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000 
FXUS63 KDTX 201123
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
723 AM EDT Sun Aug 20 2017

.AVIATION...

High pressure will bring VFR conditions throughout the forecast 
period.  Light winds and good radiational cooling is generating 
areas of shallow fog which will quickly dissipate after sunrise. 
Light/variable winds will become southwest under 10 knots on the 
backside of this high by mid/late morning with just a few diurnal 
cumulus possible within a rather dry airmass. Weak surface flow and 
daytime heating could bring a lake breeze up to or through DTW late 
afternoon/evening backing winds more south southeast but would remain
under 10 knots. Light southwest flow tonight will bring increasing 
dewpoints. Patches of high clouds from convection in the midwest may 
make it over the taf sites, however, there should still be enough 
radiational cooling to produce a bit more widespread fog in the 4-6 
mile range towards sunrise Monday.

//DTW THRESHOLD PROBABILITIES... 

* None.

&&

.PREV DISCUSSION...
Issued at 400 AM EDT Sun Aug 20 2017 

DISCUSSION...

High pressure covering much of the country east of the Mississippi 
during the morning will become centered more along the Atlantic 
coast during the afternoon. This will ensure a sunny start to the 
day across SE Michigan after some patchy and shallow fog around 
sunrise. Light and variable wind will then take on a more southerly 
component and help boost temperatures into the mid 80s most 
locations. Model soundings indicate the boundary layer will be too 
dry for anything more than a few cumulus but thickening cirrus is 
expected late in the day as MCS debris drifts eastward from the 
Plains. These clouds are timed too late to have an impact on 
afternoon temperatures and then will thin during the evening and 
allow some radiational cooling tonight. Guidance lows in the lower 
to mid 60s look good. 

Larger scale weather features in the Plains today will have an 
increasing influence on Great Lakes conditions Monday and especially 
by Tuesday. Mostly zonal flow aloft through the northern tier of 
states is producing a classic lee side surface trough while the 
upper level wave over central Canada is supporting a cold front as 
far south as the Dakotas. These features intersect a warm front over 
the Missouri valley that is the focus for low level jet forced MCS 
activity. Ongoing nocturnal convection during the early morning is 
expected to follow a standard daytime weakening trend while zonal 
flow guides cloud remnants and any residual MCV into the southern 
Great Lakes. The latest model solutions then look reasonable with 
the slow eastward migration of the surface features into the Midwest 
tonight. Some surface based convection in shown over the northern 
Great Lakes this afternoon and evening while remaining capped 
farther south toward Iowa and Illinois. This will set up the genesis 
region for round 2 of low level jet forced MCS activity on the edge 
of the 850-700 mb cap centered on Iowa, much farther east than 
activity occurring early this morning. The strongest convection 
should dive southeast along the instability gradient from there 
while substantial cloud debris and even some MCV supported showers 
could make it into Lower Michigan by late Monday morning into 
afternoon. 

A new round of short wave induced height falls is also projected to 
develop over central Canada Monday into Monday night which will lead 
to a pause in the eastward progress of the cold front. The Canadian 
short wave will produce a surface wave along the front about at the 
same time mid level monsoonal moisture is drawn into the westerlies 
from the southwest states. A new round of deep warm/moist advection 
will produce additional MCS development over the Plains and Midwest 
as the low pressure system matures. The deepening upper wave will 
provide strong forcing and a strong wind profile while the 
instability axis/theta-e ridge spreads northward over the Great 
Lakes ahead of the front. These large scale features will sustain 
organized convection through Lower Michigan late Monday night 
through Tuesday before the front exits eastward by Tuesday evening. 

After the Tuesday frontal passage, global model solutions maintain a
sharper upper level trough, and even some signs of a closed low, 
over eastern Canada by Wednesday. This will open the door for 
stronger high pressure to develop over central Canada and spread 
colder air into the Great Lakes Wednesday into Thursday. The latest 
round of guidance temperatures now offer highs in the upper 60s in 
the Thumb region by Thursday which match up better with 850 mb 
temperatures in the 5-10C range. Modifying high pressure then holds 
during the second half of the week and into next weekend.

MARINE...
High pressure centered over Michigan will gradually slide to the 
east today maintaining a light mainly southwesterly flow through 
Monday. Increasing moisture and a slowly advancing cold front will 
bring showers and thunderstorms late tonight across northern Lake 
Huron. This chance will spread south during the day Monday and 
continue until the strong cold front sweeps through Tuesday 
afternoon. Winds will then become strong from the northwest and 
continue through the end of the week. 

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....DRC
DISCUSSION...BT

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