Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221939
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
339 PM EDT FRI JUL 22 2016

.Discussion...

The dewpoint has fallen into the 50s in Huron County on a light west
wind, well ahead of the approaching moisture boundry.
Downsloping off the glacial ridge appears to be the only
explanation. Regardless, the heat advisory is dropped for Huron as
dewpoint front will be arriving shortly anyway.

Veering deep layer flow and weak height falls as a shortwave tracks
northeast of the Great Lakes region is modeled to shunt this
boundary about halfway through the CWA overnight. Upper 50s or low
60s dewpoints will dominate across the north. Southward progress
will slow upon the departure of height falls. However, second and
stronger wave presently over Manitoba will sweep east taking roughly
the same road within the mean flow and kick the boundary safely out
of the area by around sunrise. Low 60s (or lower) Tds areawide by
midmorning, with the exception of the immediate Ohio border where
some of the guidance is allowing 70s dewpoints to creep back in
during the day. Very dry airmass beneath strong subsidence will set
the stage for a clear and hot day as the NAM indicates dry adiabatic
mixing to 750mb. The only thing preventing area wide mid/upper 90s
will be the lake aggregate high present under weak gradient
conditions. An easterly gradient, lake breeze, or a combination of
both will spread into the area during the afternoon confining highs
to around 90 north of I-69. Locations south of M-59, aside from
higher elevations, should easily reach the mid 90s. The heat
advisory will not be extended due to the low humidity as well as the
opportunity for relief tonight as dewpoints fall.

Sunday`s forecast is lower confidence. The trough over the Pacific
Northwest will eject east northeast as it tracks toward Hudson Bay
by Sunday night. Emerging low-level jet over the northern plains
will likely foster thunderstorms/possible MCS over the Dakotas/Upper
MS valley Saturday into Saturday night. The remnants of the MCS and
attendant convectively enhanced wave will wash over the area late
Saturday night and the first half of Sunday. At this time, the
prospects for organized convection locally appears rather poor given
northward displacement of the LLJ and lacking SB instability early
Sunday. The more interesting period will be late Sunday evening into
Sunday night per current NWP timing. Height falls and modest PV
advection juxaposed with the lower tropospheric warm conveyor and a
moderate wind field could yield convection worthy of keeping an eye
on. Southerly gradient will spell a return to muggy conditions, but
highs on Sunday will be limited to around 90 on account of cloud
cover.

Deeper moisture progged to exit by Monday with drier dewpoints
filtering in as well. Model consensus supports high pressure
building in at the surface and lingering into Wednesday promoting
mainly dry weather. Temperatures will still be above normal with 850
mb temps in the upper teens and guidance indicating highs in the
upper 80s, but not quite as warm as the current airmass. Low
predictability toward the end of next week, but a general trend
toward lowering heights/broad troughing supports transition to a
less-warm and possibly wetter pattern.

&&

.MARINE...
A dew point boundary working southward across southern Lake Huron
and the Thumb may produce an isolated shower or thunderstorm late
this afternoon and evening across southern Lake Huron.  Other then
that, high pressure over the Mid West will provide a west northwest
flow across the lakes through Saturday morning.  As the high passes
through, winds will become light and variable Saturday afternoon.
Winds will become easterly Saturday night then veer to the southwest
while increasing by Sunday afternoon ahead of an advancing cold
front. This front will bring showers and thunderstorms across the
lakes that will linger into Sunday night.  The new week will
start off with dry weather on a northwesterly flow.

&&

.PREV DISCUSSION...
Issued at 115 PM EDT Fri Jul 22 2016

AVIATION...

Weak pressure pattern will provide light winds with a westerly
component through this evening while mixing up to about 6k ft may
bring a few higher winds gusts.  Winds will become variable after
sunset and through most of Saturday morning before mixing brings
back a westerly component.  Warming aloft will increase cap strength
allowing only a few late afternoon and evening cu 5-6k ft.  A dew
point boundary will be settling across the northern taf sites this
afternoon and evening. There may be a enough convergence along this
to produce a narrow band of broken cu with a very slight chance of
breaking the cap and producing an isolated storm.  Chances are too
slight and area too limited to mention in MBS and FNT tafs.

For DTW...winds will start off taf period variable or light
northwesterly but should shift more westerly with daytime mixing
along with a few higher winds gusts mixing down late afternoon and
evening.  Winds will go light and variable tonight and become more
westerly component Saturday afternoon as boundary mixes.  Just a few
to sct cu 5-6k ft possible today and expect clear skies tonight and
Saturday as increasing inversion aloft caps off cu development.
Some cirrus is possible through taf period from any convection
that may fire upstream.

//DTW Threshold Probabilities...

none


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 10 PM EDT this evening FOR MIZ047-048-053>055-
     060>063-068>070-075-076-082-083.

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

$$

DISCUSSION...JVC/DT
MARINE.......DRC
AVIATION.....DRC


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