Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221716
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1216 PM EST Wed Feb 22 2017


.AVIATION...

Complex fog/stratus pattern continues today and will through the
night as visibilities range from 1/2 to plus 6 across lower Michigan
and southward along with ceilings from a few hundred to clear.  Main
pattern is a southwest flow of a very moist boundary layer ahead of
an approaching weak cold front.  This front will sweep through
southeast Michigan in about the 09-14z time frame Thursday.  Until
the passage of the front the aviation community will have to deal
with moving areas of visibilities and stratus with ceilings ranging
from ifr to vfr this afternoon becoming more lifr to mvfr tonight.
Narrow band of light showers are expected along the cold front with
best coverage over the northern taf sites closer to the stronger
upper forcing. After frontal passage winds will veer to the northwest
with drier boundary layer air that will scour out any fog and low
stratus starting late Thursday morning.

For DTW...metro has been right on the eastern edge of the more
expansive stratus and fog shield.  Diurnal heating and mixing should
push visibilities to 6sm or greater for a while this afternoon with
ceilings oscillating 2500 to 3500 but could briefly get something
lower. Winds will remain around 10kts from the southwest.  After
sunset, nocturnal cooling will likely leave to a more stratus
development and lowering of ceilings and visibilities especially
after 06z. There will me a small chance for light shower activity
around 12z with a frontal passage. After, drier northwest flow will
scour out any fog and low stratus.

//DTW THRESHOLD PROBABILITIES...

* Moderate in ceilings at or below 5000 ft through the TAF period.
  low for ceilings 200 ft late tonight/early Thursday morning
* moderate for visibilities 1/2 mile late tonight/early Thursday
  morning.

&&

.PREV DISCUSSION...
Issued at 539 AM EST Wed Feb 22 2017

UPDATE...

Over the past hour there has been a rapid expansion of stratus across
much of the southern sections of the forecast area. There has also
been an increase in the low level winds. These factors have caused
substantial improvements to the visibilities. The exception is across
the Tri Cities and thumb region where the IR imagery suggest the fog
is thicker. The stratus has also failed to lift that far north. Thus
the dense fog advisory will be cancelled for all but the northern
two tiers of counties this morning.

PREV DISCUSSION...
Issued at 256 AM EST Wed Feb 22 2017

DISCUSSION...

Low stratus, dense fog, and patchy drizzle have persisted through
this morning beneath a stout surface-based inversion. The primary
forecast issue in the short term is rate of burn-off of this low
moisture and subsequent temperature response. Spread amongst the 00z
guidance seems to encompass all outcomes, ranging from early
clearing and highs approaching 70 to persist stratus well into
tonight and highs struggling to 60 in spots. Worth noting that low
clouds over Wisconsin yesterday morning completely eroded by 18z
with unfettered insolation. Clouds streaming off the closed low to
the south may impede burnoff through the morning over the far SE
CWA, but suspect that late Feb insolation and steadily increasing
southwest gradient will be too much for stratus to overcome given
the lack of ongoing maintenance. The official forecast retains
overcast conditions through 15z with a steady burn-off thereafter -
quickest across the north. Mid 60s will be easily reachable for any
locations that clear out. Based on the current stratus forecast,
elected to move forward with highs centered around the mid 60s. All-
time February records are still on the edge of the uncertainty
envelope. Refer to the climate section for this and additional
climate record information.

Expect something close to a repeat performance tonight as low
pressure lifts across the straits. Inversion will strengthen
coincident with increasing warm advection aloft. Steadily increasing
surface gradient will likely force more of a stratus, rather than
fog, component. WAA, mixed boundary layer, and extensive low cloud
will keep lows potentially in the low 50s southeast of the glacial
ridge, about 15 to 18 degrees warmer than average high temperature
values. As the cold front settles south, high temperatures on
Thursday will settle in the 50s, shy of record values in the low
60s. Cooler NE flow will allow diurnal cooling into the 30s through
the night Thursday.

Despite some continued difficulty amongst the NWP in handling the
large scale trough interaction with smaller scale features over the
east Pac and Canada, consensus remains in a low tracking from around
Kansas City to Alpena on Friday. Antecedent longwave amplification
will allow a couple jet to emerge Thursday night, igniting
widespread stratiform rain along and north of the surface warm front
to our south. As deep layer isentropic ascent up the warm frontal
slope intensifies with the strengthening LLJ, embedded thunder will
be possible by late Thursday night into early Friday morning.

High temperature and severe potential on Friday and Friday evening
will be dictated by the surface low track/strength and degree of
clearing in the warm sector. At this time, the GFS/GEM appear to be
suffering from convective feedback issues while the EC/NAM agree on
an aggressive northward push of the warm front, precip moving well
north, and highs approaching 70 degrees south of 8 Mile (see climate
section again). A line of thunderstorms seems to be more or less a
sure bet Friday night simply given the extremely strong dynamic
forcing that will be present in the warm sector. A few hundred j/kg
of elevated CAPE and 50+kts bulk shear will support at least a small
hail threat. Nocturnal timing will not be favorable for much in the
way of surface-based convection, but deep and strong unidirectional
flow preclude ruling out sub-severe straight line winds.

MARINE...

Light to modest southerly winds are advecting very moist air atop
the cold lake surface, resulting in dense marine fog across Lake
Huron. Expectations are for strengthening southerly flow during the
course of the day to push the fog toward the northern half of the
lake late today into tonight. 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.

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 again a chance for some gale force gusts.

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.

     Dense Fog Advisory until 4 PM EST this afternoon for LHZ421-422.

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

$$

AVIATION.....DRC
UPDATE.......SC
DISCUSSION...JVC
MARINE.......SC
CLIMATE......JVC


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