538
FXUS63 KDLH 272340
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
640 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

- Widespread moderate to locally heavy rainfall will return
  Thursday night, ending Friday afternoon. The heaviest
  rainfall is most likely along and north of the Iron Range into
  the Arrowhead of far northern Minnesota.

- Isolated severe thunderstorms are possible (risk level 1 out
  of 5) in northeast Minnesota and northwest Wisconsin Friday
  afternoon and evening.

- Residual showers Saturday in northeast Minnesota give way to
  a dry Sunday before the next round of moderate to locally
  heavy rainfall is forecast to return Monday into Tuesday.

&&

.DISCUSSION...
Issued at 339 PM CDT Thu Jun 27 2024

A beautiful partly sunny day has given way to some increasing clouds
as the high pressure responsible for our brief dry weather slides
off to the east towards Wisconsin. On tap is a low pressure system
coming in from the west with an attendant warm front. This warm
front is currently located over South Dakota and is snaking its way
down into central Nebraska and will continue to lift northward
eventually making it to our area Friday. This warm front will be
responsible for the showers and storms that arrive in the area
overnight into Friday. For those wondering about the heavy rainfall
threat with this setup, the overall threat is lower than previous
events which is certainly good news for us considering the recent
heavy rainfall and continued saturated soils across the entire
Northland. The reasons are as follows 1) while the moisture
transport certainly is there, the moisture is not completely coming
straight from the Gulf of Mexico but rather is being slightly
modified from the Desert southwest. As such this limits how much
moisture will be brought up into our area. 2) The best forcing looks
to be up along the warm front near the Borderlands of Minnesota and
also south of us along the Minnesota River valley. The various 6z
and 12z model suites consistently paint a swath of heavy rain (2-4
inches) near the Borderlands although focused into Canada with the
warm front. However, the caveat being if the warm front does not
make it as far north as the models indicate then this could spell
trouble for our area as this is likely where thunderstorms could end
up training over the same areas. As such WPC does have all of the
Northland in a marginal risk for excessive rainfall. When looking at
the CSU machine learning probabilities both the ARI and UFVS both
show a higher possibility (15-30%) of excessive rainfall. Again
something to certainly keep an eye on particularly if the front does
not make it as far north as predicted. Overall, widespread rainfall
amounts of 0.50-1.00 inches are expected across most of the
Northland, with locally higher amounts of 1-2 inches for the North
Shore which terrain influences, and also along the International
Border closer to the warm front. Given high uncertainty in the
placement of higher totals, a Flood Watch was not issued. However,
this will have to be closely evaluated for locations near the
International Border.

Regarding the severe thunderstorm threat Friday, while forcing from
the mid levels is present, the threat is muted some by weak mid
level lapse rates and a narrow window of CAPE values in the 1000-
1500 j/kg range. Cloud cover from morning storms will also be a
concern for how much afternoon buoyancy develops. Deep layer shear
of around 40-55 knots is certainly sufficient for organized
convection which both the GFS and RAP 13 deterministic models show.
Much of the Northland is in a SPC marginal risk (risk level 1 of 5)
with a slight risk (risk level 2 of 5) further south into central
and southern Minnesota which is where the better forcing and
instability will reside. This coincides well when looking at the CSU
machine Learning probabilities which paints a swath of 5% wind and
hail probabilities for the Northland for a more marginal and
condition severe risk.

Looking ahead, Sunday will bring a respite from precipitation with
sunny high pressure in place across the Northland. However, this
break is short lived as the next wave approaches the Upper Midwest
Monday into Tuesday. While details will still have to be worked out,
the setup has a similar appearance to previous events the past
couple of weeks with a heavy rain and severe thunderstorm risk that
will have to be closely watched.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 621 PM CDT Thu Jun 27 2024

VFR conditions this evening will lower as a warm front moves
northward tonight and overnight MVFR/IFR ceilings will accompany
showers and embedded thunderstorms. Brief LIFR conditions are
possible, but confidence is low that they will be widespread.
These will most likely occur over the Iron Range and Arrowhead,
affecting HIB. Winds will increase out of the south with this
system as well, with gusts up to 25 kts in the early morning.
Conditions will slowly improve as the system moves west to east
Friday afternoon and evening.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 339 PM CDT Thu Jun 27 2024

Winds for tonight will shift from onshore flow to southeasterly
winds late tonight. The winds will begin to pick up as night
falls, with stronger winds of up to 15 kts and gusts of 20 kts
possible. Wave heights may reach up to 2 feet with the strongest
winds. Rain showers tonight will continue into Friday with
embedded thunderstorms.

For Friday, as the storm system from the west continues
eastward winds will switch to southerlies and be strongest
around noon, being up to 20 kts with gusts of up to 25 kts
possible on the Southern Shore. Thunderstorms and rain are
still likely throughout the morning. Wave heights may reach up
to 3 feet on the North Shore. The winds and wave heights will
decrease into tomorrow night. Small Craft Advisories may (30-50%
chance) be needed on Friday.


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.

&&

$$

DISCUSSION...CJM
AVIATION...KML
MARINE...AP