Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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090
FXUS63 KDTX 160744
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
344 AM EDT Tue Jul 16 2019

.DISCUSSION...

A look at satellite imagery shows SE MI positioned in between a
weakening mid level trough over the Midwest and the remnant
circulation of Barry lifting from the Mid MS Valley into the
western Ohio Valley. Currently mostly clear skies prevail over the
area as the waning convection over the Midwest is lifting
northeastward away from the area with the southwesterly flow and the
moisture/precip shield associated with Barry is now approaching the
state line. The trough will stall across northern MI while the
parent low tracks east from northern Ontario into Quebec today but
as Barry continues north it will get picked up by the trough and
shear out while tracking NE through Ohio and Lake Erie. This all
leads to southern MI being placed in the NE flank of the system most
of the day today with several waves of energy emanating from the low
through the region. Initial moister surge will occur this morning
on the nose of the 30 knot low level jet. This will quickly moisten
the column from the mid levels downward as PWATs jump from 1.6" (per
recent SPC mesoanalysis) to over 2" (and eventually around 2.25"
later today). Showers and thunderstorms will spread northward
through the morning encompassing most of SE MI by this afternoon.
Models advertise CAPE values reaching 1000 J/kg this afternoon
during peak heating but we will again lack shear with consensus
below 20 knots. The very moist sounding will also prevent much in
the way of favorable lapse rates in the column. With that in mind,
severe weather is not anticipated today but heavy rainfall is a
concern especially later this afternoon when CAMS advertise wider
coverage of convection due to peak heating. Even with clouds
streaming in early today, highs will still reach into the 80s with
higher readings likely north of I69 where clear skies will last
longer into the day. This pattern will linger through the overnight
hours though convection will likely wane.

Barry will be an open wave by early Wednesday with the surface low
likely near western Lake Erie. This will keep SE MI within the
stronger forcing closer to the center of the low with showers and
thunderstorms persisting into the afternoon hours. A mid level wave
racing out of the Plains will reach Lower MI early in the day
helping to shunt Barry east away from the area. Newest EC has a
weaker wave now phasing with Barry but these fast zonal waves are
tough to get a handle on so will have to wait and see what kind of
upstream convective response it generates. Still being in the moist
and unstable airmass, strength of storms will garner watching. Model
soundings look to increase shear later in the day while also
beginning to warm the lower levels creating a cap.

Attention then turns to the strong ridge that will slide into the
region in the wake of this trough. Zonal flow across southern Canada
will allow very warm air to lift northward under the ridge as 500 mb
heights climb toward 590 dam with 850mb temps around 23-24C. with no
other factors considered, this pattern should produce temps in the
low/mid 90s (possibly upper 90s Friday and Saturday) across the area
from about Thursday through Saturday. Really the only thing to
prevent this would be MCS activity dropping through, but as flat as
the flow is being advertised with the strength of the westerlies to
the north and strong cap over southern MI, would assume the bulk of
this activity would stay north of the area. At this point Heat
Headlines look pretty likely during this stretch.

&&

.MARINE...

A frontal boundary slowly pushing south across Upper Michigan and
the approach of a weak area of low pressure across the western Ohio
Valley will strengthen the southwesterly gradient across the lakes
today. The strongest winds will be across Saginaw Bay out into
central Lake Huron today, where gusts of 20 to 25 knots are
expected. This suggests hazardous small craft conditions over
Saginaw Bay. Winds and waves will decrease tonight as weak low
pressure lifts into Southeast Michigan and causes the gradient to
relax. This low and the associated humid and unstable airmass will
likely support some thunderstorms across the region. The low will
depart to the east on Wednesday with a warm front forecast to
approach from the west on Thursday. This will support a modest
uptick in southerly winds on Thursday.

&&

.HYDROLOGY...

The remnants of Tropical Storm Barry will lift across the Ohio
Valley and into Southern Michigan today and tonight. The resulting
tropical airmass and weakly unstable atmosphere will support
numerous showers and thunderstorms across the area this afternoon
and tonight. The convection may persist into Wednesday as the low
will be slow to exit east of the region. Any shower or thunderstorm
will be capable of producing intense rainfall rates. While rainfall
totals across the area will show a high degree of variability, some
locations may see total rainfall amounts exceed two inches between
this afternoon and Wednesday morning. This will pose the risk of
flooding in low lying and poor drainage areas as well as in the more
heavily urbanized areas of metro Detroit.

&&

.PREV DISCUSSION...
Issued at 1203 AM EDT Tue Jul 16 2019

AVIATION...

After storms ended during the evening, SE Michigan is positioned
between a dying MCS across northern Wisconsin and the tropical
remnants of Barry over the Ohio valley. A shower or thunderstorm
occurred at all of the terminals last evening and left wet ground
over a wide area which will promote patchy MVFR fog. A few hours of
clear sky and light wind also contribute during the late night before
SW wind and clouds increase late in the night. Light showers
associated with Barry reach DTW toward noon and spread northward
toward FNT during the afternoon. There is also a gradual lowering of
ceiling toward entry level MVFR which is indicated in observations
tonight closer to the surface low. Afternoon timing in SE Michigan
brings duration into question and the forecast will tie restriction
to showers for now. Timing and coverage of any thunderstorms would be
late in the day with instability in question due to the earlier
clouds and showers. Prefer to save the mention of storms for
evaluation in later updates.

For DTW... Some light MVFR fog is possible during the late night
after the earlier showers and storms and before SW wind increases
late tonight. High clouds move in and lower toward 5000 ft during
the late morning leading to a chance of VFR showers.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling 5000 ft or less during afternoon.

* Low for thunderstorms late afternoon into Tuesday evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 8 AM this morning to 6 PM EDT this
     evening for LHZ421-422.

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

$$

DISCUSSION...DRK
MARINE.......SC
HYDROLOGY....SC
AVIATION.....BT


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at www.weather.gov/detroit.



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