Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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106 FXUS63 KGRB 171151 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 651 AM CDT Mon Jun 17 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - There is a Marginal to Slight risk of severe storms across the region today. The best chance of severe storms will be across parts of central and north central WI this morning, and over northern WI later this afternoon and evening. - There is a Slight Risk of excessive rainfall today, mainly west and north of the Fox Valley. A complex of storms with heavy rainfall will move through central, north central and far northeast WI this morning, and additional thunderstorms with heavy rainfall may occur over northern WI later this afternoon and evening. There is a continued risk of excessive rainfall from Wednesday through Friday. - Well-above average temperatures are expected through Tuesday. Heat indices may reach the lower 90s in the Fox Valley today, and middle to upper 90s across most of the forecast area on Tuesday. - Periodic thunderstorm chances are possible through much of the week. Some strong storms and locally heavy rainfall may be possible at times. && .DISCUSSION... Issued at 422 AM CDT Mon Jun 17 2024 Short Term...Today...Tonight...and Tuesday Conditions were quiet across GRB CWA early this morning, with an unstable (MUCAPE 1500-2000 j/kg) but capped (CINH of -150 to 300 j/kg) air mass in place. However, upstream convection has rapidly expanded and become more organized over central and southern MN and NW IA, due to strong WAA/moisture convergence on the nose of 40 kt low-level jet, possible MCV and in the presence of a cold front. This activity is expected to move into GRB CWA this morning, and will pose a heavy rainfall and at least marginal severe risk. Upstream convection will move into the forecast area this morning, most likely between 13z-14z. Most models suggest the MCS will move across the northwest two-thirds of the CWA; closer to the position of the incoming cold front, and the current forecast follows this scenario. Will watch trends closely early this morning and adjust farther south, if necessary. Given with fairly strong CAPE, steep mid-level lapse rates of 7.5 to 8 C/km and deep layer of 25 to 35 kts over the NW part of the forecast area, suspect at least a marginal risk of severe storms will exist as the line of storms arrives. In addition, we will likely pick up a quick half inch to an inch of rain, which could lead to minor urban flooding. This convection should move out of far NE WI around midday. The cold front is expected to be bisecting the CWA from central into NE WI this afternoon, with increasing southerly flow resulting in overrunning. This should result in a continued threat of thunderstorms, especially over N WI during the late afternoon and evening. The severe threat is uncertain due to the stabilizing effects of the morning convection, but locally strong storms and pockets of heavy rainfall will be possible. The front will lift back north as a warm front and move out of the forecast area overnight, leading to a period of dry weather that will persist through Tuesday. Partly cloudy skies and south winds gusting to 30 mph will reinforce the hot air mass over the region, with heat indices soaring into the middle to upper 90s Tuesday afternoon. Highs today should range from the lower to middle 70s far northwest to the middle to upper 80s southeast. Lows tonight should be in the middle 60s north to the lower 70s south. Highs on Tuesday will be mainly in the upper 80s and lower 90s. Long Term...Tuesday Night Through Sunday 500mb ridge across the eastern United States will flatten by the end of the work week, resulting in an active westerly flow pattern into next weekend. For Tuesday night, thunderstorms are expected mainly along the weak cold front approaching the area from the west. Some stronger/severe storms are possible across north-central during the evening with CAPE values around 2,500 J/KG. The storms are expected to gradually weaken during the late evening and overnight. On Wednesday, the GFS model is quicker with the surface frontal passage compared to the NAM/ECMWF/Canadian models. NAM Bufkit soundings on Wednesday indicated around 1,000 J/KG of CAPE and 0-6km shear values around 30 knots which would support strong storms and possibly a few isolated severe storms into Wednesday evening. The greatest risk of severe weather would be from central into northeast Wisconsin. On Wednesday night, the surface front sinks southward into southern Wisconsin, resulting in a dry period across the far north. The front is expected meander across the region into next weekend with a few rounds of showers and storms on the north side of the boundary. A more potent system is expected to send the front northward as a warm front Friday night into Saturday. Showers and storms are expected along the warm front with a few strong or severe storms possible. A cold front is expected to move across the area Saturday night. No significant changes were made to the Sunday period. High temperatures during the period will run at or above normal. && .AVIATION...for 12Z TAF Issuance Issued at 644 AM CDT Mon Jun 17 2024 A cold front has pushed into the northwest part of the forecast area, and MVFR ceilings have formed in the shallow cool air behind it. A line of thunderstorms was approaching from northwest WI and eastern MN, and is expected to impact the western TAF sites between 14z and 17z. The tail end of these storms may brush through GRB around midday, but locations farther south are expected to remain mainly dry. Additional showers and storms should impact mainly northern WI later this afternoon and evening as the front lifts back north as a warm front. Persistent low clouds over northern WI should gradually improve tonight as the warm front lifts north. LLWS is expected to develop overnight tonight. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch/Eckberg AVIATION.......Kieckbusch