Severe Thunderstorm Warning 35, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
322 PM EDT Mon Jul 15 2019

.DISCUSSION...

Convection has fired as expected, with latest SPC mesoscale Analysis
indicating MLcapes 1000-1500 J/kg on the western fringe of the CWA,
with effective build shear above 30 knots generally north of I-69.
An isolated marginally severe thunderstorm or two remains possible
through the  bulk of daylight hours, but weak mid level lapse rates
suggests otherwise with just torrential downpours due to the
tropical nature of the airmass. Subsidence/modest drying out at the
700 MB level behind the mid/upper wave exiting Lake Huron is
expected to produce a dry late evening into the early morning hours
of Tuesday.

Remnant circulation/moisture of Barry over the low-mid Mississippi
River valley being sheared off to the northeast and northern fringe
looks to clip southeast Michigan tomorrow, as the closed 500 MB low
opens up. PW values exceeding 2 inches south of I-69 with 700 MB dew
pts pushing 7 C and possibly even 8 C, record territory for Mid July
around here. The main moisture surge is actually going to occur
around 12Z Tuesday when nose of the 800-700 MB jet crosses just
across the southern Michigan border. Stronger winds then are shunted
off to the east during Tuesday, with 0-6 KM bulk shear generally
under 20 knots. Thus, no severe weather is expected with the weak
instability/mid level lapse rates. Once again, torrential rainfall
will be the main hazard and should not take much to set off diurnal
enhanced showers and embedded thunderstorms (see ARW), lingering
into the early evening. With activity/clouds already arriving to
start the day, temperatures likely holding in the 80s, with Tri-
Cities and northern Thumb region likely seeing the warmest temps.

Reasonable agreement amongst models with an upper level disturbance
coming out of the Central Plains and tracking through Lower Michigan
on Wednesday, helping to kick remnant open 500 MB trough of Barry
off to the east. Still a lot of moisture to work (PW values around 2
inches/700 MB dew pts still aoa 5 C) with to generate showers and
thunderstorms, as MLcapes push above 1000 J/kg and potentially up to
2000 J/kg, depending on timing and strength of the disturbance.
Localized enhancement of 0-6 KM bulk shear reaching around 30 knots
(probably along/north M-46 once again per NAM) could support an
isolated severe threat, but mid level lapse rates still look to be
weak (under 6 C/km). 850 MB temps around 18 C, supportive of maxes
around 90 degrees, but with showers and thunderstorms around and
moist low levels (surface dew pts aoa 70 degrees), probably going to
hold temps more in the 85-90 degree range.

Heat will increase at the end of the week as an upper level ridge
sets up over the central plains before expanding eastward allowing
the 591dam to move into southern MI on Friday and Saturday. Both of
those days will have highs in the mid 90's (possibly upper 90's in
Detroit itself) with dewpoints in the mid 70's giving heat index
values well into the 100's. Lows Thursday night on will only get
down into the mid 70's.

A low begins to develop over the northern plains Thursday morning
and moves over the Upper Peninsula Thursday night. This system pulls
hotter muggier air into SE MI helping to create those mid-90's on
Friday and Saturday. There will be a moderate chance of rain
Thursday night through Friday with this system's passage. A weak mid-
level disturbance looks to move from Wisconsin into SE MI Saturday
afternoon with could bring a chance of scattered showers and
thunderstorms.

&&

.MARINE...

Prevailing late day southeasterly winds will increase modestly while
gradually veering to southwest overnight as a warm front lifts
through the region. A 10 to 20 knot southwest wind will remain in
place through Tuesday. Strongest winds likely noted across Saginaw
Bay during this time, where conditions may near advisory levels for
small craft. Southwest winds will diminish Tuesday night as the
gradient eases. Winds will then turn light and variable for
Wednesday. Increasingly moist and unstable air across the region
over the next couple days will lead to increasing chances for
thunderstorms.

&&

.HYDROLOGY...

A warm front will lift across southeast Michigan during the
afternoon and evening hours. This frontal passage timed favorably
with diurnal destabilization will provide the focus for a scattered
coverage of showers and thunderstorms during this time. Any
thunderstorm activity will bring the potential for localized heavy
rainfall, with amounts in excess of an inch possible. There will
again be a chance for showers and thunderstorms both Tuesday and
Wednesday, particularly during the afternoon and evening hours, as
tropical moisture associated with remnants of Barry enter the
region. Potential exists for locally intense rainfall rates to
develop within any activity given the high moisture content. This
could lead to poor drainage flooding of susceptible low lying and
urban areas.

&&

.PREV DISCUSSION...
Issued at 1239 PM EDT Mon Jul 15 2019

AVIATION...

Warm front on pace to lift across southeast Michigan during the late
afternoon and evening periods. This frontal passage timed favorably
with diurnal destabilization will provide the focus for a scattered
coverage of showers and thunderstorms during this time. Recent model
guidance continues to center this development primarily within the
20z to 00z window. Outside of any thunderstorm activity, VFR
conditions will prevail with the late day diurnal cu gradually
fading with sunset. Winds hold modestly from the south through the
period.

For DTW...scattered coverage of thunderstorms expected to develop
across the area during the late afternoon and evening periods. Most
likely window for activity to impact the terminal and surrounding
airspace centered between 21z and 00z.

DTW THRESHOLD PROBABILITIES...

* Moderate in ceilings at or below 5000 ft late this afternoon and
  evening.

* Moderate in thunderstorms impacting the airspace late this
  afternoon and evening.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

DISCUSSION...SF/KDK
MARINE.......MR
HYDROLOGY....MR
AVIATION.....MR

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

Hazardous Weather Outlook
National Weather Service Detroit/Pontiac MI
955 AM EDT Mon Jul 15 2019

MIZ047>049-053>055-060>063-068>070-075-076-082-083-160900-
Midland-Bay-Huron-Saginaw-Tuscola-Sanilac-Shiawassee-Genesee-Lapeer-
St. Clair-Livingston-Oakland-Macomb-Washtenaw-Wayne-Lenawee-Monroe-
955 AM EDT Mon Jul 15 2019

This hazardous weather outlook is for southeast Michigan.

.DAY ONE...Today and Tonight

Scattered thunderstorms producing locally heavy rain are expected to
develop this afternoon with daytime heating, then dissipate this
evening. Isolated severe thunderstorms producing wind gusts to 60
mph will be possible in the 3-8 PM time frame, especially north of
I-69. Storm motion will be east at 25 mph.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

An influx of tropical moisture Tuesday into Wednesday will provide
the chance for thunderstorms. Humid and unstable air will sustain the
chances for thunderstorms Thursday into Friday as well.

The afternoon heat index is forecast to reach 98 to 105 degrees
Thursday, Friday, and Saturday over much of the area. There will be
minimal relief at night due to elevated humidity, especially in the
Detroit urban heat island. A heat advisory or excessive heat warning
will be warranted during this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

LCZ460-LEZ444-LHZ361>363-421-422-441>443-462>464-160900-
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-
955 AM EDT Mon Jul 15 2019

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

.DAY ONE...Today and Tonight

Scattered thunderstorms are expected this afternoon and evening as a
warm front lifts through southern Michigan. Widespread severe
weather is not expected but an isolated wind gusts to 50 knots
cannot be ruled out. Storm motion will be east at 20 knots.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

An influx of tropical moisture Tuesday into Wednesday will provide
the chance for thunderstorms. Humid and unstable air will sustain the
chances for thunderstorms Thursday into Friday as well.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

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

SF

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