Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 190445
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1145 PM EST Sun Feb 18 2018

.AVIATION...

Dry low level conditions will hold firm overnight period. This will
sustain plenty of clear sky across the lowest 10 kft into the early
morning period. Winds remain light southeasterly tonight, leaving a
favorable environment for low level wind shear to develop as
southwest winds strengthen across the 2000 ft level. A strong surge
of low level moisture will then accompany a warm front into the
region on Monday. This will lead to a progressive deterioration of
conditions throughout the daylight period. Increasing potential for
an extended window of IFR/LIFR in light rain/drizzle Monday
afternoon and evening as the warm front struggles to lift north
across the region. A localized region of dense fog plausible in the
vicinity of the frontal boundary, but timing and location carries
enough uncertainty to preclude a specific mention. Greatest
opportunity may center post-sunset Monday evening as near surface
saturation increases as nocturnal cooling commences.

For DTW...Clear skies across the lowest 5000 ft expected through mid
morning /11z-12z/. Rapid reduction in cigs thereafter, with
increasing potential for LIFR stratus for the afternoon and early
evening period. A period of dense fog plausible should warm
front linger in the vicinity and struggle to lift north. Confidence
in occurrence of 1/2 to 1/4 mile vsby still too uncertain at this
stage to include a defined mention in TAF.

/DTW THRESHOLD PROBABILITIES...

* High in ceilings dropping below 5000 ft Monday morning /12z-13z/
  and remaining below thereafter.

* High for ptype as rain Monday.

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

* Very Low in occurrence of embedded thunderstorms late Monday.

&&

.PREV DISCUSSION...
Issued at 314 PM EST Sun Feb 18 2018

DISCUSSION...

A substantial amplification in the long wave pattern will occur
across NOAM over the next couple of days. The upper wave now rotating
across the Pacific Northwest will deepen as it dives into the
southern Rockies by Tuesday, carving out a high amplitude trough
across the wrn US. Meanwhile, a mid level ridge will strengthen off
the coast of the Carolinas over the next couple of days. A slow
moving frontal boundary will lie between these two systems and will
impact the Great Lakes region for the next two to three days. Return
flow around the mid level anticyclone off the Carolina coast will
sustain a steady transport of gulf moisture into the Great Lakes
region. Precipitable water values are forecast to rise toward 1.4
inches across Se Mi by Tuesday, extremely high for mid February.
Persistent upper jet support will sustain good frontal forcing
across the low to mid tropospheric front over the Great Lakes region
Mon into Wed. This combined with the significant moisture transport
and probable mid level short wave impulses will support periods of
rain Mon into Wed.

Remnant mid level dry air will keep Se Mi precip free through
tonight. The lead edge of the low-mid level moisture plume will then
lift into the Mi/Oh border early Mon morning. Strong low level
southwest flow (925-850 winds of 50-70 knots) will primarily force
the better isentropic ascent south of the state line through the
first half of the day Monday. Nonetheless, isentropic upglide
farther up the frontal slope should still support widespread rain
across metro Detroit and Ann Arbor. The low level flow will then
back slightly Mon afternoon/evening, allowing the moist axis and
ribbon of good isentropic ascent to make a steady northward push
across srn Mi. This will support widespread rain across the
remainder of the forecast area by late Mon afternoon.

A sfc warm front will develop across nrn IN/OH Mon morning. This
front will attempt to lift north into Se Mi Mon afternoon. However,
strong high pressure will expand across nrn Ontario Mon afternoon,
leading to the development of a light northeast wind component off
Lake Huron. This will result in an increasing thermal gradient
across the warm front. Current model solutions do not bring the
front into the I-94 corridor until late Mon afternoon/evening where
temps will experience a late day surge into the 50s. North of the
front, temps will likely hold in the 30s and 40s. A sfc wave
forecast to lift into the wrn Great Lakes late Mon night and Tuesday
will help drive the warm front farther north into Se Mi. Recent model
solutions suggest the front may have difficulty clearing the Tri
Cities and northern thumb region Tuesday, which may keep them
significantly cooler than the rest of the forecast area. Conditions
in the warm sector however will be characterized by dewpoints into
the upper 50s and temps well into the 60s. As the front lifts north
Mon night/Tues, the high degree of sfc moisture is likely to support
a period of fog. If that front fails to clear the Saginaw Valley and
thumb region, Tuesday may have considerable fog across the far north.

Ample moisture, weak elevated instability and persistent low level
frontal forcing with potential short wave influences will support
periods of showers (with a few thunderstorms) Tues and Tues night.
The frontal boundary will drift to the east on Wed as the mid level
ridge gets suppressed. Persistent mid level frontal forcing may
however sustain showers well into Wed afternoon. Overall, total
model QPF from Mon through Wed remains in the 1 to 3 inch range,
with the GFS remaining on the higher end of model QPF. If elevated
convection is a little greater, there is certainly the potential for
some over achievement. Even though this rainfall will span three
days and there is not too much water in the remaining snowpack, this
rain/snowmelt over still frozen ground suggests rises in area
rivers/streams are likely.

Expansive high pressure will move in over the region starting
Wednesday night and holding into the overnight hours on Thursday.
Conditions across the area during this time will remain dry as the
high pushes east.  Models then have things turning around and
becoming more active as longwave troughing sets up across the
central and western CONUS.  This allows for some lows to move up
along the flow and bring unsettled conditions to Southeast Michigan.
 As far as temperatures are concerned, it looks like Thursday will
be the coolest day out of the extended period with highs in the
upper 30s.  Otherwise, temperatures look to hover in the 40s to
round out the weekend.

MARINE...

Southerly flow will persist through tonight in the wake of surface
high pressure exiting off to the southeast. Increasing low-level
warm air advection will increase stability over the lakes, keeping
wind gusts generally around 25 knots, although a few sporadic gusts
to 30 knots over the open waters of northern Lake Huron will be
possible. A slow-moving frontal boundary will approach and stall in
vicinity of the region Monday and remain in place through much of
Wednesday, with several waves of low pressure riding up along the
front. There continues to remain uncertainty as to the exact
placement of the frontal boundary, which will have implications on
both wind speed and direction over the local waters. Depending on
where the front eventually sets up, brisk southwesterly flow will
prevail to the south, with east/northeasterly flow north of the
front. Periods of rain will accompany the frontal boundary, along
with potential thunderstorms Monday and especially Tuesday.

HYDROLOGY...

A slow-moving frontal boundary will approach and stall across the
region Monday through Wednesday, with several waves of low pressure
riding along the front during this time. Abundant moisture and very
mild temperatures will accompany the frontal boundary leading to a
complete melting of any remaining snowpack. Several periods of rain
will accompany this front as well, with the heaviest rain likely
occurring during the day Tuesday. Thunderstorms will also be
possible during this period as well leading to enhanced rainfall
rates.

Rainfall totals of 1-3 inches will be possible through midweek, with
the potential for even higher amounts in areas of convection and
training rain segments closest to the frontal boundary. Some
uncertainty still remains regarding the exact placement of the
frontal boundary, although confidence is increasing in the highest
rainfall totals occurring from the Saginaw Valley to the M-59
corridor.

With the rainfall falling over a duration of three days, flooding
concerns will be greatest for area rivers and streams, although
ponding of water on roadways and low lying areas will certainly be
possible across much of the region. Significant rises in area rivers
and streams, including potential sharp rises from ice breakup due to
the very mild temperatures will likely occur leading to potential
Minor flood stages being exceeded on a few rivers and streams.

CLIMATE...

Record high temperatures will be possible across much of southeast
Michigan Tuesday. Here is a look at record high temperatures for
Tuesday, February 20th:

Detroit     63 (2016)
Flint       61 (1930)
Saginaw     62 (1930)

With the high moisture content, good chance to break the high
minimum records for February 20th as well:

Detroit     47 (1930)
Flint       45 (1930)
Saginaw     46 (1930)

&&

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

$$

AVIATION.....MR
DISCUSSION...SC/SP
MARINE.......IRL
HYDROLOGY....IRL
CLIMATE......SC


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