Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 160446
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1146 PM EST Wed Nov 15 2017


.AVIATION...

Low level moist cyclonic flow and moisture advection off Lake
Michigan will sustain an overcast strato cu field across Se Mi into
Thurs evening. Ceilings will be predominately MVFR through the
morning, although ample fluctuation is expected. A secondary upper
level short wave passing across Se Mi early Thurs morning may
provide some brief light rain/snow showers.

For DTW...Ongoing low level cold air advection will support some
gustiness to the westerly winds through the morning. There has
however been some noted brief decrease in winds upstream as a result
of some cooling near the sfc. With the depth of cold air increasing
during the morning, mixing should support an uptick in winds during
the morning. With gusts possibly topping 25 knots, crosswind
thresholds may be exceeded. The boundary layer and ground temps will
remain warm enough to melt any snow on contact from possible early
morning snow showers.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5kft tonight through Thursday afternoon.

* Moderate in precipitation type being a mix of rain and snow this
  morning.

* Moderate in westerly wind gusts exceeding crosswind thresholds
  Thursday morning.

&&

.PREV DISCUSSION...
Issued at 858 PM EST Wed Nov 15 2017

UPDATE...

The upper level wave now rotating across the I-69 corridor has been
sustaining more widespread showers across the thumb region. These
will exit east over the next hour with the departure of the upper
wave. This will support a continued decreasing trend to the coverage
of showers. Ongoing low level cold air advection under westerly flow
will however support some additional shower development off Lake
Michigan, aided by lift ahead of a secondary short wave now
approaching central Lake Mi from Wisconsin. Despite the appearance of
this wave on satellite, mid level dry air and limited lake modified
inversion heights will keep the coverage and intensity of any
overnight rain/snow showers limited. An update to the forecast will
be issued shortly to reflect the latest precip trends.

PREV DISCUSSION...
Issued at 314 PM EST Wed Nov 15 2017

DISCUSSION...

Good upper wave was moving through the Great Lakes region this
evening with another good shortwave over the upper Mississippi River
valley. All of these move through the region tonight. Widespread
rain in the moisture plume well ahead of the front will push east of
the forecast area within a couple of hours, but additional showers
in advance of the cold front over SW Lower Michigan will continue to
affect SE Lower Michigan through about 01z to 02z.  Surface low will
continue to deepen over the lakes, keeping strong cyclonic flow over
the region through the overnight hours and into Thursday morning.
All of the residual forcing is focused to the northeast of the
region, but may just clip enough of the Thumb Region to keep the
chance POPs through Thursday morning. Ensemble forecast plots
suggest that most of the forecast area dries out before the boundary
layer sufficiently cools to have much if any mix with snow.  The one
exception may be the Thumb region were some melting snow is expected
to mix with any left over showers overnight. Those same ensemble
forecast plots also indicate wind gusts up to 30 to 35 mph for
Southeast Michigan post frontal into Thursday morning which is in
line with models that do not have any wind over 40kts anywhere in
the mixed boundary layer.

It will take all day for the cyclonic flow to loosen its grip on the
region. Given the high moisture content up to 850 mbs, expect mostly
cloudy skies through the day, but no forcing for precipitation. With
the cloud cover and similar model 850 temps, like the cooler
guidance numbers closer to 40 degrees rather than mid 40s.

A skinny surface ridge of high pressure building in for Thursday
night will allow for some partial evening clearing and light winds.
However, good WSW flow aloft will already be pushing high and mid
clouds back over Lower MI by late Thursday night and Friday.

Looks like the best push of moisture advection and deep forcing
waits until Friday night as the next deepening system moves into the
Great Lakes. All models are continuing the trend of a slower
evolution of the system which keeps the surface low at its deepest
point over the eastern lakes. This continuation of the slower
evolution will keep showers in the forecast through the entire day
on Saturday and push the strongest of the winds late Saturday into
Saturday evening. Will maintain a slight chance of thunder late
Friday night and early Saturday. Almost no CAPE, but mid level lapse
rates of 6.5C and traditional parameters such as Showalter index
less than zero suggests the slight chance.

Cold air advection behind the departing low pressure system will
cool things considerably for Saturday night into the rest of the
weekend, as well as allow for some lake enhanced flurries to hang
around late Saturday especially for the eastern Thumb region. 850 mb
temps approaching values in the negative teens Celsius and continued
cloud cover will translate to highs only reaching the mid 30s on
Sunday. Breezy, but mostly dry, conditions will persist most of
Sunday as a stronger pressure gradient develops between the
departing/strengthening low and building high pressure over the
southern CONUS. This surface ridge will start to push into SE
Michigan on Sunday night and lead to some clearing in the skies
which will help lows overnight Sunday drop to the mid 20s.

Upper ridging to begin passing over the Great Lakes on Monday and
will keep things quiet for the first half of the work week.
Southwest flow around the high pressure drifting toward the mid
Atlantic coast and an increase in thicknesses will help moderate
high temperatures back into the 40s.

MARINE...

Southerly wind gusts up to 25 - 30 knots will continue across the
lakes and bay as low pressure travels northeast of Michigan into
Ontario. As the low continues to move out of proximity to Michigan,
a cold front will move in behind it, causing winds to veer from
south to southwesterly, and eventually west to northwest by the late
morning hours on Thursday. The advent of cooler air will decrease
stability and increase the mixing depth, allowing for isolated gusts
up to 40 knots to be seen over the lakes, mainly during the mid to
late morning hours. Both wind gusts and waves are expected to relax
late Thursday into Friday morning as high pressure builds across the
Great Lakes. Advisories will be in effect tonight and overnight for
both wind gust and wave concerns.

HYDROLOGY...

Ongoing precipitation from an advancing cold front will continue
into through the evening hours, depositing an estimated .25 - .5
inches of rainfall accumulation through SE Michigan. High pressure
will then build back into Michigan, keeping the area dry through
Thursday and the better part of Friday, however, dry conditions will
be short-lived as additional rainfall is expected Friday evening
into Saturday. A strengthening low pressure system will bring
persistent rain during this time frame, with possible accumulation
totals ranging anywhere between .5 - 1 inch.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 5 PM EST Thursday for LHZ361>363-462>464.

     Small Craft Advisory until 5 PM EST Thursday for LHZ422.

     Small Craft Advisory until 4 AM EST Friday for LHZ421-441>443.

Lake St Clair...Small Craft Advisory until 5 PM EST Thursday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 5 PM EST Thursday for LEZ444.

&&

$$

AVIATION.....SC
UPDATE.......SC
DISCUSSION...RBP/TF
MARINE.......AM
HYDROLOGY....AM


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