Gale Warning 17, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
305 PM EDT Thu May 3 2018

.DISCUSSION...

Active weather over the next 24 hours.

Strong upper wave over southern Manitoba this afternoon beginning to
phase with the large central plains storm system, and merging height
fall centers will converge over Lake Huron/Georgian Bay tomorrow
afternoon.

Moist airmass (12z DTX sounding indicated PW values of 1.23
inches/223 percent of normal) in place this morning drying out a bit
late this afternoon as right entrance forcing of jet streak exits
(taking that narrow line of showers at press time with it), but even
better surge of moisture will be arriving tonight as deepening low
pressure tracks through the western Great Lakes, with PW values
pushing above 1.5 inches, which is near record or record territory
for early May Per SPC climatology page.

How fast the warm front lifts north will determine exactly how much
rain/flooding potential, as best mid level FGEN looks to be over
northern Wisconsin/northern Lower Michigan overnight. Model trends
are for deeper/farther northwest solution, with a slower timing,
which leads to cold front passage through southeast Michigan Friday
afternoon, increasing the chances for wind advisory criteria (gusts
45-50 MPH), as 12z NAM now indicating 55 Knots at 850 MB early
Friday afternoon (which the Euro/Regional GEM also have), with a
chance of a convective line developing, supporting winds of 55 to 60
MPH, especially the farther east one heads. Have issued wind
advisory tomorrow for all of southeast Michigan, but highest winds
expected to be east of U.S. 23.

This is in addition to the damaging wind threat tonight with the 50+
knot low level jet in the warm sector tracking through and impinging
mid level dry slot. However, with the overnight timing, it appears
the low levels will struggle to destabilize, with 1000-850 MB capes
mostly around 250 J/kg to perhaps 500 J/kg, and thus the intent to
just maintain marginal chance of severe storms. Still will have be
leary of the enhanced low level (0-1KM) wind shear in excess of 35
knots, leading to possible spin up/tornado, with the highest values
over Tri-Cities region near the low/triple point.

Once winds die down early Friday evening, much quieter weather in
store for the Weekend under predominately northwest confluent flow,
but a weak shortwave trough/cold front will swing through during
Sunday bringing potential for showers, but stretched out upper level
PV/jet diving into Midwest could rob bulk of the moisture with the
better forcing potentially over Iowa/western Ohio Valley.

An expansive high pressure system will build in across the Great
Lakes throughout Monday, ending rain chances and bringing plenty of
sunshine to SE MI as temperatures peak in the mid-60s for a daytime
high. A second high pressure system will then push east across the
Canadian Provinces Tuesday into Wednesday and will center across
Maine by 18Z Wednesday, with a low setting up across southern
Minnesota during this time. Anticyclonic flow across the western
Atlantic will help pump warmer air into Michigan throughout
Wednesday, with 850 mb temperatures peaking up to 12C by 00Z
Thursday. The combination of sunny skies and southerly flow will
allow temperatures to push back into the low to mid-70s by Tuesday
and Wednesday.

The next chance for rain and thunderstorms will move in Thursday
through early Friday as the low centered over southern Minnesota on
Wednesday slowly pushes east across Michigan. Low pressure and upper-
level troughing will be the main forcing with rain seen throughout
Thursday, with an advancing cold front continuing rain chances
through early Friday.

&&

.MARINE...

Post frontal fog will linger across southern Lake Huron well into
tonight. Low pressure is forecast to track across the lake Friday
morning/early afternoon driving a cold front across Lake St Clair
and western Lake Erie Fri afternoon. A few thunderstorms will
precede this low tonight. There is a chance for strong thunderstorms
along the front on Friday. Strong winds are also possible along this
cold front on Friday. There is moderate confidence in gale force
wind gusts south of Port Sanilac on Friday, mainly late morning into
the afternoon. The low will exit east of the area Friday night, with
the gradient quickly relaxing thereafter. This will support a steady
decrease in the winds. High pressure across the southern Great Lakes
will support generally tranquil boating conditions on Saturday.

&&

.HYDROLOGY...

Showers and thunderstorms will develop/increase in coverage tonight
with the approach of an upper level short wave and associated low
pressure system. Widespread rainfall amounts of four tenths of an
inch up to an inch are possible tonight, with the higher amounts
expected across the Saginaw Valley. There is a good deal of
atmospheric moisture present, so locally higher rainfall totals in
thunderstorms are possible.

&&

.PREV DISCUSSION...
Issued at 1252 PM EDT Thu May 3 2018

AVIATION...

A cold front located just north of FNT as of 1630Z will slowly inch
its way southward this afternoon and evening, reaching PTK around
20Z and DTW around 23Z. This front will be marked by a wind shift to
the north-northeast. The cool marine modified post frontal airmass,
intruding into an increasingly moist boundary layer, will be
characterized by low clouds (IFR and/or LIFR) and some fog/drizzle.

Low pressure will organize over Iowa today and lift into northern
Michigan by Friday morning. Increased southwest flow in advance of
this low will advect some modest elevated instability into Se Mi
later this evening into the overnight, providing a good chance for
some thunderstorms. Increased southerly flow at this surface will in
turn drive the front back north as a warm front during the
overnight, leading to a wide array of ceiling heights. The
associated cold front will be driven across Se Mi late Fri
morning/early afternoon. very windy conditions and strong storms are
possible along this front.

For DTW...While diurnal daytime destabilization may support some
thunderstorms in the region late this afternoon/early evening, the
more probable time period of thunderstorms will be after 01Z. The
frontal passage and wind shift to the north-northeast is expected
between 23Z and 00Z.

DTW THRESHOLD PROBABILITIES...

* Medium in ceilings below 5000 ft today, high tonight and Friday
  morning.

* Low in thunderstorms this afternoon. Moderate tonight into Friday
  morning.

* Low in crosswind thresholds being exceeded Friday afternoon.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Wind Advisory from 9 AM to 7 PM EDT Friday for MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

Lake Huron...Gale Warning from noon to 7 PM EDT Friday for LHZ443.

     Small Craft Advisory from 9 AM to 7 PM EDT Friday for LHZ421-422-
     441-442.

Lake St Clair...Gale Warning from noon to 7 PM EDT Friday for LCZ460.

Michigan waters of Lake Erie...Gale Warning from noon to 7 PM EDT Friday for LEZ444.

&&

DISCUSSION...SF/AM
MARINE.......SC
HYDROLOGY....SC
AVIATION.....SC

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
958 AM EDT THU MAY 3 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0700 AM     HEAVY RAIN       TECUMSEH                42.01N 83.94W
05/03/2018  M1.88 INCH       LENAWEE            MI   CO-OP OBSERVER

            24 HOUR RAINFALL TOTAL

0900 AM     HEAVY RAIN       4 ESE TAYLOR            42.21N 83.19W
05/03/2018  M1.00 INCH       WAYNE              MI   TRAINED SPOTTER

            12 HOUR RAINFALL TOTAL

0900 AM     HEAVY RAIN       MONROE                  41.92N 83.39W
05/03/2018  M2.20 INCH       MONROE             MI   CO-OP OBSERVER

            24 HOUR RAINFALL TOTAL

&&

JD