FXUS63 KBIS 181440 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 940 AM CDT Sat Jul 18 2026 .KEY MESSAGES... - Seasonably warm temperatures in the mid 80s to lower 90s today, then hot conditions return on Sunday with high temperatures and heat index values around 95 to 100. - Scattered severe thunderstorms are possible Sunday afternoon and evening. Expected hazards include hail as large as 2 inches in diameter and damaging winds up to 70 mph, with a tornado possible. - Critical fire weather conditions are possible across parts of southwest and south central North Dakota on Monday. - Cooler, but still near to slightly above normal temperatures are favored through most of next week. && .UPDATE... Issued at 940 AM CDT Sat Jul 18 2026 Little updates needed this morning. Morning fog has dissipated, while mid to high level clouds move into western portions. Rest of today will see continued above normal temperatures with perhaps a few showers across the west. Overall the forecast remains on track. UPDATE Issued at 648 AM CDT Sat Jul 18 2026 Patchy fog has become more prevalent and deeper than was anticipated. Several observation sites and webcams show visibility less than a quarter mile, especially from south central North Dakota to the James River Valley and Devils Lake Basin. A Special Weather Statement has been issued to address the patchy dense fog, which should dissipate by 9 AM CDT. && .DISCUSSION... Issued at 510 AM CDT Sat Jul 18 2026 Upper level ridge has re-amplified upstream, with its axis from along the Alberta/Saskatchewan border through eastern Montana and Wyoming early this morning. A surface high pressure is centered over North Dakota, which has allowed temperatures to fall into the 50s for the first time in several days and patchy fog to develop despite increasing high clouds. The fog has reduced visibility to a quarter mile in some spots at times, but believe this to be shallow fog and very dissimilar to the dense fog outbreak from 24 hours ago. The fog should be short-lived this morning, giving way to a mix of clouds and sun with seasonably warm high temperatures in the mid 80s to lower 90s. Weak shortwave energy rounding through the top of the ridge could bring some sprinkles or light rain showers to parts of the area throughout the day, but model soundings show clouds bases well above 10,000 ft, and there is also little to no CAPE forecast through this evening. Weak disturbances may continue rounding through the top of the ridge tonight into Sunday morning, and a warm front is expected to enter western North Dakota by early Sunday morning. This could lead to more widely scattered showers and perhaps a few thunderstorms as the warm air advection drives MUCAPE to around 500-1000 J/kg. CAMs favor any showers or storms diminishing over central North Dakota by late Sunday morning as the magnitude of warm air advection decreases, but not all CAMs simulate convection to begin with. The early day passage of the warm front will allow hot and humid conditions to return to most of western and central North Dakota Sunday afternoon. Forecast highs in the southwest quadrant of the state, including Bismarck, are around 100 degrees, with lower 90s in the far northwest and Turtle Mountains area, and mid to upper 90s elsewhere. Higher forecast dewpoints in the 60s on Sunday lend to a maximum heat index forecast that is near or greater than the high temperature forecast for most locations. This places much of southwest and central North Dakota at risk for heat indices around 100, with the highest confidence in exceeding 100 over south central North Dakota. The forecast maximum wet-bulb globe temperature risk is also solidly in the Extreme category over south central NorthDakota, and patches of Extreme reach as far north as the Highway 200 corridor. Confidence is increasing in an isolated to scattered severe thunderstorm threat Sunday afternoon and evening. A potent shortwave is forecast to dig into central Saskatchewan Sunday afternoon, forcing mid level height falls over the Northern High Plains. A cold front with very weak baroclinicity attendant to the surface cyclone near the Saskatchewan shortwave is forecast to enter western North Dakota early Sunday afternoon and gradually drift eastward, reaching northeast to south central North Dakota by late evening. Most CAMs are simulating enough forcing, diurnal BL heating, and/or cooling aloft to overcome MLCIN and initiate deep moist convection at some point mid to late afternoon. Initial storms appear favored to develop somewhere from northwest to north central North Dakota, with additional development farther south in the late afternoon to early evening. Weak to moderate forcing in an antecedently capped environment with shear and deep layer wind vectors all perpendicular to the surface cold front strongly favors a discrete mode, although CAMs do want to trend toward more of a mixed/cluster mode by early evening, likely owing to the potential for strong cold-pool establishment and propagation within a deep and well-mixed boundary layer. Forecast CAPE along and ahead of the cold front approaches 3000 J/kg, with 0-6 km shear around 40 to 50 kts and increasing over time. All these environmental parameters would support supercells with very large hail up to 2 inches in diameter and damaging RFD winds up to 70 mph. Upscale growth into linear complexes or bowing segments seems unlikely at this time, but if this were to occur, the most likely maximum wind gust forecast would need to be revisited. Finally, despite high LCLs and weak low level shear, there is a conditional risk for a tornado with a very similar setup to what was observed last Thursday. Forecast CAPE and shear would both be sufficient for tornadogenesis with any supercell that remains anchored to the vorticity-rich and baroclinically-weak surface boundary. The Saskatchewan shortwave is forecast to dive into the northern Red River Valley and head toward the western Great Lakes on Monday, bringing a stronger and more baroclinic cold front through the region. Precipitation chances are very low with this cold front, and there is little to no buoyancy forecast to be available. The timing of the cold front moving from north to south during the daytime hours is likely to limit highs to around 80 to 85 across the north. But in southern North Dakota, the timing is such that compressional heating could give a local boost to high temperatures, which are still forecast to reach around 90 to near 95. Windy conditions are expected on Monday with the cold air advection, tightening of the surface pressure gradient, and mean BL layer winds around 25-30 kts. Strong diurnal mixing could lower dewpoints into the 40s across parts of southwest and south central North Dakota Monday afternoon, yielding RH around 20 to 25 percent. With northwest winds sustained around 25 mph and fuels reported to be rapidly drying from southwest North Dakota to around Lake Oahe, critical fire weather conditions could develop Monday afternoon. Tuesday is still favored to be the coolest day next week with highs in the mid 70s to mid 80s as surface high pressure extends from Alberta to North Dakota. The cooldown may be shorter lived than previously anticipated though as ensembles now favor a quicker departure of the downstream trough over the Great Lakes, allowing the upstream ridge to shift east off of the Rockies by next weekend. The NBM now returns lower to mid 90s for highs south and west of the Missouri River Wednesday through Friday, with mostly 80s to the north and east. And looking further ahead, there is a distinct shift of the temperature distributions in the warmer direction next weekend, with the rate of increase of the 75th percentile outpacing that of the 25th percentile (increasing spread, but the 75th percentile already exceeds 100 degrees at Bismarck, for example). Precipitation chances remain quite low next week, but the northwest flow could become more active in latter parts of the week. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 648 AM CDT Sat Jul 18 2026 Patchy dense fog will continue across central North Dakota early this morning, with visibility reductions as low as a quarter mile at times. The fog should lift by mid morning, and VFR conditions are otherwise anticipated through the forecast period. A few sprinkles or light showers are possible in western North Dakota later today, followed by a 20 percent chance of scattered light showers and a perhaps a thunderstorm late tonight. Winds will primarily be south to southeast through the forecast period, with speeds around 5-15 kts through the afternoon, strongest in western North Dakota, then closer to 10 kts at all terminals overnight. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Anglin DISCUSSION...Hollan AVIATION...Hollan