Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 251140
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
740 AM EDT Tue Apr 25 2017


.AVIATION...

Organized moist isentropic ascent is occurring from southeast to
northwest through the cwa at press time. This has led to substantial
moistening with VFR/MVFR stratus tracking into southeastern
Michigan. Some light sprinkle activity developing north of the I 69
corridor at the moment, but overwhelming trend per regional mosaic
is that shower activity will remain east of the terminals this
morning. Later today, best warm frontal forcing will stay
progressive pushing well to the north. This will lead to an
amplifying ridge for tonight and Wednesday. Models are very strong
with the signal for high stability throughout the 3.0 to 12.0 kft
agl layer. Could see some persistent cloud at 5000 or 6000 ft agl
before the subsidence inversion can lower down through that level.


//DTW THRESHOLD PROBABILITIES...

* High for ceilings at or below 5000 ft this morning.

&&

.PREV DISCUSSION...
Issued at 351 AM EDT Tue Apr 25 2017

DISCUSSION...

The end of the long stretch of dry air is drawing near as a broad
and deep longwave trough develops over the western two thirds of the
country. Plenty of energy within this trough as 150+ knot jet feeds
into it out of the north Pacific. For the most part, the area will
remain dry through Wednesday evening as the downstream ridge
steepens in response to this trough. One caveat to this will be a
short period this morning when a band of moisture in a region of
isentropic ascent lifting out ahead of the cutoff low over the SE
Conus clips the eastern Great Lakes. Looks like the moisture will be
largely in the 4-10kft layer with dry resident airmass at the
surface needing to be worked over to get precip to reach the ground.
Looks like the wind field will quickly reorient themselves as the
low drifts up the coast today which will pull the moisture and
forcing back east of the region. So just a brief period this morning
of a slight chance of light rain in the forecast around the eastern
Thumb, but could end up being more virga than anything.

Will keep a good deal of clouds around today with southeasterly flow
which will moderate temperatures somewhat, but the resident airmass
has proven to be good for temps nearing 70.  So expectations are for
much the same, hedging a little lower along the lake shadow for our
eastern locations. Lows tonight will be on the mild side, mostly in
the low 50s, as dewpoints climb with sustained southeasterly flow.

Strong wave will be entering the base of the longwave trough on
Wednesday which will tighten the SW gradient between the trough and
east coast ridge. Initially this will set up the moisture and
instability corridor over western MI and WI.  Strong WAA with winds
turning more to the south will send temperatures up toward 80 as 700
to 850mb warm layer spikes in the mid teens. This warm layer should
cap off any attempts at showers drifting east into the area or
developing overhead with the strong mid/upper level lapse rates and
weak upper level instability. Having said that, the SW to NE slope
of the moisture/instability plume may end up clipping part of the
Saginaw Valley thus they will have a chance of showers and
thunderstorms in the forecast.

Best activity over SE MI will occur on Thursday as a wave noted
earlier exits the base of the trough and lift northeastward into the
Great Lakes. The associated surface low will pull a cold front
across lower MI. Even a few days out, models are struggling to come
together on orientation of the jet streaks and strength of the
trough. Still enough support with an afternoon cold front, a few
hundred J/kg of CAPE, shear values over 40 knots, and good moisture
to support high chance pops for showers and thunderstorms.

May get a brief break from showers on Friday before the trough
ejects the next few waves through the weekend. Models do agree with
bringing rain in Saturday ahead of the next low, persisting through
Sunday.

MARINE...

A long duration of moderate southeasterly flow will exist through
Wednesday as the region remains between exiting high pressure and
low pressue lifting into the Mid Mississippi Valley.  Sustained wind
of 15 to 20 knots at times, but with a higher degree of stability
under this pattern limiting the gust potential.  Winds turn
southwesterly as low pressure lifts into great lakes on Thursday.

&&

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

$$

AVIATION.....CB
DISCUSSION...DRK
MARINE.......CB


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at www.weather.gov/detroit.



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