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
109 FXUS63 KBIS 190857 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 357 AM 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. && .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 /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1225 AM CDT Sun May 19 2024 VFR conditions to begin the 06Z TAF period. Expect increasing mid level cloudiness from south to north through the night and into Sunday morning. Sunday afternoon into Sunday evening, there will be lowering clouds north with a hit and miss shower. Added a VCSH at KXWA and KMOT later in the TAF period. In the south, especially from KBIS to KJMS, there will be the potential for showers and thunderstorms late afternoon through the evening. The favored area looks to be south of KBIS so added a VCSH around 2300 UTC. AT KJMS we added a VCTS beginning around 01 UTC. Increasing low level clouds will also lift into the area with the potential for MVFR-IFR around KBIS-KJMS and south after 00Z Monday. Will add a scattered layer MVFR at this time and monitor. Light winds to begin the TAF period. Winds will become south to southeast Sunday morning and then shift east to northeast later in the day. Western and northern Taf sites will shift to northerly aft 00Z Monday. winds generally 10 to 20 knots aft 12Z Sunday but southeast flow will be on the higher side of this range Sunday afternoon. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...TWH AVIATION...TWH