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Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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624 FXUS63 KGRB 132337 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 637 PM CDT Tue Aug 13 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - A few showers and storms will continue through early this evening, especially near lake breeze boundaries in eastern and far northern WI. Severe weather is not expected. - Areas of fog expected late tonight into early Wednesday. Locally dense fog may cause travel concerns for the early morning commute. - Next chances for potentially heavy rainfall will arrive from the southwest Wednesday evening and persist through Friday. Localized flooding will be possible in low-lying and urban areas. - Conditions hazardous to small craft will be possible on Lake Michigan Thursday and Thursday night. && .DISCUSSION... Issued at 232 PM CDT Tue Aug 13 2024 Short Term...Tonight and Wednesday A few showers and storms will continue to develop this afternoon and early evening, as daytime heating has caused MLCAPE to increase to 300-600 j/kg. The activity should become focused near weak boundaries, especially the lake breezes over eastern WI (off Lake Michigan) and far northern WI (off Lake Superior). Other than locally heavy downpours and brief gusty winds (inverted-V soundings), no major concerns are expected with the storms due to weak deep-layer shear and a lack of forcing. With high pressure lingering through tonight and Wednesday, expecting mainly dry conditions to prevail. Warmer temperatures in the mid-levels should prevent a repeat of today`s daytime isolated convection. Perhaps of greatest concern during the period will be fog potential overnight into early Wednesday. Very light winds (5 knots or less) at the surface and aloft should combine with clear skies to allow areas of fog to develop after midnight. The fog is expected to become locally dense in river valleys and other sheltered low-lying areas, and may cause travel concerns for those with an early morning commute. Did not make any significant changes to temperatures, other than lowering min temperatures a few degrees in the typical cool spots of NC WI. Long Term...Wednesday Night Through Tuesday Main focus for the extended revolves around heavy rain potential Wednesday night through Friday as an organized surface low tracks from the central Plains through the western Great Lakes. Although severe potential looks to be low, some embedded storms will be possible across central Wisconsin on Thursday. Otherwise, main threat with this system will be localized flooding in urban and low-lying areas. Rainfall potential... Expect rain chances to arrive from the southwest late Wednesday evening ahead of increasing warm air advection/isentropic lift. Moisture transport will also be on the rise during this time as shortwave energy propagates across the northern Plains and saturates the column from the top down. As the surface low approaches Thursday morning, PWATs will likewise increase into the 1.75 to 2" range, about 150 percent of normal for this time of year. Isolated flooding will thus be possible, especially in urban and low-lying areas. Current thinking is that flash flood potential will be relatively limited due to a recent stretch of dry weather and prolonged rainfall duration. This being said, flash flooding would remain in the realm of possibility with any convective activity/embedded thunderstorms given slow storm motion of under 10 knots. The SPC currently highlights portions of central to east-central Wisconsin under a marginal risk for severe weather Thursday afternoon given CAPEs approaching 1,000 J/kg; therefore suspect that the main flash flood threat would be in this area. Regardless, abundant moisture and warm cloud depths exceeding 12,000 feet suggest the presence of efficient rain producers on Thursday. Current model guidance shows rainfall amounts of around 1.25 to 1.5" from central to east- central Wisconsin through Friday morning. Rest of the extended... Remnant shortwave energy spinning over the Great Lakes on Friday should be enough to sustain scattered showers across the forecast area through Saturday. Otherwise, conditions look mostly quiet through mid-week as weak high pressure settles over the Mississippi Valley and northwest mid- level flow shunts any instability to our south and west. && .AVIATION...for 00Z TAF Issuance Issued at 637 PM CDT Tue Aug 13 2024 Isolated showers or thunderstorms over northeast Wisconsin will end a few hours after sunset. Otherwise clear skies are expected tonight and Wednesday, with areas of ground fog late tonight through 13z Wednesday. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch/Goodin AVIATION.......RDM