Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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990
FXUS63 KDTX 300747
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
347 AM EDT Thu Mar 30 2017

.DISCUSSION...

The storm system that will bring us wet weather the better part of
the next two days is still centered over Missouri early this
morning. The longwave trough is quite deep, reaching down into the
Gulf of Mexico and the strong southerly flow in advance of it is
proving quite efficient with moisture transport as leading showers
associated with the warm front draped across the Ohio Valley.
Showers this morning are being generated by broad isentropic ascent
along the warm frontal slope. There has been a few enhanced bands
through the early morning hours, but a deep low level dry layer of
around 7kft is eating away at most precip before it can reach the
ground. All models agree, and have agreed for a few days now, that
widespread showers will affect the region Thursday and Friday as the
low slides east just south of the MI border. I will be hitting on a
few potential issues with the system vs regurgitating high pop/high
qpf forecasts once again.

Initial concern remains the snow potential across our northern
counties. This is not a slam dunk forecast by any means and
confidence is actually decreasing with this package, but potential
still exists. Model soundings start off cold (but with no moisture)
and quickly trend to a deep isothermal layer hovering right around
0C. Surface dewpoints remain in the upper 20s north of I69 whereas
temperatures look to be stuck in the mid 30s. So wet bulbing could
swing the isothermal profile to the snow production side.
Additionally, the earlier model runs were hinting at a narrow fgen
band lighting up over the area, but so far the initial band lit up
further south and a second band looks to be converging over northern
lower. Regardless, setup still suggest snow is possible before
turning to all rain and will stick with a forecast of "up to an
inch" of wet snow possible before the changeover.

Next issue will be potential for thunder. As the warm front draws
nearer this afternoon, some elevated instability and marginally
favorable mid level lapse rates will lift along the front possibly
resulting in a few thunderstorms. With the low tracking along the
warm front tonight just south of the area, will keep a mention of
thunder going til the low gets east of the area.

Deep plume of moisture and the 850mb jet will be pushed east of the
area by Friday but the upper low and trailing deformation region of
the surface low will remain over SE MI through much of Friday. The
low remains cutoff from the main flow thus slowly drudges east. How
fast the trailing showers will end will depend on how fast the
surface high in its wake can build into the area. In addition, mid
level ridge will begin building into the Great Lakes Saturday
morning.

The weekend will shape up to be fairly nice (dry) with temperatures
climbing each day from 50 Saturday to mid 50s Sunday. Active pattern
will continue into the new week though with a system sliding through
every couple days. Next system looks to slide through Sunday night
and Monday with another coming around Thursday.

&&

.MARINE...

There will be a steady increase in easterly winds today into
tonight. This will be the result of the increase in gradient due to
the approach of sfc low pressure into the Ohio Valley with
persistent strong high pressure anchored over Quebec. Lingering
shallow cold air will also support neutral to slightly unstable
conditions across Lake Huron. This easterly wind direction will
support hazardous conditions to small craft today through the day
Friday. The strongest winds will occur tonight across central and
northern Lake Huron. There remains high probability that wind gusts
will reach 30 knots, with a chance for a brief period of gale force
wind gusts (duration of which should remain less than three hours).
The winds will back toward the northeast tonight into Friday morning
before weakening later in the day Friday as the sfc low exits the
region to the east and weakens.

&&

.HYDROLOGY...

Low pressure over the Mid Mississippi Valley today will transport
abundant moisture into a slow moving frontal boundary across
southern and central Lower Michigan. This will result in multiple
intervals of showers with a few thunderstorms also possible.
Portions of central Lower Mi and the thumb region will see snow
during the first half of the day before temperatures warm. The low
will drift across the northern Ohio Valley tonight before exiting
the region to the east late in the day Friday. This will sustain
intervals of showers into Fri evening.

Some of the precipitation will be moderate to heavy at times. Total
two day liquid rain totals are now expected to range from eight
tenths of an inch up to an inch and a half. This will certainly lead
to rises on area rivers. There is a potential for locally higher
amounts, especially within any thunderstorms. The slow moving nature
of the forcing on Friday also raises some concerns for some locally
higher totals. These factors do suggest a potential for some minor
flooding.

&&

.PREV DISCUSSION...
Issued at 1152 PM EDT Wed Mar 29 2017

AVIATION...

Mid level FGEN banding will bring brief period of -ra/virga early in
the forecast with cigs to lower VFR, but expect widespread cig and
vsby restrictions in rain/br (some snow KMBS?) to hold off until 12z
or so. As low level moisture continues to funnel northeast into the
area, expect cigs to lower to IFR and eventually LIFR at times by
late today as warm front stalls near Michigan/Ohio state line and
low pressure encroaches from the southwest and provides additional
lift (and moisture) for the area.

For DTW...VFR conditions should basically hold through the night
with a transition to MVFR early Thursday morning and most likely IFR
by afternoon/evening. East/northeast flow will persist and gust into
the 20 to 25 knot range during the day Thursday.

//DTW THRESHOLD PROBABILITIES...

* Low for ceilings at or below 5000 feet through 11z, medium 11z-
  14z, high beyond 14z Thursday.

* High in precipitation falling as rain, but low that thunderstorm
  will impact terminal Thursday.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 5 PM this afternoon to 4 AM EDT Saturday
     for LHZ421-422-441>443.

Lake St Clair...NONE.
Michigan waters of Lake Erie...Small Craft Advisory from 8 AM this morning to 10 PM EDT this
     evening for LEZ444.

&&

$$

DISCUSSION...DRK
MARINE.......SC
HYDROLOGY....SC
AVIATION.....DG


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