250
FXUS63 KMQT 181116
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
716 AM EDT Wed Sep 18 2024

.KEY MESSAGES...

- Extended stretch of well above normal temperatures continues
  through at least Saturday with highs mainly in the upper 70s
  and 80s.

- A cold front brings scattered showers and a few thunderstorms
  late Thursday into Friday.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 333 AM EDT Wed Sep 18 2024

Water vapor imagery and RAP analysis show mid-level troffing over
the western U.S. and downstream ridging from the Upper Mississippi
Valley to New England. A vigorous shortwave is over northern
Ontario, and it is producing a cluster of tsra about 180 miles n of
Isle Royale. Recently, a few shra have developed w and sw of Duluth
on the eastern edge of the low-level jet and within a local 850mb
theta-e ridge. Closer to home, for the 3rd day in a row, it`s an
incredibly warm early morning for mid Sept in the downslope areas
near Lake Superior from western to n central Upper MI. Stirring s
winds are holding temps up into the upper 60s and lwr 70s as of 07z,
and for the third night in a row, Big Bay is the warm spot. Two
nights ago the temp at Big Bay was 76 at 07z, last night it was 75,
and currently, it`s 74F. Just as in previous nights, temps fall off
significantly to the e and s. Across s central and eastern Upper MI,
temps are as low as the mid 40s F at traditional interior cold spots
as a drier column has further enhanced radiational cooling on this
night, but temps ranging thru the 50s F are generally the rule. With
the cool conditions, patchy, shallow radiation fog has once again
developed in that area. The patchy fog, locally dense, will burn off
an hr or so after sunrise.

Another unseasonably warm day is on the way under sunny skies.
Models show mid morning 850mb temps today about 0.5C lower over the
eastern fcst area and maybe about 1C higher over the w. So, overall,
today`s highs will be about the same as yesterday, maybe a degree
lower e and a couple of degrees F warmer w. In general, expect low
to mid 80s e and mid to upper 80s F w. As in recent days, southerly
winds will hold temps to the 70s F near Lake MI. The low-level air
mass today is a little drier than yesterday as noted by 850mb dwpt
depressions, and this will result in sfc dwpts mixing out a bit lwr
than yesterday as well. Much of the fcst area, except areas
immediately downstream of the southerly flow off of Lake MI, will
see dwpts fall thru the 50s with low end in the upper 40s F. This
will drive RH down thru the 30s with low end slipping into the 25-
30pct range at some of the typically lower RH locations.
Fortunately, wind gusts will generally be no higher than the 10-
15mph range this aftn, providing some limiting of fire wx concerns.
Still, the ongoing lengthening dry spell is becoming an ever greater
concern for wildfire potential. Over the last 2 weeks, pcpn has been
been less than 50 pct of normal across all but nw Upper MI, and
large areas are at less than 25 pct of normal. Many locations have
not seen any rain for at least a week.

&&

.LONG TERM /TONIGHT THROUGH TUESDAY/...
Issued at 325 AM EDT Wed Sep 18 2024

We get one more mostly dry, late summer-like day on Thursday before
the high pressure ridging over us gives way to a cool front moving
in from the west late Thursday through Friday. Afterwards, expect
temperatures to decrease closer to normal, with a low pressure over
the Canadian Prairies lifting towards Hudson Bay and another low
lifting from the Desert Southwest/Southern Rockies into the Upper
Midwest possibly bringing back rainfall over us as well next week.

Another mostly clear night is in store tonight as the ridging
persists but slowly weakens over us with time. As temperatures cool
during the overnight hours, we could see some patchy fog develop in
the south central and near Lake Michigan late as the temperatures
reach the dewpoint. Overall, thinking low temperatures tonight will
get into the 50s, with a few spots in the interior central possibly
getting into the upper 40s via the help of the radiational cooling.
Moving into Thursday, expect another very warm day and mostly sunny
skies. While we won`t be as warm as the past few days, we can still
expect high temperatures to get into the low to possibly mid 80s in
the interior areas. Fire weather concerns should be lessened
Thursday too, as min RHs aren`t looking to get below the upper 30
percents. In addition, rainfall looks to finally make its way into
our area come Thursday as troughing from the Plains begins to push
into our far west. As this happens, we could see some isolated
showers and maybe a stray storm or two during the morning hours near
Ironwood, in addition to partly cloudy skies over the rest of the
western U.P. throughout a significant portion of the day. While CAMs
are generally showing the showers and storms dying out and avoiding
the Upper Peninsula by the early afternoon hours, there looks to be
another line of convection that develops over Minnesota late in the
day that makes its way into the U.P. after sunset. This line of
convection looks to follow a cool front moving from west to east
across the area late Thursday into Friday as the parent low lifts
from the Canadian Prairies towards western Hudson Bay. While not
much rainfall is expected with this cool front, we could see some
heavier downpours in the stronger showers and storms that produce
some locally soaking rainfall over the U.P. as guidance shows PWATs
around 1.50 inches along the frontal boundary. While the European
ensemble shows us that we do have enough instability to get
thunderstorms and showers going, with bulk shear remaining fairly
modest (25 knots or less) across the area, no severe weather is
expected at this time along the cool front. With the thicker cloud
cover overhead, we could see some record high minimum temperature
records broken Thursday night (and possibly Friday night too across
the eastern U.P.). The cool front looks to leave our area by Friday
night as weak ridging fills in behind it.

Model guidance begins to significantly diverge past this Saturday as
each medium range suite has different strengths and locations for
two vertically-stacked lows over the CONUS that could impact our
weather. The first of which is one over the Canadian Prairies
Saturday that lifts towards Hudson Bay for the latter half of the
weekend. This low looks to bring another cold front over us Saturday
night into Sunday. This front may bring us some additional showers
and thunderstorms across our area during that time period, but with
the lifting mechanisms weakening as it moves over us, some guidance
looks to keep us dry but cloudy through the latter half of the
weekend. However, once this front passes, expect to see temperatures
closer to normal with highs only getting into the lower 70s post
cold front on Sunday to the mid to maybe (?) upper 60s come Monday.
A second vertically-stacked low looks to lift from the Desert
Southwest and the Southern Rockies towards the Upper Midwest early
next week. Depending on how the cold front of the first low phases
with the developing warm front of the second low, as well as where
the second low tracks, we may or may not receive rainfall during the
first half of next week; while the GFS and Canadian suites are
generous with the rainfall over us early into mid next week, the
Euro is suggesting that we will remain dry through the remainder of
the period. Hopefully, the former two will occur, as we really need
some meaningful rainfall across our area.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 716 AM EDT Wed Sep 18 2024

Under a warm, dry air mass, VFR will continue thru this fcst period
at IWD/CMX/SAW.

&&

.MARINE...
Issued at 325 AM EDT Wed Sep 18 2024

Light winds of generally 20 knots or less continue today into
Thursday before southeast to southerly winds pick up to 20 to 25
knots over the north central lake late Thursday ahead of an
approaching cool front from the west. As the front weakens while
traveling eastward across Lake Superior Thursday night into Friday,
expect the winds to die down to 20 knots or less again by Friday
morning. The light winds continue through Saturday as weak ridging
moves through the Upper Great Lakes, before possibly another cold
front from the west increases winds to greater than 20 knots
Saturday night/Sunday.

As for thunderstorm chances over Lake Superior the next several
days, outside of a stray thunderstorm or two near Isle Royale early
this morning, expect the lake to remain storm-free until the cool
front reaches the far western lake near Duluth Thursday morning.
Shower and storm chances continue over the far western lake Thursday
before a line of convection moves from west to east across the lake
along the cool front late Thursday through Friday. There is a
marginal risk (2+% chance) for some strong, erratic winds and
damaging hail over the far western lake Thursday. As the showers and
storms move eastward into a less favorable environment, the severe
weather threat diminishes. The last of the showers and storms looks
to leave eastern lake Superior by Friday night.

&&

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

&&

$$

SHORT TERM...Rolfson
LONG TERM...TAP
AVIATION...Rolfson
MARINE...TAP