834
FXUS63 KMQT 202018
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
418 PM EDT Fri Sep 20 2024

.KEY MESSAGES...

- Isolated showers and maybe a thunderstorm possible this evening
east half. Patchy fog forming late tonight/early Saturday mainly
central and east.

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

- Multiple rounds of precipitation possible through the first half
of next week. Thunderstorms that do form are not expected to be
severe at this time.

- Temperatures around normal are expected to return next week.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 356 PM EDT Fri Sep 20 2024

Latest water vapor imagery and RAP analysis shows shortwave trough
slowly progressing east through the east half of Upper Mi with the
visible satellite imagery showing widespread diurnal cu across the
U.P. Subsidence/mid-level drying behind this shortwave feature has
resulted in dry conditions today over western Upper Mi. Central and
eastern sections of the U.P. have seen a few isolated showers pop up
in the vicinity of the mid-level trough axis and focused along
outflow boundaries/lake breezes especially east of MQT in the past
hour. This environment has also been more favorable for convection
as lower to mid 60s dew points have led to MLCAPE values approaching
1000 j/kg central and east. However, build up of convection over the
central and eastern U.P. has been largely inhibited by strong mid-
level drying as noted on fcst soundings. Afternoon temperatures have
been mostly in the 70s although a few lower 80s readings have been
observed over the interior west.

Other than some lingering isolated showers/t-storms over the east
mainly early this evening, expect dry conditions to prevail as
shortwave ridging and associated subsidence builds across the area
from the west. Moist dew points in the upper 50s and lower 60s along
with clearing of diurnal cu and light winds will likely lead again
to patchy fog forming overnight into portions of central and eastern
Upper Mi. Fog could become locally dense over eastern portions.
Expect min temps generally lowering into the 50s with a few upper
40s readings possible over the typical cool spots of the interior
west.

&&

.LONG TERM /SATURDAY THROUGH FRIDAY/...
Issued at 415 PM EDT Fri Sep 20 2024

Active weather pattern to begin the long term forecast as the
sensible weather will be dictated by the evolution of multiple
shortwaves passing in the vicinity of the Upper Great Lakes through
early next week. Following Saturday`s well above normal
temperatures, more seasonal temperatures return Sunday and beyond
with highs in the 60s. While there is enough spread in the ensembles
in the back half of the week to keep slight-chance (~20%) PoPs in
the forecast for the eastern portions of the UP through the week,
ensembles have continued to trend more dry with each ensemble suite
run. Beyond next week, ensembles still favor ridging over the
central CONUS, potentially leading to downstream high pressure over
the Upper Great Lakes, which aligns with the CPC 8-14 day and 3-4
week precip outlooks which put the UP in a below normal precip
pattern.

Saturday will begin dry as weak surface ridging fills in behind the
departed cold front. Mostly clear skies will allow highs to climb
back to around 80. While this is unseasonably warm, the NBM gives
less than a 5% chance of breaking a record high at the MQT WFO.
However, if the WFO does break 80, it would be the most 80 degree
days in any September, showing how unusually warm this stretch has
been. The break in the clouds and precip will be brief however as a
~1005mb low will quickly jet along just east of the Manitoba/Ontario
line, bringing showers and non-severe thunderstorms to the UP for
overnight Saturday through Sunday along the low`s cold front. Recent
runs have brought this low closer to the UP, which means that
dynamic support for rainfall and thunderstorms should be better. No
severe weather is expected though as HREF mean SBCAPE Saturday
evening is only around 500 J/kg at most, though 0-6km shear at least
looks modest at around 30 kt. Precip totals for this system look to
be around a quarter of an inch, so nothing extreme, but welcome
rainfall for a lot of areas that have struggled to get precipitation
this month.

Once the front departs Sunday night, the next feature to watch will
be a 500mb trough that will exit the Four Corners region Saturday
night. Ensemble spread is still high as to the impacts of this
system as the trough could potentially interact with a Alberta
Clipper-style trough that will be approaching the Upper Great Lakes
at approximately the same time and there is disagreement as to the
strength of each system and the track of the resulting surface
features. Regardless of the exact solution, the NBM continues to
trend more dry, with the western UP now strongly unlikely to see
precip (PoPs less than 15%) and the eastern portions only have PoPs
around 30%. If clear skies can verify Monday and Tuesday morning,
interior low temperatures could get a bit cold, with bias-corrected
MOS guidance suggesting lows in the upper to mid-30s in the interior
west Monday and the widespread interior on Tuesday. Should mid-30s
verify, there is a chance for patchy frost (~20%) those mornings.
Moving into the second half of the work week, the 12Z GEFS shows
anomalous ridging building over the Northern Plains and Canadian
Prairie with 500mb height anomaly reaching +20 dam over Manitoba by
Thursday morning. Downstream high pressure of that ridge would tend
to have the UP rather dry moving into late September, and with the
GEFS showing preference for anomalous ridging over the central CONUS
throughout the run, the CPC outlooks of less than normal
precipitation will be on-track.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 358 PM EDT Fri Sep 20 2024

MVFR conditions have cleared out this afternoon. Expect VFR to
prevail at most of the terminals through the period with the
exception of some MVFR to IFR fog developing at SAW later
tonight into early Sat morning.

&&

.MARINE...
Issued at 415 PM EDT Fri Sep 20 2024

Westerly wind gusts to 25 knots over the western portions of Lake
Superior will gradually diminish tonight now that the cold front has
completely passed over the lake. Localized surface ridging will keep
wind gusts under 20 kt until Saturday evening, where another passing
cold front will allow westerly and northwesterly wind gusts to 25
knots over the western half of the lake Sunday morning and up to 30
kt over the eastern portions of the lake during the day Sunday. This
will force waves up to 4 feet along the shores of the Keweenaw
Peninsula Sunday morning and waves of 4-6 feet over the east half of
the lake throughout Sunday. Thunderstorms are possible with this
front, but are not expected to be severe. Winds are currently
forecast to be below 20 kt next week, but a couple of shortwave
troughs approaching the Upper Great Lakes in the first half of the
week could force a few gusts to 25 kt, but uncertainty is too high
at this time to say exactly where, when, and how those gusts may
occur.

&&

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

&&

$$

SHORT TERM...Voss
LONG TERM...GS
AVIATION...Voss
MARINE...GS