Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 250413
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1213 AM EDT MON JUL 25 2016

.AVIATION...

After a convincing start during the early evening, thunderstorms
continue to underachieve within the instability axis over lower
Michigan. Suspect activity is mostly elevated with a few cells
reaching moderate intensity and then settling back down again to
more ordinary strength without really tapping full CAPE potential.
Observational evidence really does not support much more except
possibly some increase in coverage for the balance of the night
before the broken line and clusters exit SE Michigan within the 10-
12z timeframe. A few hours of MVFR ceiling and visibility is
expected with the frontal passage followed by improving aviation
conditions in all areas during the day. Northwest wind has potential
to gust near 20 knots as it brings still warm but less humid air
into the region.

For DTW... Showers/storms over central and southwest lower Michigan
still have a chance to develop eastward toward the terminal. These
are timed into DTW in 06-09Z time range and will likely exit all of
SE Michigan 10-12Z. MVFR ceiling/visibility in fog will be swept in
by the cold front with or shortly after the main area of
showers/storms followed by improvement by mid morning.

//DTW Threshold Probabilities...

* Moderate for thunderstorms between 06-09Z.

* Moderate for ceilings at or below 5kft toward sunrise through
  early morning.

&&

.PREV DISCUSSION...
Issued at 927 PM EDT Sun Jul 24 2016

UPDATE...

Mid evening mesoanalysis indicates MLCAPE pushing 3500 J/kg over
SW lower Michigan at press time with the instability axis
extending northeast toward Saginaw Bay while decreasing to "only"
2000 J/kg. That being the case, convection so far has struggled
against larger scale subsidence and low level capping as shown in
the DTX evening sounding. The APX sounding is more representative
of incoming conditions with less of a cap but still relatively
weak mid level lapse rate. This is also expected to change as the
upper ridge overhead moves eastward in favor of weak height
falls/cyclonic flow over the Midwest. Hourly mesoanalysis shows
this as an area of steeper 700-500 mb lapse rates over southern
WI/northern IL set to move into lower Michigan. There is also good
potential for a component of lapse rate increase due to
radiational cooling aloft within the dry layer above 600 mb. These
elements will provide a more favorable environment for storms to
develop and persist within a gradually decreasing instability
axis along and ahead of the cold front as it moves through SE
Michigan overnight. Expect scattered to numerous coverage with
most activity to our east around 12z. The SPC marginal risk for
severe looks good for just a few of the strongest storms in this
high CAPE/low shear environment. Downburst wind will be the main
concern but only within deeper cores or longer lived multicell
clusters.

PREV DISCUSSION...
Issued at 311 PM EDT Sun Jul 24 2016

DISCUSSION...
MCs that has been slowly passing across southeast Michigan will
continue to weaken this afternoon as it exits. Temperatures remained
quite steady during the day a bit far from forecasted highs but as
clouds thin, several hours of decent amount of sunshine the rest of
this afternoon and evening will push most location into the 80s.
Two boundaries remain across the area that will be the main focus for
convection the rest of the day.  One outflow boundary is laid out
across central lower from about Saginaw bay/Thumb westward and the
other is from about Toledo back to southern Lake Michigan.  Broken
line of showers and thunderstorms have developed along the northern
boundary but have been weakening somewhat as it pushes southward away
from main cold pool aloft. Expect this boundary to make it near i69
corridor before stalling this evening.  The better chance for shower
and thunderstorm development will be more westward were the better
instability lies.  The southern boundary is a bit stronger as
a result from the cooler air from todays MCs and substantial heating
across northern Indiana as this area has had a good amount of
sunshine all day.  Expecting regeneration of storms along this
boundary from nw Ohio back into sw lower Michigan.  Most activity
should remain south and west of the cwa but some showers could spill
over into Lenawee and Monroe counties as main flow aloft is from the
southwest.

Main cold front is moving through eastern Wisconsin and that will
push slowly through the area overnight. Not much dynamical forcing
with the front, just mainly surface convergence.  Southeast
Michigan will not likely get into the good deep instability as that
will remain to our south, shunt off by todays MCs and boundary to
the south.  Only expecting scattered showers and thunderstorms to
accompany fropa. The front should be close to exiting the area
around sunrise.  Will still carry a chc for precip far southeast
corner Monday morning as this area will still be close to the front.
Drier air will slowly work in behind the front with dewpoints
starting off the day still in the upper 60s in the north to lower
70s south but dropping a 10 or so degrees by end of day.  With
plenty of moisture in the boundary layer, expect a rapid
development of cu shortly after sunrise with clouds slowly
thinning and diminishing throughout the day from nw to se.   It will
still be quite warm Monday as airmass behind front more drier then
cooler.

Zonal upper flow Wednesday over the Great Lakes will transition to
cyclonic by the end of next week/weekend as a series of shortwaves
act to carve out a trough. Midrange deterministic models time the
lead disturbance for Thursday, so Wednesday will likely be another
dry and warm day. Then, indications are that a low-level circulation
attendant to the upper height falls will slowly track across the
lower Great Lakes. This could focus a more well-defined period of
precipitation, but still significant model spread with respect to
the timing and placement, so have kept general chance PoPs Thursday
through Saturday. Temperatures are expected to trend back toward
normal late next week.

MARINE...

A cold front will move across the region tonight turning the winds
from south/southwest to west/northwest. Speeds are expected to
remain below 15 knots. High pressure will set the stage for light
and variable winds on Tuesday.

HYDROLOGY...

Additional showers and thunderstorms are possible in advance of a
cold front tonight. Widespread rainfall is not expected - however
localized downpours are still possible, capable of totals up to an
inch.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...DRC/DT
MARINE.......Mann
HYDROLOGY....Mann


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