Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
611 FXUS63 KGRB 072352 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 652 PM CDT Sun Jul 7 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Isolated strong thunderstorms are possible through this evening. Main threats with any stronger storms will be gusty winds, hail, and heavy rain. Severe weather is not currently 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. - Some rivers, creeks, and streams across east-central Wisconsin will continue to run above bankfull due to recent rainfall. - A warmer/drier summer pattern may be in store toward the end of next week and into next weekend. && .DISCUSSION... Issued at 232 PM CDT Sun Jul 7 2024 Short Term...Tonight and Monday The latest RAP analysis and satellite/radar imagery show several shortwaves spinning over the northern Plains and northern Mississippi Valley. Northeast Wisconsin is positioned on the eastern periphery of these systems with moisture advection occurring in the low levels, and difficult to resolve impulses embedded with southwest flow aloft. These impulses have supplemented the 1000-2000 j/kg of surface based instability analyzed across the region to generate scattered showers and storms. Coverage has been highest over northwest Wisconsin, but think coverage will continue to increase over north-central and northeast Wisconsin as we approach peak heating late this afternoon. A strong to near severe storm is possible given the deep layer shear of 25-30 kts. Focus of this forecast is storm trends and heavy precip potential. Storm trends: After a period of storms over north-central WI this afternoon, convective allowing models indicate that a broken line of storms will move into north-central Wisconsin around mid to late evening along a weak cold front advancing eastward. These storms should be weakening as diurnal instability is lost. There may be sufficient instability leftover for a strong storm to occur, but severe weather is not expected. A second area of showers and embedded storms remains expected to move into central and east-central Wisconsin after around 3 am associated with a shortwave out of the central plains and augmented by a modest 25 kt low level jet. While there is up to 1000 j/kg of elevated instability, severe thunderstorms are not expected as effective shears are only around 20 kts. Probabilities remain low (10-30%) for rainfall amounts of 1/2" or greater, but slow storm motion around 10 kts and precipitable water values around 1.6 inches indicate some potential for heavy rainfall if convection is more widespread/potent than what it indicated in models. Shortwave troughing will be overhead for the rest of Monday. While precip early in the day will likely exit in the morning, instability of 1000-2000 j/kg will lead to redevelopment of showers and storms in the afternoon. Higher chances appear northwest of the Fox Valley where the heating curve will be less impacted by morning precip. Fog potential: Besides precipitation, guidance is also showing potential for dense fog over north-central Wisconsin late tonight. This makes sense with the precip that has occurred today. Will add to the HWO. Long Term...Monday Night Through Sunday Moisture, instability, and a weak shortwave will keep the chance for pulse showers and thunderstorms in the forecast through Tuesday. The lack of better dynamics and lift should keep coverage fairly low across the region during this period, with the best chances during the afternoon with peak heating. The next feature of interest is where Beryl ends up during the middle part of the week. NWP models seem to agree that our area will largely miss out on this feature; however, the region will still see rain as a mid level shortwave and associated positively tilted trough dive southeast from Canada through the western Great Lakes region. Instability showers and/or thunderstorms will be possible Thursday afternoon; however, with a lack of any significant dynamics or forcing coverage is expected to be isolated at best. Some weak ridging is expected to keep Friday dry, with isolated to scattered showers and thunderstorms possible next weekend as some shortwave ridge riders track through the western Great Lakes on the periphery of a larger scale ridge in place across the central CONUS. Temperatures during the week will be right around normal through Thursday. Temperatures will then warm to a few degrees normal on Friday and several degrees above normal by next weekend as the upper level ridge builds in across the central CONUS. && .AVIATION...for 00Z TAF Issuance Issued at 652 PM CDT Sun Jul 7 2024 An upper trough will produce scattered showers and thunderstorms as it moves slowly from Minnesota to Wisconsin tonight and Monday. The activity will be most abundant during the afternoon and evening hours and decrease overnight. There may also be some patchy ground fog late tonight where rain has fallen. Outside of any convective activity and ground fog, VFR conditions are expected. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....MPC/Kurimski AVIATION.......RDM