Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 141825
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
225 PM EDT Sat Apr 14 2018


.AVIATION...

Mostly IFR conditions will persist through this forecast period as a
warm front remains south of the Michigan state line with abundant
moisture pushing northward. The first round of precipitation that is
resulting in FZRAPL from Flint northward and rain showers to the
south is pushing east of Michigan with somewhat of a clearing behind
it. Suspect that some drizzle conditions may develop after the first
batch of widespread rain exits. Have include TEMPO groups covering
the 00Z to 04Z  time frame for freezing rain ahead of the next round
of widespread rainfall tonight as the temperatures continue to move
southward to affect the remaining terminals. Very gusty northeast
winds will persist through this TAF period with gusts of 20-30 knots
across most TAF sites, with the exception of MBS where gusts around
40 knot are coming off of Saginaw Bay. Little thunder has occured
this afternoon and is unlikely the rest of this afternoon with the
warm front remaining to the south.  The next surge of precipation
will return by 06/07Z and temperatures at all TAF sites will likely
be at freezing or below. FZRA will be the main concern through the
overnight time frame until tomorrow morning until temperatures begin
to rise above freezing.

For DTW... Temperature trends suggest a quicker push of the cold air
and reaching DTW a slightly earlier. Current forecast has
temperatures reaching 32 degrees around 03Z. With the potential for
drizzle conditions this evening, have added a TEMPO group for
freezing drizzle from 00Z to 04Z before freezing rain becomes
prevailing. Expect freezing rain to switch back over to rain around
10-12Z. Abundant low level moisture will easily keep ceilings below
5,000 ft through this TAF period.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less tonight through Sunday morning.

* Low for ceiling 200 ft or less.

* Low for thunderstorms tonight.

* Low in precip type as FZDZ through 04Z tonight. Medium for ptype
  of FZRA from 04-12Z.

&&

.PREV DISCUSSION...
Issued at 1126 AM EDT Sat Apr 14 2018

UPDATE...

Strong mid-level cold push this morning has rendered the inversion
insufficient to produce freezing rain, and this will remain the case
until at least early afternoon before the thermal field begins to
respond to the approach of the upper low in advance of the
northward-advancing warm conveyor. Observations and reports suggest
ptype is predominantly snow, snow pellets, and sleet. Reduced ice
accretion totals for this morning, stopping just short of removing
them altogether as a narrow band is still plausible between M59 and
M46. Early data indicates the forecast for tonight is still in good
shape, so all headlines will remain in effect for now.

The wind response across the northern counties this morning has been
impressive. Port Hope was gusting to 47 mph before it ceased
reporting while wind gusts well in excess of 50 mph have been
reported at the Bay County shoreline with 45 mph penetrating inland
toward Saginaw Bay. Wind issues will continue to be addressed in WSW
products to reduce overall headlines.

Lakeshore flooding is repsonding in line with expectations for strong
northeast wind, though the pending forecast update will include a
slight increase to water levels for Bay County. Given the lack of
impactful fzra at the moment, main concern is the rapid rise of the
Saginaw River in Downtown Saginaw. Flow reveral occured first this
thing morning and minor flood has been achieved well ahead of even
this morning`s updated forecast. With no indication of slowing,
suspect rises will continue in some fashion until the gradient
slackens a bit, which is expected to occur later this afternoon.

PREV DISCUSSION...
Issued at 327 AM EDT Sat Apr 14 2018

DISCUSSION...

Through much of the night, the more persistent precipitation has
been focused across the northern Great Lakes, a little higher up
the mid tropospheric frontal boundary draped across the state. A
plume of deep moisture has been lifting northward from the Lower
Ohio Valley, aided by strengthening low-mid level southwest flow
ahead of the upper low meandering across the central plains. This
moisture will advect into Se Mi during the predawn hours. As it
interacts with the deep layer frontal boundary over the region,
precipitation will increase in intensity and expand in coverage across
the forecast area. Modest mid level instability will also support
some scattered thunderstorms, providing brief intervals of higher
intensity precip. Deep moist isentropic ascent within the entrance
region of an upper jet over eastern Canada will shift to the east of
the forecast area late this afternoon with the help of the departure
of a lead mid level short wave feature. This will cause some mid
level subsidence/drying to expand across the area, transitioning
precip to drizzle/freezing drizzle late this afternoon into tonight.

Sfc low pressure tracking across the mid Mississippi Valley today
and arctic high pressure expanding across northern Ontario will
establish a strong northeast gradient across Lower Mi. This will
result in shallow cold air advection that will persist through the
day and into tonight. Sfc temps are forecast to drop below freezing
across the Saginaw Valley and thumb during the morning, with
subfreezing temps expanding south during the day (pushing into the
Irish Hills by late afternoon). This will transition the rain over
to freezing rain across the northern half of the forecast area. Some
contraction of the mid level frontal boundary may lead to enough
cooling in the column to support sleet across the Saginaw Valley and
thumb. While the intensity of the precip wanes to drizzle later in
the day, continued temperature drops (possibly into the upper 20s
north of I-69) will lend itself to slick spots on the roads.

Another round of widespread precipitation is forecast to arrive
overnight and persist through much of the day Sunday. This will be
associated with the warm conveyor belt of the upper low expected to
move from the plains across the Mid Ms Valley on Sunday. The arrival
of this widespread precip overnight into Sun morning will be when
temps over a good portion of the forecast area will be at or below
freezing. An increase in the mid level warm layer will also reduce
the chances for sleet with this second round of precip. The amount
of precipitation, with some convective elements may lead to periods
of heavy freezing rain. There has been a trend toward a little
colder sfc temps, with the bulk of model solutions now bringing sfc
temps down to freezing to the I-94 corridor overnight. This will
prompt the issuance of a winter wx advisory for freezing rain for
Washtenaw and Wayne Counties tonight/Sun morning. Concern for a
little colder temps along the Irish Hills has prompted the upgrade
to a warning for Livingston and Oakland Counties. Total ice
accumulations of a quarter to half inch look reasonable (although
there is certainly the potential for some locals to see icing up to
an inch). Given the expected intensity of the rain and thermal
profile, the better icing accretion today is expected to be north of
I-69. Little additional icing is expected later today as precip
intensity wanes. The next round of icing, possibly significant, will
then be overnight into Sun morning. With the approach of the sfc low
Sun afternoon, low level moistening will likely cause temps to rise
above freezing Sun afternoon. The stronger gradient will also shift
to the northern Great Lakes on Sunday, so winds will actually weaken
during the course of the day.

In addition to icing potential, strong winds will be problematic
today. First off, the east-northeast winds and wave action will lead
to rises on wrn Lake Erie and Lake St Clair, with significant
flooding possible along the Lake Erie shoreline. Strong northeast
winds funneling down Saginaw Bay will also cause flooding along the
shoreline in Bay/Tuscola Counties. Wind gusts near the Lake Huron
shoreline are expected to top 40 MPH at times. Funneling down
Saginaw Bay will support a corridor of enhanced winds stretching from
Bay County across portions of Saginaw and Midland Counties. Wind
gusts in this region may exceed 50 MPH today. Rather than complicate
already complex headlines, the strong winds will be mentioned in the
WSW as part of the winter storm warning.

The upper low is forecast to rotate east of the forecast area on
Monday. This will shift the winds to the northwest and result in a
deepening of the cold air, with the moist axis well to the
northeast. Colder temps with some rain/snow showers will result.

MARINE...

An approaching low pressure system and strengthening pressure
gradient will increase wind and wind gusts across the Great Lakes
through the day. Channeling down Saginaw Bay may further enhance the
winds there. ENE gusts of 30 - 40 knots will persist this morning
through most of Sunday. Resultant wave heights will range between 10
- 14 feet across nearshore Lake Huron through this timeframe, with
waves up to 5-6 feet possible in the inner Saginaw bay. Gale
warnings are in effect for the majority of Lake Huron now through
Sunday evening. Small craft advisories will remain in effect for
Michigan waters of Lake Erie, Lake St Clair and nearshore waters of
Lake Huron south of Port Sanilac through at least Sunday afternoon.

HYDROLOGY...

A wet weekend is in store as a large low pressure system tracks
through the region. Scattered rain showers have been ongoing for 24
hours now with little fan fare across Mid MI but coverage and
intensity will increase this weekend with widespread 2-3 inches of
liquid precipitation expected to fall in the next 48 hours.
Convection may lead to some locally higher amounts. Cold air
funneling southward through the state today will result in precip
type issues with freezing rain and/or sleet likely occuring.
Locations along and north of M59 will see the most ice accumulation
where as the Detroit Metro will see a much shorter duration of
freezing rain later tonight for a few hours. In addition to
precipitation, strong ENE flow will bring the chance to see
lakeshore flooding across Bay and Tuscola county, and down into
Wayne, Macomb and Monroe county. As a result, lakeshore flood
warnings and an advisory are in effect for the five counties
mentioned.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 8 PM this evening to noon EDT Sunday
     for MIZ075-076-082.

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

     Winter Storm Warning from 6 PM this evening to noon EDT Sunday for
     MIZ068>070.

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

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

     Lakeshore Flood Advisory until 8 AM EDT Sunday for MIZ070.

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

     Gale Warning until 4 PM EDT Sunday for LHZ421-441-442-463.

     Small Craft Advisory until 5 AM EDT Monday for LHZ443.

     Storm Warning until 4 PM EDT this afternoon for LHZ422.

     Gale Warning until 4 PM EDT Sunday for LHZ422.

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

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

&&

$$

AVIATION.....AA
UPDATE.......JVC
DISCUSSION...SC
MARINE.......DRK
HYDROLOGY....DRK


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



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