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Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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395 FXUS63 KBIS 170853 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 353 AM CDT Sat Aug 17 2024 .KEY MESSAGES... - Areas of near surface smoke from distant wildfires will continue through much of the day, but should start to diminish from east to west in the afternoon and into the evening. - Areas of dense fog will be possible across portions of western and much of central North Dakota through the morning hours. A Dense Fog Advisory has been issued. - Expect low to medium chances (20 to 40 percent) for showers and thunderstorms across the west this morning. An isolated thunderstorm or two will be possible northwest or north central this afternoon and evening, possibly strong. - Low to medium chances (20 to 50 percent) for showers and thunderstorms return to the forecast Monday afternoon through Tuesday. A few strong storms will be possible. && .DISCUSSION... Issued at 353 AM CDT Sat Aug 17 2024 The main story in the near term for western and central North Dakota is lowered visibility from dense fog and/or near surface smoke from distant wildfires. Automated observations and traffic webcams suggest that areas of dense fog are starting to settle in across portions of the west and much of the central, leading to visibility values of a quarter mile or less in some locations. We decided to go ahead and issue a Dense Fog Advisory for these areas as CAMs suggest it should only become worse and more widespread through the early morning hours. Complicating the fog threat is the addition of reduced visibility from near surface smoke. The HRRR and RAP smoke models suggest that near surface smoke will gradually diminish from east to west through the day and into the evening. However, it remains unclear how long smoke aloft may stick around. Both of these threats could make for hazardous driving conditions out on the roads this morning. At the mid to upper levels, a closed low continues to spin over the Great Lakes region with a ridge draped over the northern Plains. A weak shortwave was noted on water vapor satellite imagery over eastern Montana near the slightly flattened mid level ridge axis, bringing modest height falls to eastern Montana and western North Dakota. This modest forcing will maintain low to medium chances (20 to 40 percent) for showers and thunderstorms across the west through much of the morning. This activity will struggle to organize in our area as the ridge starts to build again and heights rise across the west. Rising heights will limit convection most of the afternoon and evening, but a couple of the CAMs suggest a conditional chance for a thunderstorm or two. If a storm can get going across the far west, forecast soundings suggest it would have around 500 to 1000 J/kg of MLCAPE and 45 to 55 knots of deep layer shear to possibly work with. Thus, while convection is uncertain given rising heights, if a storm can form it would have the potential to become strong to marginally severe. Precipitation chances will then diminish through the evening. Highs today will range from the mid 70s northeast to the mid 80s southwest and lows tonight will mainly be in the mid 50s to the lower 60s. Sunday will be a bit warmer and a bit drier with highs mainly in the 80s (upper 80s west). The thunderstorm environment will be fairly similar to today across the southwest with a little less shear. However, we will see rising heights through the day as the ridge amplifies overhead with very little in the way of upper level forcing. Thus, convective initiation appears unlikely for now. Better chances for showers and storms (20 to 50 percent) may come Monday afternoon through Tuesday as a stronger wave starts to move in, flattening the ridge. Highs on Monday will range from the lower 80s east to the lower 90s west. We should also see widespread dewpoints in the the low to mid 60s which should lead to around 2000 J/kg of MLCAPE across the west. Deep layer shear will be fairly weak through the afternoon around 20 to 25 knots, but we may see that increase to around 30 to 35 knots around and after 00z. Given said environment, a few isolated strong to marginally severe storms will be possible west. The story may be very similar on Tuesday depending on wave timing, but maybe a bit further into the central and east. Storms should move out to the east by Tuesday evening, but most solutions keep us either in near zonal or gradual southwest flow aloft through the rest of the week. Thus, a few weak waves may bring low precipitation chances to the area at times mid to late week. Highs on Tuesday will be similar to Monday, ranging from the upper 70s and lower 80s east to the upper 80s and lower 90s west. Wednesday may be the warmest day of the week with highs forecast to range from the mid 80s east to the low to mid 90s west. Highs then back off into the upper 70s to upper 80s Thursday and Friday. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1232 AM CDT Sat Aug 17 2024 The main challenge for the 06z TAF period will be reduced visibility from near surface smoke and/or fog. MVFR visibilities will be possible with any near surface smoke through the period, but fog may lead to IFR visibilities or lower later tonight and into Saturday morning. For now, we will keep visibilities for any one specific site in MVFR categories, but lower values are certainly possible. A stray shower or storm will be possible across the far west tonight or Sunday morning. && .BIS WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 11 AM CDT /10 AM MDT/ this morning for NDZ002>004-010>013-018>023-033>036-042-045>047-050. && $$ DISCUSSION...ZH AVIATION...ZH