Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 250733

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


Cold front and pre-frontal trough continue to work through Lower
Michigan early this morning as an upper trough swings through the
western and northern Great Lakes. Stronger convection so far this
morning has been firing ahead of the pre-frontal trough axis (now
over Southeast Michigan), closer to where a plume of high low/mid-
level theta-e is washing over the area and where surface dewpoints
have pooled into the mid and upper 70s ahead of the cold front
dropping through northern Lower Michigan. Best chance for
precipitation therefore looks to be over the southern and far
eastern portions of the forecast area over the next few hours. The
cold front over northern Lower Michigan will continue to drop south
through the remainder of Michigan through about 14Z. There will
remain a chance for a shower or even a thunderstorm until the front
exits. This is supported by light radar returns and surface
observations over western Michigan.

Upper trough axis will push east by afternoon. Large-scale
subsidence behind the trough and confluent flow aloft/jet left
entrance region will work with incoming dry air behind the cold
front to bring mostly sunny skies by late afternoon. Despite cold
frontal passage overnight, temperatures are expected to remain very
warm and above normal. Even with rain and clouds during much of the
first half of Sunday, temperatures still managed to surge into the
mid/upper 80s for most of the area by late in the day. Model data
points to only a slight cooling in the 925-850mb layer, and combined
with good insolation after morning clouds/convection clears, falling
dewpoints, and a warm start to begin the day, we should manage to
see highs in the mid 80s to low 90s. Dewpoints, as mentioned, will
fall as drier air pours in behind the front. Values in the 70s this
morning are expected to fall closer to 60 by the end of the day, in
line with latest MOS guidance and upstream observations over the
U.P. and Wisconsin. Overall drop in humidity will allow heat indices
to run only a few degrees above actual temperatures, and stay below
heat advisory criteria.

High pressure building into the area from the west will become
centered overhead tonight into Tuesday, providing dry and quiet
weather. Good radiational cooling will finally allow for a night with
temperatures near to only slightly above normal in the upper 50s to
mid 60s (except upper 60s over Detroit heat-island). Little thermal
advection and mostly sunny skies again on Tuesday should keep max
temperatures solidly in the mid and upper 80s, with cooler readings
near the lakeshores where the lake breeze will work inland in the

Next chance for precipitation looks to arrive Wednesday through
Thursday as upper energy dropping through Ontario slowly pushes a
cold front down into the state. Airmass does not look to be overly
moisture-laden and front looks to have little to no upper level
support. Low chance pops from inherited forecast still look
appropriate. Chance for showers and thunderstorms then continues
into the weekend as upper ridge amplification over the western U.S.
steers small upper waves down into Michigan in west to northwest
flow. This should help max temperatures cool closer to normal for
the end of the week.



The cold frontal passage across Lake Huron will occur during the pre
dawn hours. The front will then track across Lake Erie this
afternoon. Winds will veer to the west with the passage of the cold
front. The post frontal gradient will weaken, thus keeping wind
speeds primarily below 15 knots. High pressure will expand across
the southern Great Lakes through mid week. This will keep winds
generally light and variable.


Issued at 1213 AM EDT Mon Jul 25 2016


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.


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



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