Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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517 FXUS63 KGRB 111152 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 652 AM CDT Thu Jul 11 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Small chances (30% or less) for showers and storms this afternoon/evening this afternoon and Friday. Severe weather not expected low, but storms could produce locally heavy downpours. - Warmer and more humid conditions arrive this weekend through early next week. Heat index values in the 90s are expected over central, east central and parts of far NE WI Sunday into Monday. Heat indices could approach advisory criteria over the southern CWA on Sunday, unless thunderstorm development occurs. - Increasing moisture and instability, combined with a couple short-waves and cold frontal passages, could lead to a few rounds of strong to severe storms this weekend into early next week. && .DISCUSSION... Issued at 418 AM CDT Thu Jul 11 2024 Short Term...Today...Tonight...and Friday Main forecast concerns will be where to include small shower/storm chances, fog potential and cloud trends. Shower/Storm Chances & Cloud Trends: Dry conditions are expected to start the day, with some low clouds and fog over the north and mid and high clouds over the south. The mid and high clouds will linger over the south into the late morning and early afternoon, with the low clouds over the north mixing out this morning. The more widespread shower/storm activity will be well to our south today, closer to the stronger shortwave energy and deeper moisture. But a weaker piece of shortwave energy will track across the area today within the broad upper level trough over the region. Combined with daytime heating producing SBCAPEs up to 1000 J/kg, isolated showers and storms will again be possible, mainly over the southern CWA. The Lake Michigan lake breeze could also help kick off or enhance any activity. Severe weather is not expected, but a brief heavy downpours is possible (PWATs around an inch). Soundings showing an inverted-V, but just not much wind to mix into. Any wind would have to come for a storm that can pulse up and generate some brief wind of its own (microburst). Any shower/storm activity will decrease in the late afternoon and evening as instability weakens and the focus shifts south. Further north, the influence of the weak surface high pressure, less moisture and a weak cap looks to keep things dry. But can`t rule out a sprinkle or a shower near the MI border along the Lake Superior lake breeze. A lingering/ stray shower is possible tonight, but expect most/all will stay dry. Models advertising another weak shortwave on Friday that could touch off an isolated shower or possible storm. But some uncertainty if the boundary layer will be a little too dry and if the cap will hold down any activity. Fog Potential & Temps: Fog is trying to expand and thicken across parts of central and northern WI, just north of the thicker mid/high clouds, but it seems to be struggling so far. There should be some expansion of the fog through sunrise across central and northern WI, then it will lift/burn off through mid-morning. Fog will be possible again tonight as winds will remain light, skies will be mostly clear and another sharp low-level inversion setting up. Will carry some patchy fog overnight into early Friday, mainly northwest of the Fox Valley where the HREF and SREF are highlighting the best chances. Temps will be at or slightly above normal today into Friday, with highs mainly in the low to mid 80s and lows in the 50s across the north and in the lower half of the 60s across most of central WI and the Fox Valley. Temps near Lake Michigan will remain slightly cooler. Dewpoints in the low 60s will keep a touch of humidity in the air across the Fox Valley, but the Northwoods looks to mix out today with dewpoints in the 50s, possibly some 40s in the sandy soil areas. Heat indices should remain in the 80s on Friday as we ease into a period of higher heat and humidity. Long Term...Friday Night Through Wednesday The main concerns in the extended will be the growing storm concern for the weekend and early next week as warm and moist airmass moves into the region. Heat...A warmer and more moist airmass will push into the western Great Lakes Friday night through Saturday. This will bring daytime high temperatures well into the 80s by Saturday and keep them there Sunday and Monday as well. Depending on active weather, portions of the area may even hit the low 90s. At the same time, dewpoints will be on the increase by Saturday, pushing into the middle to upper 60s and low 70s by Saturday night. Suffice to say it will be hot. Whether we get to heat advisory remains in low confidence, as precipitation may disrupt the better heating, but the best chance will still be on Sunday. The heat will depart towards the middle of next week after a cold front crosses the region early in the week. Precipitation... The influx of warmth and moisture will also generate ample instability in the region each afternoon Saturday through Monday. Each day will see a chance for storms, but there is plenty of uncertainty in terms of timing and strength. Saturday...Saturday appears to have the weakest capping in place, so some isolated convection will be possible in the afternoon. The better threat will be later in the day however, as a shortwave crosses the better instability axis to our west. Any storms that form there may organize and come west late Saturday, crossing the region in the early to mid overnight hours. Bulk shear Saturday is still modest, around 20 to 30 knots but mid-level lapse rates will be decent around 7-8 C/km. This modest upper support coupled with the low level instability would support at least isolated severe wind and hail Saturday and Saturday night. Sunday...The first challenge for Sunday will be resolving any potential active weather from Saturday, which could stabilize the region a bit, especially further north. Sunday also has much stronger capping in the mid-levels, which may further inhibit any storm development, at least for the afternoon. Finally, a shortwave crosses sometime late Sunday, which may be sufficient to break the cap, especially as bulk shear values quickly increase over the course of the day. If storms form, would currently place the best bet to be across central to southern WI, where the instability axis is at its greatest. Monday...Finally, a cold front is expected early next week, which will serve as the next chance for organizing precipitation in the area. If this occurs in the late afternoon and evening, this would favor another round of strong to severe storms across the region. && .AVIATION...for 12Z TAF Issuance Issued at 652 AM CDT Thu Jul 11 2024 Ground fog will continue to lift across northern WI early this morning. Mid and high clouds will continue to spread across central and eastern WI today, exiting through the day. Some lower clouds are expected at times today into tonight, but mainly VFR conditions are expected. An isolated shower and storm is possible later this morning and afternoon. Some ground fog will once again be possible overnight into early Friday. Winds will remain light. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Bersch/Uhlmann AVIATION.......Bersch