Marine Weather and Tide Forecast for Big Bay, MI

SHORT TERM /THROUGH TONIGHT/
Issued at 232 PM EDT Fri Apr 18 2025

Upper air pattern consists of a 500 mb ridge across the ern half of the U.S. with a deep trough down into the western half of the U.S.
and a shortwave in the northern plains. The shortwave over the northern plains moves into the upper Great Lakes 12z Sat while troughing remains over the central and southern Rockies. A sfc cold front bisects the U.P. this afternoon with also a lake breeze component kicking in out ahead of the cold front as what happened at SAW and the NWS office here. When that happened, thick upslope fog with the northeast wind and low clouds came in and this will continue into this afternoon until the cold front passes through the eastern and southern cwa. Expect a resurgence in development of showers along the cold front later this afternoon and have been seeing a drizzle area growing across the central U.P. this afternoon. This is covered well in the going forecast and will not make many changes to the going forecast.

LONG TERM /SATURDAY THROUGH FRIDAY/
Issued at 331 PM EDT Fri Apr 18 2025

Deep moisture plume will have shifted east of the local area by Saturday morning, with positively tilted trough sweeping through.
Forecast soundings show enough low-level moisture to squeeze out some upslope-enhanced rain/snow showers over the western UP early Saturday; otherwise, expect a dry weekend. Temps moderate with highs in the low 40s to low 50s Sat increasing to mid-40s to mid-50s Sun.

As the northern part of the full-latitude positively tilted trough shifts east over the weekend, it will leave behind a cutoff low over the Southwest/southern Plains. This low will eject NEwd, opening up and going negatively tilted Sunday night into Monday as it enters the upper Great Lakes. Ensembles have started to hone in on the track of the attendant surface low from near Kansas City across northern lower MI into Lake Huron, but ensemble spread increases toward 00Z Tuesday. Cluster analysis shows the two most likely outcomes (which are about equally likely) are different in the pressures within and to the NW of the low track. Resultant QPF differences with these scenarios are such that a slightly weaker/eastward low track shifts heavier QPF over the eastern/southern UP (amounts ranging from 0.25 in the west to 0.75 in the east), while a stronger/westward track puts us squarely in the heavier QPF (a more widespread 0.75-1.25"). The latter scenario also brings accumulating snow into the equation due to evaporative and dynamically forced cooling, mainly over the interior north- central and west. Probs of > 3" from the EPS/GEFS range from about 20-50%, with > 6" snow 20% or less. Given the time of year and time of day, with some of this potential snow occurring during the daylight hours Monday, it would be likely be low impact due to warm surface temps, but something to monitor nonetheless. River responses can also be expected on the warm side of this system, which will be have to monitored where significant snowpack still exists over the eastern UP.

Following this system, midlevel heights will tend to rise as flow evolves toward quasi-zonal. As this occurs, a couple of waves will bring additional rainfall chances for the middle part of the week.
Tendency toward flat ridging will support a warming trend, especially toward the end of the week.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
Issued at 1233 PM EDT Fri Apr 18 2025

A prolonged IFR period will continue at IWD until late Sat morning when MVFR conditions occur. CMX will be plagued with upslope fog and low ceilings and will stay LIFR/VLIFR through tonight and then improve to VFR by late Sat morning. SAW will continue with upslope fog and low clouds and be LIFR/VLIFR through the period. SAW could also see some rain late this afternoon and tonight.

MARINE
Issued at 331 PM EDT Fri Apr 18 2025

Areas of fog will continue at times through tonight. Northwesterly winds will increase modestly to 20-25 kt over the east half tonight into Saturday. Winds will be 20 kt or less Saturday night into Sunday night before increasing as a low pressure system approaches from the south. Winds will back from easterly to northerly Monday while increasing to around 25 kt.

MQT WATCHES/WARNINGS/ADVISORIES
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.