Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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691 FXUS63 KBIS 150930 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 430 AM CDT Sat Jun 15 2024 .KEY MESSAGES... - There is a Slight Risk (level 2 out of 5) for severe thunderstorms late this afternoon through the early overnight hours tonight, covering most of western and central North Dakota. - There is a Marginal Risk (level 1 out of 5) for severe thunderstorms Sunday across far southcentral and southeastern portions of the state. - There is a Marginal Risk to Slight Risk (level 1 to 2 out of 5) for severe thunderstorms Monday across far central and eastern portions of the state. - Breezy to windy west winds may return across much of western and central North Dakota on Sunday. - After above normal temperatures today, below normal temperatures are forecast Sunday through at least mid next week. && .DISCUSSION... Issued at 430 AM CDT Sat Jun 15 2024 Isolated to scattered severe thunderstorms still expected today into tonight across portions of western and central North Dakota. This morning, a low level just could bring a few isolated thunderstorms to eastern areas, while a developing surface low and weak wave in southwest flow aloft brings some showers to the west. Surface low then looks to develop through the day today, setting up a warm front across much of the state. High temperatures will rise slightly today as a result, with some southwestern sites seeing highs in the lower 90s. Southerly flow at the surface will advect higher dewpoints in today. NBM forecast afternoon dewpoints in the mid 60s. Perhaps this is a touch high as dewpoints of this magnitude are as far south as Nebraska at this time. However, even dewpoints in the upper 50s to lower 60s combined with strong heating today will bring abundant amounts of instability with MUCAPE over 2000 J/KG, and some areas even seeing up to 3000 J/KG. Shear will also be robust today, with 0 to 6 KM shear up to 50 knots. The limiting factor during the day will be capping. This breaks down later this afternoon through this evening when another more potent shortwave aloft moves through. An isolated severe storm is possible ahead of this wave, although the highest confidence in timing for today`s severe weather will be when this mid level shortwave moves through. Given this the highest confidence in timing for today`s severe weather is roughly 5 PM to 1 AM CDT. Storm mode will greatly determine today`s hazards. The shear vector is generally west to east today, until it becomes more along the cold front tonight. Thus if storms linger into the late evening or overnight hours, a linear storm mode can be expected. However, storms that can go earlier in the evening have the potential to be discrete or at the very least multicluster. These storms will be the ones to watch for all hazards. High CAPE and high shear aside, hodographs showing good veering this evening, giving fair amount of 0 to 1 KM and 0 to 3 KM SRH. STP values over 1 are also found during this time. LCLs are about 1000 m, which would be adequate for tornado development. Thus any discrete cell that forms early in the severe window will have the possibility of creating a tornado or two. Large hail will also be of concern today given mentioned parameters. Historical data showing a lot of cases with similar parameters bringing baseball size or larger hail. Would like to see perhaps a touch higher shear to have higher confidence in this larger sized hail. The tornado threat also may tone down hail slightly. Still decided to raise the max hail size today to tennis ball size. The wind threat also remains high today. Kept in 70 mph winds with some isolated 80 mph gusts. This again goes along with what will the storm mode be. The higher wind gusts would likely be if severe weather goes later and closer to the cold front. This timing brings high DCAPE over 1000 J/KG and 0 to 3 KM shear 25 to 30 knots. MUCAPE could be little higher for these stronger winds, although will be adequate. Thus kept wind values messaged as is. Of note too are higher Pwat values and average storm motions. Thus heavy rain could also be possible today. Cold front should progress quickly tonight across the CWA, moving or diminishing severe weather during the early to mid overnight hours. A switch to westerly winds may also be found, and they could become breezy at times. Lows tonight behind this front will be in the lower 50s in the west, while near 60 degrees can be expected in the east. A generally post frontal day is then expected for Sunday. Look for cooler temperatures and breezy to windy westerly winds. Some areas in the north and west should still be monitored for potential advisory level winds. SPC maintained a Marginal Risk for severe weather in southcentral and southeastern portions. Shear will remain high, although instability looks limited. Perhaps as the front stalls an isolated severe storm is still possible in these areas later in the day through the night. Highs on Sunday look to be in the mid 60s to mid 70s, with some lower 80s in the far southeast. Lows Sunday night look to be mid 40s to mid 50s. Of note too for Sunday will be lowering RH values in the afternoon into the 20s. Fuels may still be too green for fire weather concerns, although breezy to windy winds and lowering RH could bring at least some increased concerns. The front remains stalled for Monday, then is reinforced by another cold front through Monday night. This could bring the next round of showers and thunderstorms. SPC now has a Marginal to Slight Risk across central and eastern North Dakota. Shear will again be high on Monday, although CAPE is somewhat modest though increased over Sunday. Large hail and damaging winds right now look to be the main threats. Another post frontal day could then be found on Tuesday, with further cooling of temperatures into the 60s. Lingering showers and thunderstorms may also be found. Tuesday night into Wednesday morning could then be quite cool for some areas. NBM forecast temperatures are currently in the 40s for most areas. ECMWF EFI values for Min T during this time period though are around -0.8. Looking at the NBM 25th percentile gives some lows in the upper 30s across the west Wednesday morning. Something to monitor perhaps. A gradual warmup could then be in store for mid to late next week in a zonal to perhaps slightly southwesterly flow. Another broad trough could approach the area mid to later in the week, returning near daily chances for showers and thunderstorms. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1253 AM CDT Sat Jun 15 2024 Isolated thunderstorms look to be found tonight, along with mainly VFR conditions. Breezy southeasterly winds will diminish tonight. Saturday could see some lower clouds in the morning, perhaps approaching MVFR ceilings to a few areas. Southerly winds could also become breezy again for some locations. Saturday afternoon through Saturday evening could then see isolated to scattered showers and thunderstorms. A few may be severe at times. Confidence in timing of these storms is currently low to modest, although did use some VCTS at this time. Stronger storms could also bring some brief MVFR conditions. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Anglin AVIATION...Anglin