Severe Thunderstorm Warning 101, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
808 PM EDT Thu Aug 24 2023

.AVIATION...

Thunderstorms are filling in rapidly along the wavy front stalled
across central and SW Lower Mi this evening, taking advantage of
high instability south of the front and a strong wind field aloft.
Severe intensity is likely and a Severe Thunderstorm watch is in
effect until 1 AM. Damaging wind is the primary storm hazard with
large hail and torrential rainfall also likely. There is also a low
risk of tornadoes, both in discrete cells and within longer lines
that may develop. Borderline MVFR/IFR visibility restriction occurs
in the strongest storms while they sweep through from MBS at
issuance time to DTW around 02Z and then exit eastward by 05-06Z.
Early evening observations indicate expansive IFR ceiling across
northern Lower Mi and MVFR farther west across northern WI. These
clouds are projected to move into SE Mi on light NW wind as low
pressure carries the front southward late tonight. MVFR during the
morning improves to VFR Friday afternoon before scattering late in
the day The clouds hold during the morning and Friday morning

For DTW... A 02-03Z time of arrival is on track for the storms
strongly building across central and western Lower Mi. Severe
intensity is likely until about 04-05Z with some residual showers
possible until shortly after midnight. Borderline IFR/MVFR ceiling
fills in behind the storms late tonight and Friday morning.

.DTW THRESHOLD PROBABILITIES...

* High for thunderstorms 02-05Z this evening.

* High for ceiling at or below 5000 ft this evening and
  Friday morning.

&&

.PREV DISCUSSION...
Issued at 354 PM EDT Thu Aug 24 2023

DISCUSSION...

Enhanced risk of severe thunderstorms this evening.

Outflow from the morning convection tracked west, keeping the
elevated surface dew pts (70s) at bay across far southwest Lower
Michigan. Finally beginning to see a release of the higher dew pts
toward the CWA (78 degree dew pt at Hillsdale as of 230 PM), and
will keep the heat advisory for areas along and south of I-94, as
sunshine near the Ohio border will push maxes to around 90 degrees
and heat indices of 100 degrees or greater by sunset.

A high degree of instability is in place over southwest lower
Michigan, with mid level lapse rates aoa 8 C/km and MLcapes of 4000
J/kg with eroding low level cin/cap. Upper level wave/jet streak and
associated surface low over Wisconsin should be sufficient trigger
to support rapid development of thunderstorms early this evening.
Favorable combination of shear and instability will be supportive of
supercells initially, with just enough low level shear and low lcl's
to support possible isolated tornadoes along and just north of the
surface low/warm front, which looks to ride somewhere between I-94
and I-69 corridors. Surface dew pts around 80 degrees over the
Western Ohio Valley allowing for SBcapes up around 7000 J/kg, which
will also be feeding in to the system, and an eventual MCS with
damaging winds appears to be the likely outcome by late this
evening, as the system then tracks off into the eastern Great Lakes.
CAMS solutions (HRRR/ARW/FV3) are at least converging toward the
general concept, with the main impact to southeast Michigan during
the mid evening (7-11 PM) hours. Even though the system looks
progressive, flooding rainfall remains a big concern with the
exceptional moisture content, and quick 1-3 inches of rainfall seems
plausible underneath the severe storms/complex. Any training of
cells with the strengthening low level jet would support higher
totals, but does not appear to back around enough, maintaining a
mostly near due west-east direction.

Sheared out/elongated upper level wave over Central Canada on track
to swing through the northern Great Lakes tomorrow, leading to
cooler and drier Canadian air filtering into the Great Lakes region
over the Weekend as longwave trough takes hold over New England/Mid
Atlantic region. Still, can't rule out isolated showers/drizzle on
both Friday-Saturday, as low level moisture (sfc-925 MB) will be
stubborn/slow to mix out, with dew pts not falling back into the
comfortable 50s until Saturday with 40s possible for Sunday.

Speaking of cooler, both Euro and GFS are indicating a longwave
trough developing east of the Mississippi River Valley by mid week,
with 1000-500 MB thicknesses lowering into the 550s DAM over Lower
Michigan, as 850 MB temps progged to bottom out in the mid single
numbers Wednesday morning (although the 12z EURO is not as amplified
as the 00z run). Lake effect showers will have to be watched to
potentially impact the eastern Thumb region before the sprawling
high pressure moves overhead Wednesday night-Thursday.

MARINE...
Relatively light winds across the marine zoned today with a stalled
frontal boundary laid out across central Michigan through far
southern Lake Huron. This brings general east flow across much of
Lake Huron and southwest flow from Lake St Clair to west Lake Erie.
Strong to severe storms look increasingly likely late this afternoon
into tonight as the boundary becomes a focal point for development.
This activity will mainly affect portions of far southern Lake Huron
south to Lake Erie.  Northerly flow at 10 to 15 knots behind a front
will then begin to work southward through Lake Huron in the wake of
this system tonight, eventually bringing north flow to Lake Erie by
tomorrow morning. Winds bring elevated waves to the southern Lake
Huron, but it looks to hold below Small Craft criteria for tomorrow.
Another front Friday night into Saturday morning will come with
slightly stronger cold air advection resulting in gusts of 20 to 25
knots. The building waves into the nearshores of southern Lake Huron
will likely bring Small Craft Advisory conditions for Saturday.
Isolated showers will also accompany this frontal passage Friday
night. Waves decrease Saturday night into Sunday as high pressure
builds into the region. The next low pressure trough and front
arrives early next week bringing a return to unsettled conditions.

HYDROLOGY...

Numerous showers and thunderstorms are expected to develop this
evening. Most areas should see rainfall totals in excess of half an
inch. Prolific rainfall is expected with the strong to severe
thunderstorms however, which will put down a quick 1-2 inches of a
rainfall in a short period. Highly localized totals of 3 inches or
more are not out of the question with any training storms, which
would lead to more significant/flash flooding, especially over areas
which received heavy rainfall from last night. The Detroit Metro
region looks to be in a favorable position to receive the majority
of the rainfall tonight based on the expected surface low track near
the I-94 corridor.

Bulk of the rainfall should be over by midnight, with slowly drier
and cooler conditions setting in for Friday and especially this
weekend.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.

&&

AVIATION.....BT
DISCUSSION...SF
MARINE.......AA
HYDROLOGY....SF

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

Hazardous Weather Outlook...CORRECTED
National Weather Service Detroit/Pontiac MI
541 PM EDT Thu Aug 24 2023

MIZ047>049-053>055-060>063-068>070-075-076-082-083-251000-
Midland-Bay-Huron-Saginaw-Tuscola-Sanilac-Shiawassee-Genesee-Lapeer-
St. Clair-Livingston-Oakland-Macomb-Washtenaw-Wayne-Lenawee-Monroe-
541 PM EDT Thu Aug 24 2023

This hazardous weather outlook is for southeast Michigan.

.DAY ONE...This Afternoon and Tonight

Numerous strong to severe thunderstorms are expected to develop
early this evening and continue through the evening hours before
tapering off after midnight. All hazards will be in play, damaging
wind gusts to or in excess of 70 mph, large hail, flooding rainfall,
and isolated tornadoes. Storm motion will be northwest to southeast
at 45 mph.

A Heat Advisory in effect for areas along and south of I-94 through
early this evening as heat indices reach around 100 degrees.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Dispatchers please notify your emergency managers immediately...
Spotter activation may be needed late this afternoon and evening.

LCZ460-LEZ444-LHZ361>363-421-422-441>443-462>464-251000-
Lake St Clair-
Michigan Waters of Lake Erie from Detroit River to North Cape MI-
Lake Huron from 5NM east of Mackinac Bridge to Presque Isle Lt
beyond 5 NM off shore-
Lake Huron from Presque Isle Light to Sturgeon Point MI beyond 5NM
off shore-
Lake Huron from Sturgeon Point to Alabaster MI beyond 5NM off shore-
Outer Saginaw Bay SW of Alabaster to Port Austin MI to Inner Saginaw
Bay-Inner Saginaw Bay SW of Point Au Gres to Bay Port MI-
Port Austin to Harbor Beach MI-Harbor Beach to Port Sanilac MI-
Port Sanilac to Port Huron MI-
Lake Huron from Port Austin to Harbor Beach beyond 5NM Off Shore-
Lake Huron from Harbor Beach to Port Sanilac beyond 5NM Off Shore-
Lake Huron from Port Sanilac to Port Huron beyond 5NM Off Shore-
541 PM EDT Thu Aug 24 2023

This hazardous weather outlook is for portions of Lake Erie, Lake
Huron and Lake St Clair.

.DAY ONE...This Afternoon and Tonight

Numerous thunderstorms are expected to develop by early this
evening, some of these storms will likely be severe sometime between
4 PM - Midnight. All hazards will be in play, damaging wind gusts to
or in excess of 60 knots, large hail, torrential rainfall, and
isolated waterspouts. Storm motion will be northwest to southeast at
40 knots.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Dispatchers please notify your emergency managers immediately...
Spotter activation may be needed late this afternoon and evening.

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

SF