Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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
907 FXUS63 KDLH 161842 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 142 PM CDT Sun Jun 16 2024 .MESOSCALE... Issued at 117 PM CDT Sun Jun 16 2024 Persistent low level cloud cover has stuck around across much of the Northland into early this afternoon, tampering temperatures down a bit (~5 degrees) relative to the previous forecast, though we are starting to see some signs of clearing on visible satellite imagery in parts of northern MN and NW WI. Despite this cloud cover, strong southerly moisture advection and warm air advection into the Northland combined with steepening mid- level lapse rates (7-7.5 C/km) has led to the development of 1000-2000 J/kg of MUCAPE across central into North-central Minnesota. A capping inversion is still in place over the Northland, but short-range guidance has come into better agreement on this cap breaking by mid-afternoon just to the west of Cass/Itasca/Koochiching Counties in north-central MN. Once the cap does break, storms will have access to 0-6km bulk shear of 40-50 knots and mostly straight hodographs. This would provide initial storms with enough of a cape/shear combination to fire off discrete supercells along and just ahead of the cold front and move eastward into our north-central MN counties, with the primary threat being large to very large hail (1-2" size). As storms become more surface-based late this afternoon (4-6pm), storm motion should shift more southeasterly, eventually growing upscale into a line/cluster of storms into the evening hours. At that time, the threat would shift to more damaging wind potential, with some marginally large hail potential as storms track into the Twin Ports, Arrowhead, and NW WI during the evening. Also can`t rule out a low-end tornado threat (<5% chance) during the late afternoon into evening given there will be some slight turning in the low levels that could give these storms access to around 100 m2/s2 of effective SRH, with the best environment in the Twin Ports to NW WI. Severe storm potential should wane and exit to the east/southeast of the area by late evening, generally around the 10pm-midnight timeframe this evening. && .KEY MESSAGES... - Scattered storms are possible this afternoon and evening (~50% chance). A few storms may become strong to severe (5-15% chance) with large hail being the main threat, but damaging winds and perhaps a tornado also possible. - Very heavy rain and potential for locally considerable flash flooding is possible (40-60% chance), especially in northeast Minnesota. Scattered strong to severe storms are possible as well (15% chance), with large hail being the main threat. - Rain and storm chances will continue through the end of the week and into next weekend. && .DISCUSSION... Issued at 400 AM CDT Sun Jun 16 2024 The first of several rounds of heavy rain is happening right now, mainly impacting northwest Wisconsin. This initial surge of rain and embedded non-severe thunderstorms will continue northeast through the morning, eventually ending as the upper level wave moves off to the northeast. Rainfall amounts thus far have been about as expected, with higher observed amounts just over 0.7". Radar estimates suggest totals around or just over an inch may have fallen across parts of southern Price County. All-in-all, this is transpiring as expected, and we could end up with localized amounts up to ~2" before this ends later this morning. Hydro-wise, no major concerns at this time, but some localized minor flooding still can`t be ruled out. In the wake of this first round of rain, strong southerly warm and moist air advection will bring some pretty impressive instability for this afternoon, especially so in northwest Wisconsin where MUCAPE values around 2000-3000 J/kg, possibly approaching 4000 J/kg, will lead to the potential for some strong to severe storms. As has been mentioned in previous discussions, this will be a conditional threat with strong capping aloft in place. We also have some weak subsidence aloft that negates some synoptic influence. But, models have been persistent enough about having some frontal boundaries around this afternoon, which will likely be enough to bust the cap and lead to the potential for isolated to scattered strong to severe storms this afternoon and evening. The initial threat, and the most likely threat, will be for very large hail (2" in diameter or more) with the strong instability in place, especially with the first discrete cells that form. There`s also enough veering in the low-levels, particularly northwest Wisconsin, such that a tornado can`t be completely ruled out (though hodographs are not perfectly favorable for tornadic supercells). Damaging winds can`t be ruled out if storms are able to organize into a line, which would be most likely in the evening. Temperatures will be quite warm today, topping out in the mid to upper 80s for east-central Minnesota into northwest Wisconsin. This isn`t warm enough to warrant a heat advisory, but the heat could be hazardous for sensitive groups, especially for those without good access to hydration or air conditioning. After sunset, we should lose most instability for a while, leading to perhaps a brief break in rain for many places. We then get another strong push of warm and moist air attendant with passing upper-level shortwaves that will be favorable for widespread rain and thunderstorms. This is looking like it will start off as a widespread cluster of rain and non-severe storms through mid-day Monday, then perhaps another reorganization that will favor northeast Minnesota as we go into Monday evening and night as strong low-level frontogenesis sets up. This is when we will see the greatest threat for flooding, and with excessive PWAT values around or perhaps slightly higher than 1.75" (near or at maximum climatology), we will be looking at the potential for 2-3" of rainfall (perhaps locally higher) through Tuesday, with the best potential for this just north of the Brainerd Lakes, stretching into the Iron Range, north towards International Falls, and east towards Ely. The WPC has placed this area under a moderate risk for flash flooding (40-60% chance). The latest trends suggest that the warm front will be at least somewhat transient, so that will reduce the threat for extreme flash flooding to some extent, favoring instead a broader risk for considerable flash flooding. We decided not to issue a Flash Flood Watch for this update as we continue to narrow down the area most susceptible for flash flooding, but a Flash Flood Watch will likely be needed. In addition to the flooding threat, instability will increase again Monday night into Tuesday morning, and there will be a threat mainly for large hail with some of the thunderstorms most likely on the southern end of the rain closer to the warm front. Couldn`t rule out some strong winds as well, but right now large hail seems to be the biggest threat (5-15% chance). There remains a threat for isolated to scattered severe storms on Tuesday as a cold front passes through, and this is still looking more likely to be a damaging wind threat moreso than any other hazard, though some large hail could be possible. We retain a slight risk (15-40% chance) for excessive rainfall from the WPC for much of the region with the combination of rain expected Monday night, then finishing off on Tuesday with the storms moving from west to east. We are still looking to see a brief break from the active weather with high pressure on Wednesday, but looking ahead through the end of the week and next weekend, models suggest that the active pattern will continue with more rain and storm chances. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 116 PM CDT Sun Jun 16 2024 Stubborn onshore flow off of Lake Superior has led to periodic intrusions of dense fog into KDLH and North Shore terminals along with LIFR to VLIFR ceilings. Expect these low ceilings and fog to hang around into mid afternoon until winds can take on a more southerly direction. IFR ceilings at KHIB should also rise to MVFR by mid-afternoon. Otherwise, the remainder of the area is sitting under MVFR ceilings. Confidence has increased in the development of scattered showers and thunderstorms along a cold front in north-central Minnesota later this afternoon initially as individual storms, and then potentially growing into a line of storms this evening as storms and the front push southeast. Still need to pinpoint the exact timing of storms to terminals downstream, so amendments are likely later this afternoon and evening. There is a 15% chance that some of these storms could be strong to severe, containing very large hail (2"+ in diameter initially during the afternoon in NE MN). Damaging winds are also possible, but would become the primary threat this evening as storms transition into a line. Ceilings are expected to lift to VFR this evening. Some MVFR to locally IFR visibilities likely with the storms. There will be a brief break in precipitation tonight before another round of showers and storms move in from the southwest later tonight into Monday morning. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 143 PM CDT Sun Jun 16 2024 Dense fog continues to persist along the Twin Ports and North Shore, so have extended the Marine Dense Fog Advisory through this evening due to the weather pattern not really changing until storms move over the Lake this evening. Scattered storms, with a 15% chance of becoming strong to severe, develop along a cold front over north-central Minnesota this afternoon and push east into western Lake Superior this evening. Still expect the strong to severe storm threat to end around mid-evening as storms push southeast and weaken. Large hail and gusty, erratic winds will be the main threats with the storms. Expect onshore flow for most places the rest of today, with a shift to southwesterly overnight, then back to onshore flow out of the east to northeast on Monday. Winds may gust to around 15 kt today, decreasing tonight, and then gust to around 15 knots again on Monday. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. MARINE...Dense Fog Advisory until 1 AM CDT Monday for LSZ140>145. && $$ MESOSCALE...Rothstein DISCUSSION...JDS AVIATION...Rothstein MARINE...Rothstein