Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 182338
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
738 PM EDT Thu Apr 18 2019


.AVIATION...

Near surface low pressure center is lifting northward through
portions of the cwa which is pushing the cold front progressively
eastward through the taf terminals. Richest theta e content will
drift eastward even though midlevel front will become increasingly
stalled out in close proximity to the cwa. Expecting a wane in
precipitation activity for a good chunk of the evening and tonight
with loss of active isentropic ascent/warm advection. Not a clean
forecast, however, has frontal dynamics do remain lagged behind the
front and will persist overnight. This could allow for occasional
light rain activity to work across the area, although activity
should be high based. Near surface cold air oozing across the area
should support some laminar MVFR potential IFR stratus. Substantial
midlevel moisture return/theta e advection will lift northward into
the area from the south after 09Z tonight. Solid width to
frontogenesis will lead to widespread rain prevailing in the 09-21Z
time window. Impressive, uncommon NNE winds developing Friday
afternoon between 20-30 knots.

For DTW...Lull in prevailing rain expected through the evening and
much of the overnight. MVFR to IFR is expected due to the shallow
cold air advection. Midlevel theta e advection and moisture return
is expected after 09Z tonight as next low pressure impulse rides
along the front.

.DTW THRESHOLD PROBABILITIES...

* High in cigs at or below 5000 feet.

&&

.PREV DISCUSSION...
Issued at 331 PM EDT Thu Apr 18 2019

DISCUSSION...

Mild and moist airmass in place over southeast Michigan today, as
12z DTX sounding checked in PW Value of 1.09 inches/235 percent of
normal, with high temperatures climbing well into the upper
60s/around 70 degrees, despite clouds and showers around. Still
chance for an embedded thunderstorm through the daylight hours, with
SBcapes of 100-200 J/kg. Much colder and continued rainy conditions
tomorrow and Saturday.

Positive tilted northern stream trough axis over the Upper
Mississippi River Valley this afternoon, with strong upper wave/jet
energy diving south through the plains, which will merge with the
southern wave, leasing to closed 500 MB low over the southern
Mississippi River valley by Friday morning. The position of the
frontal boundary will be key over the next couple of days. It does
look like the frontal boundary will have enough forward momentum to
at least clear southeast Michigan early this evening, with much
colder/stable air filtering in through tonight as low level winds
veer around to the northwest and then northeast with showalter index
climbing above 10 C. However, with the southern system deepening and
the trough axis going negative tilt during Friday, southeast
Michigan looks to be in a favorable position for moderate to heavy
rain with respect to upper level divergence/trowal/deformation
position. Considered flood watch, but flood guidance suggests we
should be able to handle 1-2 inches of rain over a long duration.
However, if we take another good shot of rain (more than the current
half an inch projected) Friday night-Saturday as the 500 MB low
circulation tracks into the Eastern Ohio Valley, will probably start
to have some flood issues beyond the urban/small stream type.
Tightening baroclinic/frontal zone and a modest increase in
instability/mid level lapse rates will lead to a bit less confidence
in location of moderate/heavier rain on Saturday, as areal coverage
of activity will not be as high compared to this evening/tonight and
tomorrow.

Prolong/strong northeast winds (25-30 KTS) over southern Lake Huron,
especially focused within Saginaw Bay, will draw concern for
Lakeshore flooding as well Friday-Saturday, and have issued a
lakeshore flood advisory for the southern Lake Huron Basin/Saginaw
Bay, as high confidence in Saginaw Bay levels reaching and exceeding
48 inches above LWD. For Western Lake Erie, right now looks like
there will be too much of a northerly component to push water levels
to flooding levels.

Weak surface flow will begin to back to the southwest at the start
of the extended period with a ridging pattern in place on Sunday.
This will help dry out the low levels throughout the day, although a
thin mid level deck will struggle to fully burn off before diurnal
heating can maximize during the afternoon. Surface temps should top
out a few degrees above normal in the low to mid 60s with dry
conditions. NAM/ECMWF currently hinting at some brief showers at the
start of the period as they try and push a weak shortwave downstream
/around the inflection point between the ridge and upper trough from
the Appalachian low/. Weak negative omega values /if sustained into
04.20 operational runs/ could eventually nudge a mention of slgt chc
for Sunday showers.

GFS and ECMWF are still out of sync with the timing of the FROPA on
Monday. ECMWF brings the cold front in quite a bit earlier as it
drifts through. Continuing slgt chc to chc showers all day Monday
with a pre-frontal, frontal, and post-frontal progression expected.
Sfc-500 mb moisture boundary will linger around the southern half of
the CWA into Tuesday, but with weak forcing, only kept up to chc
across the Detroit Metro area for Tuesday morning. Overall, Tuesday
will be mainly dry with temps in line with normal values. Showers
return Tuesday night and Wednesday ahead of an approaching low
showing vertical continuity and decent Gulf moisture supply. An
upper level disturbance with isentropic lift may also develop,
helping to initiate showers before the comma head moves in /assuming
the GFS verifies/. It should be noted that the ECMWF solution
differs greatly this far out as it keeps the FA dry through Friday
morning. Temps during the first half of next week will be close to
seasonal.

MARINE...
Winds will go NNW behind passage of a cold front this afternoon and
continue into the night.  A surface low pressure system will move
along the cold front across northern Ohio on Friday. This will
produce strong NNE winds across all the DTX marine zones Friday into
Saturday prompting small craft advisories based on winds and waves.
This will also produce possible lake shore flooding along Saginaw
Bay.  Winds and waves will gradually diminish during the day
Saturday. The next chance for advisory type winds and/or waves will
come Monday night and Tuesday with another northeasterly wind event.

HYDROLOGY...

A prolong period of rain is expected for southeast Michigan from
today through Saturday.  Though the rain overall will not be heavy,
a 48 to 60 hr period of rain will added up with around an inch
across the far NW Saginaw Valley to over two inches near the Ohio
Border.  With the rainfall drawn out, area rivers should run high
but are not expected to flood. Widespread ponding of water in poor
drainage, roads and low areas will be likely, especially around the
Detroit Metro area on south.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Advisory from 8 AM Friday to 5 PM EDT Saturday for
     MIZ048-049-054-055-063.

Lake Huron...Small Craft Advisory from 4 AM Friday to 4 PM EDT Saturday for
     LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory until 10 AM EDT Saturday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 AM EDT Saturday for LEZ444.

&&

$$

AVIATION.....CB
DISCUSSION...SF/KK
MARINE.......DRC
HYDROLOGY....DRC


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