Marine Weather and Tide Forecast for Ellison Bay, WI

DISCUSSION
Issued at 230 PM CDT Thu Apr 24 2025

Ths afternoon through Friday night:

700mb moisture continues to keep scattered to broken clouds through this afternoon with drier air near the surface to 850mb remaining in place keeping the region dry overall. However, the low levels will start to moisten back up later this afternoon as showers begin to push in from the west that are currently in east-central MN.
Models indicate that drier air over the area may fight the incoming moisture off for a bit but will eventually be overcome later this afternoon and certainly into the evening. The forcing will also increase later this evening with an upper level shortwave sliding in and some low level WAA. Showers will start pushing in with this moisture and increased forcing and will overspread the area overnight into Friday morning. No storms are expected with this as MUCAPE remains 0 across the area, the only slight chance (10%)
for a rumble of thunder would be in the southwest portions of the CWA

Showers will gradually push out over the course of the day Friday as the shortwave and corresponding mid level moisture pushes out.
Moisture and thus clouds may linger a bit longer but precip should end by the mid to late afternoon across the CWA Friday night higher pressure will be pushing in behind this system with the upper low a bit more delayed but lack of moisture aloft will likely keep things largely dry overnight. The most recent models have kept some precip chances Friday night with the upper low tracking through. There does look to perhaps be a strip of moisture associated with it which could yield a brief period of showers though lower levels may prevent much in the way of showers from reach the ground which is why we only included 20-35% chances Friday night. Into Saturday morning large scale ridging will become the dominant upper level feature, drying things out.

Saturday through Thursday night:

This weekend looks likely to be dominated by large scale ridging and high pressure with dry conditions expected. The only slight change to that is the potential for some shower activity Sunday evening/night as a low pressure system nudges in from the west. The upper levels keep the ridge in place with perhaps some weak shortwave activity embedded in the ridge. Clouds seem likely with this especially will 700mb level moistening up as well but the lower levels remain fairly dry suggesting as this pushes in dry air could really fight off any rain potential for quite awhile into the evening before anything would start to fall. In addition, overnight storm chances would be possible with this as some instability slides in with this system but any stronger storms would likely be further west with the better shear.

Into Monday it is becoming increasingly likely that some shortwave activity aloft could bring some showers and storms during the day Monday. This may play a role in what might occur later in the day and especially into the evening but as the surface low pulls through WI, models indicate the potential for strong storms across parts of WI. The better severe potential is likely located further south and west but the southern portions of the CWA will definitely see risks for strong to severe storms as well Monday evening and night.
Instability will be at least 1000 J/kg and according to models appears likely to remain surface based well into the evening. In addition deep layer shear looks likely to be in the 50-60 kt range certainly keeping things organized into the late evening hours, especially with the increasing LLJ into the evening.

The question remains around the timing of storms and how much instability we will still have and whether it will be surface based by the time it comes through. Currently this remains a situation with all hazards being possible. CWASP values around 0.8-0.9 somewhere in WI suggests the potential for strong storms with tornadoes being a hazard. The decreasing instability in models into the evening also suggests possibly less of a hail threat but with the main threat likely being wind depending on storm mode. There still remains some uncertainties however, especially as it relates to timing because slight shifts in timing could greatly alter what our potential ends up looking like.

Into Tuesday the front will have come through, very likely preventing chances for stronger storms. Showers will be possible on the backside of the low but overall by the evening higher pressure will be pushing in behind this system with weak ridging overhead.
Models keep things dry Wednesday with actually fairly good agreement overall. Thursday looks like there will be potential for activity with a developing low overhead and a shortwave aloft. Behind that shortwave into Friday models start to diverge a bit, especially in the upper levels. While large scale ridging will likely be the dominant feature the shape and track of the ridge starts to change and will likely impact precip trends into the weekend.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
Issued at 137 PM CDT Thu Apr 24 2025

for 18Z TAF Issuance Issued at 1235 PM CDT Thu Apr 24 2025

VFR conditions will continue across the area this afternoon into this evening. However, a few sprinkles are still possible towards KOSH through mid afternoon. Later this evening and overnight, CIGS are expected to drop into the IFR or lower category, reaching KMTW shortly after 12z. Rain is expected to develop across central and north-central WI later this evening, then spread eastward into east-central and northeast Wisconsin overnight into early Friday morning. Increasing northeast to north winds are expected tonight and then continue into Friday afternoon and evening. Gusts of 25 to 30 knots are possible at KGRB tonight, and across much of the area Friday into Friday evening. Rain should end from west to east Friday afternoon with diminishing winds and clearing skies Friday night.

KGRB/KATW...VFR conditions will continue this afternoon through much of tonight. There is still some model uncertainty when the low clouds and rain would arrive late tonight into early Friday morning. The greatest uncertainty exists in the 12z-15z time period. Did slow the timing of the steadier rain and low clouds by an hour or two. Rain is expected to linger into the early afternoon, then diminish and end by 21z-22z. Based on bufkit soundings, did increase winds/wind gusts later tonight into Friday afternoon, especially at KGRB where winds will be funneling down the bay later tonight. Winds will gradually diminish and skies will become mostly clear Friday night.

MARINE
Issued at 1105 AM CDT Thu Apr 24 2025

Tonight we will gradually see a low pressure system lift northeast through the southern Great Lakes area. This will increase the pressure gradient, especially Friday afternoon and evening bringing 20 to 30 kt northerly winds to the nearshore.
Thus a Small Craft Advisory has been issued for these breezy northerly winds from 1am Friday until 4am Saturday and possibly lingering a bit longer. Waves are not expected to be a concern given the northerly wind direction.

GRB WATCHES/WARNINGS/ADVISORIES
WI...None.
MARINE...Small Craft Advisory from 1 AM Friday to 4 AM CDT Saturday for LMZ521-522-541>543.