Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
023 FXUS63 KBIS 292240 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 540 PM CDT Wed May 29 2024 .KEY MESSAGES... - Severe thunderstorms remain possible through this evening, with the threat diminishing during the overnight hours. This threat will begin in the west late this afternoon or early this evening then spread eastward into central portions. Hail up to the size of ping pong balls and 70 mph winds are the primary threats. - With this storm complex, there is an 80 to 90 percent chance of a wetting rain (a tenth of an inch or more) for much of western through central ND, including the James River Valley. - Breezy to windy southeast winds will remain into this evening, especially in west and central portions where winds could gust up to 50 MPH. A Wind Advisory remains in effect for these locations. - Temperatures will cool slightly on Thursday, then go on a warming trend to near to slightly above average through the weekend. - Shower and thunderstorm chances may linger across the north and east for Thursday. They may then be isolated to scattered on Friday. Periodic shower and thunderstorm chances will then return Sunday through the first half of next week. && .UPDATE... Issued at 540 PM CDT Wed May 29 2024 ** MESOSCALE DISCUSSION ** Strong-severe storm risk is increasing in far western ND and is expected to peak in the 23 to 02 UTC (6 pm to 9 pm CDT) window. As of 22 UTC, low-level convergence is increasing along the ND/MT border region, with veering winds upstream in MT resulting in a more well-defined surface wind shift. Satellite images show deepening cumulus along/ahead of the wind shift north all the way to the Canadian border, and objective analysis data reveals that MLCIN has diminished as far north as McKenzie County. The residual capping along the wind shift in Williams and Divide Counties may also diminish sufficiently for sustained convective initiation in those areas in the next 1-2 hours. MLCAPE on the order of 1500-2000 J/kg will promote intense updrafts, but their individual longevity will be limited by weak effective-layer shear on the order of 20-30 kt. We therefore continue to expect multicellular to transient supercell structures in this event, with peak hailstone sizes from quarter to ping pong ball size. Large temperature-dewpoint spreads and the high-based nature of storms presents an outflow wind risk, as well, especially in southwestern ND where DCAPE exceeds 1000 J/kg. However, 0-3-km bulk shear has diminished to less than 20 kt, which will likely limit a more organized damaging wind risk, instead favoring a more transient wind threat of 60-70 mph with any clustered or collapsing storms. Mean winds and right-moving supercell motion vectors (which would apply to any transient supercells) favor a general east-northeast motion around 20 kt this evening. Based on these speeds and extrapolation along with recent Warn-on- Forecast (WoFS) guidance, the convection would reach a line from roughly Watford City to Dickinson and Hettinger in the 00 to 01 UTC time frame. The southwestern ND area has the relatively highest, albeit still modest deep-layer shear, largest bouyancy, and weakest capping, so the severe-storm risk will be greatest in that area. Further north, in Williams and Divide Counties and vicinity, the environment is less favorable for organized severe storms due to deep-layer shear being weakest there. Moreover, further east in central ND, residual capping is also expected to marginalize the severe storm risk later this evening as convection reaches that area in a few hours. CJS && .DISCUSSION... Issued at 320 PM CDT Wed May 29 2024 A Severe Thunderstorm Watch is now in effect across western North Dakota until 10 PM CDT. A slight risk of severe weather remains through tonight, more so later this afternoon through this weekend. The overall threats has not change much since this morning. Thermal ridge will bring ample amounts of mildly capped CAPE. The stronger shear however still looks to remain behind the cold front and not necessarily in the warm sector. This effective shear of around 30 knots may not be enough to sustain stronger super cells. This combined with higher LCLs and hodographs still indicating the better helicity is in the 0 to 3 KM level than the 0 to 1 km level has lead to lower confidence in an isolated tornado threat. Thus will stick to the large hail and strong winds. Hail up to ping pong ball size still seems the more likely size, although an isolated golf ball size is possible. High DCAPE and adequate 0 to 3 KM shear also indicate a decent wind threat today with gusts up to 70 MPH. Timing wise, look for storms to start developing in the late afternoon especially across the southwest. Then look for upscale growth through the evening that pushes eastward. The shear vector to the disturbance today will promote multicell and clusters. Perhaps a discrete cell is possible initially, although the approaching cold front will make this threat short lived. By early to mid evening storms become more clusters to lines of storms and slowly progress eastward into the overnight hours. The cold front progressing eastward may start to tamper with the instability perhaps lowering the hail threat, although the wind threat will remain into central portions. So overall between now and around midnight local time in western and central portions be sure to monitor for the latest severe weather watches and warnings. Overnight this looks to transition into a broad line of showers and thunderstorms. Some stronger storms may be embedded at times through tonight. Otherwise the strong southeast winds will become a breezy westerly wind behind the front tonight, with breezy southerly winds lingering in the east ahead of the front. There remains a Wind Advisory into early evening for these strong southeasterly winds. Lows tonight will be mild and generally in the upper 40s to upper 50s. Cold front will continue its eastward push through Thursday with a broad trough lingering in the north. Shower and thunderstorms will be found along this front in the east, with some isolated to scattered coverage possible in the north. Temperatures will slightly cool behind this front, with breezy westerly winds also found. A broad trough pattern then looks to linger on Friday. This could bring about near normal temperatures and some isolated to scattered showers and thunderstorms. The threat for severe weather looks low at this point. A dry and warming pattern then looks to start the weekend on Saturday. Sunday continues to be warmer. Another passing wave could bring a few showers and thunderstorms. An active yet mild pattern could then be found to start next week. The chances for severe weather at this point are low, although the CSU-MLP does have some low probabilities, more so on Sunday. Something to monitor through the weekend. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1245 PM CDT Wed May 29 2024 Mainly VFR conditions with breezy to windy southeast winds will be found through this afternoon. Later this afternoon through this evening showers and thunderstorms look to develop across the west and gradually push eastward. A few of these storms could be strong to severe and bring brief MVFR conditions. A cold front will then push eastward tonight bringing widespread showers and thunderstorms. Lower clouds with this front along with showers could also bring some MVFR conditions. Showers and a few thunderstorms could linger across the east and north Thursday morning. Lower clouds and MVFR conditions will gradually lift to VFR levels through Thursday morning. A breezy westerly wind may also be found. Some low level wind shear is possible during passage of this front, although confidence is not high enough to include at this time. && .BIS WATCHES/WARNINGS/ADVISORIES... Wind Advisory until 8 PM CDT /7 PM MDT/ this evening for NDZ001>003-009>011-017>021-031>035-040>046. && $$ UPDATE...CJS DISCUSSION...Anglin AVIATION...Anglin