Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 142355
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
655 PM EST Wed Feb 14 2018

.AVIATION...

Deep low level moisture plume will steadily lift north into the
region early tonight. Rapid deterioration of conditions expected
from south to north over the next several hours. Recent
observational trends upstream lend greater confidence for LIFR
conditions to eventually emerge in low clouds and/or fog most
locations by early morning. Dense fog development carries less
certainty, with low stratus potentially becoming the predominant
restriction. Confidence for visibility of 1/2 mile or less
at any one location remains low at this time. Model guidance
sustains an extremely moist environment across the lowest 1000 ft
well into Thursday. Plausible some form of low stratus holds tough
during the daylight period, although shrinking moisture depth may
leave this moist layer vulnerable to erosion and bring rapidly
improving conditions by late morning.

For DTW...Rapid reduction of ceilings forthcoming within the next
couple of hours, bases expected to settle into the 300-400ft range
overnight. An accompanying component of fog expected as well. There
is the potential for visibility to fall below 1/2 mile during the
early morning period, although confidence in occurrence remains
quite low.

/DTW THRESHOLD PROBABILITIES...

* Low for cigs/vsby to fall below 200 ft and/or 1/2SM

* High for ceiling below 5000 ft through Thursday morning, then
  medium Thursday afternoon.

&&

.PREV DISCUSSION...
Issued at 351 PM EST Wed Feb 14 2018

DISCUSSION...

Full insolation and mixed near surface environment facilitated by
increased gradient flow has resulted in very pleasant weather today
across southeastern Michigan. Surface temperatures this afternoon
have easily climbed into the lower to middle 40s for a majority of
the area, which are roughly 10 degrees above normal for this time of
the year.

Lower tropospheric surge of moisture that was dislodged from the
Gulf of Mexico yesterday is making a run directly at southeastern
Michigan. Timing offered by the previous forecast discussion remains
on target and is expected to begin lifting across the border and
into southern sections of the forecast area by 00Z this evening.
Overall activity is tied to the lead edge of a prior nocturnal jet
cycle that will only become accentuated along the southeast flank
of a midlevel cyclonic circulation over portions of WI/IL and Lake
Michigan. Deterministic solutions have been onto this moisture surge
for days, resolving splotchy qpf for Lower Michigan for the duration
of tonight. Hi resolution models are now onboard with aggressive
resolution of the surface moisture in latest HRRR solutions. Always
difficult to buy all in potential erroneous boundary layer/over
saturated data, but observational evidence upstream shows some vsbys
of less than 1SM with some light precipitation reports. Still not
completely convinced dense fog will develop over the snowpack here
in southeastern Michigan tonight but confidence on this bearish idea
is very low. In fact, did include areas of drizzle and fog in the
public forecast. Future shifts can monitor trends. No moisture or
dynamics supportive for precipitation outside of drizzle.

Early Thursday, theta e plan view progs support the passage of a low
to midlevel cold front that will very efficiently support dry air
advection in the 1000-2000 ft agl layer. This should be enough to
shut down any lingering drizzle into the early Thursday period.
Clouds will likely support temperatures that are cooler than today
for a good chunk of the day until late day warm advection takes a
hold of then. Highs probably wont make it in until Thursday evening.

Late Thursday becomes active for much of Lower Michigan as the next
frontal wave passes through the Ohio River Valley. Highest QPF will
remain well south, but models show a sizable area getting impacted
by overrunning precipitation. Somewhat noisy on which level in the
elevated frontal slope will activate, with latest guidance
suggesting some activity occurring along or north of I 69. Very well
developed 800-600mb frontal slope will be in place directly over the
heart of the cwa which will lead to low static stability in the
midlevels. Fair question to bring up possibility for some thunder
particularly during the 21-02Z timeframe south of I 96. Will not add
an explicit mention at this time with neutral lapse rate structure.
However, strong model consensus exists for convective rain showers
in the 21-02Z within zone of favorable low level deformation. Bulk
of the liquid amounts exceeding .25 inch will occur in that window.
Precipitation to occur ahead of the cold front, which will support
warm precipitation types.

Aggressive surface ridging Friday will lead to dry weather, a modest
northwest breeze, and temperatures ranging in the upper 20s to lower
30s.

High pressure exiting the region on Saturday will bring continued
dry conditions through much of the day as highs top out in the low
30s. A quick-moving upper wave accompanying a jet streak surging
across the northern US will bring a brief chance for snow showers
Saturday evening. An amplifying upper level ridge centered along the
East Coast will then build into the region on Sunday lifting the jet
northward into southern Canada and bringing quiet weather to end the
weekend as highs approach 40.

An active stretch of weather then begins early next week as the
region remains between an amplified ridge along the East Coast and
trough over the Western US. Low pressure lifting across the region
on Monday will act to strengthen a frontal boundary to the west of
SE Michigan while increasing deep southerly flow pulls Gulf moisture
northward over the region. Model guidance is coming into better
agreement that the frontal boundary will remain just west of SE
Michigan while a series of low pressure systems tracking along it
bring a prolonged period of rainfall through Tuesday.

MARINE...

Moderate southwest flow today will begin to decrease into the
evening as a surge of moisture northward brings drizzle and fog into
the Great Lakes region. Milder air will result in more stable
conditions over the lakes and thus winds will be limited to 25 knots
or less.  A cold front will drop southward Thursday night and will
result in some stronger northwest winds. The colder air will allow
more unstable conditions and the potential for winds to reach gales
for a short period of time. Anticipate the duration to be short
enough to not issue any Gale Watches at this time. Gusts mainly
around 30 knots will be more likely Thursday night early Friday
morning before a high pressure arrives by Friday afternoon and
brings calmer conditions.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....MR
DISCUSSION...CB/JD
MARINE.......AA

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



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