Sunrise 5:15 AM   Sunset 8:21 PM Moonrise 6:45 PM   Moonset 4:00 AM

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LMZ522 Expires:202405212000;;594590 Fzus53 Kgrb 211057 Nshgrb
nearshore marine forecast national weather service green bay wi 556 am cdt Tue may 21 2024
for waters within five nautical miles of the shore on lake michigan
lmz521-522-212000- 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- 556 am cdt Tue may 21 2024
.small craft advisory in effect from this evening through Wednesday afternoon - .
Today - E wind 10 to 15 kts. Patchy fog in the morning. A slight chance of showers and Thunderstorms in the afternoon. Waves 2 ft or less. Tonight - SE wind 10 to 20 kts veering S 15 to 25 kts after midnight. Gusts to around 30 kts. Rain showers likely in the evening. A chance of Thunderstorms. A chance of rain showers after midnight. Waves 1 to 3 ft building to 3 to 5 ft in the late evening and overnight. Wednesday - SW wind 15 to 25 kts with gusts to around 30 kts. Partly cloudy in the morning then clearing. Waves 3 to 5 ft subsiding to 2 to 4 ft late in the afternoon. Wednesday night - SW wind 10 to 20 kts with gusts to around 25 kts. Clear. Waves 1 to 3 ft.

LMZ500
No data

FXUS63 KGRB 211111 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 611 AM CDT Tue May 21 2024

Updated aviation portion for 12Z TAF issuance

KEY MESSAGES

- Impactful strong to severe storms are anticipated across portions of the area today into this evening. The areas most likely to see severe weather will be central to east-central Wisconsin. Damaging winds, large hail, and a few tornadoes will be possible with the stronger storms.

- Several rounds of heavy rainfall today and this evening may also pose a flooding concern.

- Chance of showers and thunderstorms across northern Wisconsin Thursday afternoon into Thursday evening.

- Better chance for showers and thunderstorms over all of northeast Wisconsin Friday afternoon into Saturday morning.

DISCUSSION
Issued at 232 AM CDT Tue May 21 2024

Short Term
Today
Tonight...and Wednesday

Despite cloud cover, areas of dense fog have formed across much of the area early this morning with abundant low level moisture and light winds across the region. Although some areas may not receive dense fog this morning, overall the dense fog should be ubiquitous enough to continue the Dense Fog Advisory through this morning across the entire region. The dense fog should lift this morning with daytime heating as the boundary layer winds mix to the surface.

Attention then turns to the convection expected today and this evening. Hi-res models indicate there will be two rounds of convection; one moving from west to east from late morning through early this afternoon and another moving through this evening.

The first round of showers and thunderstorms will track through later this morning into the early afternoon north of a warm front lifting north across the western Great Lakes region. These initial storms are not expected to be severe as they will mainly be elevated with limited instability.

The bigger concern are the storms that are anticipated this evening. This activity will be driven by a pronounced negatively tilted mid level trough and attendant shortwave along with a surface cold front. Although some supercells are possible ahead of the main activity, the convection is expected to quickly develop into a QLCS that will track through the area from west to east this evening. Although instability isn't overly impressive with MUCAPEs around 1000 J/kg, bulk shear values are off the charts at 40 to 60 knots. Hodographs indicate quite a bit of low level shear and helicity, especially across central Wisconsin, which will bring increased probabilities for tornadoes (10-14%) across this area. North and east of this area for enhanced tornado risk the probabilities are lower but are certainly not zero. The most prevalent severe weather type is expected to be straight line winds given the linear nature of these storms and very strong winds, 60-70 knots, just above the surface. The probabilities for wind damage are rather high given these factors with 30-44% across central and east-central and 15-29% across north-central and northeast Wisconsin. Large hail will also be a threat as there is some cooling and enhanced CAPE in the hail growth zone from these deep updrafts.

The main area of concern will be central Wisconsin for all threats as supercells will have a better chance of developing or tracking through this region before conglomerating into a QLCS. Central and east-central will be the primary areas of concern for the wind threat and possible QLCS tornadoes where instability and shear will be maximized with the best chance to be in the warm sector for surface based storms. Further north, although the severe weather threat is lower, this area could also see strong to severe storms.

In addition to the severe potential, flooding could be an issue from these storms with two rounds of heavy rainfall expected today and this evening. Despite the fast moving nature of the storms, PWATs of 1.4 to 1.6 inches are expected, representing the climatological maximum for this time of year, along with long skinny CAPE profiles.

Behind the cold front, cooler temperatures and lower dew points are expected on Wednesday. Some showers could linger, especially across north-central Wisconsin, under cyclonic flow as a shortwave tracks through the western Great Lakes region.

Long Term...Wednesday Night Through Monday

Models indicate a progressive pattern to exist through early next week as a series of Pacific upper lows/shortwave troughs move across the northern tier of states. This would bring periodic precipitation chances to northeast WI. Timing of these systems will be the main forecast challenge. Temperatures for the most part to average near normal.

Wednesday night and Thursday...
Dry conditions are expected Wednesday night as the large system responsible for the stormy weather continues to lift north over western Ontario and weaken. A prevailing southwest wind at 5 to 10 mph should keep fog at bay through the night despite mostly clear skies. Min temperatures to range from the middle 40s north, upper 40s to lower 50s south. There is a concern that a weak frontal boundary will drop south and potentially stall over northern sections of the Great Lakes on Thursday. There may be enough convergence along this boundary to generate a chance of showers and a few thunderstorms across northern WI by the afternoon. Have added a pop to the forecast along with more cloud cover. Otherwise, partly cloudy skies can be expected over the rest of the forecast area with max temperatures in the upper 60s to around 70 degrees north, lower 70s near Lake MI and middle to upper 70s south.

Thursday night and Friday...
This boundary is parallel to the mean flow aloft which means it is not going anywhere fast. May need to carry a small pop over the north Thursday night, but any precipitation would be spotty and light. The rest of the area should remain partly cloudy with min temperatures near 40 degrees far north, upper 40s to around 50 degrees south. A better chance for showers will arrive on Friday as a mid-level shortwave trough moves into the Upper MS Valley, preceded by a cold front that is forecast to reach western WI late in the day. Marginal instability may allow for some thunderstorms to develop, but too early yet to discern severe storms potential.
Max temperatures on Friday to be in the middle 60s near Lake MI, mainly lower to middle 70s inland.

Friday night and Saturday...
Showers/storms will continue through at least Friday evening as the shortwave trough moves northeast toward Lake Superior and the cold front sweeps east across the rest of WI. The far north and far eastern part of the forecast area may see this precipitation linger past midnight before ending. Early indications show that most of Saturday appears to be dry with weak high pressure in the vicinity. Models are waffling a bit with this high pressure, thus confidence for a completely dry Saturday still has some doubt.
Little change in air mass will bring max temperatures on Saturday into the middle to upper 60s near Lake MI, around 70 degrees north and lower to middle 70s south.

Saturday night and Sunday...
Model differences continue into Saturday night with the possible existence of a fast-moving, weak shortwave trough. If this trough comes to fruition, it would be a chance of showers to eastern WI so have kept a small pop in the forecast for now. This weak system would exit the region by Sunday morning and with little synoptic forcing evident, it appears that most of Sunday would be dry. Max temperatures on Sunday appear to mirror Saturday which would be close to normal.

Sunday night and Memorial Day...
The next prominent upper low/shortwave trough is progged to move from the northern Plains into the Upper Midwest on Memorial Day.
Latest timing among the models would keep any morning festivities precipitation-free, but expect precipitation chances to increase over central WI in the afternoon. There is potential for this system to slide south enough to keep any showers away, so stay tuned. Max temperatures to remain near normal with upper 60s lakeside, around 70 degrees north and lower to middle 70s south.

AVIATION
for 12Z TAF Issuance Issued at 611 AM CDT Tue May 21 2024

Conditions ranged from VFR to VLIFR this morning with some fog and low clouds across the region. The fog should lift this morning with daytime heating as the boundary layer decouples.

There appears to be two rounds of showers and thunderstorms expected to track through the area today. The first will roll through later this morning from west to east through the early afternoon hours. This initial convection is not expected to be severe.

The second round is expected to track through this evening from west to east as a cold front sweeps through the area. These storms are expected to be strong to severe with damaging winds, large hail, and a few tornadoes possible. These storms will be aided by very gusty winds just off the surface, which will cause wind shear, with strong thunderstorms bringing these winds to the surface at times. Showers will be possible overnight as the main line of showers and thunderstorms tracks off to the east.
Conditions could fall to IFR/VLIFR at times in the rounds of showers and thunderstorms.

GRB WATCHES/WARNINGS/ADVISORIES
Dense Fog Advisory until 10 AM CDT this morning for WIZ005- 010>013-018>022-030-031-035>040-045-048>050-073-074.

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