Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 072021
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
321 PM EST Wed Dec 7 2016

.DISCUSSION...

The stacked upper level low currently over Ontario, will continue to
trek off to the northeast and into Quebec by Thursday.  This will
keep the area in an active pattern through the end of the week with
snow showers possible Thursday into Friday before better potential
for snow moves in late in the upcoming weekend.

The rest of the day today will remain dry with winds out of the
southwest slowly veering to the west through Thursday night. Clouds
diminished this morning leading to partly sunny skies which will
continue into the overnight hours before clouds thicken up with
another boundary coming across tomorrow. Gusty winds will also
continue into tomorrow as the pressure gradient tightens. With the
area positioned in the trough and westerly winds in place on
Thursday, some lake effect bands could possibly reach into Southeast
Michigan during the day. Better chances for snow, however, will
remain over on the west side of the state. At this point, only
expecting light accumulations of snow with the flurries and light
snow showers over Southeast Michigan as colder air encompasses the
region.

Things start to calm down on Friday as the pressure gradient
slackens and any snow shower activity starts to lessen.  By Friday
night, ridging moving in will bring some drier conditions back for a
brief period.  As far as temperatures, expect cold temperatures to
continue into the weekend as 850 mb temps stay in the -10C to -15C
range.

Westerly winds throughout Saturday morning and afternoon will bring
the slight chance to see lake effect flurries, with minimal
accumulations expected. The main story for the extended forecast
continues to be the developing low pressure system over the Central
Plains, expected to push into the Great Lakes region Sunday into
Monday. Accumulating snow is likely, with the big question being
timing of the snow and how much we`ll see. Latest 12Z ECMWF model
run has some considerable differences from its 00Z suite. Placement
of low pressure is now tracking further north, clipping SE MI
throughout Monday. Additionally, new ECMWF exhibits a stronger and
strengthening low Sunday into Monday. As a result, QPF fields are
significantly higher, bringing the bulk of the precipitation Sunday
night into Monday morning. GFS and GEM 12Z suites bring the bulk of
the snow Saturday night into Sunday. ECMWF also exhibits significant
differences in the temperature field with respect to height. The
intensification and placement of the low in the ECMWF allows
temperatures to straddle the 0 C isotherm for our southern counties
Monday morning, which would influence precipitation type.

Main message at this point, expect snow as late as Saturday
night, with the chance continuing as far out into Monday. However,
with the lack of model convergence, especially with the new 12Z
ECMWF model suite, exact timing and accurate snowfall estimates
cannot be made at this time. With the low moving out late Monday,
temperatures will not break the freezing mark for daytime highs,
and will in fact cool down even further, with temperatures
projected to sit in the lower 20s for a high on Wednesday.

&&

.MARINE...

Gusts to low end gales will ease this evening allowing the gale
warning to expire on schedule. However...gusty southwest winds will
continue to gust to near-gales through the day Thursday. A cold
front will track from northern Lake Huron Thursday afternoon to Lake
Erie Thursday night. Frontal passage will be accompanied by a wind
shift to the northwest in addition to an increase in lake effect
snow squalls. Building high pressure south of the Great Lakes will
allow moderate winds to take hold for the end of the week before the
arrival of the next low Sunday into Monday.

&&

.PREV DISCUSSION...
Issued at 1235 PM EST Wed Dec 7 2016

AVIATION...

Moisture mixed out early giving way to scattered coverage from KPTK
north. Lake enhanced moisture field warrant carrying scattered
through the day with brief CIGS not out of the question. Confidence
in cigs is low given the tendency for guidance to overestimate
moisture upstream...left all locations scattered today based on
observational evidence. Westerly flow will put PTK/FNT downstream of
Lake Michigan tonight where there is an increased probability of bkn
MVFR. Preferred guidance does not yield a strong signal for ceilings
in the Detroit area until the 8-12z period. Stout westerly wind will
persist through today with gusts continuing across the north.
Arrival of colder air and a stronger gradient will force gusts to
pick up around Detroit during the overnight hours.

KDTW...Brief broken ceilings will be possible this evening as weak
upper energy slides across the area 23-04z. Confidence in ceiling
development during this time is low. Included mention of prevailing
-SN with no vsby limitation Thursday morning given liklihood of
flurries based on favorable thermodynamic profiles. Transition to -
SHSN with arrival of upper trough bringing lake enhanced snow across
the state.

//DTW Threshold Probabilities...

* Low for cigs aob 5kft 23-04z. High after 10z.

* High for ptype of SN


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 10 PM EST this evening FOR LHZ363-421-441-462.

     Small Craft Advisory until 10 PM EST Thursday FOR LHZ422-442-443.

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

$$

DISCUSSION...SS/AM
MARINE.......JVC
AVIATION.....JVC


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



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