Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 151053
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
653 AM EDT Sun Apr 15 2018


.AVIATION...

Winter storm well underway with a combination of freezing rain and
sleet spread across all of southern MI. This is mainly resulting in
IFR conditions with a few sites briefly bouncing up into MVFR. As
the low pressure center draws nearer, though the bulk of the precip
will be shed north and east, lowering inversions will keep IFR, and
possibly LIFR, CIGs and VSBYs across the area. The main surge of
moisture looks to only last a couple more hours via regional radar
mosaic, but models show the deeper plume getting pulled back west
into area through the early afternoon. Warm air will lift into the
area as well soon after 12Z which will transition precip type from
FZRA/PL to all rain. MBS may be the outlier and keep the freezing
conditions well into the afternoon. Winds will again be gusty out of
the NE but will switch around to westerly as the low lifts directly
over head this afternoon.

For DTW... Temperature will start off at the freezing mark before
rising into the mid 30s soon after day break. This will allow rain
to become the predominate ptype vs the FZRA and PL currently
ongoing. Both precipitation and low ceiling will contribute to IFR
through the day followed by LIFR as the surface low moves very near
DTW late in the day into the evening.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less through the forecast.

* Low for ceiling 200 ft or less.

* Moderate for FZRA from 12-14Z. Low after 14Z.

&&

.PREV DISCUSSION...
Issued at 321 AM EDT Sun Apr 15 2018

DISCUSSION...

Freezing rain will continue to overspread Se Mi early this morning
as the warm conveyor belt associated with the upper low parked over
the IA/MO border advances northward across Lower Mi. As of 07Z, sfc
temps are below freezing across the entire forecast area (with
Monroe County now at 32 deg). Persistent east-northeast winds
associated with arctic high pressure of 1043 mb over northern Ontario
has funneled shallow cold air into the area. Of concern is not only
the sub freezing temps, but the degree of dry air that has funneled
into the region (sfc dewpoints over much of Se Mi are in the 20s,
with readings in the teens northeast of London, ONT). The result
will be a slow response in raising sfc wet bulb temps, especially
across the northern half of the forecast area.

The upper low will only slowly rotate into nrn Illinois by evening,
placing the warm conveyor over Se Mi through much of the day. Recent
hi res solutions suggest some degree of decrease/breaks in the
precip late morning into early afternoon. The lead push of mid level
height falls associated with the approaching upper low will however
slowly advance from southwest to northeast across the forecast area
late this afternoon through the evening, resulting in an increase in
precipitation during the later portion of the day. Deepening of the
elevated warm layer will result from the very warm and moist air
advancing atop the shallow cold layer (nice connection to the Gulf
noted on water vapor). The rain originating from an increasingly
warmer environment will help to offset the near surface cooling.
More importantly, the approach of the associated surface low,
forecast to lift into far SE MI/NW OH will help advect a little
warmer sfc temps into the area. The result will be temps rising
above freezing from south to north during the course of the day.

Icing accumulations will therefore be dependent on the timing of
this warming. Icing accums below a quarter of an inch look
reasonable along/south of an Ann Arbor to Detroit line where the
warming will be a little earlier. Icing accums of at least a quarter
inch still look reasonable in the warning area. The longer period of
freezing rain across the Saginaw Valley/Thumb (and potential for
this region to see temps hold in the upper 20s a little longer)
suggests ice accums will likely exceed a half inch. Gusty east winds
this morning will increase the risk for tree damage as icing
increases. The winds will weaken during the course of the afternoon
as the sfc low approaches.

Mid level dry air will overspread Se Mi during the night and through
Monday morning as the Upper low rotates across the northern Ohio
Valley. Winter-like conditions will however maintain their grip on
the region as the upper low drives cold air across the Great Lakes.
Deep layer moisture will slowly lift north of the forecast during
the day Monday while surface low pressure lifts into Lake Huron.
Lingering low level moisture, cyclonic flow and mid April diurnal
heating may however support some sct rain/snow showers. The 00Z
model solutions indicate redevelopment of the upper low over the
Great Lakes region Mon Night. Deeper moisture forecast to advance
into Se Mi with potential upper level support and cold air advection
will bring the chance for snow showers Mon night into Tues morning.
The thermodynamic profile on model soundings is even indicative of
potential heavy snow showers. Cold air will then maintain its grip
on the region into at least mid week.

MARINE...

A strong northeasterly gradient has been in place across the Great
Lakes as we are located in between a 30.80 inch high over James Bay
and a 29.70 inch low near southern Lake Michigan. The long duration
marine wind event will continue through this afternoon but with an
upgrade to a Storm Warning across the northern half of Lake Huron.
Guidance strongly suggests this increase to be warranted and current
observations are already near 40 knots. Gales will continue as is
across the rest of the basin with small crafts over Lakes St Clair
and Erie. Significant wave heights over the open waters will range
from to 10 to 15 feet over the next 24 hours with maximum wave
heights approaching 25 feet over west-central portions of the basin.
Hazardous wave conditions will likewise persist in the nearshore
zones...especially near the tip of the Thumb...until late tonight.

HYDROLOGY...

Wet weather continues across the region today as a slow moving low
pressure system tracks through the region today through Monday
night. After a lull in precipitation over the last several hours,
the next surge of moisture has started lifting north through
southern Michigan. Precipitation will be fairly heavy into this
afternoon before rates decrease for this evening and tonight. With
temperatures sub freezing, precipitation will fall as freezing rain
and sleet before transitioning to rain from the Ohio border
northward this morning. An additional 1 to 2 inches of rainfall is
forecast for southeast Michigan this morning through Monday
afternoon. In addition to the precipitation, strong northeast winds
are causing lakeshore flooding off of Saginaw Bay into portions of
Bay and Tuscola County. This is also resulting in a Flood Warning
for the Saginaw River due to excess water pushed into the river from
the Bay. Wayne, Macomb, and Monroe County will also be affected by
these northeasterly winds and experience lakeshore flooding off of
Lake St. Clair and Lake Erie. Lakeshore Flood Warnings and an
Advisory are in effect for these counties into this afternoon.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EDT this morning for MIZ075-076-
     082-083.

     Winter Storm Warning until noon EDT today for MIZ060>063-068>070.

     Lakeshore Flood Warning until 4 PM EDT this afternoon for MIZ048-
     054-076-083.

     Winter Storm Warning until 4 PM EDT this afternoon for MIZ047>049-
     053>055.

     Lakeshore Flood Advisory until 4 PM EDT this afternoon for MIZ070.

Lake Huron...Gale Warning until 10 PM EDT this evening for LHZ363-441>443-
     462>464.

     Gale Warning until 2 PM EDT this afternoon for LHZ421-422.

     Storm Warning until 6 PM EDT this evening for LHZ361-362.

Lake St Clair...Small Craft Advisory until 4 PM EDT this afternoon for LCZ460.

Michigan waters of Lake Erie...Gale Warning until 2 PM EDT this afternoon for LEZ444.

&&

$$

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


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