentially cause these storms to strengthen temporarily, but at the moment, we aren`t seeing much in terms of strengthening. The Severe Thunderstorm Watch continues for the time being. Otherwise, the forecast remains on track, with minor edits to PoPs and sky coverage to keep in line with the storms moving through the area. .UPDATE... Issued at 920 PM CDT Sun Jun 30 2024 Thunderstorms have increased over southeast Montana over the past hour from around Garfield and Hysham east to Miles City. This is within an areas of strong low level and mid level lapse rates and MUCAPE up to 2000 J/KG. Coordinating with SPC GGW and BYZ, will be issuing a Severe thunderstorm watch that includes Golden Valley, Billings and McKenzie counties in North Dakota. Uncertain about the eastward extent of the convection, but with current activity increasing and the low level jet expected to increase think it`s warranted to include at least a portion of ND in the watch. Will always be able to then cancel of things don`t pan out, or expand a bit later if needed. Updated text products will be transmitted shortly. .UPDATE... Issued at 603 PM CDT Sun Jun 30 2024 Thunderstorms continue over central ND and are also develop in the higher elevations of Wyoming and southeast Montana. , as well as around the Black Hills. Any convection over southeast Montana would have a hard time making it into the state this evening. Later this evening and overnight, aided by an increasing low level jet, convection from Montana will have a better probability of making it into western ND, and perhaps strong to severe. Until then, look for breezy to windy conditions this evening with variable cloudiness. Made some small adjustments to sky cover with more cloud over eastern portions of central ND early this evening and then increasing clouds late from west to east. && .DISCUSSION... Issued at 314 PM CDT Sun Jun 30 2024 This afternoon, a very shallow upper ridge was moving over eastern Montana, with an upstream trough deepening over the Pacific Northwest. At the surface, a low pressure continued to deepen over northern Wyoming, while a broad surface high stretched across Minnesota, creating breezy to windy southeast winds across western/central North Dakota in between these surface features. These winds have been gusting up to around 40 mph, but have been staying below advisory criteria as expected. Scattered radar returns have been persistent through the day, although with such high cloud bases, these have been virga, with no evidence of precipitation making it to the ground. The main forecast concern tonight is the potential for strong to severe thunderstorms, particularly across western North Dakota. High-res guidance has been painting a similar picture through the morning, with convection developing off the higher terrain in central Montana later this afternoon ahead of the trough base before moving east into North Dakota. A 50kt low- level jet is also forecast to develop over eastern Montana and western North Dakota late this evening. Moisture will be a bit lacking, with both current and upstream dewpoints (as far south as Nebraska) only in the 50s, and the 12Z HREF paints a narrow plume of MUCAPE values of 1000-1500 J/kg across western North Dakota. The main concern we see at this point is that forecast soundings continue to advertise significant capping across the entire forecast area. Although a Level 2 of 5 risk does extend into far western North Dakota, at this point the potential for any severe thunderstorms tonight is quite conditional, but recent CAMs runs support the idea that convection will weaken as it crosses into North Dakota. The low-level jet will sustained scattered showers and thunderstorms, however, as the wave moves west to east across the forecast area through the night. As the previous shift noted, there is a low but non-zero chance for storms to re-intensify as they get further into central North Dakota late tonight into Monday morning, entering an environment with slightly greater moisture. We are still carrying the Marginal Risk (level 1 of 5) across most of our central counties, which seems appropriate to cover this potential. The convection overnight and into Monday morning is a large forecast concern in determining how the potential severe thunderstorm threat on Monday will evolve. The deeper trough base aloft will approach from Montana, while at the surface a weak cold front and surface low will progress west to east through the day. Continued southerly low-level flow and richer moisture will boost dew points into the 60s, with a plume of higher instability extending north-south across the central Dakotas and overlaid with around 40 knots of 0-6km shear. CAMs are consistent in developing scattered storms across much of the Dakotas, although are inconsistent in storm mode and progression through the evening. HRRR forecast soundings advertise long hodographs, favoring a hail threat, although the uncertainty in storm mode is still a concern when deciding the threat ceiling. We did decide to increase the hail size in our messaging to up to the size of ping pong balls, and kept the damaging wind gust magnitude at 60 mph. Storms exit the area through Monday evening, but precipitation chances return briefly on Tuesday as a transient wave moves through cyclonic flow aloft. The active pattern is the main story of the work week as we stay in a broad troughing pattern, with temperatures near to slightly below normal Monday through Wednesday. Unfortunately, chances for precipitation on Independence Day continue to increase, with the latest blended POPs advertising widespread 60 to 80 percent chances of rain through the day. Ensemble members are honing on a deep trough base and potentially closed low moving through the Northern Plains Thursday into Friday, bringing showers and thunderstorms to the area. CSU Machine learning probabilities continue to show a low chance for severe weather on the holiday, however. With this wave of precipitation, most locations have a 50 percent chance of at least 0.25" of rain. Thursday also looks like the coolest day of the extended period based on NBM temperature percentiles, with highs in the lower to mid 70s. Behind the upper trough, ridging is likely to begin building over parts of the western CONUS, leading to warmer temperatures on Friday and Saturday. Ensemble members are then advertising a few different solutions regarding the evolution of the synoptic pattern. Guidance is split on where the ridge axis will be located by the end of the weekend, with one potential solution having it over the Northern Rockies, while another has it much further west off the coast of British Columbia with subsequent downstream region over the Northern Plains. There seems to have been a slight downward trend in potential high temperature ranges from the latest NBM runs, although precipitation chances still look relatively low starting Saturday and continuing into the middle of next week. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 12350 AM CDT Mon Jul 1 2024 Thunderstorms are moving into northwest North Dakota, and will continue to move east throughout the night. KXWA will see gusty, erratic winds, as well as moderate to heavy rain for a few hours, with all other terminals potentially seeing showers and thunderstorms nearby later on in the night. Generally MVFR/VFR ceilings are expected with these. Gusty southeasterly winds are expected across all terminals overnight, with all locations tapering off apart from KJMS, which will remain breezy until around 00z. Some low stratus may develop behind these showers as they move through, reducing ceilings to MVFR in some areas. However, KJMS is expected to see some IFR ceilings around 18z, lasting through the remainder of the TAF period. As the current wave of showers and thunderstorms move out of the area Monday morning, a second wave of showers and thunderstorms are expected to develop, arriving around 22z and continuing through the end of the TAF period. The greatest chances for precipitation will be across the south central and southern James River Valley, including KBIS and KJMS. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Besson DISCUSSION...Jones AVIATION...Besson