Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
092 FXUS63 KMKX 252018 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 318 PM CDT Thu Apr 25 2024 .KEY MESSAGES... - Active pattern Friday afternoon through this weekend. Multiple rounds of showers/storms will result in locally heavy rainfall. - Severe storm risk possible Friday through this weekend, with uncertainty remaining in exact timing and placement. - Additional chances for precipitation mid to late week next week. && .SHORT TERM... Issued 318 PM CDT Thu Apr 25 2024 Tonight through Friday night: Low pressure deepening in the lee of the Colorado Rockies overnight will increase the PGF across southern Wisconsin as a warm frontal feature lifts slowly towards the region. Expecting mainly dry conditions throughout the overnight hours, although cloud cover and southeasterly winds are expected to increase from west to east overnight into Friday morning. The first rain shower activity looks to be lacking in CAPE and favorable lapse rates, so expecting an initial round of light to moderate rainfall Friday morning into Friday afternoon. Late Friday afternoon into Friday evening as the surface warm front lifts northward into central Wisconsin and low pressure pushes northeastward into the northern Great Plains, MUCAPE above 500 J/kg and mid level lapse rates (700 to 500 mb) between 6.5 and 7 degrees C/km may lead to elevated thunderstorms hail cores. 0 to 3 km helicity is also quite high (300 to 500 m2/s2), but a thick stable layer near the surface should keep convection elevated. Mid level lapse rates continue to increase overnight to 7 to 7.5 degrees C/km, while MUCAPE in far southern Wisconsin increases to near 1000 J/kg. However, the warm front progressing farther northward will remove a trigger from the region late Friday night into Saturday morning. Any convection that does develop will be isolated during this time period. MH && .LONG TERM... Issued 318 PM CDT Thu Apr 25 2024 Saturday through Thursday: Saturday, some clearing is possible as southern Wisconsin remains in the warm sector. GFS indicates potential for an outflow boundary from overnight Plains convection to produce thunderstorms across southwestern Wisconsin as early as Saturday morning, although confidence in this feature is low due to the necessitation of precursory convection. Southerly winds and increasing temperatures within the warm sector will result in high temperatures in the upper 70s and dewpoint temperatures in the lower 60s. Plenty of MUCAPE (global models are noting a potential of over 1500 J/kg), a warm and moist surface layer, and bulk shear of 40 to 45 kt all support sustained convection. However, trigger placement and timing is the main question for convective potential on Saturday. As the original parent low moves northward into Ontario, its weak cold front interacts with a developing warm frontal feature associated with a second low developing off the lee of the Colorado Rockies. This frontal feature is modeled to remain hovering over central Wisconsin to central Iowa, but its exact location remains in question. As the main trigger to convection for the Saturday time period, the timing and placement of this feature will be pivotal in the intensity and placement of widespread convection. As the second low pressure system propagates along its warm front into the Upper Midwest on Sunday, WAA continues across southern Wisconsin. Disparities from run to run and model to model continue into Sunday as well as far as the northern extent of the warm frontal boundary, and therefore how far north into central Wisconsin warm, moist, unstable air is able to remain in place. The cold frontal passage of this second low pressure system Sunday afternoon into Sunday night will be the main trigger for convection. This day remains most in question as far as intensity of any severe weather, due to its dependence on frontal timing. Will continue to monitor as the event approaches. From Saturday through Sunday, PWATs of 1 to 1.5 inch are forecast across the region, leading to locally heavy rain concerns. Places that see multiple rounds of thunderstorms will be more prone to heavy rain impacts. Cold front moves out by Monday morning, with southwesterly winds and quieter weather expected through Tuesday before additional shortwaves progress across the region midweek. MH && .AVIATION... Issued 318 PM CDT Thu Apr 25 2024 VFR conditions continue throughout today and into tonight, with increasing VFR cloud cover late tonight through Friday morning. Showers look to progress southwest to northeast Friday morning through Friday evening, with a few rumbles of thunder developing Friday evening in southwestern Wisconsin. Friday afternoon into Friday evening, ceilings will rapidly fall as a warm front with widespread showers pushes northeastward into southern Wisconsin late Friday afternoon through Friday night. Chances for scattered thunderstorms push northward into much of southern Wisconsin Friday night. MH && .MARINE... Issued 318 PM CDT Thu Apr 25 2024 Light winds continue into this evening as high pressure of 30.4 inches remains in place over the northern Great Lakes region. As this high exits eastward and low pressure of 29.3 inches develops in the central Great Plains overnight, southeast winds will begin to increase. As low pressure approaches Minnesota Friday into Friday night, expect southeasterly winds to continue to increase, with some gusts approaching gales possible Friday night into Saturday. A Small Craft Advisory for wind and waves is in effect for nearshore regions throughout this time period. Another low pressure system around 29.5 inches will move northeast across the Great Lakes Region Sunday into Monday, which will bring gusty southerly winds to the southern half of the Lake and northeasterly winds to the northern half. Showers and thunderstorms are possible Friday night through Sunday night, with the best chances for thunderstorms Friday night, Saturday afternoon and night, and Sunday afternoon and night. MH && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...7 AM Friday to 7 PM Monday. && $$ 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