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LMZ522 Expires:202405180200;;381712 Fzus53 Kgrb 171931 Nshgrb
nearshore marine forecast national weather service green bay wi 230 pm cdt Fri may 17 2024
for waters within five nautical miles of the shore on lake michigan
lmz521-522-180200- green bay south of line from cedar river to rock island passage and north of a line from oconto wi to little sturgeon bay wi- green bay south of line from oconto wi to little sturgeon bay wi- 230 pm cdt Fri may 17 2024
This afternoon - SE wind 5 to 10 kts. Mostly Sunny. Waves 2 ft or less. Tonight - S wind 5 to 10 kts. Mostly clear. Waves 2 ft or less. Saturday - S wind 5 to 10 kts increasing to 10 to 20 kts in the afternoon. Mostly Sunny. Waves 2 ft or less. Saturday night - S wind 10 to 15 kts veering W 5 to 10 kts after midnight. A chance of rain showers. Waves 2 ft or less.

LMZ500
No data

FXUS63 KGRB 171916 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 216 PM CDT Fri May 17 2024

Forecast discussion for routine afternoon forecast issuance

KEY MESSAGES

- Dense fog is possible over the lakeshore counties and the nearshore waters of Lake Michigan late tonight through Saturday morning.

- There is a chance of thunderstorms in north-central Wisconsin through early this evening.

- There is a chance of thunderstorms Saturday afternoon and evening. Some of these storms may become strong to severe across north-central and central Wisconsin.

- Additional shower and thunderstorm chances are expected early next week. While too early to determine any severe risk, there is an increasing likelihood for locally heavy rain to occur.

- Warm temperatures expected this weekend into early next week.

DISCUSSION
Issued at 215 PM CDT Fri May 17 2024

Short Term...Tonight and Saturday

An upper trough will track through the northern Great Lakes through this evening, which could produce an isolated shower or thunderstorm across far north-central Wisconsin through early this evening. Upstream radar reflectivity is rather unimpressive with high based clouds associated with this feature as it is moving through northwest Wisconsin. Model soundings indicate rather meager instability as the trough moves through north-central Wisconsin, with MUCAPEs on the order of 300-600 J/kg, and bulk shear around 30 knots. In addition, there is a very dry airmass in place across that area, as evidenced by dew points of 45 to 50 degrees. Therefore, confidence is low (20-30 percent) in anything developing across far north-central Wisconsin as this feature moves through and if storms do develop, they are not expected to be severe.

Mostly clear skies and light winds should prevail across the region overnight as southeasterly flow keeps overnight lows on the warm side. The southeasterly flow could once again bring in some fog from Lake Michigan later tonight into early Saturday morning, with models indicating the impacts will mainly be confined to the lakeshore counties. Given tonight will be another day removed from the precipitation from the day and night before, this seems like a reasonable solution. Lows tonight are expected to mainly be in the lower to middle 50s inland, with upper 40s near the lakeshore.

Saturday is expected to be a warm day across northeast Wisconsin as surface winds turn south or south-southwest and 850 mb temperatures rise to 13-16 degrees Celsius. This will allow daytime highs to climb to around 80 across north-central, with low to mid 80s across central and east-central Wisconsin, and cooler temperatures in the 70s or 60s near the lakeshore. Despite the warm temperatures, dew points in the 50s should limit the humidity across the region on Saturday and keep heat index values a few degrees cooler than the ambient temperature.

An approaching cold front will bring the chance for showers and thunderstorms to central and north-central Wisconsin from west to east late Saturday afternoon. A ribbon of decent instability, with MUCAPEs around 1000 J/kg, and bulk shear values of 20 to 30 knots are expected ahead of the approaching front. Given the better instability Saturday afternoon, along with a surface cold front, there is a chance (5% probability) that these storms could become severe with damaging winds and large hail the primary threat west of the Fox Valley.

Long Term...Saturday Night Through Friday

Models look consistent in showing an eastern CONUS upper ridge/ western CONUS upper trough developing this weekend and persisting through Tuesday. This pattern will bring a southwest flow aloft into WI, bringing a warm, moist air mass into WI. Several mid- level shortwave troughs are forecast to eject from the trough and potentially bring several rounds of locally heavy rain to northeast WI. Eventually, this trough gets kicked out of the western CONUS into the Great Lakes region mid-week with more rain chances. Temperatures to be above normal through Tuesday, then settle below normal during the latter part of next week.

Saturday night and Sunday...
Scattered showers with diminishing thunderstorms to accompany the cold front/mid-level shortwave trough across the forecast area Saturday evening before shifting to the east overnight. Drier air advecting into the region behind the cold front will bring decreasing clouds later Saturday night and allow for min temperatures to range from the middle to upper 40s north-central WI, to the middle to upper 50s east-central WI. A weak area of high pressure to drift across WI on Sunday, providing for a sunny start to the day. However, clouds are expected to gradually increase in the afternoon as moisture begins to gather in the vicinity of the now-stalled cold front situated over the Midwest.
Temperatures will remain on the warm side away from Lake MI with readings in the middle 70s to around 80 degrees (upper 60s to lower 70s lakeside due to onshore winds).

Sunday night and Monday...
The stalled boundary becomes a warm front and starts to lift northeast toward western sections of the Great Lakes Sunday night.
Meanwhile, the first of several mid-level shortwave troughs will lift into the Midwest within the southwest flow aloft. Anticipate increasing isentropic lift and moisture transport to bring rain chances back to northeast WI after midnight, especially over central WI. Min temperatures to be in the lower 50s north/near Lake MI, middle to upper 50s south. This shortwave trough is forecast to lift northeast through the western Great Lakes and when combined with persistent isentropic lift, anticipate showers to be likely across all the forecast area on Monday. There will be a chance for thunderstorms as well, but both instability and shear look weak, thus severe storms look unlikely. Max temperatures Monday to be in the upper 60s to around 70 degrees near Lake MI, lower to middle 70s north and middle 70s to around 80 degrees south.

Monday night and Tuesday...
Low-end precipitation chances look possible Monday night as models indicate a frontal boundary to linger over WI. Showers and thunderstorms to increase again on Tuesday as the next shortwave trough moves northeast from the central Plains and will be accompanied by a strengthening area of low pressure and cold front. The gulf will be wide open and a 50 kt south-southwest low-level jet should easily bring moisture northward into the Great Lakes. PW values reach around 1.5 inches, so locally heavy rain is possible. Severe storm potential is conditional depending on instability. Bulk shear values of 40+ kts may allow for some storms to become strong, so will need to watch this system in the coming days. Max temperatures Tuesday to range from the middle to upper 60s lakeside, mainly lower to middle 70s inland.

Tuesday night and Wednesday...
Showers/thunderstorms likely to persist through at least Tuesday evening depending on which model(s) ends up correct as this system continues to track northeast toward southern Ontario and the cold front sweeps east. By Wednesday, the mean flow begins to shift as the western upper trough quickly moves east and is already approaching the western Great Lakes by Wednesday afternoon. There does not appear to be any frontal boundaries in the vicinity and gulf moisture to have been shunted east. Precipitation trends look down for Wednesday, but with that upper trough not far away, cannot completely dismiss precipitation chances for now. Max temperatures for Wednesday to cool a bit with lower to middle 60s north-central, middle 60s to near 70 degrees elsewhere.

Wednesday night and Thursday...
Weak high pressure will attempt to bring a break to precipitation chances Wednesday night into Thursday. Mean flow to be nearly zonal by this time, thus max temperatures on Thursday to be close to normal with lower to middle 60s north-central/near Lake MI, middle to upper 60s elsewhere.

Thursday night and Friday...
Serious model timing issues arise late next week with the next shortwave trough/cold front. A slower movement would keep Friday dry, while a faster movement would bring rain chances back as early as late Thursday night. Have followed the blended model solution and will bring small chance pops into the area on Friday.

AVIATION
for 18Z TAF Issuance Issued at 1229 PM CDT Fri May 17 2024

VFR conditions and partly to mostly sunny skies were noted across the TAF sites early this afternoon. VFR conditions are expected through Saturday morning as a low pressure system approaches from the west late Saturday morning. Some high based showers are possible across far north-central Wisconsin late this afternoon, but is expected to mainly stay away from KRHI. Late tonight into early Saturday morning some low clouds and fog could move inland from Lake Michigan, possibly to the MTW/2P2 and 3D2 airports.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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