Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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981 FXUS63 KDLH 232355 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 655 PM CDT Sun Jun 23 2024 .KEY MESSAGES... - Isolated storms likely through early this evening. Severe weather is not expected. - Highly conditional chance of severe thunderstorms Monday and Monday night (risk level 2 out of 5). All severe hazards are possible and will be dependent on storm mode and timing. - Slight chance of non-severe storms Tuesday then quieter Wednesday. Thunderstorm chances return Thursday night and Friday. && .DISCUSSION... Issued at 443 PM CDT Sun Jun 23 2024 A broad upper low centered over north-central Ontario this afternoon will propagate southeastward tonight into the western Great Lakes and New England by 12Z Monday. Showers this morning over much of the Northland gave way to mostly sunny to partly cloudy skies this afternoon. The sunshine allow temps to climb into the middle and upper 70s, except in the Arrowhead where clouds loitered. Those temps and the low-level moisture flux from this morning`s rain allowed MLCAPE values to push into the 750-1250 J/kg range this afternoon, more than sufficient for a few isolated storms to develop. With the limited instability and ample 0-6 km shear of 45-55 kts, a few storms may briefly become strong with small hail to half-inch diameter, wind gusts up to 40 mph, occasional cloud-to-ground lightning, and brief heavy rain. The storms should taper off through early evening with the loss of daytime heating and use of available instability. Patchy fog may develop tonight in response to clearing skies, light winds, and recent precipitation. The main focus for Monday through early Tuesday morning is the highly conditional potential for strong to severe thunderstorms on Monday afternoon into Monday night. A warm front will be lifting north towards the CWA through the day Monday, bringing WAA and moisture advection (PWAT of 1.5-1.9") into the area. This will result in very warm temps tomorrow for the southern half of the CWA, with highs in the low to mid 80s. Aloft, a steep elevated mixed layer will be moving into the region, with mid-level lapse rates increasing in excess of 8-8.5 degC/km by the late afternoon and early evening hours on Monday. The resulting MLCAPE values are expected to become high to possibly extreme, with models showing highest amounts around 3000-3800+ J/kg. This high instability will be combined with a favorable shear environment, where 0-6 km bulk shear magnitudes will be around 45-50 knots. Given the favorable thermodynamics and dynamics at play tomorrow, the SPC has our CWA highlighted in a Slight Risk, with the main focus on very large hail and damaging winds, although tornadoes cannot be ruled out if storms can become surface based near the warm front. There is one major caveat to mention for tomorrow`s severe weather potential, which is that there will be an appreciable cap present through the day. This greatly decreases confidence for tomorrow, which is currently still low. The aforementioned EML will be warming temps around the 700-800mb layer to 12-16 degC, increasing MLCIN above 200-300 J/kg by the late afternoon hours tomorrow. There is some suggestion from a few CAMs that this cap will be able to be overcome by the early evening hours tomorrow. This is most likely a result of a combination of a surface trough/occluded front advancing from the west and the nocturnal LLJ strengthening and allowing elevated convection to develop. Provided that the cap is able to be overcome tomorrow (which is far from certain), the two primary severe hazards will be very large hail up to 2" in diameter and damaging winds up to 75 mph. Large hail will be most likely in north-central Minnesota, where convective initiation will be occurring near an approaching cold front and MUCAPE will be abundant. Storm mode from the CAMs has been highly variable between the different models. However, there is some consensus that briefly discrete cells will be transitioning more linear Monday evening. This change in storm mode would limit the large hail potential to fairly early in the event with damaging winds becoming the main hazard as convection propagates eastward. Storm mode will also determine the tornado potential tomorrow, with a tornado or two being possible if convection is able to remain more discrete. There is plenty of low-level curvature in hodographs, with high 0-1km SRH of 100-200 m2/s2. As storm mode becomes linear, a QLCS tornado may also be possible. However, damaging winds are the main concern with a linear storm mode. It is worth mentioning that if a MCS is able to develop by the late afternoon hours tomorrow in western MN, a derecho producing winds to or possibly in excess of 75 mph is not out of the question for tomorrow, mainly occurring south of U.S. 2 across the CWA. In the latest Day 2 Convective Outlook from SPC, this potential has been highlighted with a 15% hatched area for damaging winds. However, this potential is still highly dependent on the cap breaking at the right time and is uncertain given the disagreements among the models. Overall, tomorrow`s severe weather potential is shaping up to be either a "boom or bust" type event. One final note about tomorrow is that flash flooding is currently not expected, as these storms will be moving through the area fairly quickly and QPF will likely remain under 1.5 inches by early Tuesday morning. While widespread flooding is unlikely, ponding on roadways and minor flooding of low-lying areas will still be possible given that soils are well saturated across the CWA. The progressive pattern continues on Tuesday with a shortwave trough propagating eastward across the region and a weak cold front diving southeastward out of Canada during the afternoon and evening. A few showers or storms may percolate along the boundary. Neither severe weather nor additional flooding are expected with the Tuesday storm chances. High pressure makes a one-day-only appearance for Wednesday with quieter conditions expected. Another surge of warm air aloft will accompany a northward moving warm front Thursday. Isentropic forcing for ascent over the warm sector will lead to chances of showers and possibly thunderstorms. The precip chances appear to hold off until late afternoon or evening and spread northward with time. Precip chances persist on Friday as an area of low pressure propagates northeastward across the region. A cool front will follow Friday night with high pressure to return on Saturday. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 654 PM CDT Sun Jun 23 2024 Isolated showers are expected to diminish around sunset and are not likely to affect terminals this evening. Winds will become light to calm, and with mostly clear skies, fog will become possible at the usual spots tonight (most likely HIB/DLH/HYR, but also possible at BRD/INL). On Monday, VFR conditions prevail. Wind speeds will gradually increase from the south with gusts 15 to 20 kt in the afternoon. There will be a 30 to 60 percent chance for thunderstorms starting during the afternoon. Timing and potential for storms remains uncertain as this is a conditional threat, meaning that all ingredients have to come together just right for storms to form. If they do, all hazards for severe weather, including damaging winds, large hail, and perhaps tornadoes will be possible. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 443 PM CDT Sun Jun 23 2024 Light winds of around 5 knots persist tonight. With a weak pressure gradient overhead, the wind directions will be influenced by terrain and onshore flow, and will be variable by location and time. Low pressure will move eastward across the region Monday and Monday night. Expect winds to become southeasterly and easterly gradually backing northeast, particularly in the southwest arm of the lake, by evening. Wind speeds will increase to 5 to 10 knots with gusts up to 15 knots. There is a chance of thunderstorms, mainly Monday evening, which may be strong to severe. Hail up to an inch in diameter is possible. Strong winds are not out of the question. There is a small chance of wind gusts of 45 to 60 knots if storms coalesce into a line during the late afternoon or evening. Winds turn southwesterly and strengthen on Tuesday to 15 to 20 knots with gusts of 18 to 25 knots. A Small Craft Advisory may become necessary. A cool front will propagate southeastward Tuesday afternoon and evening. Winds will veer northwesterly behind the front and wind speeds will diminish. 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...None. && $$ DISCUSSION...Huyck/Unruh AVIATION...JDS MARINE...Huyck/Unruh