Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 271523

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
Issued by National Weather Service GAYLORD MI
1123 AM EDT Thu Jul 27 2017

Issued at 1123 AM EDT Thu Jul 27 2017

13z surface/composite analysis shows a cold front sagging southward
across southern Lower Michigan...with a 1013mb frontal wave over far
southwest Lower.  Surface winds have pretty much taken on a
northerly component across southeast Lower this morning...low level
theta-e gradient actually lies a bit farther north.  On the "cool"
side of the boundary (in a low level theta-e sense anyhow) has been
a band of clouds and rain/drizzle which has been mostly along/north
of the I-69 corridor though some radar returns have spilled into
northern Oakland County.  Early visible imagery suggests some of the
northerly flow associated with cool outflow from these showers
(boundary/undular bore look to clouds moving through southern
Oakland/Livingston counties and into Jackson/Calhoun counties).
Meanwhile...clouds have thinned out over the southern third of the
forecast area. 12z soundings show moisture gradient from north-
south across the state with precipitable water off DTX sounding of
1.41 inches...and about half that at APX (and lots of sun across
the northern part of the state to boot). Water vapor imagery also
shows this dry air push from the north...with the tail end of a
short wave trough/PV anomaly clipping Georgian Bay.

Modified 12z DTX sounding for 86/67 yields around 800J/kg
MLCAPE... with the best low level focus for potential convection
this afternoon mostly likely closer to the Ohio border where
better convergence should be (synoptic and that associated with
above mentioned outflow). There are some suggestions that enough
lingering instability inland from Saginaw Bay...not totally sure
about this so for now will focus precip threat over the southern
half of the area given above reasoning.



Showers with isolated thunder will work through KMBS/KFNT early in
the forecast along slowly advancing cold front. While some activity
will be possible further south later today, confidence in the extent
of coverage remains dubious. MVFR/lower VFR stratus is poised to
settle through the area behind this front with the lowest cigs KMBS.
WHile skies may very well scatter out from late afternoon into the
evening as the front continues into the Ohio Valley, developing cool
northeast flow off of Lake Huron will most likely bring some cigs
back overnight.

For DTW...Ceilings around 5kft will be possible in wake of passing
cold front later this morning into this afternoon. Any showers in
area of front should be isolated this afternoon.


* Medium in ceilings aob 5000 ft this afternoon.

* Low in thunderstorms this afternoon.


Issued at 240 AM EDT Thu Jul 27 2017


Weak but wavy cold front trailing the upper trough moving into
Quebec will slowly sink through Southeast Michigan early this
morning and today. Ribbon of higher theta-e will slide through the
area ahead of the front, helping to trigger showers and
thunderstorms. Radar imagery this morning shows the most organized
areas of showers over northern Michigan and over Lake Michigan,
right along the frontal boundary. These lines will sink into a less
favorable environment over southern Michigan where warmer air aloft
resides, and expect convection to weaken this morning. The lack of
cold air aloft will be a deterring factor for redevelopment along
the cold front later today as it sinks southward. Instability looks
limited per RAP/HRRR forecast soundings, likely why higher-res model
output is showing low coverage of showers/tstorms. Will only keep
POPS at a scattered coverage today. Biggest threat from storms will
be heavy downpours. The front/surface trough will slide south of the
Michigan state line this evening, ending the threat for convection.

Next upper wave on track to dive through the area is currently
showing a nice presentation on water vapor imagery over southern
Saskatchewan/Manitoba. This wave will deepen as it encounters better
jet support in a right entrance region, before it dives through
Lower Michigan Friday. Forcing and -16C cold pool at H500 will try
to promote shower/tstorm development as moisture wraps around
deepening low pressure over the Ohio Valley. Moisture layer isn`t
that deep though per model soundings, and looks to really limit
coverage. The deepening low will also increase the northerly
pressure gradient over the region, as high pressure also builds into
the northern Great Lakes. Winds will become a little gusty, and cold
air advection will become reinforced by flow off Lake Huron, keeping
max temperatures in the 70s for most locations.

High pressure will build over the area for the weekend, bringing
tranquil weather and a warming trend to temperatures. The beginning
of the work week looks fairly dry as well, with the next good chance
for showers/tstorms looking to hold off until mid-week when a cold
front drops through the area.


Southwest winds will decrease during the night as a slow moving
front slides south across Lake Huron. This front will stall over
southern Michigan on Thursday. Post frontal northerly winds will
increase during the course of the day across southern Lake Huron.
Winds will turn northeast into Saginaw Bay. Funneling across the
relatively warm waters of the bay will support an uptick in the
winds, likely gusting over 20 knots. This may support small craft
advisory conditions. Northeast winds will actually increase Thursday
night into Friday as high pressure expands across the northern Great
Lakes while low pressure holds fairly steady across the Ohio Valley.
Small craft advisory conditions are likely over most of the
nearshore waters during this period. The gradient will then relax on
Friday as the high expands into the eastern Great Lakes. This will
allow winds and waves to decrease.




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