Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 252313
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
713 PM EDT Sat Mar 25 2017


.AVIATION...

Northeast to east flow north of frontal boundary over the Ohio
Valley will maintain IFR conditions overnight in general. Rain
shower activity should be minimal and most likely KFNT/KMBS after
00z. MVFR/LIFR fog will most likely develop overnight within this
moist low level environment. Low pressure will wobble into the
region on Sunday and pull the aforementioned front slowly north.
Shower activity will increase from mid/late morning into the
afternoon as daytime heating leads to some low level instability
which will interact the low level forcing/upper support of the
system. Ceilings/visibility should slowly increase with this
transition to showery weather.

For DTW...Expect VFR cigs tonight (perhaps occasional MVFR this
evening) with some degree of fog developing within cool, moist
easterly flow. Low pressure will bring showers by midday with cigs
trending towards MVFR with this activity. Winds will veer from ENE
this evening to SE late tonight into Sunday to S late in the day as
this low pulls a frontal boundary north through the area.


//DTW THRESHOLD PROBABILITIES...

* High for cigs below 5000 feet much of the forecast.

* Low for cigs/vsby aob 200 FT or 1/2SM late tonight.

&&

.PREV DISCUSSION...
Issued at 307 PM EDT Sat Mar 25 2017

DISCUSSION...

Closed mid level circulation anchored over the mid Mississippi
valley this afternoon will only slowly drift to the east over the
next 12 hours.  Steady northward expansion of upper ridging
immediately downstream will become an increasing influence on local
conditions through tonight.  Existing axis of mid level frontal
forcing continues to drift northward across the I-69 corridor and
points northward.  While ascent tied to this feature will continue
to diminish with time as upper jet support pulls to the east, some
persistence to light shower development will likely continue into
the evening before greater stability takes hold.  Additional pockets
of moisture tied to weak shortwave energy streaming out of the main
circulation may also skirt close to the western CWA border /highway
23 corridor/.  However, model guidance suggests greater large scale
forcing associated with the upper low will largely remain west of
the region through the overnight hours.  This will limit the
prospects for additional rainfall prior to daybreak, particularly
south of the M-59 corridor.  Just enough uncertainty yet given our
downstream position to refrain from removing pops completely, but
will lean drier overall for the tonight period.  Gradual warming
across the lowest 850 mb will limit the nocturnal cooling response
tonight. Temperatures may actually drift upward by the early morning
period. This will cap lows within the 35 to 40 degree range.

Eastern flank of the deep layer ascent/diffluence associated with
the upper circulation will begin to expand eastward across lower
Michigan on Sunday.  This positioning will favor a higher
probability for shower development with westward extent during the
daylight period, perhaps leaving the eastern thumb region dry until
very late.  Modest low level warming will gradually lift
temperatures into the 50s through the day.  The thermal response
carries some dependence on coverage of showers, leaving some doubt
as to the overall response.  12z NAM seemingly too cold relative to
other guidance and will continue to lean more optimistically,
particularly during the afternoon as low level flow backs.
Diminishing stability will leave the potential for embedded thunder,
but overall limiting in support for potentially greater convective
organization.  Circulation and accompanying mid level cold pool
/-20C at 500 mb/ projected to pivot across the region early Sunday
night.  Period of enhanced convergence capitalizing on diminishing
stability will likely refocus a more concentrated area of convection
along the eastern face of the inbound surface wave and associated
warm front sometime late afternoon/early evening.  Freezing levels
at 8000 ft or less, so possibility for hail with any greater
convective depth.

Associated cva/deformation with the passage of a weakening
circulation overhead will sustain a disorganized coverage of showers
through early Monday morning.  Ample residual low level moisture
with minor/brief cooling at 850-925 mb with the trailing cold
frontal passage will retain a high coverage of cloud cover on
Monday.  Surface conditions will change little with retention of a
west-southwest flow.  Temperatures will hold on the warmer side of
normal, with readings of at least mid-upper 50s.

Progressive lower amplitude wave remains projected to translate from
the central plains through the lower Ohio valley early next week.
Lower Michigan remains positioned along the immediate northern
extent of the next emerging corridor of mid level warm air advection
tied to this feature.  Upper jet support is lacking with this
system, so a stronger mid level fgen response appears unlikely.
There will be a window for moderate isentropic ascent and the
trailing deformation to lift across the border Monday night/Tuesday
morning as the wave slips across the Ohio valley.  The outcome would
be a relatively quick shot, but of potentially moderate intensity
rainfall focused south of the M-59 corridor.  Main point of
uncertainty appears to be exact location, as model guidance wavers
on the latitudinal positioning of the northern edge.

A weak surface low will continue to bring the slight chance for
light rain showers, focused south of I-69 throughout Tuesday
morning, before exiting northeast into New England. Cloud cover will
gradually clear throughout Tuesday afternoon and into Wednesday, as
a large surface high pressure system starts to edge into the Great
Lakes region. Dry conditions and plenty of sunshine are expected for
the mid-week period, as temperatures remain seasonal with highs in
the lower 50s.

Models are still trying to pick-up on a developing low pressure
system that has the potential to move across Michigan Friday into
Saturday, bringing additional rainfall to the region. Much like
yesterday`s 12Z model suites, the GFS keeps the track of the low
well south of the Great Lakes, moving from Texas and into Tennessee
Thursday into early Friday. Both the GEM and ECMWF runs display a
more northerly track, running the low from TX by Wednesday night,
moving over MI by Friday night, which would bring a widespread
precipitation shield across MI. Additionally, internal model blends
are calling for at or slightly above freezing temperatures early
Friday morning, which would bring the potential for a rain/snow mix.
H owever, may have to up temperature values in the coming days as
ECMWF and GEM models keep conditions mild, with 850 C temperatures
peaking up to 10C through Friday morning.

MARINE...

Northeast winds gusting to around 25 knots over Central Lake Huron
extending into Saginaw Bay this afternoon, but with high pressure
over Eastern Canada retreating to the East, winds will become more
east-southeast Tonight into Tomorrow, with the higher winds gusting
around 25 knots confined to the northern third of Lake Huron. Winds
will become light everywhere by Sunday Night as weakening low
pressure tracks into the Central Great Lakes. Light winds will
persist early next week, but prolonged northerly winds over Lake
Huron could promote waves building to near 4 feet in the southern
basin.

HYDROLOGY...

Wide ranging rainfall totals from last night and todays activity,
with around 1 inch along the I-69 corridor, to very little rainfall
toward the Ohio Border. It looks to become mainly dry Tonight before
showers return Tomorrow, continuing into the evening hours before
tapering off Sunday Night. Additional rainfall of a quarter of an
inch to half inch expected, with isolated thunderstorms potentially
leading to locally higher amounts. Either way, no flooding is
anticipated.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 1 AM EDT Sunday for LHZ421-422-441.

     Small Craft Advisory until 8 PM EDT this evening for LHZ442.

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

$$

AVIATION.....DG
DISCUSSION...MR/AM
MARINE.......SF
HYDROLOGY....SF


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