Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
057 FXUS63 KMKX 150946 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 446 AM CDT Thu Aug 15 2024 .KEY MESSAGES... - Periods of off and on showers with a few thunderstorms this morning and early afternoon. Then an additional round of scattered showers and thunderstorms will be possible this evening where a strong/severe storm or two cannot be ruled out. - Moderate to heavy rainfall will be possible with today`s activity. There is a high probability (>70%) of seeing widespread rainfall up to and exceed half an inch across much of southern WI, but amounts nearing/exceeding one inch (50-60% chance) will be limited to southwestern WI. Cannot rule out localized minor flooding with any pockets of heavy rainfall. - Gusty southeast winds and building waves on Lake Michigan will create hazardous conditions to small crafts and beachgoers today through the evening. Thus both a Small Craft Advisory and Beach Hazard Statement is in effect for today. - Scattered shower and thunder chances continue Friday through Saturday. && .SHORT TERM... Issued 442 AM CDT Thu Aug 15 2024 Today through Friday: Showers will continue to gradually spread into southern WI from the southwest through the morning as low-level WAA, nose of a 30 knot 850 mb jet, and band of low-level frontogenesis work their way across the region. Given this low-level forcing aligning with PWATs exceeding 1.5 inch, will continue to see off and on periods of moderate to heavy showers through daybreak and push east. While GLM is picking up on some sparse lightning activity to our southwest in eastern IA/western IL, much of this activity looks to miss our area this morning as it is anchored to where the MUCAPE > 500 J/kg resides. Most models including the 06z HRRR and 00z HREF keep this instability out of our neck of the woods through the morning. Thus much of this morning activity will likely come through our CWA as moderate to heavy rainfall. We begin to see instability creep up toward a couple hundred to 1000 J/kg of MUCAPE through the afternoon. This will contribute to thunderstorms chance picking up on the backside of the morning round, but with the departing low-level forcing (WAA, LLJ, and band of frontogenesis), this will result in a limited window of thunderstorms (16z-21z) this afternoon. There still looks to be a lull in activity for the afternoon allowing the environment to recover a bit and may see southwestern areas of the CWA to see MUCAPE around 1500 J/kg. While, the low-level forcing from the morning has departed, there will be a surface cold front paired with a mid-level impulse working its way through the area generally after 00z. Some CAMs pick up on additional convective redevelopment as this second round of forcing pushes through the area, but with the later timing this evening may work against it as we lose daytime heating. Additionally the better environment looks more favorable further south in IL. Nevertheless there remains a potential for some thunderstorms later this afternoon/evening, especially for areas south of I-94 toward the WI/IL border. Also with some meager 0-6km shear approaching 30- 40 knots, if any storms develop and can grow upscale this evening, still cannot rule out seeing a strong or even severe storm or two, especially along the WI/IL border in southwest/south-central WI. The main concern with any stronger storm would be the damaging wind and or hail threat, but a brief spin up would not be out of the realm of possibility given the surface boundary and 0-3km CAPE around 100 J/kg. In addition to storm chances, looking at some widespread moderate to heavy rainfall today. Given the moist airmass, prolonged period of rainfall, and PWATs topping off around 2 inches, there looks to be a high potential (>70%) for much of southern WI to see around or more than half an inch of rainfall. There also looks to be a potential (50-60%) for pockets of higher rainfall exceeding 1 inch, which could result in some localized minor flooding concerns. While any deep shower/storm has the potential to produce such amounts, the best chances for these higher rainfall totals seem to be for areas southwest of Madison. Otherwise, expect showers and storm activity to decrease overnight. Expecting scattered shower and thunderstorm chances pick back up on Friday as the surface low meanders across northern WI while the mid- level trough digs down across the Upper-Mississippi River Valley. Lastly with the pressure gradient increasing between the departing surface high across the eastern Great Lakes and incoming surface low, expect southeasterly winds to increase through the day. This will result in stronger onshore flow and building waves along southern WI Lake Michigan beaches and create life-threatening rip current and swimming conditions today. Would be best to avoid swimming in these dangerous conditions. Wagner && .LONG TERM... Issued 442 AM CDT Thu Aug 15 2024 Friday night through Wednesday: Low pressure gradually shifts east to MI, but some scattered showers and a stray thunderstorm or two will be possible during the daytime hours. Then Sunday through early next week looks drier as the upper- level ridge builds across the central CONUS and surface high pressure establishes itself over the Midwest. While expecting a drier pattern through next week, still cannot rule out some low-end rain chances as long range models hint at some mid-level shortwaves overrunning/undercutting ridge. Wagner && .AVIATION... Issued 442 AM CDT Thu Aug 15 2024 Widespread showers with an isolated thunderstorm or two continue to spread in from the southwest this morning. Will gradually see lower ceilings and visibilities upstream spread in with this shower activity through the morning and persist until the early afternoon hours. Expecting a lull in activity this afternoon, but lower ceilings are likely to linger. May see additional shower and thunderstorm develop this evening as a cold front works its way into the region, but coverage and impacts remain in question given the lower confidence. Otherwise, today will see gusty southeasterly winds pick up through the afternoon as well before easing tonight. Additional scattered showers and thunderstorms bringing lower flight conditions are expected again on Friday, but coverage is not looking as widespread as today. Wagner && .MARINE... Issued 442 AM CDT Thu Aug 15 2024 Departing high pressure moving across the eastern Great Lakes and incoming low pressure tracking into MN will bring increasing southeasterly winds to Lake Michigan today. Looking at gusts up to around 25-30 knots through the afternoon/evening along with chances of thunderstorms as this system tracks into the Lake Superior region. The stronger onshore winds and building waves will result in hazardous conditions for small craft through this evening. Low pressure then looks to linger over the Upper Great Lakes through Friday with more southwesterly winds before turning northerly on the backside of the low for the weekend. High pressure looks to build into the region for the start of next week bringing lighter winds across Lake Michigan. Wagner && .MKX WATCHES/WARNINGS/ADVISORIES... WI...Beach Hazards Statement...WIZ052-WIZ060 until 7 AM Friday. Beach Hazards Statement...WIZ066-WIZ071-WIZ072 until 1 AM Friday. LM...Small Craft Advisory...LMZ643-LMZ644 until 7 AM Friday. Small Craft Advisory...LMZ645-LMZ646 until 1 AM Friday. && $$ 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