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
809 FXUS63 KBIS 172257 AFDBIS AREA FORECAST DISCUSSION National Weather Service Bismarck ND 557 PM CDT Fri May 17 2024 .KEY MESSAGES... - Severe Thunderstorm watch until 02z. - Scattered severe thunderstorms are possible this evening. The expected hazards will be damaging winds up to 70 mph and hail up to quarter size. - Windy and cooler on Saturday with highs mostly in the 60s. - Daily chances (40%) for showers and thunderstorms continue through the weekend and into early next week. && .UPDATE... Issued at 557 PM CDT Fri May 17 2024 ** MESOSCALE UPDATE ** The primary severe-storm risk the next few hours will be in the form of damaging winds of 60-70 mph from the Hettinger area toward Fort Yates, Linton, and toward Ashley/Wishek and into Stutsman, LaMoure, and Dickey Counties. The northern edge of the more sustained damaging wind risk will likely be limited by the sagging, though gradually-decelerating outflow boundary/radar fine-line extending from Carrington to Steele and now to the south of Bismarck/Mandan. The storms near Hettinger are on the leading edge of stronger forcing aloft and increasing low- and deep-layer wind fields, including 0-3-km bulk shear increasing to at least 25 kt. The area ahead of that convection and south of the outflow boundary will have sufficient bouyancy to present an organized damaging wind risk, assuming it does not outrun the increasing winds aloft to the west, or that the outflow boundary does not progress to the south too quickly. Otherwise, the boundary layer to the north and west has cooled and the severe-storm risk is diminishing in west central and north central ND. The storms immediately north of the outflow boundary, e.g., near the Bismarck/Mandan area toward Carson and Elgin, are likely elevated and pose a more marginal severe risk given the cooler boundary layer in that zone. UPDATE Issued at 241 PM CDT Fri May 17 2024 Quick update that there is now a Severe Thunderstorms watch for most of western and central ND until 02z. Hazards are still 70mph winds and quarter sized hail. It may need to be expanded into the far southeast, but we will see how the storms go. && .DISCUSSION... Issued at 200 PM CDT Fri May 17 2024 The upper level wave has started to move into the state, as seen in satellite with agitated mid level clouds at 18z. Near the Montana/North Dakota border near Glendive, MT, south to Bowman, ND and over to Glen Ullin, ND cumulus has started. We should be warmer than our convective temperature now, so more and more cumulus should start to pop in the next hour, especially with the diffluence over head from the upper level wave. The latest SPC update at 1630z expanded the slight risk through the whole CWA. Some CAMs have isolated storms forming now before the main cold front moves through and forms a line. The main threat is still 70mph winds because of a lack in CAPE, and the storm mode. The storm mode is a line because the shear vector will be parallel to the cold front, continuously allowing new convection to form in the line. DCAPE look very favorable with values around 1000 J/kg, and model soundings have an inverted V with steep lapse rate. This allows the wind to mix down very easily. So the isolated storms that form now, will then combine into a line as the cold front moves in. Timing on the line forming looks to sometime around 21-23z. The CAMs are all a little different on the which storm mode they start as. The line will move west to east, leaving our area around 03z. Most CAMs are confident on that. Then on the back side of the front, more showers and possibly thunderstorms will form again in the west, lasting through the night. Saturday will be breezy on the backside of this front with cold air advection and a tight pressure gradient. Westerly winds will gust to 40mph, with sustained winds at 30mph. We will most likely need a Wind Advisory from Saturday morning, until around 00z. Since we have active storms today, we will wait until the overnight period to issue that. Highs on Saturday will be much cooler in the 60s, this cooler trend will continue through the weekend. Flow aloft this weekend will remain southwest with another low and wave moving through Sunday and Monday. Chances for showers and thunderstorms will continue through the forecast period with the highest chances ending Monday when the southwest flow relaxes some. Mid next week the flow is weak in a quasi-zonal flow. Another big low pressure possibly forms in the Pacific Northwest Wednesday. This could bring another round of storms with diffluence flow aloft and southerly flow at the surface Thursday and Friday. Temperatures look to stay slightly below average in the low to mid 60s through Friday. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 200 PM CDT Fri May 17 2024 VFR this afternoon until strong thunderstorms move west to east between 21 and 03z. Overnight light rain may continue until the early morning. Winds will gust around 20kts today from the southwest increasing to 35kts from the west by Saturday morning. Skies will clear out by late morning Saturday except near KMOT where 3kft ceilings could linger, left it as SCT for now until we get more confidence. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ MESOSCALE...CJS DISCUSSION...Smith AVIATION...Smith