Severe Thunderstorm Warning 19, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1223 PM EDT Sat Jun 1 2019

.AVIATION...

Continued challenging forecast over the next 6-12 hours as rapidly
destabilizing environment amidst a slowly southward sagging cold
front and multiple outflow boundaries fuels shower and thunderstorm
development this afternoon through late this evening. Based on
latest trends in hi-res guidance, it appears there may be 2 main
rounds of convection with the first between 18z-22z, and the second
00z-04z focused more over the southern TAF sites. Amendments will
still likely be needed as near term trends are closely monitored.
Hail up to 1 inch and gusty winds in excess of 40 knots will be
possible with the strongest thunderstorm activity. Thunderstorm
chances rapidly diminish after midnight as drier and cooler air
moves in behind the departing frontal boundary. MVFR/IFR conditions
possible with any thunderstorm activity, with a period of post-
frontal MVFR ceilings likely late tonight before clearing out
towards the end of the period. Winds will largely be dependent on
outflow boundary placement into this evening, with more dominant
southwest flow 10-15 knots emerging at times. Flow becomes northwest
behind the front heading into Sunday.

For DTW...Current thinking is there will be 2 rounds of convection
18-22z and 00z-04z, although amendments may be needed as confidence
in these time windows is still on the lower side. Any storm that
develops will be capable of 1 inch hail, gusty winds in excess of 40
knots, and heavy downpours possibly reducing visibility into LIFR
range.

.DTW THRESHOLD PROBABILITIES...

* Moderate for ceilings below 5kft this afternoon and evening.
  High tonight into early Sunday morning.

* Moderate in thunderstorms this afternoon into the evening. Low in
  potential timing.

&&

.PREV DISCUSSION...
Issued at 410 AM EDT Sat Jun 1 2019

DISCUSSION...

Multiple opportunities exist today for convective development over
Southeast Michigan as various trigger mechanisms pass through the
area within the westerly flow. The potential for isolated severe
thunderstorms exist with areas south of M 46 in Southeast Michigan
designated as a Marginal risk in the latest SPC Day 1 Outlook. There
is low confidence in exact timing of thunderstorm activity for any
specific area.

High CIN profile, consistent with midlevel ridging was noted in the
01.00Z KDTX raob this evening between 3.0 and 9.0 kft agl. A
legit little ridge is in place at this hour with model data showing
572 dam H5 heights nosing into Lower Michigan with distinct negative
absolute vorticity bubble centered overhead as of 06Z. Crisp surface
trough, a surface reflection of mass convergence directly along the
edge of the capping is just north of the I 69 corridor. The
anticyclonic vorticity maximum will remain in place through 12-18Z,
then rapidly push eastward during the afternoon. First item is the
cluster of elevated thunderstorm activity that is advancing
southeastward across western Michigan. The thunderstorms are being
fed by a modest MUCAPE plume of 500-1000 J/kg that is leeching off of
the greater instability reservoir to the southwest over IL/WI. It
remains possible the thunderstorms could hold together in some
fashion as midlevel lapse rates will be steep enough to support it.
However, with the ridging in control through the mid morning and
virtually no shear to work with, the tstorms are expected to weaken
with little to no storm organization. No significant threats exist
with the early morning activity.

As the thermal ridge aloft works across the area this morning,
models are highlighting impressive 850-700mb lapse rates at 8-9
C/km. This will lead to rapid destabilization of the atmosphere with
MLCAPES greater than 1500 J/kg, possibly reaching 2000 J/kg for the
afternoon hours. A big forecast question for the today period is
what magnitude of CIN will persist within the 850-900mb layer.
Forecast soundings dance around providing a very messy picture. It
has been noted the shallow convection parameter in some of the non-
explicit convection models kick in, causing the capping inversion to
instantaneously vanish. CAM solutions are a little more stubborn
with the CIN layer. While this does not cast doubt on PoPs and the
likelihood for convection today, it does present low confidence in
exact thunderstorm timing.

Given the differential positive vorticity advection with the exit of
the AVA bubble, and models showing a fire hose of convective
generated shortwave energy directed at the forecast between 18-06Z,
expecting shower and thunderstorm development to become likely after
the noon hour today. Have included a low chance PoP this morning to
account for elevated instability and ongoing activity tracking
towards the cwa. Greatest forcing will occur this afternoon and
evening with height falls as ridge pushes eastward and amplifying
convergence/cold front advances towards Southeast Michigan.

Out of respect for the midlevel lapse rates, the forecast messaging
is that isolated severe thunderstorms will be possible today over
all of Southeast Michigan. Uncertainty exists with severe weather
potential north of M 46 as a signal exists that higher 925-850mb
stability could compromise instability. Weak deep layer shear and
fairly short hodograph will be a limiting factors for today.
Additionally, the extreme forecast instability advertised by some of
the model solutions is likely out of reach with modeled sfc
dewpoints some 5 degrees too high. The primary threats are damaging
wind gusts to 60 mph, large hail, lightning and heavy rainfall.

Impressive deep column cold advection will occur Sunday over the
Great Lakes region as 539dam 500mb closed low digs southward toward
Georgian Bay. Rapid longwave change will bring straight northerly
flow to Southeast Michigan. Pattern supports deep system relative
isentropic downglide which should clear skies out early Sunday
morning. Forecast soundings show freezing heights crashing to about
5000-6000 ft agl. With daytime heating, this is expected to result
in some instability shower development after 18Z. Hit or miss popup
showers and introduced a low chance PoP. Highs Sunday should be in
the middle to upper 60s, but notably cooler with dewpoints back in
the 40s.

Surface high pressure will be in place for Monday and Tuesday
leading to quiet weather. After a cool morning, temperatures are
expected to rise into the middle 60s Monday, with some air mass
moderation, low 70s Tuesday.

MARINE...

A cold front currently draped across the central Great Lakes will
drop southward through the southern Great Lakes today while and
ripples of low pressure track along it. This will likely result in
multiple rounds of thunderstorms, especially south of Port Huron.
Winds will largely remain below 20 knots while varying in direction
dependent on frontal position. Wind and waves will increase on
Sunday as stronger northwest flow brings cooler air into the region.
Wind gusts will increase to 20 to 25 knots over the open waters of
Lake Huron and waves exceeding 4 feet are possible across Outer Bay
and southern Lake Huron. This could require a Small Craft Advisory
to finish the weekend.

HYDROLOGY...

Showers and thunderstorms are likely this afternoon and evening.
Average rainfall is expected to be around half an inch, but strong
to possibly severe thunderstorms could push localized totals to 2
inches or greater, which could cause flooding issues, especially in
the Detroit Metro Area. Cooler and drier air will follow for the end
of the Weekend into early next week.

&&

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

AVIATION.....IRL
DISCUSSION...CB
MARINE.......DRK
HYDROLOGY....DRK

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

Hazardous Weather Outlook
National Weather Service Detroit/Pontiac MI
439 AM EDT Sat Jun 1 2019

MIZ047>049-053>055-060>063-068>070-075-076-082-083-020845-
Midland-Bay-Huron-Saginaw-Tuscola-Sanilac-Shiawassee-Genesee-Lapeer-
St. Clair-Livingston-Oakland-Macomb-Washtenaw-Wayne-Lenawee-Monroe-
439 AM EDT Sat Jun 1 2019

This hazardous weather outlook is for portions of southeast
Michigan.

.DAY ONE...Today and Tonight

Thunderstorms will become likely this afternoon and evening ahead of
an approaching cold front. The potential exists for isolated severe
thunderstorms for all of Southeast Michigan, primarily between noon
and 10 PM EDT. Low confidence exists in the exact timing of
thunderstorm activity. The primary threats will be wind gusts to 60
mph, hail to 1 inch, lightning, and heavy rainfall. Thunderstorm
activity will track from west to east at approximately 40 mph.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Dispatchers...please notify your emergency manager that spotter
activation may be needed this afternoon.

LCZ460-LEZ444-LHZ361>363-421-422-441>443-462>464-020845-
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-
439 AM EDT Sat Jun 1 2019

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

.DAY ONE...Today and Tonight

Thunderstorms will become likely this afternoon and evening ahead of
an approaching cold front. The potential exists for isolated severe
thunderstorms for all of Southeast Michigan, primarily between noon
and 10 PM EDT. Low confidence exists in the exact timing of
thunderstorm activity. The primary threats will be wind gusts to 50
knots, hail to 1 inch, and lightning. Thunderstorm activity will
track from west to east at approximately 35 knots.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Small Craft Advisories may be needed Sunday night and Monday for the
southern Lake Huron basin as northerly flow develops over the region.

.SPOTTER INFORMATION STATEMENT...

Dispatchers...please notify your emergency manager that spotter
activation may be needed this afternoon or evening.

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

CB

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