Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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867 FXUS63 KDLH 170607 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 107 AM CDT Mon Jun 17 2024 .KEY MESSAGES... - Scattered storms this afternoon into evening. Some of these storms could become severe (15-20% chance) with 1-2" hail being the main threat during the afternoon, but transitioning to damaging winds during the evening. There is also a low-end threat for a tornado (<5%). - Very heavy rain and potential for flash flooding (50-70% chance), potentially localized considerable flash flooding, especially from central MN into the Iron Range and south into portions of NW WI Monday and Tuesday where a Flash Flood Watch has been issued. Scattered strong to severe storms are possible as well (15% chance) again Monday PM into Monday night and again on Tuesday. - Rain and storm chances return late this week into next weekend. && .DISCUSSION... Issued at 444 PM CDT Sun Jun 16 2024 Rest of today - this Evening: A few thunderstorms have begun initiating across Koochiching and northern St. Louis counties ahead of the cold front. So far these storms have remained sub-severe for the most part, though a few have been a little stronger with the potential to produce hail to the size of pennies around quarters in one or two of them. The environment along and ahead of the cold front remains highly unstable, with MUCAPE now having reached 1500-3000 J/kg across much of the Northland, highest with southward extent as a result of steep mid-level lapse rates (7-7.5 C/km). Low-level lapse rates have been a bit poorer, so the main threat through the remainder of the afternoon is primarily large hail (up to 1-2" in diameter), though some localized wind gusts to 60 mph cannot be ruled out as storms become surface based as the capping inversion erodes. O-6km bulk shear of 40-50 knots will continue to favor initial development being initially discrete cells given mostly straight hodographs with initial storm motion to the east to northeast. Short term guidance does suggest storm development along the cold front to occur in central MN, as well, due to the cap eroding there, too. As we push into the evening, storms will gradually propagate east along and just ahead of the cold front, potentially growing upscale into a broken line or cluster of storms. This transition in storm mode would also transition the primary severe hazard threat being more in the form of damaging winds to 60 mph, with a large hail threat (1") as storms track into the Arrowhead, Twin Ports, and NW WI. Still can`t rule out a low-end tornado threat (<5% chance) this 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, mainly around 10pm- midnight. Some locally heavy rainfall (quick 0.5-1") will be possible with any storm, though the localized basis should preclude minor flooding potential. Persistent cloud cover much of the day has also limited the high temperatures that were forecast, with most locations peaking in the 70s, though parts of east-central MN into western Wisconsin have touched the low 80s with dewpoints around 70 degrees. This has led to heat index values peaking mainly less than 90 degrees. Monday - Tuesday Heavy Rain/Flooding Threat: There will be a brief break in rain during the first half of the overnight hours tonight, but then another push of strong moisture advection along with a passing weak upper-level shortwave will favor the return of widespread rain/non-severe storms moving in from our south early Monday morning and persisting into mid-late Monday morning along and north of the stationary surface front setting up across central Minnesota into NW WI. A second round of developing showers/storms Monday afternoon pushes northward and sets up in northern and northeastern MN Monday evening into Monday night along and north of a northward moving warm front (formerly the stationary front). This later Monday round is when the heaviest rain and flash flooding threat will be maximized as PWATs reach above 1.8-2" (near maximum of climatology), though an additional round of showers and storms are likely to develop along and ahead of a cold front Tuesday PM leading to lingering flash flooding potential on Tuesday/Tuesday night if storms track over the same locations with these several rounds. With that said, there is still a bit of uncertainty in CAM guidance on where the heaviest rain will fall through Tuesday evening depending on how quickly the stationary front/warm front moves northward on Monday. We will be looking at 1-3" of rainfall across the Northland, with localized amounts of 3"+ (15-30% chance) from the Brainerd Lakes to the Iron Range and areas southeast, generally in line with locations where a Flash Flood Watch has been issued. The Flash Flood Watch is in effect from 1 PM Monday to 7 AM Wednesday to capture the several rounds of heaviest rainfall and lingering flooding concerns. Shifts to the coverage and locations of heaviest rainfall and locations are still likely, so changes to the Flash Flood Watch coverage and duration are likely to change. Monday - Tuesday Severe Potential: For later Monday into Monday night, there is an additional threat for scattered severe storms along and north of the northward pushing warm front. These storms will be predominately elevated in nature, so the main risk will be large hail, but there will also be a lower end threat for damaging wind (5% chance) and perhaps a tornado (2% chance) for storms nearest to the warm front. Tuesday will also see a potential for severe storms (15% chance), primarily along an eastward pushing cold front on Tuesday afternoon and evening as the surface low pushes northeast of the Northland. The CAPE/shear combination--with shear being parallel to the cold front--would support more of quick upscale growth into a line of storms, so the main threat would be in the form of damaging wind gusts, with a lesser threat of hail up to the size of quarters. The severe threat diminishes with eastward extent into north-central WI later Tuesday evening with the loss of daytime heating. Mid-Week Lull: There will be a brief break in precipitation by mid-week (Wednesday-Wednesday night) as surface high pressure moves through the region. Additional Late Week/Weekend Active Weather: Looking ahead into late this week into next weekend, models point to another active pattern of showers and storms with some heavy rain and severe potential yet again, though confidence at this timeframe is lower due to varying model solutions regarding the timing of shortwave troughs and surface lows. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 107 AM CDT Mon Jun 17 2024 VFR conditions are expected to prevail early this morning ahead of showers lifting in from the southwest closer to daybreak. Showers are expected to increase in coverage through the day along with intensity leading to MVFR visibilities. Some thunderstorms will be possible during the afternoon and early evening hours before showers take back over with MVFR visibilities and ceilings. Light winds tonight will become easterly Monday as a boundary stalls out across the region. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 938 PM CDT Sun Jun 16 2024 Dense fog will persist from the Twin Ports to the North Shore through late evening or early morning. We`ve extended the Dense Fog Advisory through 5 AM CDT from Taconite Harbor to Grand Portage. Fog will also be possible along the South Shore but it`s not expected to be as widespread. A few thunderstorms will be possible tonight, mainly along the South Shore. An isolated severe storm is possible capable of producing hail and gusty and erratic winds in excess of 40 knots. Winds will switch to west to southwest overnight, then back to onshore flow out of the east to northeast on Monday. Winds will gust to around 15 knots again on Monday and increase a bit into Monday night. More thunderstorms are expected Monday into Tuesday. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...Flood Watch from this afternoon through Wednesday morning for MNZ019-025-026-033>038. WI...Flood Watch from this afternoon through Wednesday morning for WIZ001-006-007. MARINE...Dense Fog Advisory until 5 AM CDT early this morning for LSZ140-141. && $$ DISCUSSION...Rothstein AVIATION...BJH MARINE...Melde