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LSZ148 /o.exp.kdlh.ma.w.0035.000000t0000z-231005t2345z/ 641 Pm Cdt Thu Oct 5 2023
.the special marine warning will expire at 645 pm cdt...
the affected areas were... Lake superior west of a line from saxon harbor wi to grand portage mn beyond 5nm... Oak point to saxon harbor wi... Outer apostle islands beyond 5 nm from mainland...
the showers have weakened and no longer pose a significant threat to boaters. A gale warning remains in effect for this area until 12 am cdt tonight.
lat...lon 4673 9060 4674 9068 4687 9063 4695 9044 4713 9035 4714 9013 4672 9040 time...mot...loc 2340z 265deg 35kt 4710 9010 4694 9019 4679 9044

LSZ100
No data

FXUS63 KDLH 100628 AFDDLH

Area Forecast Discussion National Weather Service Duluth MN 1228 AM CST Sun Dec 10 2023

KEY MESSAGES

- Additional snow accumulation over northwest Wisconsin and portions of the Minnesota Arrowhead will range from a dusting up to 2 inches overnight. The highest totals expected over northern Iron County with snow amounts dropping to a dusting up to a few tenths outside of Iron County.

- Gusty northwest winds will weaken overnight. The strongest winds will be found along the North Shore, including the MN-61 corridor.

- Gusty winds return again Monday night into Tuesday.

- Cooler and mostly dry to start the week, then warming well- above average late this week.

UPDATE
Issued at 1228 AM CST Sun Dec 10 2023

The radar presentation and corresponding satellite imagery associated with the initial gravity wave band of snow over Douglas County and the western portion of the southwest arm of Lake Superior has dissipated. Strong northwest winds in the 0-2kft layer sharply veer northerly above 2.5kft per NAM forecast soundings at DLH and LUT. Drier air aloft upstream of the North Shore removed support for snow production in the wave.
The wind shear between 2 kft and 3 kft also seems to have a decoupling effect on the depth of the wave.

In fact the gravity wave itself is still in place given that the wind direction remains favorable and the North Shore itself hasn't moved perceptively. GOES-E shortwave IR imagery reveals a tight gravity wave train over western Lake Superior. This is of a shallow gravity wave which lacks the vertical depth to contribute much snow. GOES-E water vapor imagery suggests there may be additional surges of moisture propagating through the flow and interacting with the wave over the next several hours, which may temporarily produce additional accumulating snow over portions of Douglas County. Will let the advisory ride for the time being and reevaluate in a few hours.

We still expect to see lake-effect bands set up in the next hour or so which would bring additional accumulating snow to Iron County.

Will need to reevaluate the current Winter Weather Advisories for Douglas and Iron Counties prior to their scheduled expiration at 3 AM.

UPDATE Issued at 1006 PM CST Sat Dec 9 2023

A strong gravity wave has set up in the lee of the North Shore terrain ridge this evening. While it was expected, the snowfall rates within it may be higher than previously anticipated.
WSR-88D has been showing signals for higher snowfall rates of over an inch per hour over northern Douglas county since about 02Z, which is on top of what we already had forecast there, putting total snowfall amounts in the 2 to 4 inch range. While this is a fairly localized heavy snowfall, and it is nearly over, it is right over highways 2 and 53 when we haven't had much snow so far this season. So, I have issued a Winter Weather Advisory until 3 AM for this event. At the rate the snowband has begun to diminish we may be able to cancel it early.

DISCUSSION
Issued at 315 PM CST Sat Dec 9 2023

Rest of Today - Early Sunday:

Early this afternoon, regional surface analysis depicted low pressure centered over western Lake Superior with a cold front draped across NW WI down into central IA. Radar imagery and area webcams show precipitation moving into NW WI as a rain/snow mix initially behind the cold front, but colder air behind the front farther west into NE MN has changed precipitation to snow for most. Expect the transition to all snow to continue into NW WI this evening as colder air works in behind the cold front and temperatures fall below freezing. Expect slick roads from the snow to continue to spread eastward as temperatures cool, as well. In addition to the snow, gusty northwest winds behind the cold front are expanding across the Northland, with many locations in north-central and NE MN already seeing gusts to 25 to locally 40 mph. Wind gusts could reach upwards of 40-45 mph along the North Shore of Lake Superior this evening until around or shortly after midnight. Have held off on issuing a Wind Advisory for portions of the North Shore given the expected localized nature of gusts at or slightly above 45 mph. The stronger winds combined with falling snow will continue to drop visibilities to around or below a mile at times, leading to additional driving hazards on area roadways for this evening.

Snow comes to an end for most areas from west to east by the end of this evening aside from the South Shore, where gravity wave- induced snow in northern Douglas and Bayfield Counties will linger into early tonight and lake-effect snow in Iron County that will persist into early Sunday morning given added moisture from Lake Superior. Total snowfall accumulations across most of the area should amount to around 1-2 inches. Meanwhile, HRRR probability-matched means indicate the potential for 2-3 inch totals in Douglas and Bayfield Counties where the gravity wave- induced snow persists, and 3-6 inches of accumulations in northern Iron County (locally 2-4 inches in central Ashland County). A Winter Weather Advisory is in effect for Iron County into tonight where snowfall amounts will be highest.

Sunday - Monday:

Drier weather and relatively cooler, but near normal temperatures return for Sunday through daytime Monday as the colder airmass behind the cold front settles into the region.
Expect low temperatures in the teens and high temperatures in the upper 20s to low 30s both days.

Late Monday - Tuesday:

As a low pressure system traverses the southern shore of Hudson Bay from late Monday into early Tuesday, another cold front will once again move through the Northland, with shortwave energy aloft grazing the northern portions of the Northland. The airmass in the wake of this front will be pretty dry, with PWATs around 0.1". However, some model soundings do show the potential for just enough saturation in the dendritic growth zone aloft to squeeze out some very light snowfall with this clipper Monday night into Tuesday, though the potential for seeing measurable snowfall is very low (less than 20%).

Additionally, winds will once again be gusty with with and behind the passing cold front, with gusts up to 25-40 mph (local gusts up to 45 mph along the North Shore). Add in high temperatures reaching the 20s on Tuesday, and daytime wind chills may only top out in the single digits to low teens.

Late Next Week:

The latter half of next week looks warmer and drier as ridging aloft moves over the Upper Midwest. There is fairly high confidence in temperatures rising into the low to mid 40s on Thursday (15-20 degrees above normal), while Thursday and Friday low temperatures in the 20s will be similar to what normal highs are for mid-December.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/
Issued at 1228 AM CST Sun Dec 10 2023

A strong low pressure system to the east is moving off to the east, causing an area of stratus with MVFR/IFR ceilings over the area.
Snow showers are still affecting several terminals, with visibilities reducing to MVFR in places, but otherwise VFR. The snow showers to slowly come to an end over the next few hours. MVFR/IFR ceilings will linger overnight, then gradually return to VFR around mid-day Sunday, though timing is somewhat uncertain. Northwest winds of 10 to 15 knots with gusts in the 20 to 25 knot range will gradually diminish overnight, dropping to around 10 knots in the 09Z- 12Z time range, and remaining there while the direction slowly becomes westerly after 18Z.

MARINE
Issued at 315 PM CST Sat Dec 9 2023

The start time of the Gale Warning for the North Shore and Small Craft Advisory for the South Shore had been pushed back a couple of hours due to the delayed start time of the stronger northwest winds on Lake Superior until now. The strongest winds along the North Shore should be along and north of Silver Bay where gusts up to around 40 knots are expected. The Gale Warning extends down to the Twin Ports where gusts up to Warning also extends down to the Twin Ports where 35 knots are expected.

Small crafts are in effect for the South Shore where wave heights will quickly build to 4 to 7 feet this evening, highest in the Outer Apostle Islands. Winds and waves subside from Sunday morning into Monday morning increasing again Monday afternoon with strong southwesterly winds shifting to west- northwesterly Monday night into Tuesday as another cold front moves through the Northland.

DLH WATCHES/WARNINGS/ADVISORIES
MN...None.
WI...Winter Weather Advisory until 3 AM CST Sunday for WIZ001-004.
MARINE...Small Craft Advisory until 10 AM CST Sunday for LSZ121-145>148- 150.
Gale Warning until 4 AM CST Sunday for LSZ140>144.

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