Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 180005
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
805 PM EDT Wed May 17 2017


.AVIATION...

Closed PV anomaly with extreme tilt to shortwave trough over Iowa is
leading to a focused area of 1000-500mb geopotential height falls
over the northern Mississippi River Valley this evening. Clusters of
severe thunderstorms have been ongoing in that region for much of
the afternoon. Model data is resolute in keeping the PV anomaly
relatively compact as it spins out and weakens while lifting
northward, directly through Wisconsin tonight and early Thursday.
Closer to home, persistent ridging will be breaking down this
evening in response to broad upper level jet maximum lifting across
southeastern Michigan. Therefore, a non zero chance for
precipitation will begin this evening. The breakdown of the ridge
will be concurrent with midlevel cooling and advection of elevated
instability into the region. However, dry ambient near surface
environment will keep midlevel capping in place through the 5.0 to
10.0 kft agl layer. As a result, not expecting any convection to
survive the trip into southeastern Michigan tonight. Should be just a
night of convective debris cirrus. Additionally, low level wind
shear of 50 knots down to 1.5 kft agl will become an issue this
evening with shrinking planetary boundary layer.

Some noise or mixed signal exists as to what exactly the top-end
will be on southwesterly wind gusts Thursday. Pattern recognition
and environmental wind field in place tonight suggests another late
morning/afternoon period where southwest winds could reach 35 knots.

High uncertainty exists with regards to thunderstorm potential
Thursday afternoon. Models are suggesting a prefrontal trough will
focus the highest low level theta e content, and instability to the
immediate south and east of the forecast area. How this will play
out remains unknown as a strong cold front will push through
southeastern Michigan during peak diurnal heating. NWP is split on
whether or not thunderstorms will develop over the area. A threat
for severe weather will exist with any thunderstorms that do develop
Thursday afternoon. The most favorable time window for thunderstorm
development close to DTW would be 2100-0000Z.

//DTW THRESHOLD PROBABILITIES...

* Very low for thunderstorms through noon Thursday. Low for
  thunderstorms late afternoon and early evening Thursday.

&&

.PREV DISCUSSION...
Issued at 315 PM EDT Wed May 17 2017

DISCUSSION...

Very warm and windy weather persists tomorrow, sharply cooler for
Friday.

Record setting warm airmass in place, see climate section below.

Upper level system over the central Plains is on the move, becoming
unraveled and sheared out as it progresses northeast, continuing to
call into question whether any shower or thunderstorm activity will
develop over southeast Michigan Tonight into Tomorrow. The issue is
the main 850-700 MB Theta-E/moisture advection is already sliding
east of Southeast Michigan by around 9z Thursday, and 12z model
trends are just for areas mainly south of M-59 to build mixed layer
capes in excess of 1000 J/kg to possibly as high as 1500 J/kg.
Even though the 12z NAM seems a bit high on instability, indicating
a plausible dry scenario for the CWA, with the cold front not
flaring up until early evening, along and just south of the Michigan
border. Day 2 out of SPC has expanding the slight chance of severe
along the Michigan/Ohio Border, with marginal for rest of southeast
Michigan. With strong wind fields, any thunderstorm will be capable
of producing damaging winds. In fact, the gradient winds could be
flirting with wind advisory criteria within the well mixed boundary
layer out ahead of the cold front. Even this afternoons winds did
very well within the horizontal rolls of the cu field, reaching
around 35 knots. Soundings indicating solid potential for wind gusts
of 40 knots tomorrow, as temps rise back into the 80s, with mid to
upper 80s south of M-59. Will defer to night shift to issue wind
advisory if need be.

There will be a good infusion of low level cold air, as trough
slides through Ontario tonight, and impressive low level temp
gradient is progged to set up over Lower Michigan by 21z Thursday, in
excess of 20 degrees at the 925 mb level from northwest to southeast
across the State.

Strengthening low level northerly flow Thursday Night with winds
becoming slightly east of due north off Lake Huron by Friday morning,
leading to a chilly start to the day on Friday, as 925 mb temps fall
to around zero. Assuming we are able to mix out the low clouds
underneath the low inversion, late day highs around 60/lower
60s looks attainable with the mid May sun.

The forecast is calling for mins in the 40s Friday night, as it looks
like warm advection mid clouds will be around, otherwise a dip into
the 30s is possible, especially Thumb region.

Surface low pressure will move up across the western Great Lakes
Saturday and into Sunday.  Southerly flow ahead of the cold front
will bring high temps back into the upper 70s by Sunday before
cooling back off for the start of next week.  This low will bring
chances for rain/storms to the area starting later Saturday into
Sunday. Cold frontal passage looks to move through by Sunday night
as cooler westerly flow comes in behind the front. Temps for the
beginning of the week are expected to stay in the upper 60s.

MARINE...

A well-mixed environment and tight surface pressure gradient will
continue to generate gusts to 35 knots over the land into early
evening. While the relatively cool waters of the Great Lakes will
provide stability and limit wind gusts over the water, areas near
the shoreline will see higher gusts to about 30 knots bleed over
from the land areas. Windy conditions will become more widespread on
Thursday as a cold front approaches, with speeds even increasing a
little. Gusts to 30-35 knots are expected over the southern portion
of Lake Huron, Lake St Clair and Western Lake Erie, with highest
gusts located near the shorelines. The Small Craft Advisory for the
nearshore waters has been extended through tomorrow.

A few rounds of showers and thunderstorms will also be possible,
first late tonight and then again tomorrow afternoon and evening. If
storms do develop, they could be strong to severe tomorrow.

Winds will flip to the north as a cold front drops through the
Central Great Lakes late Thursday into Thursday night. Speeds will
initially be gusty, but then decrease by early Friday morning. The
long duration of northerly winds late Thursday through Friday may
however allow wave heights to build in excess of 4 feet,
necessitating Small Craft Advisories for the Lake Huron nearshore
waters into Friday.

CLIMATE...

Record Daily High Minimum Temperatures likely set at all 3 climate
sites, as temperatures are not expected to drop below 70 degrees by
Midnight.

The new record High Minimum values for May 17 based off this
mornings lows.

Flint   68 (2017) vs old record 62 (2015)

Detroit 68 (2017) vs old record 67 (1962)

Saginaw 69 (2017) vs old record 63 (1977)

Flint and Saginaw both making a run toward their record daily high values
this afternoon as well, but probably coming up couple degrees short.

Record Highs For May 17th:
Flint   89 (1962)
Saginaw 89 (1936)
Detroit 93 (1962)

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 8 PM EDT Thursday for LHZ422.

     Small Craft Advisory until 4 PM EDT Friday for LHZ421-441>443.

Lake St Clair...Small Craft Advisory until 8 PM EDT Thursday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT Thursday for LEZ444.

&&

$$

AVIATION.....CB
DISCUSSION...SF
MARINE.......HLO
CLIMATE......SF


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



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