Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 230450
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1150 PM EST Wed Feb 22 2017


.AVIATION...

Stratus has had trouble consolidating in southerly gradient flow
this evening, but current trends as of 04z-05z suggest coverage is
slowly increasing. Better area of stratus over northern lower MI
will settle through area with frontal boundary overnight so will
maintain a trend to MVFR cigs and MVFR/IFR vsbys as low level into
the 12z-14z period. Will remove light shower mention with fropa from
all but KMBS as upper support strips away to the east before front
makes much progress into area. Conditions will improve back to VFR
on Thursday, but return to MVFR/IFR late in the forecast as area of
forcing in advance of next developing system to the west brings an
expand area of rain towards 06z Thursday evening.

For DTW...Current MVFR to lower VFR stratus should slowly expand
overnight and lower as moisture pooled along frontal boundary sags
south into terminal late. After VFR conditions midday Thursday into
Thursday afternoon, initial lift/moisture from next system will then
bring expanding MVFR cigs Thursday evening IFR cigs/vsbys in rain
and fog after 06z.

//DTW THRESHOLD PROBABILITIES...

* Medium in ceilings at or below 5000 feet into Thursday morning.

* High in ceilings at or below 5000 feet after 06z Thursday evening.

&&

.PREV DISCUSSION...
Issued at 333 PM EST Wed Feb 22 2017

DISCUSSION...

Seasonably mild and moist environment firmly entrenched across SE
Michigan late this afternoon.  Extensive component of stratus
emmersed within the predominant and strengthening low level
southwest gradient proving the only real hinderance in blowing past
record level temperature readings. Regardless, now sitting at
roughly 25 degrees above normal. For record temperatures through
Friday...refer to the climate section below.

Tonight...Progressive low amplitude northern stream wave to
translate across the northern great lakes late tonight/early
Thursday.  Maintenance of a moderately mixed southwest gradient into
the existing moist pre-frontal profile will continue to support a
high coverage of low stratus overnight. Gradient likely minimizes
the fog component relative to last night. Window for possible shower
development after midnight under modest pre-frontal convergence and
a glancing shot of cva /tri-cities & thumb/.  Rumble of thunder not
out of the question, given a weakly unstable mid level environment.
Retention of very mild conditions with fropa not expected until mid-
late morning Tuesday.  This will favor lows generally holding in the
50s most locales.

Thursday...Shallow cold air advection commences Thursday, the
advective process most notable across the thumb as flow veers to
northerly and taps into the cold lake Huron waters.  Slow removal of
the existing low stratus under this process, with subsequent diurnal
cu development favoring a mostly cloudy condition.  This points to a
somewhat muted diurnal temperature response with a broader north to
south thermal gradient, but with temperatures still residing well
above normal thanks to the mild morning start and weakish cold air
advection.

Thursday night/Friday morning...Strong height falls lifting into the
central plains to elicit a classic downstream response, with an
extensive corridor of warm air advection tied to deepening southwest
flow emerging immediately downstream of strong southern plains
cyclogenesis. Developing isentropic ascent working across the
northward advancing warm frontal slope will subsequently translate
into an increasing coverage of rain from the Ohio valley into lower
Michigan overnight through Friday morning.  Diminishing stability
under strong theta-e advection will yield an elevated thunder
component to the heaviest cells.  Cold low level easterly flow
beneath this ascent will allow temperatures to dip down into the mid
30s north to lower 40s south.

Friday afternoon/Friday night...Surface low projected to slowly
weaken as it lifts northeast from near Kansas City early Friday
morning to northern lake Huron Saturday morning.  While the
corresponding forecast evolution at the larger scale remains largely
static, less definition to smaller scale details will continue to
cast the usual uncertainty that comes with defining cold season
severe weather potential.  This uncertainty derives from
establishing the speed and degree to which the warm sector can work
into southeast Michigan. 12z NAM maintains a slow northward
migration of the surface warm front during the day, suggesting the
surface reflection does not make a concerted northward push until
late Friday into Friday evening. A reasonable expectation given the
high likelihood of early day showers and lingering low stratus under
easterly flow.  A late upward push in temperatures and corresponding
infusion of higher dewpoints /50s/ thereafter, but within an
environment absent of meaningful forcing prior to 00z aside from the
warm front.  Worth noting that 3 km NAM output does hint at possible
isolated development on the surface warm front/thermal gradient,
owing to an aggressive push of mid 50s dewpoints and corresponding
increase in MLCAPE - >1000 J/KG - at the frontal interface. Possible
this solution is too aggressive with the immediate warm sector
destabiliztion, but always a consideration.

Linear arc of forcing/convergence working into a moderately
destabilizing thermodynamic profile likely translates into a line or
bands of convection over eastern IL/IN Friday evening.  Rapid
expansion of this activity across the northern Ohio valley and lower
Michigan overnight.  Quality of the low level thermodynamic profile
comes into question locally, with some degree of stability
potentially in place across the lowest 2-3k ft. Steep mid level
lapse rates backed by strong dynamic forcing and ample deep layer
shear will support organized elevated convection, which could prove
sufficient in generating a greater wind gust risk despite
questionable near surface parameters /particularly closer to the
Ohio Border/.

MARINE...
Warm and moist southwesterly flow over the colder waters is
producing ares of low stratus and fog,  mostly over the northern
half of Lake Huron.  Low pressure will slide across the straits
region late tonight before exiting northeast of Lake Huron by
daybreak Thursday. The result will be a veering of the winds to the
northwest, bringing drier air across the lake and thereby scouring
out lingering fog.  Some light rain showers may accompany this system

Deepening low pressure is forecast to move from Iowa to northern
Michigan on Friday. Easterly winds will increase across Lake Huron
in response. There is fairly high probability that gusts across the
northern and central portions of the lake will reach 30 knots, with
a chance for some gale force wind gusts. Gusty winds will then ensue
Friday night into Saturday as the system lifts northeast of the
region, with a better chance for gale force gusts with a longer
duration.

CLIMATE...

All-Time February high temperature records
DTW...70 (1999)
FNT...68 (1999)
MBS...67 (1930)

Record high temperatures for February 22

DTW...65 (1930)
FNT...65 (1930)
MBS...67 (1930)

Record high minimum temperatures for February 23
DTW...43 (1930)
FNT...47 (2000)
MBS...42 (1930)

Record high temperatures for February 24
DTW...59 (1976)
FNT...57 (2002)
MBS...60 (1930)

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Dense Fog Advisory until 7 AM EST Thursday for LHZ361>363.

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

$$

AVIATION.....DG
DISCUSSION...MR
MARINE.......DRC
CLIMATE......JVC


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