Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211745
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1245 PM EST Wed Feb 21 2018

.AVIATION...

Late morning satellite imagery indicates some texture in the low
cloud field due to daytime heating on boundary layer moisture
lingering post front. This suggests MVFR stratocu will continue
through early afternoon and then begin breaking up from MBS
southward mid to late afternoon. The decreasing cloud trend will be
forced by surface high pressure building into the northern Great
Lakes. A weak thermally induced pressure trough is indicated in
model data developing over interior sections of Lower Michigan which
could sustain clouds a little longer within the low level
convergence zone. This is a low confidence feature this time of year
but will be monitored for potential delays in the clearing trend. A
steady northeast gradient flow is then expected to develop tonight
and scour out any remaining low clouds through Thursday morning.

For DTW... MVFR ceiling will linger during the afternoon and then
diminish toward evening. VFR will then continue under high clouds
through the night. North to northeast surface wind will persist
into Thursday morning and require NE traffic flow operations. There
is a low chance of freezing rain near the Ohio border overnight into
Thursday morning, however the dry northeast low level flow presents
low probability for any activity reaching DTW.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less during afternoon. Low tonight.

&&

.PREV DISCUSSION...
Issued at 335 AM EST Wed Feb 21 2018

DISCUSSION...

Active forecast for the next week as a series of waves continues to
eject out of the longwave trough over the west coast and up through
the Great Lakes region. Seemingly each time the main wave gets
ejected, it is quickly back filled by the next wave dropping into
the trough. Thus each time it looks like the pattern will break for
a while, it quickly returns to a positively tilted trough. Broad
upper ridge over the SE conus will meander about through this
process, largely keeping the main baroclinic zone and upper level
jet near or over the state. Models want to largely keep SE MI on the
warm side of this baroclinic zone though some of the shortwaves will
brush us with cooler air on occasion. Overall temps look to hover a
few degrees above normal through the end of the month.

The flood watch will continue through this afternoon as the rain
continues to fall. Most locations to this point have received around
1.5 to 2 inches of rain. This has lead to several area rivers
reaching flood stage already with a few others forecast to reach
flood stage over the next day or so. A cold front over Mid MI will
drop through SE MI by this afternoon bringing an end to the rain but
not before another 0.25 (Saginaw Valley) to 1 inch (Ohio Border) of
rain falls. A very healthy fetch of moisture seen on water vapor
extends from the Gulf of Mexico up into Michigan continuing to feed
this dynamic pattern producing all the rain. In addition to the
frontal forcing in place, the next mid level shortwave riding along
the front is entering southern MI at press time which will bring
another window of widespread moderate showers to the area. Once this
wave lifts through the front won`t have much residency time left
before exiting the area itself around noon. All in all it still
looks like a wide swath of 2-3 inches of total rainfall will occur
across the region with some locally higher amounts possible.

Strong area of high pressure will spread across the central Great
Lakes this evening and overnight bringing a stretch of dry and quiet
weather. It will also be cooler as high temps top out in the upper
30s Thursday. There is a slight chance of some light snow Thursday
morning south of I94 as the next shortwave riding up the frontal
zone tries to bleed across the MI/OH border. With the dry air in
place with the strong surface high and northerly flow, it will be
hard for anything to make it this far north. Will leave a low pop in
for the moment to acknowledge the possibility.

Next opportunity for precip will come late Thursday night into
Friday as the next system ejects out of the trough through the
region. As with this current system, there appears to be some
phasing of northern and southern stream waves which will lead to
another feed of Gulf moisture into the system though not as moist as
this current airmass. A warm front will lift up through the area
early Friday which model thermal profile want to favor a wintry mix
north of the front before the warmer air surges in turning it to all
rain through the afternoon. After a short period of high pressure
Friday night, yet another system will lift through the region
Saturday and Saturday night bringing mostly rain once again.

MARINE...

Low pressure will lift northeast of Lake Huron early this morning a
trailing cold front pushing southeast through the region in its
wake with winds shifting to the northeast for all marine areas.
Increased instability in the colder air mass will allow gusts to
approach 30 knots this morning across northern Lake Huron. High
pressure will build into the region tonight and cause winds to
decrease. Winds will then veer to the northeast on Thursday. Winds
then shift from the south into Friday as the next low pressure
system brings additional rain.

HYDROLOGY...

Rain will continue early this morning before shifting to the east
with a cold front during the mid to late morning period. Additional
rainfall of one quarter to one half an inch will be possible with a
few higher amounts possible over far southeast lower Michigan near
the Michigan and Ohio state line.

A Flood Watch will continue into today as this additional rainfall
will only exacerbate potential flooding after the 2 to 3 inches of
rain that has fallen over the past few days. Many area rivers and
streams will be at or above flood stage with ponding of water in low
lying and poorly drained areas also anticipated.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Flood Watch until 4 PM EST this afternoon for MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

Lake Huron...NONE.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

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


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