270
FXUS63 KDLH 171801
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
101 PM CDT Fri May 17 2024

.UPDATE...
Issued at 634 AM CDT Fri May 17 2024

Mid-level clouds associated with an area of scattered rain
showers has moved over central and northern St Louis County over
the last two hours, helping to reduce the coverage of dense fog.
Webcam imagery and surface observations over the last hour have
shown continued improvement and any lingering pockets are very
likely to lift over the next hour so the Dense Fog Advisory was
cancelled early just now.

&&

.KEY MESSAGES...

- Scattered rain showers and isolated thunderstorms occur today,
  mainly in the morning and early afternoon. A few thunderstorms
  may (20% chance) occur later this afternoon and early evening
  though.

- Temperatures warm into the mid 70s to low 80s today and
  Saturday.

- Scattered strong thunderstorms, a few marginally severe in the
  eastern Arrowhead and north-central Wisconsin, remain possible
  (40% chance) in the Arrowhead and across northwest Wisconsin
  Saturday afternoon to mid-evening.

&&

.DISCUSSION...
Issued at 350 AM CDT Fri May 17 2024

Dense fog continues to be observed on surface observation
stations and shown on infrared satellite imagery in central and
northern St Louis County early this morning. An incoming mid-
level stratus shield may improve visibilities ahead of scattered
high-based rain showers, but keeping the ongoing Advisory in
place for now and will adjust end timing as observations,
webcams and/or satellite imagery indicated longer term
visibility improvements later this morning (currently expected
around 6-7 AM improving visibility though).

A warm front passes over the region early this morning, helping
to create the current scattered high-based rain showers in
north-central Minnesota that move into northeast Minnesota
closer to the dawn and sunrise hours today. Warm southerly flow
ushers in a much warmer air mass today as a result behind this
area of showers. Temperatures warm into the low-80s for the
Brainerd Lakes, east-central MN and into northwest Wisconsin
today. The South Shore lake shore communities keep fairly cooler
though as easterly flow off the Big Lake advects onshore.

Most precip chances taper from southwest to northeast this
afternoon and evening, but kept broad slight to chance PoPs in
the forecast for high-res model guidance indicating a sparse
coverage of later afternoon and early evening thunderstorms in
northwest Wisconsin, closer to the Ports and across the Iron
Range/Arrowhead. The main message is keep aware of isolated rain
shower and thunderstorm development even in this afternoon to
early evening time period today.

The warmest air pushes out of the Brainerd Lakes region tonight
and into north-central Wisconsin by Saturday creating residual
low-80 high temperatures tomorrow for east-central MN and across
northwest Wisconsin. The downsloping regions in far northern
Ashland County off the Penokees could even see mid-80s out of
this flow pattern tomorrow afternoon.

The incoming cold front associated with the warm front draping
down from low pressure centered in Manitoba later today and
throughout tomorrow creates the best chances for strong
thunderstorms in the Arrowhead and northwest Wisconsin Saturday
afternoon and early evening. A narrow wedge of just-enough
instability (800-1000 J/kg of CAPE) supported by decent mid-
level lapse rates around 8-8.25 C/km are present in mainly
northwest Wisconsin, but just pushing into the far eastern
Arrowhead by late afternoon Saturday. Available moisture within
the thermal profiles shown on high-res guidance supports dime
and nickel size hail, potentially around a quarter in size
(a.k.a low-end, marginal severe), with gusts around 50 mph
closer to an area from Bayfield to Sawyer Counties and eastward
into north-central Wisconsin; the eastern half of Cook County is
much less likely to see anything but sub-severe storms. As was
discussed previously, the shear will be the limiting factor for
the marginal severe potential over a few hour period in
northwest, but mainly north-central, Wisconsin tomorrow
afternoon.

Dry air quickly builds in behind the passing cold front Saturday
mid-evening and early night leading to dry and still-warm
conditions for Sunday.

A shortwave trough moving out of the Central Rockies on Sunday
phases with a deeper Southern Canadian Plains mid-level trough
to create the next round of storms and rain showers in the
Northland early next week. Depending on the placement of the
best forcing (somewhere in Wisconsin or eastern Minnesota) a
half-inch of rainfall is entirely possible (40-60% chance) for
east-central Minnesota and/or northwest Wisconsin Monday daytime
into Monday night. Right now, the best ingredients for severe
weather appear just south of the region, but something to watch
out for though if a northerly shift occurs over the next couple
of days.

Another mid-week system could bring another round of rain
showers to the region for later Tuesday into Wednesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 100 PM CDT Fri May 17 2024

It`s looking like we should see a nice break from any
showers/storms for the rest of the afternoon and early evening,
aside from a shower or two passing through HYR within the next
hour. While the air following behind this initial area of
clouds and showers is warm, it is also dry, and thus there isn`t
much to support additional showers/storms this afternoon. There
may be a 10-15% chance that a stray shower/storm could develop,
but not enough confidence to put in any TAFs. Later this
evening, warm air advection continues out ahead of an
approaching cold front from the west. We will likely see some
scattered showers/storms developing and passing by overnight. In
addition, periods of fog may be possible away from any
showers/storms, so expect occasional MVFR to potentially briefly
IFR ceilings and visibility tonight. LLWS is also expected
overnight with a potent low-level jet developing. The
shower/storm chances will continue through about mid-day at
Minnesota terminals, ending after the cold front passes through.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 315 AM CDT Fri May 17 2024

Dense fog remains early this morning per satellite and webcam
imagery so the Dense Fog Advisory remains in effect until 10 AM
today. Calm winds this morning become easterly at 10-20 knots
this afternoon and evening, creating wave heights to 4 feet near
the head of the lake. Held off on any Small Craft Advisory for
now, but a near-term issuance may be needed for Two Harbors to
the Twin Ports to Port Wing if those gusts do approach 22-25
knots this afternoon. Another night of dense fog may occur as
well tonight. Southwest winds increase Saturday, with gusts to
25 knots mostly expected at the head of the lake.

For the open water discussion, refer to the NWS Marquette
Area Forecast Discussion at weather.gov/mqt.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
MARINE...None.

&&

$$

UPDATE...NLy
DISCUSSION...NLy
AVIATION...JDS
MARINE...NLy