Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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811 FXUS63 KGRB 010859 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 359 AM CDT Wed May 1 2024 Forecast discussion for routine morning forecast issuance .KEY MESSAGES... - Gusty west winds from 30 to 40 mph are expected over central and eastern Wisconsin today. While recent rains will limit the fire weather potential, the gusty winds will bring a threat of isolated power line fires. - Another round of showers and storms is forecast Thursday through Friday morning. Best chance for thunderstorms will be Thursday afternoon and evening with small hail and gusty winds expected to be the main impacts with any storms that do develop. - Due to recent and upcoming rainfall, rivers and streams will be on the rise late this week. Some rivers are forecast to reach bankfull stage by Friday or Saturday. && .DISCUSSION... Issued at 359 AM CDT Wed May 1 2024 Short Term...Today...Tonight...and Thursday Main forecast concerns will be pinning down best chances for rain/thunder, how windy it will be today and temp trends as the active weather pattern continues across the northern CONUS to start off the month of May. Precip / Thunder / Cloud Trends: Low pressure will track east across Upper Michigan today, with the majority of the heavier precip ending by 12z across far northern/northeast WI as the best forcing exits. Thunder has been isolated through the early morning hours, only associated with the strongest activity. Any threat for thunder will end by sunrise as any weak elevated instability exits into MI. Lingering clouds, light showers, sprinkles and areas of drizzle is expected this morning where the low clouds remain, mainly focused across northern WI. Clouds are likely to continue for most/all of the day over the north, with at least a period of clearing expected further south. The next round of rain will arrive from the southwest on Thursday as low pressure organizes over Iowa and a push of WAA arrives. Best chances for rain will be in the later morning and afternoon hours. Thunder chances will increase in the afternoon but remain on the low side (under 20%) as the elevated instability will struggle to push into northeast WI. Winds / Fire Wx Concerns: Limited mixing and a weak inversion has keep winds in check through the overnight hours. As the low pressure pulls away this morning, a push of CAA along with more unidirectional wind will aid in the strong winds aloft to be transported down to the surface. The strongest winds and best mixing look to occur across central and eastern WI, where gusts to 40 mph are expected. NBM/HREF probabilities continue to highlight these areas with a 80%+ chance of 30mph gusts, but chances for 40mph drop to under 40% and are spotty. An inversion will limit just how far we can mix into, which look to also hold gusts under advisory criteria. The expected cloud cover over north-central WI will further limit gust potential there. No major changes in the thinking regarding fire weather as the gusty winds could lead to isolated power line fires today. But recent rainfall and winds generally staying under 40 mph will limit the threat. Potential still looks to be the greatest across central WI to far northeast WI where green up has yet to occur in the sandy soil/forested areas. Will continue to highlight in the fire weather products, but hold off on adding to the HWO. Temps / Frost Potential: Have trimmed back highs slightly today due to the clouds and CAA, but most spots still look to climb into upper 50s and 60s, with north-central WI likely holding in the low to mid 50s. If skies can stay clear overnight, lows in the low-mid 30s are likely in the Northwoods with areas of frost. If more clouds stick around, even mid clouds, temps should hold in the upper 30s and limit frost potential. Frost/freeze headlines have begun for north- central WI, so have added at least some patchy frost in the forecast for the north tonight. If cloud trends back off on coverage, a frost advisory may be needed. High temps look to hold mainly in the 50s on Thursday, with a 60 possible south of Hwy 29 possible. Long Term...Thursday Night Through Tuesday An unsettled pattern is expected to end the week through this weekend with several rounds of precipitation forecast to move through the region. The area is under a marginal to slight risk (5- 15%) for excessive rainfall Thursday morning through Friday morning. The cumulative affect of the recent and forecast rainfall does raise minor flooding concerns. A few area rivers and streams are already at or near bankfull and several others are showing increasing water levels and may reach bankfull by the end of this week. As mentioned above the CWA is under a marginal to slight risk (5- 15%) for excessive rainfall Thursday morning through Friday morning as a well organized cyclone is progged to move northeast over the upper Mississippi Valley. Periods of moderate to heavy rainfall are expected Friday morning as a right rear jet quad provides additional upper-level support to the aforementioned cyclone. A few embedded thunderstorms are also possible Friday morning, but the combination of meager 100-200 J/kg MUCAPE, 10- 20kt effective shear and southeast winds off Lake Michigan creating a stable boundary layer should keep any storms that do develop weak. Precipitation will come to an end Friday as a much drier air mass moves over the region behind a cold front. By the time rain comes to an end most areas are looking at a 40-60% chance for greater than 0.75" of QPF with up to 1" possible for areas that see the heaviest showers. The dry conditions are not expected to last long as the northern half of WI remains under the influence of the cyclonic flow from the main surface cyclone that will be slowly moving northward over Manitoba and Ontario this weekend. There is still uncertainly with exactly when the second wave of precipitation will cross the region with ensemble cluster analysis showing a broad window between late Saturday morning and early Sunday morning. Don`t expect much in the way of convective active during this time as the most recent 00Z models are showing little to no instability and modest 5-6 C/km mid- level lapse rates. Available moisture with this second wave of precipitation is substantially less than the Thursday/Friday system. Most areas are looking at a 20-30% for greater than 0.25" of QPF this weekend. Another brief dry period is expected Sunday afternoon through Monday morning as a weak ridge of high pressure moves across the western Great Lakes. Ensemble models are in decent agreement with the next system to track across the upper Midwest Monday afternoon through Tuesday. It is too far out to dig much into the details with this system, however, the current general synoptic pattern with a low center moving over the Dakotas into western Minnesota would support the possibility for thunderstorms. Details on the finer mesoscale environment will be refined as the higher resolution models come into range. && .AVIATION...for 06Z TAF Issuance Issued at 1033 PM CDT Tue Apr 30 2024 Showers and isolated thunderstorms will move across the region overnight as an upper level disturbance and surface front approach from the Plains states. Flight conditions will lower to MVFR/IFR in the precipitation. The rain will end by daybreak Wednesday. MVFR ceilings are likely west of an ESC to STE line, with VFR ceilings to the east. Southwest winds will gust to over 30 knots mostly south of a AUW to SUE line. Another weather system will bring additional showers and thunderstorms to the region Thursday and Thursday evening. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Bersch/GK AVIATION.......RDM