FXUS63 KGRB 062343 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 643 PM CDT Sat Jul 6 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Some rivers, creeks and streams across east-central Wisconsin will continue to run above bankfull due to recent rainfall. - Isolated pop-up showers and thunderstorms late this afternoon and evening could be slow moving, so locally heavy downpours are possible. Most areas will remain dry though. - A few thunderstorms on Sunday afternoon/evening could be strong with gusty winds, small hail and heavy rain. At this time, severe weather is not expected. On and off chances for showers and thunderstorms will continue Monday through Wednesday. Although the severe weather threat remains low, locally heavy rainfall will be possible. - A warmer/drier summer pattern may be in store toward the end of next week. && .DISCUSSION... Issued at 246 PM CDT Sat Jul 6 2024 Short Term...Tonight and Sunday The latest RAP analysis and satellite/radar imagery show several shortwave impulses moving east across the northern Plains and northern Mississippi Valley. Further east, conditions are more stable thanks to shortwave ridging aloft. Surface instability is estimated at around 600-900 j/kg over north-central WI and eastern WI. This instability has led to a cu field across much of the region, which has been the most agitated over north-central Wisconsin. No showers have been observed so far, but it's still possible that a few showers could pop by late this afternoon. Forecast concerns revolve around precip timing as the shortwave energy upstream approach northeast Wisconsin on Sunday. Precip chances: The chance of isolated showers and storms will likely continue into the evening hours as both the RAP and HRRR indicate instability will be slow to dissipate. After a lull in the precipitation late this evening and overnight, shortwave energy from the northern Plains will be approaching northern Wisconsin by 7 am Sunday. Modest moisture advection and little in the way of instability will lead to a swath of showers lifting northeast across the area during the morning hours. These showers look to be light and scattered in nature. Redevelopment of showers and storms is relatively uncertain in the afternoon. In general, models depict a favorable thermodynamical profile for thunderstorm development with 1000-2000 j/kg of surface based instability if showers and cloud cover do not impact the heating curve sufficiently. These factors look to have a greater impact over north-central WI than over the Fox Valley where showers are expected to be more widespread in the morning. But in general, the convective allowing models are unenthusiastic about precip chances in the afternoon, probably due to a lack of focused ascent. Have therefore lowered precip chances in the afternoon. If details change and trends support a greater potential for thunderstorm development, increasing wind fields aloft (deep layer shear 25-30 kts) could support a strong to low end severe thunderstorm. Temperatures will be near normal tonight and Sunday. Long Term...Sunday Night Through Saturday Heat ridge will remain parked across the southwest CONUS, slowly expanding eastward next week. Broad area of troughing will prevail across the Great Lakes, with multiple embedded shortwaves, keeping an unsettled pattern in place through at least Tuesday/Wednesday. Chances for drier weather arrives at the end of the week, but monitoring how strong and how far east the ridge will get, along with the track of Beryl. Temperatures look to be near or slightly above normal. Sunday evening/night...chances for storms will continue as the upper trough slowly works toward the region and a shortwave/jet cross the state. Coverage looks to be isolated to scattered. The better instability wanes by midnight, so chances for a few strong storms look to be confined to the evening hours. Gusty winds and hail would be the greatest threats. Will need to monitor for a heavy rain threat as well, with PWATs climbing to around 1.25-1.75", possibly near 2.0" in east central WI and tall/skinny CAPE profiles. If a scenario like the HRRR pans out, would have some training storms which could drop some heavy rain totals over an inch or two pretty easily which could create some hydro issues, especially in central and east central WI. Recent rain could lead to some fog development. It looks to be a fairly warm and muggy night in the Fox Valley with lows in the upper 60s and dewpoints in the mid 60s. Slightly cooler and less humid conditions are expected further north. Monday into Tuesday...upper trough slowly treks across the Great Lakes, along with an upper jet and a couple embedded shortwaves. This will keep showers and storms in the forecast, especially in the late morning and afternoon/evening hours during peak heating. Some pulse-like strong storm will be possible, but locally heavy rain appears to be the biggest threat. Rest of the period...chances for drier and warmer weather arrives in the mid to late week timeframe, but trends with the remnants of Beryl will need to be monitored as any westward shift could bring some more rain/clouds into the area. Also a little worried we will get at least clipped by some of the ridge riders next weekend. && .AVIATION...for 00Z TAF Issuance Issued at 642 PM CDT Sat Jul 6 2024 Isolated showers or thunderstorms north of a TKV to IMT line will dissipate early this evening as daytime heating ends. The remainder of the area will be mostly clear. Some ground fog could form late tonight near Lake Michigan and the area just west of the bay. If it does form, it should dissipate by 13z Sunday A warm cold front will move across the region Sunday morning and could produce some showers across central and northcentral Wisconsin. An approaching cold front could bring scattered thunderstorms to the area Sunday afternoon and night as it moves slowly across the area. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....MPC/Bersch AVIATION.......RDM