Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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740
FXUS63 KDTX 162347
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
647 PM EST Tue Jan 16 2018


.AVIATION...

Elongated ribbon of potential vorticity will settle directly over
southeastern Michigan now through the first few hours of the TAF
period. Center of lake aggregate troughing and center of surface low
pressure over southern Lake Huron basin will be extremely sensitive
to the max in convergence within narrowing and shearing trough axis.
Already seeing signs of the demise for very weak ascent over Lower
Michigan with loss in coverage of light snow activity and rising of
stratocumulus cigs. This trend should continue for the next few
hours before accelerating with drier working in below 6 kft agl. For
this round of tafs will hang onto pessimistic clouds and will
reevaluate observational data this evening, amending as needed.
Still expecting Lake Michigan plume to advect across and will need to
account for that sky fraction. Main forecast item for Wednesday will
be developing, gusty west winds 15 to 25 knots.

/DTW THRESHOLD PROBABILITIES...

* High for cig aob 5kft tonight.

&&

.PREV DISCUSSION...
Issued at 314 PM EST Tue Jan 16 2018

DISCUSSION...

The sfc low which has been nearly stationary over the southern basin
of Lake Huron through the first half of the day will be exiting into
Ontario late this afternoon/evening, dragging an associated sfc
trough axis south across the forecast area. As of 19Z, the region of
enhanced convergence extends from the thumb region into the southern
Saginaw Valley. Northeasterly low level flow from central Lake Huron
has been feeding lake moisture into this region of convergence. This
along with steepening low level lapse rates has led to brief
intervals of one inch per hour snowfall rates. The higher intensity
snow showers will work south this afternoon/evening with the
southward advancing trough/convergence axis. The convergence is
expected to weaken during the evening as the trough pushes into
metro Detroit. This suggests both a lower coverage of snow showers
with weaker intensity across the srn portions of the forecast area
this evening. The brevity of forcing still suggests accums of an
inch or less. A little stronger convergence and better lake moisture
will however support locally higher accums across the thumb region,
possibly two or three inches.

Mid level subsidence will take hold overnight as the elongated mid
level trough axis departs to the eastern Great Lakes. Subtle surface
ridging nudging in behind the departing trough may allow some breaks
in the clouds, supporting min temps down into the upper single
digits above zero. Mid level heights will then build across Lower Mi
on Wednesday. The low level flow will back to the west-southwest
overnight into Wed morning. While subsidence will lower inversion
heights, expect a release of remnant lake effect off Lake Michigan,
resulting in periodic strato cu and possible flurries across the
forecast area on Wednesday. While low level warm air advection will
nudge Wed daytime highs into the 20s, gusty southwest winds hold
wind chill readings in the single digits.

There is reasonably good agreement among the 12Z model guidance in
showing a compact mid level wave traversing the northern Great Lakes
on Thursday. This system will be moisture starved. Lake enhancement
will also largely be confined to the northern Great Lakes as warm air
advection nudges 850mb temps toward +2 C over srn Mi. So a dry
forecast will be maintain with the low level warming nudging daytime
highs into the low 30s.

A dampening upper level ridge will move overhead on Friday as high
pressure over the Southeast US allows return southwesterly flow to
continue streaming milder air into the region. This will bring dry,
"milder" conditions for Friday as highs reach the upper 30s. An
upper level trough pivoting through the Southwest US on Saturday
will induce lee cyclogenesis over the Central Plains over the
weekend. Ahead of this developing low pressure system, southerly
flow will increase through the weekend allowing temperatures to rise
further into the 40s along with moisture both Saturday and Sunday.
The uptick in moisture will bring increasing clouds and showers late
Saturday into Sunday. Model guidance then continues to track the
Central Plains low pressure system west of Lower Michigan on Monday.
This scenario would keep Southeast Michigan in the warm sector with
a period of rain while temperatures remain above freezing late
Sunday into Monday.

MARINE...

Strong and unstable southwest flow will develop as high pressure
shifts south of the area on Wednesday. Gusts to marginal gales are
probable over most Lake Huron, including Saginaw Bay and the
northern nearshore waters of the Thumb. Gusts to strong gales are
anticipated over the central open waters. Gale warnings are in
effect for the entire central corridor of the lake...including outer
Saginaw Bay. Episodes of fresh to strong southwest flow will be
common for the remainder of the week while gust potential diminishes
owing to increasingly warm stable fetch.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 10 AM to 10 PM EST Wednesday for LHZ362-363-421-
     441-462.

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

$$

AVIATION.....CB
DISCUSSION...SC/JD
MARINE.......JVC


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