955
FXUS63 KMQT 151947
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
347 PM EDT Sun Sep 15 2024

.KEY MESSAGES...

- Isolated non-severe showers and storms into early evening
  along a narrow corridor from Iron through Baraga and western
  Marquette counties.

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

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 331 PM EDT Sun Sep 15 2024

Despite large scale high pressure dominating much of the Great Lakes
and northeast CONUS, water vapor imagery does show a connection to
Gulf of Mexico/Atlantic moisture into the Upper Great Lakes
region this afternoon. This moisture connection has allowed
surface dew points to climb into the mid 60s across much of the
west half of the U.P. this afternoon. MLCAPE values near 1000
j/kg and minimal to no capping noted on soundings has led to the
initiation of a few showers and isolated t-storms over central
Iron County early this afternoon at the nose of the sfc theta-e
ridge. A few of the CAMs suggest isolated showers could continue
into early evening along a fairly narrow low-level convergence
zone and theta-e ridge axis extending from Iron into Baraga and
nw Marquette counties. With weak wind shear, none of these
storms will become strong or severe but could produce brief
heavy downpours.

After showers die out over central Lake Superior tonight with loss
of diurnal heating, much of the rest of the night should be quiet
under the dome of high pressure. Models hint that some convection
could reinitiate into north central MN at the nose of a weak LLJ
this evening, and then possibly advect into the western U.P. toward
12Z Monday, but given model uncertainty with this happening only
have slight chc pops barely reaching into the far western U.P.
toward sunrise. Given high dew points over the area it`s also not
out of the question that patchy fog could form at a few locations,
especially where showers occur.

Expect min temps tonight ranging from the mid 50s to mid 60s under
partly cloudy skies.

&&

.LONG TERM /MONDAY THROUGH SUNDAY/...
Issued at 346 PM EDT Sun Sep 15 2024

Global model guidance is in good agreement in the rex block pattern
aloft over the east half of the CONUS continuing well into next week
as troughing associated with the remnants of Francine remains over
the US Southeast and ridging persists over the Great Lakes. Ensemble
and deterministic guidance suggests erosion in the ridge aloft but
most solutions still show a blocking pattern as it becomes more of a
split-flow/cutoff-low block. The blocking pattern with anomalous 500
mb heights over the Great Lakes will lead to warmer than normal
temperatures into next weekend with the only breaks in the dry
weather coming for the west half Monday associated with weak ridge-
riding shortwaves and then again late this week as uncertainty grows
in the evolution of the pattern.

The HREF and SREF keeps slight (15-25%) PoPs in the forecast for the
western half of the UP Monday but synoptic forcing is pretty lacking
with weak to no 500mb PVA, no jet support, and only mild 850mb warm
advection. Additionally, bulk shear is weak as well with only 15 kt
or less of 0-6km shear throughout the day tomorrow. Despite all the
factors working against shower formation, if isolated showers do
form, they will have thunder potential as HREF mean SBCAPE climbs to
1500+ between Ironwood and Houghton in the afternoon. QPF seems
lacking with this as even the 90th percentile of the HREF shows 6-
hourly rain rates of a half inch or less.

Tuesday through Thursday looks to be dry with NBM PoPs below 15%.
This is due to amplified ridging from the UP to northern Ontario in
response to the cutoff low over the southeast lifting slightly north
while troughing over the western CONUS lifts northeast out of the
Rockies. 500 mb height anomaly in the GEFS grows to over +30 dam
over Hudson Bay by Thursday morning. From there, ensemble and
deterministic model spread grows significantly as there are key
differences in how troughing exiting the southern Rockies late in
the week will form a surface feature and whether or not the blocking
pattern over the eastern CONUS will remain and at what strength.
Despite this spread, PoPs remain highest over the west for the
latter part of the work week into the weekend with no rain in sight
for the eastern UP until the weekend at the soonest and even that is
only a slight (~15%) chance. Fire concerns through the week are
mostly limited by weak winds and minimum RHs remaining higher than
critical thresholds, but drying fuels will have to be monitored if
this dry stretch continues through the forecast period.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 727 AM EDT Sun Sep 15 2024

VFR will prevail thru this fcst period at IWD/CMX/SAW. Some
scattered showers and isolated storms could develop between CMX
and SAW this afternoon but should not have much impact on either
site before dissipating out over Lake Superior this evening.
Some showers could redevelop toward 12Z Monday into the west and
could reach into IWD but this probability is too uncertain at
this time to include in the TAF. Expect southerly wind gusts to
20 knots at IWD this afternoon.

&&

.MARINE...
Issued at 346 PM EDT Sun Sep 15 2024

Light winds of 20 knots or less continue through this week as
ridging remains over the Upper Great Lakes, though a breakdown in
ridging aloft into next weekend could (~50%) provide for a few gusts
to 20 kt by Sunday depending on how the surface features pan out. In
the meantime, there is a slight chance (15-30%) of thunderstorms
over western Lake Superior on Monday. Waves will remain below 4 ft
through the forecast period.

&&

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

&&

$$

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