840
FXUS63 KMQT 130533
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
133 AM EDT Sat Jul 13 2024

.KEY MESSAGES...

- Isolated diurnally driven showers/thunderstorms this afternoon.

- Seasonably warm Saturday through Monday with periods of showers
and thunderstorms, some of which could be strong to severe.

- Cooling and drying trend into the midweek portion of next week
with the arrival of high pressure.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 317 PM EDT Fri Jul 12 2024

Early afternoon water vapor imagery shows a compact cutoff low over
northern lower MI shifting east with shortwave ridging building in
over the UP. Diurnal cu are firing up over central/western portions.
Despite the synoptic-scale absence of forcing, as well as a low/mid-
level cap evident on forecast soundings and SPC mesoanalysis, a few
diurnally driven showers have developed along differential heating
boundaries. This activity should diminish quickly after sunset.
Mostly clear skies expected tonight with lows a bit milder than
previous nights with a more moist airmass and light SW flow. A few
patches of fog cannot be ruled out.

Saturday into Saturday night, the main forecast challenges are max
temps and convective chances. The latter is lower predictability
than would be expected at this time range given uncertainty in
placement and track of upstream MCS activity. Local area will be
situated on the eastern edge of a mid/upper level quasi-zonal speed
max that strengthens with time between the Four Corners heat dome
and cutoff low west of Hudson Bay. High confidence that the morning
and early afternoon hours will be dry, which should allow for
seasonably warm temperatures to build in an airmass characterized by
15-17C 850mb temps. Forecast soundings show fairly good mixing over
most interior areas which should allow highs to reach the mid-80s,
possibly upper 80s to near 90 in downsloping areas near Lake
Superior, but slightly cooler to the lee of Lake Michigan. The
mixing should allow dewpoints to lower so the net apparent temp will
likely be only a couple degrees warmer than the air temp.

A couple CAMs in the 12Z HREF suite have an MCS developing late
tonight over NW MN. If this occurs, some of this activity could
track into the western UP during the mid/late afternoon. This is not
the most favored solution with only about a 20-30% chance of
occurrence. Best potential for convection at this point is in the
Saturday night timeframe, particularly 02-08Z. Extreme CAPE values
look to set up to our SW over WI/MN (2000-5000 J/kg) as steep
midlevel lapse rates overspread a very warm/moist boundary layer,
and it`s likely that the most intense, outflow-driven MCS follows
this off to our southwest. However, convective parameters (MUCAPE
1000-2000 J/kg and effective bulk shear 25-30 kt) and HREF
updraft/updraft helicity tracks suggest that the marginal/slight
risks for the western half (categories 1/2 out of 5) are warranted.
Steep midlevel lapse rates suggest large hail is a potential hazard,
while quasi-linear CAM storm modes suggests strong wind is also a
potential hazard. Otherwise, a mild night expected with lows mainly
in the 60s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 353 PM EDT Fri Jul 12 2024

Aloft, the path of most prominent troughs and ridges is well to the
north over Canada, leaving the Upper Great Lakes in a primarily
zonal pattern through this weekend. This will lead to the primary
driver of sensible weather to be weak shortwave impulses in the
zonal flow. While the synoptic forcing may be weak and ambiguous,
hot and muggy conditions this weekend will allow for instability to
grow, allowing for the potential for strong to severe thunderstorms
over the weekend and to begin next week, especially in the form of
MCS`s. High pressure then settles over the region by Tuesday,
allowing for a cooler dry period towards the middle and late week
period next week.

Sunday, another warm day is on the horizon. The NBM looks to be on
the high side of most guidance showing highs approaching 90,
contrasting the median of available guidance showing highs on Sunday
in the low to mid 80s in the interior with upper 70s near the Great
Lakes. Moisture values increase as well, with the PWATs exceeding
1.5 inches representing the 90th percentile of climatology by the
NAEFS and GRB sounding climatology. Dew points are forecast to be
around 70 for at least some period of time for much of the UP, with
the highest chances (60-80%) of exceeding 70 being the south-central
creating quite muggy conditions. Monday looks to be similarly warm,
though slightly lower chances of dew points being oppressively high.

These hot and humid summertime conditions will be accompanied with
westerly to west-northwesterly flow at 500mb, which will allow for
some minor shortwaves to progress through the region. The
combination of a summertime airmass and the flow pattern aloft
combine for a climatologically favorable setup for convection over
the UP. As the hot and humid temperatures set up, CAPE values climb
to over over 2000 J/kg on Sunday (with the 90th percentile showing
worst-case values of over 3000) and values around half of that on
Monday. With the southwesterly surface flow contrasting the west-
northwest flow aloft, directional shear will be present, though
speed shear will be somewhat lacking. Regardless, shear will be
present enough to help maintain whatever thunderstorms do initiate,
so if forcing is present enough to realize the plentiful
instability, severe weather is a possibility for Sunday and Monday.
However, without great consensus on forcing, exact probabilities or
timings are unknown at this time. Another complicating factor is
that the NAM Nest is showing the primary storm mode Saturday is MCS-
like, which should be a good analog for conditions on Sunday and
Monday. Predicting the location of upstream MCS development is
highly challenging at time periods of 48+ hours.

By Tuesday, broad troughing aloft shifts from northern Ontario
towards the East Coast and ridging fills in behind. As a result of
the advancing ridging, high pressure to around 1020mb will keep
weather quiet Wednesday and Thursday. A cooling trend is also
expected to accompany the arriving ridging as north and northwest
flow will bring highs only in the upper 60s and low 70s Tuesday
through Thursday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 128 AM EDT Sat Jul 13 2024

VFR conditions and light winds will prevail in this TAF period. Some
fog/mist will be possible overnight at KIWD and KSAW, but confidence
is low. Guidance continues to lack concensus with tomorrow`s
convective event. At this point, it continues to look as if KIWD may
begin seeing thunderstorms by Saturday afternoon.

&&

.MARINE...
Issued at 353 PM EDT Fri Jul 12 2024

Light pressure gradient will keep wind gusts below 20 knots and wave
heights below 3 feet for the next week. The greatest hazards will
come in the form of thunderstorms which will threaten the lake
Saturday through Monday, with a few storms being potentially strong
to severe in the nearshore waters. Patchy dense fog is also a
possibility in the wake of precipitation.

&&

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

&&

$$

SHORT TERM...Thompson
LONG TERM...GS
AVIATION...JTP
MARINE...GS