Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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405
FXUS63 KDTX 060456
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1156 PM EST Mon Dec 5 2016


.AVIATION...

East winds off the Great Lakes will allow light fog (BR) and lower
stratus to fill in overnight across Southeast Michigan terminals.
Restrictions will most likely fall into the MVFR category, although
some lower ceilings are possible from PTK north. All hi-res model
data now supports improvement to vis/cigs near the Detroit terminals
around 12Z as easterly flow strengthens, and as warmer air arrives
in the low-levels to extreme Southeast Michigan and weakens the
inversion. Northern terminals should take longer to see some
improvement as the warmer wedge of air remains further south, with
only some improvement into higher MVFR at 14-15Z. Conditions will
then deteriorate again in the afternoon and evening as low pressure
lifting into the Ohio Valley spreads rain into the area. A cold
front pushing through during the evening will usher out
precipitation, but allow gusty west winds to develop.

For DTW...Flow off Lake Erie and earlier clearing to skies will
allow visibility to continue falling to MVFR early in the TAF period,
with eventual development of stratus around 1500ft expected to
follow. Warmer air in the low-level and increased easterly flow
should then allow for an improvement in ceilings/vis around 12Z
before conditions deteriorate again in the afternoon as rain spreads
into the area. Winds are expected to increase from the east-
northeast during the afternoon, between 10-15 knots. Stronger west
winds will then arrive with a cold front this evening.

//DTW Threshold Probabilities...

* Medium for cigs below 5000 feet after 08Z. High after 18Z Tuesday.

* High confidence precipitation Tuesday will be rain.

&&

.PREV DISCUSSION...
Issued at 812 PM EST Mon Dec 5 2016

UPDATE...

Clearing skies this evening have allowed for a fast drop in
temperature. As a result, forecast min temps for tonight were
lowered. Expect mins in the mid 20s to be reached by midnight-2AM
timeframe before leveling off or even starting to rise slightly as
winds turn east off the Great Lakes and allows for an increase in
low clouds.

PREV DISCUSSION...
Issued at 231 PM EST Mon Dec 5 2016

DISCUSSION...

Upper low pressure within southern stream will open as it lifts from
the Rio Grande Valley today to the Tennessee Valley midday Tuesday.
The separation of this system from main northern stream energy now
digging into the Dakotas will limit the degree of phasing between
the streams, so while abundant moisture will be pulled northeast
from the Gulf of Mexico over the next 24-36 hours as the southern
stream system ejects into the eastern CONUS, much of the rainfall
that results will pass southeast of the forecast area.

That said, 12z model cycle still suggests that weak deformation
associated with this system will brush the southeast portion of the
forecast area on Tuesday afternoon and bring a period of light rain
showers. Inverted troughing between this low pressure and the main
northern stream low well to the northwest will then pivot northeast
through the region Tuesday evening and bring the small chance of
additional scattered light showers to parts of the area.

As southern stream shortwave lifts into the northeast CONUS and
eventually dissipates, deepening upper low over the northern plains
and upper midwest will shift gradually east into the northern Great
Lakes by Wednesday. During the time frame, a full latitude upper
trough intensifies to cover much of North America. This upper level
pattern evolution will usher in the beginnings of a notably colder
period of weather with the first step down occurring Wednesday as
high temperatures only reach the 30s (as compared to lower 40s on
Tuesday).

Slight chance for flurries/light isolated snow showers exists
Thursday into Friday as a series of upper-level disturbances pushes
through the region. Bottom half of the atmosphere remains fairly
saturated throughout Thursday, with 1000-500 mb RH values ranging
between 60 - 80% throughout the day, drying out slightly by late
Friday. The main story will continue to be the advent of cold air,
as westerly winds keep temperatures capped in the upper 20`s
Thursday - Saturday, with a shot as returning to the freezing mark
by Sunday. Next potential for significant precipitation accumulation
returns Sunday into Monday as a weak low from the Central Plains
pushes into the Great Lakes region. Both the GFS and ECMWF vary in
the nature of the thermal profile and placement of the low, so both
the extent and type of precipitation cannot be derived with
confidence. Additional details will be supplemented with future
model runs.

MARINE...

Winds will transition to southeasterly on Tuesday at 15 to 20 knot
as two surface low pressure systems advance into the central United
States for the middle of the week. A cold front will push across the
area Tuesday opening the door for fresh to strong westerlies with
gusts to near-gales over the open waters of Lake Huron. Unsettled
and gusty conditions set in for the remainder of the week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 10 AM Tuesday to 10 PM EST Wednesday FOR
     LHZ441.

     Small Craft Advisory from 10 AM to 10 PM EST Tuesday FOR LHZ442-443.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....99
UPDATE.......99
DISCUSSION...DG/AM
MARINE.......JVC


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



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