Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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187 FXUS63 KDLH 172138 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 438 PM CDT Mon Jun 17 2024 .KEY MESSAGES... - Flash Flood Watch area remains unchanged with this update, though the there are still some pockets of 1.5-3" of rainfall possible with storms this evening into tonight and again on Tuesday. Highest amounts are expected along and north of the Iron Range. - Main severe threat for this evening into early tonight with elevated storms will be hail (5-10%). Can`t rule out some gusty winds for storms closer to the surface warm front. - Additional potential for a line of strong to severe storms (15%) on Tuesday as it works across the region. Main risk will be damaging wind gusts to 60, though some large hail and a low-end threat (2%) for an embedded tornado are also possible. - Additional chances for rain and storms this weekend, with heavy rainfall potential, as well. && .DISCUSSION... Issued at 439 PM CDT Mon Jun 17 2024 Rest of Today: The Northland is experiencing a brief period of rain-free weather this afternoon as showers/storms across southern MN into western WI are occurring north of the surface warm front draped across northern Iowa into central WI. There has even been some clearing between some high clouds for northern MN this afternoon with high temperatures in the 70s there, but 60s form east- central MN to the Twin Ports and NW WI where the cloud cover has hung on. This Evening - Tonight: Showers and thunderstorms make a push back into the Northland from our south starting mid-late this evening as the warm front surges northward, and persist into the overnight hours along and north of the front. CAMs are still in disagreement on the the coverage and eastward extent of these storms later this evening into tonight, but do favor the best coverage over north-central Minnesota where the better forcing for ascent will be present ahead of the approaching low pressure center. Rich moisture advection (PWATs of 1.6-1.9", near maximum of climatology for mid-June) and marginal mid-level lapse rates (6-7 degC/km) will aid in the production of 700-1500 J/kg of MUCAPE this evening into tonight. The CAPE/Shear combination would support a marginal threat for severe hail (5-10%) in the elevated storms over north-central MN. Can`t rule out some stronger wind gusts up to 50-60 mph for storms closer to the surface warm front, but the elevated nature of most storms should keep the wind threat lower (5% chance). The severe threat weakens the later we get into the overnight hours. As for rainfall, QPF amounts have continued to trend slightly downwards for this evening and tonight. Amounts generally range from 0.25-0.5" in NW WI to 0.5-1.25" in the Minnesota side of our forecast area, with the highest amounts in north-central MN where storm coverage will be better. The Flash Flood Watch remains in place as is due to some signal for localized pockets to 1.5" tonight and additional rainfall with Tuesday`s storms (more details below). These amounts aren`t too entirely high, but will likely be coming in a relatively short timeframe onto already saturated soils and in efficient rainfall rates in the storms due to high PWATs and a deep warm/moist layer in the atmosphere. Can`t rule out some ponding or minor flooding due to the rainfall, but are no longer expecting considerable flooding potential. Tuesday - Tuesday Evening: A strong Colorado low ejecting northeast into the eastern Dakotas by Tuesday morning will keep showers/storms lingering over north-central Minnesota through much of Tuesday morning as the warm front lifts towards the International Border, while the rest of the Northland could see some lingering drizzle or spotty showers given lingering low-level moisture and cloud cover. This sets the stage for how the rest of Tuesday will turn out with regards to storm development along/ahead of the cold front Tuesday afternoon and evening as it could affect whether afternoon high temperatures can become warm enough to overcome the weaker capping inversion, particularly for north- central MN where morning convective will linger longest. With that said, most of the Northland will still see a strong surge of warm/moisture advection in the warm sector ahead of the cold front, pushing high temperatures into the 80s for most with dewpoints climbing into the 70s. Combined with steepening lapse rates aloft, this could push instability values up to 2000-3000 J/kg with effective shear values around 35-40 knots. Hodographs/model soundings show predominately unidirectional winds with height above the lowest 1-2km, so quick growth to a more linear storm mode would be favored. While damaging wind gusts to 60 mph would be the main threat (15% chance) as storms initiate in the mid-afternoon over north-central MN, the low- level turning could be enough to produce a low-end embedded tornado threat (2%) in the line as storms move eastwards into northeast MN and NW WI into the evening. Large hail up to 1 inch will also be a threat in these storms, but less so than the wind threat. Storms should gradually weaken mid to late Tuesday evening as they get farther into NW WI and lose a lot of the instability with the loss of daytime heating. Rainfall may be locally heavy on Tuesday under the stronger storms, but the transient east-west movement of the cold front and storms should limit the amount of time this heavy rainfall falls in any one location. However, given rainfall from previous rounds of rainfall, the total additional rainfall from this evening through Tuesday will be a general 1-2 inches, with some localized pockets to 3 inches. Where exactly the heaviest rainfall with next two rounds of rainfall overlap still varies a bit from model to model, hence the Flash Flood Watch not being adjusted in coverage, but the best potential has shifted into northern MN. Minor flooding/ponding will be the main concern as a result of any heavy rainfall and runoff due to the decreasing potential for 3+" of rainfall (<10%) limiting the risk for more significant flash flooding to occur. The warm temperatures and humidity will likely push Heat Index values in NW WI to around 90 degrees on Tuesday afternoon. Not quite to Heat Advisory levels, but still very muggy. Wednesday - Early Thursday: The Northland gets a break from the wet weather for a brief time Wednesday through early Thursday as high pressure moves through the region. Temperatures will be more pleasant both days, with most locations seeing highs in the 70s. Late Thursday - Next Weekend: We see another shift to more active weather late Thursday into this weekend as we get into another southwest flow pattern with a warm front settling somewhere across the Upper Midwest late week and then the main upper/surface low moving through the region Saturday into early Sunday. Gulf of Mexico moisture will also be surging north (PWATs 1.6-1.9" again) with this system. Instability looks more weak to moderate, but enough to support potential low-end strong to severe storm threats for our neck of the woods on Saturday and Sunday. The main concern during this period would be additional prolonged heavy rainfall potential late week into the weekend. Still to early to pin down rainfall amounts, but NBM probabilities of >1" Thursday-Sunday are 50-80%, with >2" sitting at 30-50% for much of the Northland, though there are a non-trivial amount of GEFS and Euro ensemble members with accumulations over 3". We will need to watch trends with this late week/weekend system closely with future forecast updates. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1250 PM CDT Mon Jun 17 2024 Light rain is moving out of the vicinity of KHYR by 19Z. Otherwise, expect a period of VFR conditions under some mid/high level clouds until a batch of rain north of a warm front currently located over southern MN pushes north into the area from south to north this evening into tonight, lingering longest at KINL that will be closer to the low pressure center. Expect MVFR to IFR ceilings and some reduced visibilities with the showers and storms this evening and tonight, with some LIFR ceilings possible on the backside of the rain showers at KDLH/KHIB late tonight into Tuesday morning, and KINL on Tuesday morning. LLWS is also expected tonight at the TAF sites given a low-level jet moving into the region. Winds out of the east this evening and tonight, gradually increasing in speed, then turn southerly and gusty on Tuesday. Daytime gusts on Tuesday could reach up to 20-25 knots in the morning, and up to 25-30 knots in the afternoon ahead of an approaching cold front. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 439 PM CDT Mon Jun 17 2024 Scattered shower and storm potential over western Lake Superior very late this evening and tonight, though the threat for any severe weather looks to remain west of the Lake. Better potential for strong to severe thunderstorms late Tuesday afternoon into evening as a line of storms develops along a cold front in Minnesota and moves east over the Lake. Main concerns would be wind gusts up to 50 knots with these storms, though can`t rule out some hail up to 1 inch in diameter with those storms, either. Outside of storms, northeast winds on the Lake this evening and tonight will increase to around 15 knots. Winds veer out of the south ahead of the cold front tomorrow, with gusts approaching 25 to 30 knots in the Twin Ports and South Shore from late Tuesday morning through evening, along with some brief winds to 25 knots along the North Shore in the evening with some 2-4 ft waves. Therefore, have issued a Small Craft Advisory to account for the period of hazardous conditions to small craft Tuesday into Tuesday evening. Winds remain more tame Wednesday as drier weather briefly returns under high pressure. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...Flood Watch through Wednesday morning for MNZ010-011-018-019- 025-026-033>038. WI...Flood Watch through Wednesday morning for WIZ001-006-007. MARINE...Small Craft Advisory from 11 AM Tuesday to 1 AM CDT Wednesday for LSZ121-144>148-150. Small Craft Advisory from 9 PM Tuesday to 1 AM CDT Wednesday for LSZ140>143. && $$ DISCUSSION...Rothstein AVIATION...Rothstein MARINE...Rothstein