Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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257 FXUS63 KBIS 071746 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1246 PM CDT Fri Jun 7 2024 .KEY MESSAGES... - Isolated to scattered showers and thunderstorms will remain possible through this evening. Thunderstorms are generally expected to be below severe limits, however, an isolated stronger storm is possible in southcentral and portions of southwestern North Dakota with small hail and gusty winds being the main threats. - Isolated showers (20 percent chance for rain) are forecast for Saturday, mainly north and east of Minot, and then on Sunday (20 percent) over central and eastern North Dakota. - With high confidence it is expected to be cooler Sunday and Monday, the question is how much cooler, and then warmer for the middle of next week with high temperatures into the 80s. && .UPDATE... Issued at 1245 PM CDT Fri Jun 7 2024 Forecast overall remains on track. SPC has added a Marginal Risk of severe weather in southcentral and portions of southwestern North Dakota. The threat for severe weather overall looks to still remain very isolated today. Some HRRR CAMS are showing an isolated stronger storm later this afternoon into this evening across these areas. There is abundant shear in this area during this time period. The bigger concern though is the lack of instability. HREF ensemble data showing MUCAPE up to 500 J/KG. While surface based CAPE is higher in some instances, the elevated nature of today`s convection would be tough to tap into this. A quick change from easterly flow at the surface to westerly flow aloft could be adding some SRH and perhaps promote weak rotation in isolated storms, yet again this would require surface based storms. More looking into the elevated storm environment the hodographs become more straight. This could still help with hail production, especially given the high amounts of shear. The concern still remains the lack of instability. If a stronger storm can get going and pulse up, then perhaps hail up to an inch in diameter and wind gusts up to 60 mph are possible. For now updated the HWO to match the Marginal Risk. Messaging will remain with small hail and gusty winds as this is where our highest confidence currently resides. UPDATE Issued at 1014 AM CDT Fri Jun 7 2024 Overall limited updates needed this morning. Weak returns on the radar showing up this morning. This is likely from an advancing wave expected to move through today. With it will bring isolated to scattered shower activity starting in the north and eventually spreading chances across much of the CWA. There is some limited instability and high amounts of shear. Severe weather is not expected, yet perhaps some small hail or gusty winds are possible to any more organized storms. Overall just made minor changes to PoPs based on current trends. Expanded thunder mention in the HWO based on current SPC general risk category. UPDATE Issued at 645 AM CDT Fri Jun 7 2024 The forecast is on target with showers about to move into the northwest part of the forecast area, the Williston area, ahead of an advancing short wave trough. CAMS continue to bring this convection to the east and south as the morning wears on, intensifying to isolated to scattered thunderstorms south of Minot by this afternoon. The cloud shield associated with the showers also continued to expand in coverage. There were a few wind gusts, on the order of 20 mph, near showers in Saskatchewan. && .DISCUSSION... Issued at 430 AM CDT Fri Jun 7 2024 The surface analysis as of 4 AM showed weak high pressure centered near Bismarck with a clear sky and winds that were light, under 10 mph, and variable in direction. An inverted trough extended north through eastern Montana. Low pressure aloft was drifting south through central Saskatchewan with pockets of energy (short waves) passing through the cyclonic flow and heading toward the international border. Clouds in association with the waves were both moving through southern Saskatchewan and developing there. Radars showed an increase in reflectivity north of Glasgow, Montana, with movement to the east and south. For today that first wave, and the cyclonic flow, will bring increasing weak ascent of air parcels into the forecast area. Guidance shows an abundance of 0-6km shear forecast to be over the area but little in the way of CAPE, at least until later this afternoon, and mostly along and south of Interstate 94. Because of this CAMS bring showers into the northwest this morning and intensify them as they move south and east, but only slightly (the intensification). By intensification we mean going from showers to thunderstorms. Looking at the HRRR fields, a pocket of higher MUCAPE, on the order of 300 J/kg, is forecast to move from southwest of Bismarck to south of Jamestown during the late afternoon and into the evening. That would be the highest chance and most likely location for a stronger storm. In discussion with my shift partner we are concerned on one hand of a storm there being able to produce some small hail, but on the other hand, with strong shear, concern goes to the updrafts not being able to gain much altitude before being sheared off. We`ll have to watch to see how convective parameters change through the short term to have more confidence in the risk of small hail. Another wave brushes the northeast on Saturday with chances for showers, maybe a storm, mainly east and north of Minot. Then on Sunday, the upper low advances into the state with cooler air and shower chances in the cyclonic flow, over the central and east. Sunday should be the coolest day over the next seven with that upper low over the state, followed by warming then through at least Wednesday. The NBM 1D Viewer shows a wide range in possible high temperature outcomes on Sunday, but all lower than 70. The question then becomes, cool Sunday, but just how cool, especially north. 60s at this point would be a high expectation, but lower, mid or upper 60s will need to be determined. The Viewer then shows narrower ranges (higher confidence) for high temperatures for the middle of the week, basically 80 to 85. It does look like the 80s could be accompanied by unsettled weather as the mean H5 ridge is broken down every 24 hours or so by short wave troughs passing through it, and bringing chances for rain. By Thursday the ridge could be replaced by cyclonic flow troughing (cooler and more unsettled). && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1245 PM CDT Fri Jun 7 2024 VFR conditions generally expected through the forecast period. Isolated to scattered showers and thunderstorms could be found through this evening. Confidence was high enough to include shower mention to most sites. It was only high enough to include TS mention to the KBIS and KJMS TAF site. Precipitation looks to diminish later this evening bringing clearing skies and continued VFR conditions. VFR conditions are then expected for much of Saturday. Light winds will become easterly today. These easterly winds will then become westerly tonight into Saturday. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Anglin DISCUSSION...JPM AVIATION...Anglin