Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 150407
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1207 AM EDT Sun Apr 15 2018

.AVIATION...

Wavering IFR/MVFR will settle more into IFR as heavier precipitation
spreads into Lower Michigan later in the night. During this time,
drizzle/freezing drizzle will transition to rain/freezing rain that
will be heavy at times. Sleet is also be likely for locations from
PTK northward as strong NE wind continues to drive deeper sub
freezing air across Lower Michigan from Ontario. The center of low
pressure moving toward Toledo during the day will help lift
temperatures above freezing first at DTW during early morning but
taking until early afternoon at MBS. LIFR/IFR ceiling will also be
slow to improve due to the low being so nearby into Sunday evening.

For DTW... Temperature will settle right around the freezing mark at
the start of the forecast and then hover between 30-32 during the
night. This will make intermittent freezing drizzle possible before
heavier rain showers and freezing rain move in from the south.
Temperature is expected to rise above freezing around 12Z for a
short window of time for freezing rain compared to points north.
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 Sunday evening.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less during the night through
  Sunday evening.

* Low for ceiling 200 ft or less.

* Medium for FZRA from 08-12Z.

&&

.PREV DISCUSSION...
Issued at 1048 PM EDT Sat Apr 14 2018

UPDATE...

A quick update as the forecast remains on track and all warnings and
advisories remain in effect.

The bifurcation of the warm conveyor associated with the mature low
pressure system moving into the Midwest produced a mid level dry
pocket over Lower Michigan. This led to drizzle and freezing drizzle
over SE Michigan that was mostly on the light side based on surface
observations. Meanwhile, surface temperatures continue to settle
farther below freezing, especially along and north of I-69 where
upper 20s are common during late evening. The cooling process has
beens surprisingly slow toward metro Detroit since sunset given the
strong NE wind. Surface temperature analysis just does not show much
cold advection occurring there. Instead expect a slow leak southward
toward the I-94 corridor overnight before the next round of heavy
precipitation moves into the area. That activity is on track to
expand northward from southern Illinois and the Ohio Valley judging
by radar composite and rapid update models. When it does arrive, the
warning area will be primed for freezing rain and a period of heavy
icing for a few hours. Model soundings also show the surface based
cold air deep enough for heavy sleet as well, especially toward the
Tri Cities and northern Thumb. Upcoming forecast updates will track
the surface temperature response to the low pressure system moving
toward Toledo during the morning. This should allow temperatures to
warm above freezing during early to mid morning as far north as the
M-59 corridor and possibly the I-69 corridor toward noon.


PREV DISCUSSION...
Issued at 445 PM EDT Sat Apr 14 2018

Initial moisture push up the warm frontal slope and into the
elongated mid-level deformation axis over the Great Lakes and New
England is in the process of pushing east coincident with exiting
mid-level forcing. During this first round of precip, 2m
temperatures have fallen below freezing down to I-69 with upper 20s
in the Saginaw Valley. Cold air is indeed surviving the trip across
Lake Huron as noted by low 20s temps over much of Northern Lower.
The coincidental timing of sunset and the exit of heavier precip
will allow cold and dry advection to take over for the remainder of
the evening. Temperatures are forecast to fall below freezing down
to I-96/696 by sunset, followed by the southern extent of the Irish
Hills in Washtenaw and Monroe and finally the urban corridor by
midnight or earlier. Strong northeast wind funneling through Saginaw
Bay will continue to produce damaging winds in Bay County and
adjacent areas for the next 6 to 10 hours before veering of the wind
field allows the speed of the incoming marine winds to diminish.
Advisory criteria wind will continue to be possible in the other
Saginaw Valley counties and Huron County during this time as well.

Reports of winter impacts have been sparse so far today. As noted
earlier, the initial mid-level cold push weakened the inversion
considerably leading to predominantly snow pellets and sleet. Some
icing of power lines and roads was reported in the vicinity of
Frankenmuth, however. The probability of sleet will now steadily
diminish for the remainder of the event. For this afternoon and the
first half of tonight, this will occur to due to the encroachment of
the upper ridge axis fracturing the precipitation shield and
scouring out mid-level moisture. Strong northeast wind beneath an
inversion of this strength should produce widespread drizzle and
freezing drizzle, potentially until the next surge of moisture
arrives Sunday morning. So long as drizzle reaches the ground,
ongoing dry advection will only make matters worse by increasing
accretion efficiency during this relative lull in QPF. Motorists
should expect slick roads as early as this evening regardless of
rain intensity.

The latest guidance continues the trend of an aggressive southward
push of cold air tonight, supported by the observations of very cold
air that has already made it into APX`s area. A southward adjustment
to the freezing line has warranted an expansion of the freezing rain
area to include Macomb County for a longer period of time (upgraded
to a warning) and Lenawee County, where the advisory has been
extended south. The latter is primarily for the higher elevations of
the Irish Hills. Uncertainty is greatest near the Ohio border, but
after observing the quick ice-up invof Frankenmuth this morning in a
much less favorable scenario, will take no chances.

The next round of widespread heavy precip is modeled to arrive late
tonight and last well into Sunday. This precip shield is currently
in its formative stages over the Mississippi River valley. Showers
are blossoming over the Missouri and Illinois in response to
increasing fgen/convergence in advance of the dry air stream noted
on WV. In addition, echoes are now increasing over eastern Louisiana
and Arkansas the warm conveyor begins to ramp up in the wake of
ongoing convection in the Deep South. A confluence of these forcings
is modeled to occur as they lift into the CWA Sunday morning. It is
therefore critical to note that the 12z NMM, ARW, and recent runs of
the HRRR actually maintain two separate separate QPF maxima, casting
maximum uncertainty through the heart of the forecast area. With no
other options, maintained a compromise for QPF with some room to
adjust up and a lot of room to adjust down. The potential for
embedded convective elements precludes being too conservative at
this time. Freezing rain will end from south to north through the
day Sunday with total ice accretion forecast to range from 0.1 in
the hills of Lenawee County to 0.3" north of M59 to 0.5" north of
the I-69 corridor.

The large low pressure system will finally lift away towards the New
England region Tuesday bringing much drier conditions to the Great
Lakes region.  Northwest winds behind the departing low will
continue to bring cooler air as highs on Tuesday only get up to
around 40.  However, upper level ridging and surface high pressure
do build in over the area for the middle of the week.  This will
allow temps to moderate slightly on southwest winds.  The good news
is the rest of the extended forecast going into the start of the
weekend looks to have temps remaining in the upper 40s to lower 50s.
 Although, temps warm up slightly over the week, precipitation
chances look to increase as well.  Currently, a weaker low looks to
move across the Great Lakes region beginning late Wednesday through
early Friday.

MARINE...

A strong northeast gale over Lake Huron gusted to storms or near-
storms in inner Saginaw Bay for much of the day. Wind in the bay
will gradually decrease overnight as wind veers to easterly.
However...the gradient will remain quite strong over the lakes and
sustained easterly gales will continue through Sunday. Gusts to
storms will again be possible over portions of the central open
waters. 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 Sunday
night.

HYDROLOGY...

Conditions will remain wet through the rest of this weekend as a low
pressure system makes its way the Great Lakes. The first round of
precipitation is beginning to move east of the area, which resulted
in areas of freezing rain from Flint northward. There will be
somewhat of a lull in precipitation after this first round moves out
with the potential for some drizzle conditions before the next round
of  rainfall. Freezing rain and or sleet will most likely be to form
of precipitation overnight as the next round of widespread arrives
after sunset with temperatures reach freezing or below. The higher
ice accumulations remain north of M-59 where icy conditions have
already occurred. Once morning arrives and temperatures warm back up
above freezing, freezing rain will transition back to rain. An
additional 1 to 2 inches of rainfall is forecast for southeast
Michigan through the rest of the weekend. In addition to the
precipitation, strong northeast winds are causing lakeshore flooding
off of Saginaw Bay into portions of Bay and Tuscola County. 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 Advisory are in effect for
these counties into tomorrow.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Winter Weather Advisory until noon EDT today for MIZ075-076-082.

     Winter Storm Warning until noon EDT today for MIZ047>049-053>055-
     060>063-068>070.

     Lakeshore Flood Warning until 8 AM EDT this morning for MIZ048-054.

     Lakeshore Flood Warning until 4 PM EDT this afternoon for MIZ076-
     083.

     Lakeshore Flood Advisory until 8 AM EDT this morning for MIZ070.

Lake Huron...Gale Warning until 10 PM EDT this evening for LHZ361>363-462.

     Gale Warning until 4 PM EDT this afternoon for LHZ421-422-441-442-
     463.

     Small Craft Advisory until 5 AM EDT Monday for LHZ443.

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

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this afternoon for LEZ444.

&&

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...JVC/SP
MARINE.......JVC
HYDROLOGY....AA


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



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