Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 052030

Area Forecast Discussion
National Weather Service Marquette MI
430 PM EDT Sun Jul 5 2020

.SHORT TERM...(This evening through Monday)
Issued at 427 PM EDT SUN JUL 5 2020

Radar and satellite this afternoon show deep moist and occasionally
severe convection along the Lake Superior lakebreeze, the result of
higher dew points than yesterday. These storms exist in an
environment with mostly 1000-1500 J/kg MLCAPE (slightly more in a
narrow corridor through Menominee and Delta counties) and effective
shear around 25 kts or less which means that cores have been going
up and coming down quickly. These storms should wane as we head into
the evening and lose diurnally driven instability. In fact, radar
trends suggest that the best is already behind us.

Tonight, slight ridging will build back in overhead as a band of
theta-e advection and weak 850 mb moisture convergence lifts
northeastward across western Lake Superior and the Keweenaw. With
MUCAPE progged by the NAM to remain around 1000-1500 J/kg, a band of
elevated thunderstorms should move across these areas late tonight
into tomorrow morning. Regional radar shows these storms already
bubbling up over the Arrowhead of Minnesota so confidence is
increasing in those materializing. Model profiles show effective
shear approaching 35 kts so despite these storms being elevated,
some hail is possible as they move through. Expect that these storms
will weaken as they move eastward into the central UP after dawn.

Tomorrow will be more humid with stronger southerly return flow. Dew
points should make it well into the mid 60s or perhaps even into the
lower 70s. This means MLCAPE should reach 2000+ J/kg again tomorrow
which will lead to another day lake breeze thunderstorms, likely
initiating around 18z again or perhaps an hour earlier. Then
tomorrow late afternoon a weak cold front approaches from the west
along with a mid-level short wave. This should become the focus for
yet another round of showers and storms. Given the aforementioned
MLCAPE values and effective shear expected to be around 30 kts
again, tomorrow should be another day with strong to occasional
pulse severe storms capable of producing large hail and damaging
winds. Thus, SPC has introduced nearly all of the CWA into a
Marginal Risk tomorrow. PWATs rising to around 1.75" combined with
slow storm motions and many boundary interactions, plus multiple
rounds of storms, means the flash flood risk will increase somewhat
as well. WPC has only the western edge of the UP in a Marginal Risk
for Excessive Rainfall tomorrow but curious to see if that ends up
expanded given the soupy airmass and strong signal for widespread
storms in the CAMs.

.LONG TERM...(Monday night through Sunday)
Issued at 410 PM EDT SUN JUL 5 2020


Upper-level ridging remains anchored over the Southwest CONUS and
gradually shifts east over the Southern Plains over the next week,
with a varying degree of intensity. This far north, upper-level
ridging will start to flatten as a number of shortwaves crest the
ridge. Even with the ridge deamplifying over the Upper Great Lakes
this week, this will not bring much of a change to the ongoing
persistent heat and occasionally humid conditions as west to
southwest flow aloft continues to advect in very warm air aloft.
Still expect daytime highs to top out in the mid/upper 80s and lower
90s, and it still doesn`t look like we will get much below 60-65
degrees at night this week. The "coolest" day of the week looks to
be on Tuesday with highs in the 70s near Lake Superior and 80s
elsewhere. Wednesday and Thursday look to be the hottest days of the
week, with temperatures UP-wide (including near the shoreline of the
Great Lakes) looking to climb to around 90, with a number of sites
inland from the Great Lakes expected to climb into the lower 90s.
Will need to keep a close eye on heat indices and how diurnal mixing
unfolds later this week as models do show the potential for
dewpoints to climb into the 70s. As this heat continues this week
please remember your heat safety: drink plenty of water, take
frequent breaks if you`re working outside, avoid strenuous outdoor
activity during the peak heat of the day, and never leave any pets
or passengers unattended in hot vehicles!

The pattern change noted above will bring a much more active period
of weather as multiple shortwaves traverse the Upper Great Lakes,
with multiple chances for thunderstorms. Under a pattern like this,
the LLJ will help support the maintenance of MCSs as additional
moisture and unstable air gets advected in. Thus, it is possible we
could also see some nocturnal convection at times. Depending on the
organization of convection and how shear plays out, we could see
some strong to severe storms this week. Ahead of these waves, PWATs
look to be around 1.5-2``. Thus convection that does develop this
week will produce heavy rain. More details on what the daily
potential is for thunderstorms below.

Monday night, as a weak cold front moves into western and central
Upper Michigan models are fairly consistent in showing a line of
convection pushing west to east across the Upper Peninsula. Could be
some strong to severe storms early on Monday night, but storms
should weaken as they push east overnight. By Tuesday morning, the
weak cold front will continue to push across south-central and
eastern Upper Michigan. There could be some lingering showers and
thunderstorms around, but as high pressure starts to nose in from
the west expect a mostly dry day. The only area right now that looks
possible for thunderstorm development on Tuesday afternoon/evening
is across the south-central along the Lake Michigan lake breeze.
High pressure developing over Lake Superior on Tuesday will also aid
in pushing the Lake Superior lake breeze southward across central
parts of Upper Michigan, thus further enhancing convergence and lift
across the south-central. There is some uncertainty in the severity
of afternoon thunderstorms given the potential for morning
convection and some of the negative influences that can have on
afternoon destabilization. However, a few models to show the
potential for nice afternoon destabilizing and a pocket of steeper
lapse rates aloft, as a shortwave tracks over Lake Superior. Thus,
SBCAPE values may be able to climb to 1500-2500 J/kg that afternoon.
The shortwave will also bring a boost in deep-layer shear, with 0-
6km bulk shear showing 30-40 knots.

Wednesday a warm front will lift north across the area, bringing
back very humid conditions. There is the potentially for some
scattered convection, but for the most part it looks to remain dry.
Wednesday night into Thursday morning, as moisture transport
increases across the area thunderstorms may work into western parts
of Lake Superior and into Upper Michigan. By the time the LLJ gets
this far east, it does start to veer out and weaken, thus the level
of elevated CAPE starts to wane. Could be a sunrise surprise kind of
morning with a pesky storm or two, otherwise think thunderstorms
Thursday morning should behave.

On Thursday we will remain within the warm sector ahead of a
deepening wave progged to lift across the region Thursday night into
Friday morning. Models diverge a bit in the timing of this wave and
associated cold front, thus confidence in the timing and placement
of additional thunderstorm activity Thursday through Friday is on
the low end right now. The unstable conditions expected ahead of the
front will cause some concern for strong to severe storms. With the
limiting factor being weak deep-layer shear, it could end up being
more pulse-type convection.

Behind this front, next weekends forecast looks to be a bit cooler,
but still warm with temperatures 5-10 degrees above normal.
Northwest flow aloft looks to briefly become established, with a few
waves rotating down across the region. Thus there could be some
convection around over the weekend. Northerly wind behind the front
through a good portion of the weekend should bring some relief from
the to the heat for communities along the Lake Superior shoreline.

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 148 PM EDT SUN JUL 5 2020

In the near term, story is lake breeze thunderstorms just south of
SAW continuing to move south away from the terminal. Otherwise, no
significant weather this TAF period and conditions should stay VFR.
The things to watch for will be perhaps some additional
thunderstorms very late tonight into early tomorrow morning. Best
chances will be at CMX where a TEMPO is included; elsewhere, only
PROB30 groups. Also, slight chance that fog over Lake Superior
pushes onshore into CMX tonight with the east wind but models don`t
show much if any vis reduction so did not include it in the TAF for

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 430 PM EDT SUN JUL 5 2020

Light winds less than 15 kts are expected to continue throughout the
forecast period. Main story will be areas of fog over the eastern
lake. Not too sure what`s out there given cloud cover blocking the
view on satellite but given the high dew points and the fact that it
rained over the eastern half of the lake much of the day, there is
probably a hefty patch of it out there. And with more rain and moist
air expected the next few days, it`s likely to only expand. Did not
include any dense wording in the forecast right now since there
isn`t any evidence of that, but would not be surprised if headlines
for dense fog are needed in the near future.

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Ritzman
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