Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 182256
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
656 PM EDT Wed Apr 18 2018


.AVIATION...

Band(s) of convective showers, both rain and snow, continue to arc
northeast into the area within strong isentropic lift in advance of
approaching shortwave. This precipitation will transition into a
narrower band of mainly light snow during the course of the evening
as surface low associated with the upper wave passes to the south
and something of a pivot point for the main fgen forcing sets up
near the M-59 corridor. Will be pulling forward the timing of the
precipitation given trends early this evening with -sn ending all
areas by 06z-07z (and points from KPTK north sooner than that). MVFR
cigs should be the rule overnight, but quicker timing of the system
should bring subsidence into area on gusty northwest flow by Thu am,
so will bring clearing a bit quicker. Will maintain the wind gusts
aoa 20 knots during the day Thursday.

For DTW...Periods of rain showers/snow pellets will arc through
terminal early in the forecast. This activity may end for a time,
but fgen forcing will settle back south late evening into the
overnight, bringing a period of light snow. 03z-04z thru perhaps
07z or so. Expect MVFR cigs, which will scatter out in subsiding
northwest flow Thursday morning. Wind gusts in the 22-24 knot area
should be common in the northwest flow on Thu.

/DTW THRESHOLD PROBABILITIES...

* High for ceilings aob 5000 ft tonight, medium Thursday morning.

* Low in precipitation type as all snow early this evening. High
  after 03Z.

* Low confidence in exceeding crosswind threshold tomorrow.

&&

.PREV DISCUSSION...
Issued at 324 PM EDT Wed Apr 18 2018

DISCUSSION...
Compact mid level closed wave over eastern Iowa will track quickly
eastward across far southern lower Michigan overnight. In the
process the wave will weaken and open as it encounters and gets
absorbed into another mid level trough rotating down through the
eastern Great Lakes. Deep moisture is limited with this system and
will become more limited through the night as a surface low
associate with this wave over southern Indiana begins to initiate
convection to the south.  This will cut into moisture feed into
lower Michigan and also cut down on qpf amounts. Colder and drier
air advecting into the lower levels from the northeast will also
reduce amounts.  Looking for around a quarter inch qpf along the
Ohio border to a trace or few hundreths across northern Saginaw
Valley and Thumb. Precip this evening will start off as rain as
surface temperatures this afternoon climb into the upper 30s to
lower 40s. Thermo profile quickly goes below freezing above the
surface but stays within -10c up to about 700mb where moisture depth
for the most part ends. Dewpoints in the 20s will also rapidly lower
boundary temps from wet bulbing to the point where rain will mix
with snow around sunset then become all snow from north to south as
the night goes on. Any accumulations will be less then an inch with
best shot of accumulations along the Irish Hills across
livingston/Oakland counties and eastern tier of Thumb. Here temps
should reach freezing before precip end before daybreak. Other
locations that have best chance for accumulatlons will be Lenawee
and Monroe where duration and qpf will be longer and higher. To
reiterate, precipitation will be light to very light with this event
and any accumulations will be less then an inch and mostly on grassy
and elevated surfaces.

For Thursday, winds will increase rapidly in the morning from the
north as surface gradient becomes tight between incoming High
pressure and departing low to the east.  Weak surface trough and
flow off of Lake Huron may produce scattered lake effect snow/rain
showers during the morning from the Thumb into the northern metro
Detroit area. Skies will clear from west to east in the afternoon as
flow becomes northwest. Highs Thursday will still only reach into
the 40s but feel like the 30s from 15 to 25 mph gusty winds.

Large high pressure will move into the Great Lakes for the end of
the week bringing clear skies, lighter winds but still cold nights
Thursday and Friday with lows in the 20s and 30s.  Highs Friday will
be much better then of late in the upper 40s to low 50s but still
well below normal.

A prolonged stretch of calm, dry conditions will continue into the
weekend and early next week as an upper ridge and surface high
pressure slowly migrate east over the region. Other than some
passing high clouds across the southern half of the CWA on Saturday,
mainly sunny skies are expected through Monday. A relatively cool
air mass will gradually moderate during this timeframe allowing
highs to rise into the 50s over the weekend before reaching the 60s
early next week. The next chance for precipitation then looks to
return during the middle part of next week as a shortwave drops
through the region.

MARINE...

Low pressure tracking through the Ohio Valley this evening, with
strong northwest winds developing behind the low late tonight into
tomorrow. Wind gusts of 25 to 30 knots will be common over Lake
Huron, with brief gusts to low end gales possible over the southern
Lake Huron basin early Thursday evening.

Large high pressure will expand across the region on Friday and will
persist across the region through the weekend, resulting in light
and variable winds.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 2 AM Thursday to 4 PM EDT Friday for
     LHZ421-441>443.

     Small Craft Advisory from 2 AM to 4 PM EDT Thursday for LHZ422.

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

$$

AVIATION.....DG
DISCUSSION...DRC/JD
MARINE.......SF


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