Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221058
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
558 AM EST Thu Feb 22 2018


.AVIATION...

Patchy MVFR stratus, mainly KFNT/KMBS this morning. Otherwise, just
expect a thick mid deck in the 10-15kft range today. Approaching low
pressure will bring a return of stratus overnight tonight with light
precipitation towards end of the forecast, KPTK south (KFNT north
just after forecast window). This will either be -ra or -fzra as
temperatures will be very near 32F and slowly rising by that time.
Rain showers will then continue into Friday morning with MVFR/IFR
cigs.

For DTW...Generally expect VFR cigs today/this evening with just
thick deck around 10kft (but a few patches of stratus may bring
brief periods of lower MVFR cigs. More widespread low stratus will
work in late tonight into Friday morning with light precipitation
starting late tonight as -ra/-fzra changing to all -ra quickly on
Friday morning as temperatures climb.


/DTW THRESHOLD PROBABILITIES...

* Low of ceilings below 5000 feet briefly this morning, high late
  tonight into Friday morning.

* Low in differentiating precipitation type between -ra and -fzra
  late tonight.

&&

.PREV DISCUSSION...
Issued at 328 AM EST Thu Feb 22 2018

DISCUSSION...

Strong surface high has spread across the Great Lakes while the very
active frontal boundary remains south of the area draped across the
southern Ohio Valley. This will lead to mostly dry conditions today
as we mainly deal with cirrus debris from activity to our south. On
that note, the possible exception to the dry forecast would be
locations south of I94 which could see a period of light snow or
flurries this morning as a wave rides along the front through OH.
Current regional radar mosaic lines up well with hires models in
terms of the sharp northern edge to the precip shield and keeping it
just south of the state line. This adds confidence to limiting pops
to our southern most zones at the moment. There is a brief window
from about 10-15Z when the wave itself passes to the south where
there is a northern extension to the precip shield on radar. This
could clip Lenawee and Monroe Counties thus they have been left with
a chance pop for light snow. Not expecting much in the way of
accumulations as qpf is limited to a couple hundreths and dry
northeasterly flow will help keep most of the precip as virga
anyway.

The dry stretch won`t last long as the next mild level wave and
associated surface low will lift through the Northern Great Lakes
Friday. A trough/occluded front draped south will connect it to a
second wave which will be riding up along the main front still
draped to our south. The strong surface high will be moving off to
the east Thursday night while still keeping a hold over SE MI with
dry easterly flow. Soundings show a mid level dry layer slowly
saturating after midnight Thursday from the top down as elevated
portion of the warm front lift through southern MI. Surface air will
be just below freezing which adds a layer of complexity to the
forecast with ptype. Model soundings continue to advertise a period
of potential freezing drizzle/rain or sleet from about 06-14Z Friday
morning until stronger warm air advection with southerly flow warms
the low levels enough to result in all rain. Precip could very well
hold off til even 09-12Z as dry air could chew up much of the light
qpf on the lead edge. Better chances for precip will occur from 12-
18Z as a ribbon of enhance theta-e and fgen along the occluded front
lift through southern MI. Less than a quarter inch of QPF is
expected from this system which should not affect any lingering
flooding issues. Deep layer of dry air from about 900-400mb will
then surge into the area for the afternoon as high pressure begins
building back into the region.

Active pattern continues heading into the weekend as yet another
northern and southern stream wave combo will lift into the region
starting early Saturday. This system looks a bit stronger than
Friday mornings system with a longer duration of isentropic forcing
on the lead edge of the system, resulting in a bit more qpf.
Southern locations will see rain most of the day Saturday as the
front lifts slowly north. Locations north of I69 could stay dry til
evening. The low will lift northwest of the area Saturday night
spreading rain across all of SE MI. Drier air will then work back in
on Sunday. Currently we are expecting around a quarter to half inch
of QPF from this system. Should be noted that we could see a brief
period of mixed precip at the lead edge as surface temps hover
around the freezing mark and saturation first occurs aloft where
temps look to be cooler than -10C.

Heading into the new week upper levels will flatten out with a
surface ridge spreading back across the region. So looks like we may
find a 2 or 3 day stretch without rain. Temps will hover around the
mid 40s with the westerly flow.

MARINE...

A broad region of high pressure will build across the northern Great
Lakes today. This will maintain dry conditions over all marine areas
except possibly some light snow or flurries over western Lake Erie.
This high will also maintain light wind over the north half of Lake
Huron and northeast winds generally less than 20 knots over southern
marine areas. Wind will then veer to the south by Friday as the next
low pressure system moves into the western Great Lakes. This system
will bring a generous coverage of mixed precipitation to the region
which will change to rain as mild air lifts north in region. This
mild air will then be swept east by the associated cold front as
moderate northwest winds develop Friday night. High pressure will
move in briefly on Saturday before a stronger low pressure system
arrives Sunday.

HYDROLOGY...

Run-off from recent heavy rain and melted snow will continue to feed
creeks, streams and rivers. Flood warnings will remain in effect for
most of the primary river basins over southeast Michigan. Additional
mixed precipitation and rain on Friday is not expected to contribute
to additional flooding or prolong existing flooding as amounts will
remain generally one quarter of an inch or less. Another round of
rain will then impact the area late Saturday into Saturday night
with perhaps one half of an inch of rainfall falling in some areas.
This may impact river and stream levels to some degree, but should
not exacerbate flooding to any great degree.

&&

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

$$

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


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