Sunrise 5:52 AM   Sunset 9:10 PM Moonrise 4:21 PM   Moonset 3:10 AM

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FXUS63 KBIS 191749 AFDBIS

Area Forecast Discussion National Weather Service Bismarck ND 1249 PM CDT Sun May 19 2024

KEY MESSAGES

- Low rain shower chances (20 to 30 percent) lift south to north this morning.

- Isolated to scattered severe storms late this afternoon through the evening from the Standing Rock Reservation to the southern James River Valley. Expected hazards include large hail to ping pong ball size and damaging wind gusts to 70 mph, with a tornado or two possible.

- Below normal temperatures with daily chances for rain this coming week through the upcoming holiday weekend.

UPDATE
Issued at 1227 PM CDT Sun May 19 2024

A warm front continues to lift north across South Dakota, which can be observed on visible satellite imagery along the cloud shield near the South Dakota/North Dakota border. This boundary should continue lifting north, promoting clearing to it's south as it does. There is a rather dense area of high clouds currently located over western North Dakota, however it is fairly narrow at the moment and fast moving. Will be be able to clear out enough for robust surface based convection in North Dakota? We will have to see how things evolve over the next few hours but that's the big question. CAMs continue to show storm initiation in the 21z to 23z time frame over the south central North Dakota with the strongest UH tracks near the South Dakota border. Some CAMs have also started to pick up on a strong cell or two coming out of Montana into west central North Dakota around the same general time. SPC has expanded the Marginal Risk (level 1 out of 5) west and north to account for this potential activity.

UPDATE Issued at 945 AM CDT Sun May 19 2024

Showers are now located from around northern Stutsman and Foster counties, up into the north central and northwest. These showers should continue to be fairly light as they drift east northeast, maybe amounting to a few hundredths of rain at most. We have also started to see some clearing across the southwest and parts of the south central over the last couple of hours. This will have an impact on severe weather potential later this afternoon and evening, especially if we can get some more clearing further east before peak heating. No major changes were needed for this update. Just blended in the latest observations to the going forecast.

UPDATE Issued at 620 AM CDT Sun May 19 2024

Showers continue to lift northeast across the forecast area. We received a hundredth of an inch /0.01/ at the BIS ASOS from 1 am through 6:30 AM. We made some minor adjustments to sky cover and pops based on the latest radar and satellite imagery.
Otherwise no changes to the forecast this morning. Updated text products will be transmitted shortly.

DISCUSSION
Issued at 152 AM CDT Sun May 19 2024

Currently, a broad area of high pressure extended from eastern Montana, south and east across western and central North Dakota and into southern Minnesota. Low pressure was situated over the Northern/Central Rockies, ahead of an advancing upper level trough over the Pacific Northwest.

This morning, cyclogenesis over the Central High Plains and shortwave energy lifting northeast through a broad southwest upper level flow will result in increasing mid level cloudiness and isolated to scattered showers as a result of increasing warm advection and mid-upper level forcing. Clouds are already increasing along the ND/SD border with convection noted in north central South Dakota. The main question this morning will be how widespread will shower activity be as it lifts northward through the forecast area. Forecast sounding indicate that as the cloud cover lifts north the threat for thunder will diminish. For now have not added thunder to the forecast through the morning, but will monitor. Soundings also indicate that the potential for shower activity looks a little better as forcing lifts farther north. We utilized a blend of short term guidance to tone down the potential (mainly 20%) for showers as the activity lifts north this morning, then a little better chance later this morning into this afternoon across the north (20-40%).

This afternoon, surface low pressure exits into the plains with a surface low developing over western South Dakota. Continued warm advection with and increasing southeast surface flow will result in an increasingly moist and unstable but capped atmosphere developing over South Dakota and into southern North Dakota. Shortwave energy tracking through the upper level trough will approach the area this afternoon which should eventually provide the forcing to break the cap and initiate convection over the western Dakota, and also farther south into the Central Plains.

There looks to be a fairly small area in south central North Dakota which could see strong to severe convection this afternoon. In general, from Grant and Sioux Counties east through Lamoure and Dickey counties in the southern James River Valley. As you go north of this area, the thermal profile quickly becomes unfavorable. SPC has a marginal risk of severe weather within this area, and a nose of slight risk extending from the Central Plains north through central South Dakota and into far south central ND (McIntosh and portions if Emmons counties). The marginal risk does poke up into far southern portions of Morton, Burleigh, Kidder and Stutsman counties, but at this time it looks like the main threat will be more along the North Dakota/South Dakota border and southward.

Looking at some of the short term guidance, if we see a period of sunshine over south central ND after the mid level clouds lift north, we could possibly reach or exceed our high temperatures guidance, adding to the instability. An afternoon sounding near Lemmon SD indicates over 60 knots of bulk shear with a MU CAPE of 500-1000 J/K. The storm mode could potentially be discrete with an inverted trough poking into south central ND and nearly perpendicular bulk shear. Storm mode could also be more of a messy to linear type as with an east-west boundary along the warm front, situated along the ND/SD border. If we would happen to get an initial discrete thunderstroms over the far south central, we could definitely see golfball sized hail and potentially a tornado. Low level shear looks more favorable for discrete storms early on (early to mid afternoon) with shear profiles transforming more into a straight line hodograph (mid to late afternoon) towards 00Z UTC. With the more linear type convection the hail size would not be as large, tornado threat lower and an increase in wind damaging wind speeds. For our hazards we will include all three, but with what we think is a favoring for linear mode, we will hedge towards higher winds and slightly lower hail than for discrete cells. We will message winds to 70 mph, ping pong ball sized hail and possibly a tornado or two. We should mention that although initially dry conditions in the low levels, we see a rapid increase in moisture with high pwat air and low LCL's developing along the ND/SD border.

Some failure modes include the southeast surface flow and the potential for temperatures that do not reach our forecast highs, thus lowering the instability. If the surface low over SD is a little farther south, we could even get more of a east to northeast surface flow over south central ND, also lowering instability. I hate to say that our moisture is robbed by convection farther south, but perhaps it may be displaced some.
There is a MCS currently tracking across NE/KS. There is also a moderate risk of severe weather over Kansas this afternoon and evening which could have an eventual impact on how things develop up in our neck of the woods. I could definitely see a can in which the strong convection doesn't quite make it into ND. Nevertheless, those in the south central portion of the state should be weather aware this afternoon and evening.

Although we aren't focusing on the north as much, there is also a northern stream wave that will keep a risk of general thunderstorms tonight across all of western and central ND. The threat for severe storms though is definitely over the south.

Once convection ends tonight it looks like we will have a break in convection on Monday. Beyond Monday we will continue to see an active pattern over the region. However, closer to home, it's possible many areas could see drier conditions over the first half of the week, with an upper low to our north and a more southern track to waves moving through the mean flow. A Tuesday-Wednesday system may only clip, or even miss the forecast area. With that said we will remain within a broad southwest to, at times, a slightly cyclonic upper flow so an isolated shower/thunderstorm can not be ruled out each day. The latter half of the work week could then see the next wave provide more than just a glancing blow. This of course is well towards the end of the extended period with much uncertainty. We will remain cool through the upcoming work week with highs mainly in the 60s, and even some mid and upper 50s. Overnight lows will be mostly in the 40s, but some upper and even mid 30s can't be ruled out.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/
Issued at 1227 PM CDT Sun May 19 2024

VFR conditions will prevail through the first part of the period at all sites. However, chances for showers and storms will increase late this afternoon and into the evening hours, especially across the south central and into the James River Valley. This activity also may usher in some MVFR or low VFR ceilings to areas across the central and east, including KBIS, KJMS, and KMOT. Some guidance is a bit more bullish on potential IFR ceilings over the south central and James River Valley by late tonight or early Monday morning, but this is a low confidence solution at the moment. Thus, we will leave it out of any site specific forecast for now. A few strong to severe storms will be possible across southern North Dakota. The strongest storms are likely to be mainly along the South Dakota border but KBIS could see a storm in the vicinity and KJMS has a better chance of a storm actually moving overhead. Further north, a few scattered showers will be possible. Winds may become gusty and erratic in and around thunderstorms.

BIS WATCHES/WARNINGS/ADVISORIES
None.

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