Severe Thunderstorm Warning 24, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
314 PM EDT Fri Jun 28 2019

.DISCUSSION...
Most of the area has experienced a very warm humid day so far with
highs reaching upper 80s to around 90 under mainly sunny skies due
decent mid level capping.  This has allowed cape values to build in
the 1-2k joule range.  Exception is far northern portions of the
forecast area that received over an inch of rain in locations this
morning. This along with more clouds have held temperatures down in
the 70s to low 80s.  Main concern for the rest of today is potential
convection.  Weak 500mb wave currently passing across southeast
lower providing modestly steep lapse rates above cap.  If convection
can break the cap there is a marginal risk for some severe storms
with main threat wind gusts and large hail. Best chance for
convection to initiate will be from the Detroit area ssw along
remnant outflow boundary from this mornings convection to the north
aided by lake breeze boundaries too.  This threat will diminish with
lost of daytime heating.  Elsewhere, convection will likely to
initiate and expand this evening across the Saginaw Valley and Thumb
as a weak cold front across central Michigan slowly sags southward
to about the Ohio border by 12z Saturday.

Not much upper level support with the front as 500mb flow will
become more neutral to anticyclonic with a weaker 850mb nocturnal
jet then was with last nights/early morning convection.  Coverage
and strength of activity will gradually weaken and decrease
overnight from loss of daytime instability as it sags south. It will
remain a warm muggy night with lows upper 60s to the low 70s in the
Detroit area.

For Saturday, the surface cold front will continue slowly sagging
southward as high pressure builds down from the north.  This will
bring a gradual decrease in dew points during the day along increase
in clearer skies from the north.  Enough instability will be around
for a chance of showers and thunderstorms near the Ohio border
through early afternoon before front pushes far enough south.  Still
be a warm day with highs in the mid to upper 80s, just a bit less
humid.

Saturday night through Sunday night high pressure will slowly move
south across Lake Huron producing mainly clear skies, light winds,
low humidity and seasonable temperatures.

Next week still looks to be characterized by a "Ring of Fire" setup
where a ridge of high pressure positioned over the mid-Mississippi
Valley leads to an instability gradient over the Great Lakes and
numerous chances for showers and storms as weak waves ride along the
periphery of the ridge. The greatest chance for precipitation
currently looks to occur Monday night into Tuesday morning as a weak
cold front provides more organized forcing, but each day Monday
through the late week will feature at least a slight chance for
showers/storms in the warm and humid air mass. Highs will reach the
mid to upper 80s each day (with the exception of the Thumb which
will be in the lower 80s) with dew points generally in the 60s
bringing a muggy feel to the air. The pre-frontal air mass on Monday
may see dew points approaching 70 degrees which would result in a
max heat index in the lower 90s.

&&

.MARINE...

Weak high pressure will remain in place across the central Great
Lakes through the remainder of the weekend and into early next week
resulting in a period of favorable boating conditions with light
winds under 15 knots and minimal waves. A frontal boundary sagging
south across the region this evening into tonight will provide the
focus for renewed scattered thunderstorm development, before drier
weather returns for the bulk of the weekend. Chances for
thunderstorms will then return early next week. Any thunderstorm
will be capable of producing locally erratic winds and waves in
addition to cloud to ground lightning.

&&

.HYDROLOGY...

Showers and thunderstorms that moved across portions of the Saginaw
Valley and Thumb this morning produced rainfall totals of 1-2
inches, with poor drainage flooding across portions of the Saginaw
Valley. After a brief period of dry weather early this afternoon,
additional scattered showers and thunderstorms will be possible
heading into this evening and through at least early tonight as a
frontal boundary sags south across the region. Confidence continues
to remain low regarding exact timing of thunderstorms, with
confidence increasing that the bulk of the activity will be focused
along and south of the M-59 corridor. A very moist airmass in place
will allow for any thunderstorm that develops to be capable of
producing torrential downpours and rainfall rates as high as 1 inch
per hour. Areal rainfall totals will generally be under a half of an
inch, with 1-2+ inches associated with the strongest thunderstorms.
These rainfall totals will lead to a renewed potential for
significant poor drainage flooding of susceptible low lying and
urban areas, and river rises where basins receive heavier rain
totals. Drier weather will then prevail heading into Saturday and
continuing through the remainder of the weekend with weak high
pressure in place. Chances for thunderstorms will then increase for
early next week.

&&

.PREV DISCUSSION...
Issued at 132 PM EDT Fri Jun 28 2019

AVIATION...

Challenging aviation forecast regarding additional thunderstorm
development through the first roughly 12 hours of this TAF period,
as earlier morning convection that rolled through much of Lower
Michigan has exited leaving behind an outflow boundary draped near
the M-59 corridor. To the north of this boundary, pocket of warmer
and stable midlevel air should largely preclude any additional
thunderstorm development at least for the next few hours. South of
the boundary, unstable airmass remains in place, with potential for
convective initiation possible at any time this afternoon/evening.
The end result is a continued low confidence forecast in potential
thunderstorm timing, as hi-res guidance has poorly handled ongoing
trends. Have opted to go with VCTS at the TAF sites starting this
evening and continuing into tonight in wake of midlevel subsidence
bubble departing east and prevailing larger scale frontal boundary
sagging south across the airspace. Confidence in thunderstorm
occurrence is moderate with timing likely needed to be adjusted with
TEMPO groups based on near term trends. Period of MVFR ceilings will
accompany frontal boundary passage towards daybreak Saturday outside
of any restrictions from convection. Clearing then anticipated north
to south by the end of the TAF period. Variable wind under 10 knots
will reorient southwest 10 knots gusting 15-20 knots outside of any
thunderstorm development, and will become west/northwest in wake of
passing frontal boundary by Saturday morning.

For DTW...Confidence remains low in timing out of thunderstorms
through tonight. Will need to amend as necessary based on near term
model and radar trends.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceilings below 5kft through Saturday morning. Low
  remainder of period.

* Moderate in thunderstorm occurrence. Low in potential timing early
  this evening into tonight.

&&

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

DISCUSSION...DRC/KDK
MARINE.......IRL
HYDROLOGY....IRL
AVIATION.....IRL

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

Hazardous Weather Outlook
National Weather Service Detroit/Pontiac MI
453 AM EDT Fri Jun 28 2019

MIZ047>049-053>055-060>063-068>070-075-076-082-083-290900-
Midland-Bay-Huron-Saginaw-Tuscola-Sanilac-Shiawassee-Genesee-Lapeer-
St. Clair-Livingston-Oakland-Macomb-Washtenaw-Wayne-Lenawee-Monroe-
453 AM EDT Fri Jun 28 2019

This hazardous weather outlook is for portions of southeast
Michigan.

.DAY ONE...Today and Tonight

There is a chance of thunderstorms throughout Friday. There is a
marginal risk that these storms will be capable of producing damaging
wind gusts up to 60 mph and hail up to 1 inch in diameter. Storm
motion is west to east at 25 mph.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

There is a chance of thunderstorms early Saturday morning and a
chance for additional thunderstorms Monday through Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today and tonight.

LCZ460-LEZ444-LHZ361>363-421-422-441>443-462>464-290900-
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-
453 AM EDT Fri Jun 28 2019

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

.DAY ONE...Today and Tonight

There is a chance of thunderstorms throughout Friday. There is a
marginal risk that these storms will be capable of producing damaging
wind gusts up to 60 mph and hail up to 1 inch in diameter. Storm
motion is west to east at 25 mph.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

There is a chance of thunderstorms early Saturday morning and a
chance for additional thunderstorms Monday through Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today and tonight.

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

AM

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