FXUS63 KBIS 190944 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 444 AM CDT Tue Aug 19 2025 .KEY MESSAGES... - Dense Fog Advisory for the north and central until 9am CT. - Expect drier and warmer weather today and Wednesday, with moderate to high heat impacts possible in the afternoon. - Low chances (25 percent) for thunderstorms return Wednesday morning and Wednesday night through Thursday. - A significant cooldown starts Thursday and continues through the weekend. && .UPDATE... Issued at 442 AM CDT Tue Aug 19 2025 Issued a fog advisory in the north and central and the dense fog with visibilities around 1/4 mile are much more widespread now. && .DISCUSSION... Issued at 347 AM CDT Tue Aug 19 2025 Currently a ridge aloft is building in from Montana. The ridge axis is in eastern Montana. At the surface very light winds are present, along with temperatures cooling down to the dew point temperature. This is creating fog in the north central and east at the moment. The fog is not as dense or widespread as last night, likely due to the higher pressure and ridging pattern. The fog should dissipate shortly after sunrise as diurnal heating raises temperatures above the dew point. Today will be warm, but not the warmest of the week. The ridge is bringing in a very warm thermal ridge into western North Dakota today, where temperatures will reach into the mid 90s. Dew points will remain in the 60s today, creating the thick feeling air still. Wednesday will be the warmest of the week as the ridge axis moves over the state. At the surface a low pressure in eastern Montana will create breezy southerly winds with a pressure gradient across our area. Temperatures in the far west will reach into the lower 100s. The 90th percentile of the NBM is 105 for the Beach area, although without a warming southwest wind it could be tough. However the breezy winds will mix down that strong thermal ridge. We have issued a Heat Advisory for the west and northwest for Wednesday afternoon. With temperatures around 100 and dew points in the 60s, the heat risk levels are off the charts. Thunderstorm chances will return Wednesday. First there is a slight chance in the northwest before sunrise off a small surface trough from the low pressure. Then Wednesday night a cold front will pass from northwest to southeast, where there is a chance of storms starting when the front enters the northwest around 7pm CT. Storms are then possible along the front through Thursday evening as it sweeps through the state. SPC has a marginal level 1 risk for roughly the northern half of the state Wednesday. Timing for these are of course based on the front, so after 7pm CT, through most of Wednesday night. The CAMs have scattered thunderstorms forming on the front. MUCAPE looks to be between 1500 and 2500 J/kg ahead of the front depending on what model. Wednesday will be very warm with dew points in the 60s, so if the storms are surfaced based, there should be no shortage of CAPE. Shear is plenty as well, averaging 30kts across the models. Hail will be the main threat until a line forms, then it will be winds. The rest of the forecast looks mostly dry and much cooler as northwest flow is the pattern. Dew points will be much lower as well and high temperatures in the 70s through early next week. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1254 AM CDT Tue Aug 19 2025 VFR across most of the west and south tonight. Portions of the north, central, and east will experience fog again overnight. Expect VIS around 1sm and CIGs around 500ft or less through 14z Monday. The TAF sites affected are KMOT and KJMS. Otherwise light winds and mostly clear skies. && .BIS WATCHES/WARNINGS/ADVISORIES... Heat Advisoryfrom 1 PM CDT /noon MDT/ to 7 PM CDT /6 PM MDT/ Wednesday for NDZ001-002-009-010-017-018-031-032. Dense Fog Advisory until 9 AM CDT /8 AM MDT/ this morning for NDZ002>005-010>013-019>023-025-035>037. && $$ UPDATE...Smith DISCUSSION...Smith AVIATION...Smith