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Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
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Issued by NWS Milwaukee/Sullivan, WI
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-- Discussion containing changed information from previous version are highlighted. --000 FXUS63 KMKX 112103 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 403 PM CDT Thu Apr 11 2024 .KEY MESSAGES...-- Changed Discussion --- Localized heavy rainfall, small hail, and even an isolated land spout tornado remain possible later this afternoon / evening along a broken line of thunderstorms near our western CWA. These impacts are likely to be confined to southwestern and south central WI. - River flooding will continue through the weekend on isolated portions of the Lower Fox and Rock Rivers. - Gusty northwest winds are expected through most of Friday, with a gales expected over the open waters. - Above normal temps expected for the weekend into early next week. - Keeping an eye on thunderstorm potential next Tuesday.-- End Changed Discussion --&& .SHORT TERM...-- Changed Discussion --Issued 400 PM CDT Thu Apr 11 2024 Tonight through Friday night: We currently find ourselves on the northwestern quadrant of a deepening surface low, with a negatively tilted trough axis just west of us, and the resultant PVA favoring ascent. A north- south-oriented axis of 925mb Petterssen FGEN (as seen on Mesoanalysis) exists just west of Mineral Point and Lone Rock WI, and a line of showers and thunderstorms has strengthened along it. The descending branch of this frontogenetical convection and NVA from an exiting 500mb vort max appear to be responsible for a partial clearing of the clouds on either side of this line, allowing solar heating to further sharpen low level lapse rates and instability on either side. Mesoanalysis and HRRR forecast soundings expect roughly 500 j/kg of SBCAPE to develop on either side of the surface boundary. Light east winds east of the boundary coupled with northwest winds on the west side of the boundary create some surface vorticity along the line of storms, which may serve as an ingredient in weak landspout tornadogenesis. Given how slow moving this linear system is, localized heavy rainfall remains a concern. Small hail cannot be ruled out. Though this system appears to be stationary on radar (western edge of the CWA), note that the progression of the upper air pattern (and the cloud clearing) further east may lead storms to build on their eastern flanks, resulting in scattered to broken shower and storm coverage over our western CWA later today (just as CAMs expect). Storm coverage and intensity are forecast to decline around midnight, likely clearing out by sunrise Friday. Gusty northwest winds (gusts over 35 mph) are expected on Friday, with clouds gradually clearing out from west to east and daytime highs in the 50s. Sheppard-- End Changed Discussion --&& .LONG TERM...-- Changed Discussion --Issued 400 PM CDT Thu Apr 11 2024 Saturday through Thursday: Synopsis: The low pressure system bringing impacts to the short term weather will continue to move east into Quebec during the day on Saturday. Extending from the Dakotas into KS early Saturday morning, a compact trough axis will quickly pivot into the Lower Great Lakes Saturday night, bringing slight chances for showers and isolated thunderstorms. A weak surface low will accompany the upper impulse, allowing winds to turn out of the southwest as it moves into MN on Saturday afternoon. This will mark the beginning of an upward trend in high temperatures through the weekend, with above-normal warmth continuing into the beginning of next week. Moving across the Great Basin on Sunday, a more organized upper trough/low will progress toward the Front Range of the Rockies on Monday, ejecting into the Central Plains Monday night. Attendant surface cyclogenesis will occur beneath the encroaching trough along the CO-NE-KS border vicinity Monday afternoon. The surface low will advance through the Missouri Valley on Tuesday as its parent upper low becomes negatively tilted across the Upper Mississippi Valley. A warm front is forecast to extend east-southeast of the low, and will likely advance at least partially into southern Wisconsin as the surface low pushes east on Tuesday. Showers and thunderstorms are possible Tuesday afternoon/evening as DPVA affiliated with the approaching upper trough overspreads the warm sector building into the area from the south. Rain chances will continue into mid-late week with an upper jet streak lingering across the Western Great Lakes. Saturday Night - Early Sunday Morning: Isolated showers and thunderstorms are possible across portions of the area as the upper impulse discussed above shifts across the region. Probabilistic and deterministic QPF forecasts depict the greatest signal for rainfall over northern WI and the Upper Peninsula of MI, where a compact jet streak accompanying the impulse is forecast to track. Said signals are reflected in the afternoon update, which places the greatest (~30-40%) precip probabilities along & northwest of the I-43 Corridor. If rainfall occurs, it will have the potential to be convective in nature given a plume of steep mid-level lapse rates/resulting MUCAPE moving in from the west. Apart from some isolated, sub-severe hail, hazards are not anticipated in the event that isolated showers/storms move across the area Saturday night into early Sunday morning. Monday Night - Tuesday Night: This will be the portion of the period to watch the closest from a hazards perspective. Anticipate periods of showers and embedded thunderstorms as a combination of upper diffluence & mid-level DPVA affiliated with the approaching Plains trough shift across the area. Of particular interest will be any development that occurs Tuesday afternoon/evening as the warm front discussed in the synopsis approaches and pushes into the state. A multitude of factors -- particularly the arrival time of the most favorable forcing, as well as the impacts of any antecedent precip & cool waters of Lake Michigan on northward progress of the warm front -- will play into storm development, with many uncertainties remaining as of this forecast. Despite remaining uncertainties, early forecast soundings depict a warm sector environment with sufficient instability and overlapping shear to support at least some potential for more organized storms next Tuesday. The Storm Prediction Center has highlighted most of southern Wisconsin in a 15% risk for severe weather in its Tuesday convective outlook in light of this potential. We will continue to closely monitor forecast trends during this portion of the period. Quigley-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --Issued 400 PM CDT Thu Apr 11 2024 A broken line of showers and weak thunderstorms (oriented North to South) currently rests over southwestern WI. It is expected to gradually build to the east, resulting in scattered shower / thunderstorm coverage near KMSN and KJVL this evening, but the exact timing is uncertain. Thunder is much less likely the further east you go. Light easterly winds are expected to continue until the surface boundary (where the storms are) passes over. Afterwards, expect steadier northwest winds tonight. Storm coverage and intensity decrease around midnight, with cloud ceilings dradually descending to MVFR. Clouds then begin to lift to VFR altitude after sunrise Friday, with skies clearing out from west to east Friday afternoon. Gusty northwest winds are expected throughout the day, declining Friday night. Sheppard-- End Changed Discussion --&& .MARINE...-- Changed Discussion --Issued 400 PM CDT Thu Apr 11 2024 A low pressure system over Ohio will track northeastward, deepening to around 28.9 inches and passing Toronto Friday morning. Northwesterly gales develop over the open waters late tonight (all open waters included in Gale Warning), with gusts to around 40 kts. The strongest winds and waves will be towards the east side of the lake, as well as the northern third of the lake. Winds will gradually weaken later Friday night into the weekend as the low tracks northeast into Quebec. A small ridge of high pressure traverses Lake Michigan on Saturday, allowing gentle winds (around 15 kts) to back from northwesterly to southerly. A weak low pressure around 29.6 inches crosses the lake Sunday morning, veering winds to the north (roughly 15 kts or less) Sunday afternoon. Sheppard-- End Changed Discussion --&& .MKX WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --WI...None. LM...Gale Warning...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563- LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779- LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 AM Friday to 7 PM Friday. Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...1 AM Friday to 7 PM Friday.-- End Changed Discussion --&& $$ Visit us at weather.gov/milwaukee Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSMilwaukee www.twitter.com/NWSMilwaukee www.youtube.com/NWSMilwaukee
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