Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 191825
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
125 PM EST Mon Feb 19 2018

.AVIATION...

A warm front moving northward through Lower Michigan will maintain
LIFR conditions at all terminals during the afternoon into the
evening. The eventual northward progress of the front and warm sector
will then dictate any improvement during the night through Tuesday
morning. Upstream observations do indicate MVFR/VFR conditions in the
warm sector that is marked by wind shifting to southwest and
becoming gusty. The warm sector is expected to make it into the DTW
area during the evening and possibly as far north as FNT toward
midnight, depending on the strength of low pressure as it moves
across Lake Michigan. The wind will be light SE with LLWS ahead of
the front before stalling somewhere around MBS as the surface low
washes out in favor of new low pressure development to the south. Any
improvement to MVFR will be followed by a trend back down into IFR
as the next batch of rain moves in overnight, along with the usual
nocturnal boundary layer cloud trends. It is still early for the
inclusion of thunder at any of the terminals, while still possible,
this will be better added in later updates.

For DTW... A combination of LIFR visibility and ceiling will improve
to MVFR as a warm front moves north of the terminal. Development of
gusty southwest wind and much milder air will mark the passage of
the front which will last through the night.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less for the entire forecast.

* High for ptype as rain.

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

* Low for thunderstorms impacting terminal tonight.

&&

.PREV DISCUSSION...
Issued at 1057 AM EST Mon Feb 19 2018

UPDATE...
Not a whole lot of change to the forecast at this time. With the
moisture entering the area, there are some areas that may experience
some fog that may reduce visibility to around a mile or less. Have
added some patchy fog into the forecast. Radar trends show organized
rainfall along the warm front at the southern Michigan border moving
northward. Looks like today the radar trends will have the higher
rainfall amounts occur south of the I-69 corridor as the organized
convection lifts through.

PREV DISCUSSION...
Issued at 344 AM EST Mon Feb 19 2018

DISCUSSION...

Flood Watch will be issued with this forecast package for a long
duration rainfall event that will begin this morning and persist
through Wednesday afternoon. Models continue to advertise rainfall
totals area wide of 1-3 inches within that window of time. In
addition the last of the snowpack will melt off putting additional
water into the runoff. Still frozen soil and river, stream and lakes
may lead to flooding concerns.

Longwave pattern will undergo strong amplification today with
deepening trough over the western conus and ridging across the east.
This pattern will hold through much of the week as a train of waves
diving south out of the Alaska region reinforces the deep trough.
Lee cyclogenesis over the plains will result in a region of low
pressure that will take some time to mature as the trough continues
to deepen today, but will strengthen a baroclinic zone extending
from the central plains up through the central Great Lakes and
across Ontario and Quebec. The trough extending into the desert SW
will pick up energy from the southern stream of the jet and provide
for strong low level moisture advection as south westerlies extend
from the Gulf of Mexico up into the Great Lakes. Low level jet will
strengthen to around 50 knots today which will raise pwats quickly
up to around 1.4 inches (consensus of nearly every models). This
boundary will be the focus of several waves both aloft and at the
surface over the next few days utilizing the high moisture content,
leading to the aforementioned widespread rain event.

The event starts early this morning with a lead wave tracking
through the northern Lakes. This lead wave pulled an initial warm
front up through southern MI opening the door for southwesterly warm
air advection and moisture transport into the area. Most of the
moisture at this time is tied up in saturating the mid levels,
although a ripple along the front will bring the first batch of
showers mainly south of M59. The next surface low will not be far
behind, lifting toward southern Lake MI this evening. A stronger
warm front will get pulled northward ahead of this low, nosing into
SE MI this afternoon. Hires models are still suggesting this front
will struggle to make it much past the M59 corridor this evening,
resulting in a strong temperature gradient across the region ranging
from mid 50s near Ohio down to around 40 across the Saginaw Valley.
Strong isentropic ascent and theta e advection up this front will
bring more widespread rainfall to all of SE MI between 18-21Z this
afternoon. Rainfall will continue through the overnight as a piece
of the low lifts from northern IL up through northern lower MI. A
chance of embedded thunder will arrive with the low as showalter
indices drop to, and hover near, zero tonight into Tuesday. Though
severe weather is not expected, this will act to increase rainfall
rates and amounts across those areas.

On Tuesday, a strong vort max will rotate around the longwave
trough, pulling a stronger surface reflection up along the boundary.
This will keep the rain coming with the chance of thunder. This will
also usher in the warmest airmass with surface temps climbing into
the mid 60s. Meanwhile the dewpoints will also climb into the upper
50s lending to the already saturated airmass. The latest low will
then start to advance the boundary as a cold front as strong surface
high building over the plains starts working east. Periods of rain
will continue overnight and into Wednesday until the front can clear
the region to the east Wednesday afternoon.

The strong high will eventually build across the Great Lakes making
for a dry Wednesday evening and overnight. Shortwave ridge aloft
will also arrive for the latter half of the week. Cooler air will
return, with lows falling back into the 20s with highs through the
end of the week down to around the low 40s (which is still above
normal for late Feb). After trying to recharge, models show the
western trough sending the next pair of lows through the region
Friday and Sunday. So chances of precipitation will return although
with a break in between this time.

MARINE...

A warm front will lift north into the region today, stalling near
Saginaw Bay by early this evening. Winds will back to the east to
the north of this front with time, but remain southerly generally
from southern Lake Huron south to western Lake Erie. Wind gusts will
be limited to 20 knots on both sides of this front today. This front
will lift further north into Tuesday as a low pressure system tracks
into the central Great Lakes.

South to southwest winds will increase on Tuesday, but increasingly
stable conditions within this mild flow will cap wind gusts near 25
knots. Winds will veer to the northwest Tuesday night into Wednesday
as the aforementioned low continues into Quebec and a trailing cold
front drops through the area. Instability will increase in this
colder flow, so gusts will approach 30 knots by Wednesday over parts
of Lake Huron. Widespread rainfall with a few thunderstorms can also
be expected from later today on through Tuesday into parts of
Wednesday.

HYDROLOGY...

A warm front will lift slowly north into the area today, stalling
over parts of Michigan through Tuesday night as several waves of low
pressure track along it. Abundant moisture and very mild conditions
will accompany the frontal boundary leading to a complete melting of
any remaining snowpack. Rainfall totals of 1 to 3 inches can be
expected through midweek with the potential for even higher amounts
in areas of convection and training rain segments closest to the
frontal boundary.

While rain chances will be high area-wide through this period,
initial heavy rain potential will focus along and north of the I-69
corridor later today into tonight along this stalled front. The
focus will then shift southward Tuesday into Tuesday night as the
final low pressure system tracks into area along the front and
forces it to the southeast with time.

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...Flood Watch through Wednesday afternoon for MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

Lake Huron...NONE.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
UPDATE.......AA
DISCUSSION...DRK
MARINE.......DG
HYDROLOGY....DG
CLIMATE......DG


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at www.weather.gov/detroit.



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