UPDATE
Issued at 724 PM CDT Fri Jul 26 2024

For unclear reasons, thicker smoke at the surface never materialized this afternoon in western North Dakota. With all stations reporting 10 mile visibility and no evidence of near-surface smoke upstream in surface observations, the mention of smoke has been removed from the forecast. Periods of thicker smoke aloft will remain possible for the foreseeable future, though.

Scattered high-based showers are located from southwest to north central North Dakota early this evening. Very little lightning has been observed over the past few hours, which confirms the latest SPC mesoanalsys of MUCAPE no greater than 100 J/kg where showers are present.

Later on this evening, recent CAMs have consolidated on a solution that develops a line of storms along a low level baroclinic zone from the Standing Rock Reservation to the James River Valley around 10 to 11 PM CDT. Given the time of initiation, this convection would most likely be elevated but could have access to MUCAPE as high as 2000 J/kg and effective bulk shear near 30 kts.
While shear vectors are oriented parallel to the initiating boundary, the overall weak background forcing could dictate more of a mixed multicell/cluster mode as is being depicted by CAM reflectivity output. We are therefore expecting the potential for a few strong to marginally severe storms as a reasonable high-end outcome. The area of convection should slowly drift eastward over time, but individual storm motion parallel to the boundary could promote training in an environment with 1.5 to 1.75 inch precipitable water and warm layer cloud depths around 3 to 4 km.
This could lead to a localized risk of excessive rainfall.



DISCUSSION
Issued at 235 PM CDT Fri Jul 26 2024

Painting the synoptic picture, western and central North Dakota currently sits under the influence of southwest flow aloft as an upper level trough is starting to nudge into the region. A stacked low is located over northern Saskatchewan with a cold front extending south into central and southwest North Dakota. The stacked low and front will slowly move off east through the weekend, but western and central North Dakota will remain in persistent zonal/southwest flow for several days as broad western US troughing settles in.

For the rest of today, we will see plenty of mid to high clouds along the cold front as it moves east. Forecast soundings suggest plenty of dry air near the surface so cloud bases are fairly high.
Thus, while we continue to see radar echoes all along this boundary, it is likely that only a little bit of light rain is making it down to the surface. Later this afternoon and into the evening, instability will increase along and ahead of the cold front which will also lead to an increase in shower and thunderstorm coverage and intensity. That being said, it's a little bit unclear if showers and storms will be along or behind the front. The best chance for a strong storm or two will generally be early this evening in the vicinity of the James River Valley. MLCAPE along the front is forecast to be in the 1000 to 1500 J/kg range with deep layer shear in the 30 to 40 knot range. If storms were able to fire in the warm sector, they would have quite a bit more instability to work with, but it seems likely that substantial capping will keep this scenario from happening. Either way, the parameter space will be sufficient for some organized or semi-organized convection. The most likely scenario is a strong storm or two over the James River Valley this evening with some gusty winds to 50 mph and small hail. Storms will generally move out in the mid to late evening hours with some showers lingering through the overnight.

For Saturday, we will stay in southwest flow aloft but most of the larger scale forcing will have moved off to the east. However, a diffuse stationary boundary extending north northeast from a weak surface low over northwest South Dakota and several outflow boundaries from tonight's convection will be lingering around, likely leading to enough convergence to trigger some storms by the late afternoon and evening. Models are currently having a hard time deciding on how far west the instability axis will extend which will have a big impact on the coverage of strong to severe storms on Saturday. The most likely scenario is that we will see some isolated to scattered severe storms across the central and into portions of the Devils Lake Basin and James River Valley. The environment here will be characterized by moderate instability (1500 to 2500 J/kg MLCAPE) and deep layer shear around 35 to 45 knots. Thus, any storms that can get going here will have the potential to become severe. Hail to the size of golf balls and winds to 60 mph will be the main threats. The tornado threat appears to be fairly low, but when there are plenty of boundaries floating around, we cannot completely rule it out.
The main limiting factor will be the uncertainty regarding storm coverage given generally weak forcing, but another fly in the ointment (per some forecast soundings) could be some dry air entrainment into updrafts. Storms will once again weaken in the late evening hours, potentially giving way to some more showers overnight.

The setup on Sunday doesn't look all too different from Saturday as far as parameter space goes, but maybe a bit further south and east.
However, we will have a stronger shortwave moving into the southwest around 00z Monday, which may end up leading to some sort of cluster/MCS moving across the state through the night. It's a bit early to talk specifics, but these storms could also be strong to severe with a better wind threat potentially depending on how the boundary layer evolves.

We will then continue to have daily low to medium chances (20 to 40 percent) for showers and storms Monday through Wednesday. CSU Machine Learning guidance is also suggesting that low severe weather chances may hang around Monday and Tuesday which seems reasonable given the parameter space many of the deterministic models are suggesting.

Regarding the heat, it will be another hot one on Saturday with highs expected to be in the mid 80s to mid 90s. However, the area with the highest dewpoints (east) will be cooler than today so for now, there are no plans for further Heat Advisories. We will cool down slightly into the 80s on Sunday before the next wave of heat and humidity moves in Monday and through the week. The hottest day of the period will be on Tuesday when highs will generally be in the lower 90s to lower triple digits. Thus, more heat headlines could be needed eventually for Tuesday. We don't cool down much through the rest of the week with plenty of highs in the 80s and 90s expected through Friday.

Finally, the HRRR-Smoke model continues to be aggressive in bringing in some thicker near surface smoke to the area late this afternoon and through the night. While smoke aloft is likely to hang around for at least several more days, it looks like we may get a break from near surface smoke after tonight.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/
Issued at 724 PM CDT Fri Jul 26 2024

VFR conditions are mostly expected to prevail through the forecast period. Scattered showers will remain possible across southwest and central North Dakota this evening. Later this evening into tonight, thunderstorms may develop from far south central into eastern North Dakota, possibly impacting KJMS. Any storm would be capable of producing MVFR to IFR visibility from heavy rain, erratic wind gusts, and small hail. Saturday morning should be dry, but showers and storms could develop once again across western North Dakota Saturday afternoon. Smoke is no longer expected to reduce surface visibility, but thicker smoke aloft will remain possible for the foreseeable future.

BIS WATCHES/WARNINGS/ADVISORIES
Heat Advisory until 9 PM CDT this evening for NDZ048-051.