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000 
FXUS63 KDTX 220346
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1146 PM EDT Mon Oct 21 2019


.AVIATION...

An approaching line of showers is tied to a cold front and will 
advance across Southeast Michigan within the next couple hours. 
Aggressive mid level drying will actually support some partial to 
full clearing during the early morning hours. Wrap around moisture 
within the advection of a cooler low level air mass will then allow 
a strato cu field to develop by late morning.

The passage of the sfc cold front between 06 to 09Z will usher in 
colder low level air during the course of the day Tuesday. This will 
result in a deepening mixed layer into the stronger south-southwest 
winds aloft, leading to a moderate probability of wind gusts around 
30 knots Tues afternoon. 

For DTW...With the better push of low level cold air advection 
holding off until Tues afternoon, there will be some weakening of 
the south-southwest winds in the post frontal environment early this 
morning. There will then be a notable uptick in the winds after 14Z. 

DTW THRESHOLD PROBABILITIES...

* Moderate in ceilings at or below 5000 feet.

&&

.PREV DISCUSSION...
Issued at 914 PM EDT Mon Oct 21 2019 

UPDATE...

The bulk of the showers will exit east of the area after midnight. A
line of showers tied more directly to the cold front now advancing
across western Lower Mi will slowly push across the area overnight.
So far, a shallow near sfc stable layer and shallow convection have
inhibited much of the stronger winds aloft from mixing to the
surface. Can not rule of few brief higher gusts within some of the
higher intensity showers this evening. Overall, the going forecast
looks reasonable. An earlier update removed the mention of thunder.
This is based on no reports in the region and the overall shallow
nature of the convection. 

Winds on southern Lake Huron and the thumb region are in the process
of veering toward the south. This will alleviate the lakeshore
flooding along the Lake Huron shoreline. So the advisory will be
dropped just before midnight. Lakeshore flooding concerns will then
be directed to northern Lake St Clair as the south-southwest winds
increase during the day on Tuesday. 

PREV DISCUSSION...
Issued at 259 PM EDT Mon Oct 21 2019 

DISCUSSION... 

Area of rain showers will continue to overspread the region late 
this afternoon within theta-e plume surging north in advance of 
deepening low pressure over the Mississippi Valley. To this point, 
the only pocket of thunder is well south of the area along lead edge 
of the cloud shield. So, expect thunder chance to remain very low as 
this activity, if it persisting, should shift east/northeast through 
Ohio into perhaps parts of Lake Erie.

Shower activity will continue into the evening with an increasing 
coverage of convective elements as forcing along strong cold front 
works east into the region. Current satellite/radar representation 
of this feature shows an increasingly well defined fine line of 
vigorous (but shallow) convection. This features will pivot through 
the area within the broader area of showers during the evening. 
Isolated thunder cannot be ruled out along/behind the cold front as 
it sweeps through the area. The back edge of this activity will 
begin to work into the area by midnight and then clear the forecast 
area completely by 4am or so. 

During this time frame, southeasterly winds will steadily increase 
as boundary layer mixing increases with an ever strong pressure 
gradient in advance of the front. Gusts on the order of 30 mph can 
be expected for several hours in the early/mid evening with higher 
gusts along the Lake Huron shoreline and also be some degree over 
the Saginaw Valley where mixing depth is forecast to maximize. 

Winds will then shift to the southwest with the passage of the front 
and decrease overnight. Strong boundary layer mixing will lead to 
windy conditions by midday as the low pressure center pivots into 
the northern Great Lakes and the pressure gradient tightens notably. 
Gusts in excess of 30 mph should be common by late morning/early 
afternoon with a few higher gusts topping 35 mph during the 
afternoon.

Shower chances will return as vorticity lobe rotates through the 
area around the storm system. Best coverage would focus over the 
north/northwest forecast area where moisture quality associated with 
this lobe will be best with just isolated/scattered activity further 
south given the amount of dry air that will infiltrate the area 
overnight into Tuesday. Another chance of rain showers will come 
Wednesday night as a fast moving shortwave lifts into the region 
around the base of leftover upper trough. By this time, upper flow 
will be pseudo-zonal and quite strong so system will progress thru 
the area very quickly.

A few rain showers might still be lingering around across the 
eastern portions of the area Thursday morning as the overnight cold 
front continues pushing southeast.  This cold front will stall out 
across central Ohio as a secondary mid level wave over the Midwest 
approaches the Great Lakes drawing it back slightly Thursday night. 
This will keep a good deal of clouds around Thursday with a small 
chance for showers clipping the southeast portions of the forecast 
area late night through Friday morning as models hint at a weak 
surface wave riding up along the front.  After high pressure will 
move across the region over the weekend bringing mostly clear skies 
and seasonable temperatures.  A cold front is expected to sweep 
through early Monday bringing a slight chance for showers.

MARINE...

Strong low pressure over the Upper Mississippi River valley will 
wobble through the Western Great Lakes tomorrow. Confidence remains 
high in southeast-south gales over the open waters of Lake Huron 
this evening and tonight. Gale warnings remain in effect and will 
likely have to be reissued for parts of Lake Huron on Tuesday as 
colder air filters in from the south-southwest behind cold frontal 
passage tonight. Best chance for Gales will be across central 
portions of Lake Huron, which includes Saginaw Bay, otherwise small 
craft advisories will likely be needed for the rest of the area.  
Wind and waves will be slow to diminish on Wednesday as 
cold axis tracks through, promoting deep mixing. Lighter 
winds for the end of the work week, as westerly winds 
expected to be below 20 knots on Thursday, and below 15 knots on 
Friday as a ridge of high pressure builds through the northern Ohio 
Valley.

HYDROLOGY...

Mainly light rain around this afternoon, with moderate showers this 
evening as a cold front tracks through. An embedded thunderstorm can 
not be ruled out. Even so, basin-average rainfall expected to reside 
in the quarter to half an inch rain, thus no flooding anticipated. 
Outside of a few light showers tomorrow, the rest of the work week 
looks dry.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Warning from 10 AM Tuesday to midnight EDT Tuesday 
     night for MIZ063-070.

Lake Huron...Gale Warning until midnight EDT Tuesday night for LHZ362-363-421-
     422-462>464.

     Gale Warning until 4 PM EDT Tuesday for LHZ441>443.

     Gale Warning until 4 AM EDT Tuesday for LHZ361.

Lake St Clair...Small Craft Advisory until midnight EDT Tuesday night for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until midnight EDT Tuesday night for LEZ444.

&&

$$

AVIATION.....SC
UPDATE.......SC
DISCUSSION...DG/drc
MARINE.......SF

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