Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 242259
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
659 PM EDT Fri Mar 24 2017


.AVIATION...

Shallow front will settle south through area this evening. Modest
low level instability within warm sector is helping to fire some
convection along this boundary and hires models suggest this area of
shras and perhaps a tsra will zipper up front into area from KPTK
south. Cigs will generally remain MVFR/lower VFR with this activity.
Broader area of rain/dz/fog will expand northwest to southeast
across the area overnight as moisture continues to overrun the
frontal boundary and large scale forcing increases as low pressure
wobbles into the mid Mississippi Valley. These conditions more or
less persist through Saturday (albeit with slight improvement in the
afternoon) as the low only make very slow progresses into the Great
Lakes. IFR/LIFR conditions will prevail overnight into Saturday.

For DTW...Scattered showers should develop along front early in the
forecast with an outside chance of a tsra. This activity will fester
this evening and then be replaced by a broader area of -ra/br during
the overnight hours as the front settles south of the terminal. Cigs
should remain MVFR/lower VFR much of the evening and then steadily
lower to the cusp of LIFR/IFR late tonight into Saturday morning.
Vsbys will follow suite as well.


//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5000 FT this forecast.

* Low confidence in cigs/vsby aob 200 FT or 1/4SM late tonight into
  early Saturday morning.

* Low risk of a thunderstorm this evening.

&&

.PREV DISCUSSION...
Issued at 353 PM EDT Fri Mar 24 2017

DISCUSSION...

Upper low centered over northern Texas and Oklahoma will slowly
track east through the Plains tonight and Saturday, before beginning
to lift northward towards the Great Lakes. The frontal boundary
currently draped over central Lower Michigan will sink slowly
southward tonight as high pressure builds through Ontario and
Quebec. Main area of precipitation now over Northern Michigan and
Wisconsin will settle southward as well, filling in some as the
convergence along the front tightens in response to right entrance
region forcing from a jet streak passing through the northern Great
Lakes and eastern Canada. The FGEN forcing should provide a fairly
steady rainfall along elevated portions of the frontal boundary
tonight into Saturday, before the jet streak slides east. Main area
of rainfall will sink into the northern portion of the forecast area
this evening and tonight. Another area of rainfall is looking to
develop this evening further south, however, and should affect the
Detroit area.

Forecast models, including all higher-res runs, continue to develop
another area of showers ahead of the surface front this evening, as
it reaches roughly near the M-59 corridor southward. The increase in
activity looks to be in response to low-level convergence increasing
as the front encounters strong southerly flow, and as a modest theta-
e surge makes its way up into Michigan from Illinois/Indiana.
Stability indices continue to hint that thunder may be a possibility,
but forecast soundings show enough of a cap to justify leaving the
mention of thunder out. Rain should then fill in over all of
Southeast Michigan by early Saturday morning as the elevated portion
of the front slides solidly over the area. High coverage/more steady
rain should continue through about mid-day before it likely tapers
to showers as upper jet support is lost. Showers will then continue
through Saturday night and Sunday as the upper low lifts northward
and pushes the front back northward into the area. Activity on
Sunday should be more convective in nature, with a few thunderstorms
even possible, as the upper low and associated cold pool work
across.

Clearing and mixing into very warm air aloft has pushed temperatures
into the upper 60s to low 70s this afternoon on the south side of
the warm front. Temperatures tonight will show wide variation as the
front slowly slides through the area, dropping into the mid 30s for
the northern portion of the area and the upper 40s near the Ohio
border. Not much temperature recovery is expected during the day
tomorrow as Southeast Michigan remains on the north side of the
surface front, under clouds and rain, and we see stiff east to
northeast winds off the colder lake waters (especially Lake Huron).

A slight chance for spotty showers will exist throughout Monday as
southwest winds continue to advect warm, moist air into the region.
PoP values will steadily increase Monday night into Tuesday morning
as low pressure pushes from Missouri, into the Ohio Valley. The
chance for rain will gradually diminish throughout the day on
Tuesday as high pressure moves in from the Northern Central Plains
into the Great Lakes region late Tuesday into Thursday morning,
keeping conditions relatively dry through that period.

The next chance for precipitation will return Thursday into Friday,
as the GEM and ECMWF 12Z suites pick up on low pressure moving from
Texas/Oklahoma into Michigan. High uncertainty still exists
regarding both the timing, track, and strength of the potential low.
For comparison, the GFS long-range run keeps the system well to the
south of Michigan, centering it across Kentucky Friday night and
into West Virginia by Saturday morning.  This feature will be
something to keep an eye on as we approach next week.

MARINE...

Frontal boundary over Central Lake Huron his afternoon will sink
south tonight as high pressure builds into Ontario, leading to
northeast winds of 15 to 25 knots over Lake Huron tomorrow with
gusts briefly up to 30 knots over the mid section of the Lake early
tomorrow morning. This will lead to waves in excess of 4 feet
impacting the nearshore waters over the northern Thumb region during
the day, and small craft advisories have been issued. Winds will
become a bit more East-Southeast for the second half of the Weekend
as low pressure tracks through the western Ohio Valley and into
Lower Michigan Sunday Night. The weak low then looks to slowly pass
through Lake Huron on Monday, with generally light winds right into
Tuesday, but from the north behind the low.

HYDROLOGY...

Periods of showers Tonight and right through the weekend as a
frontal boundary meanders over southern Lower Michigan. Rainfall
totals are expected to approach 1 inch across much of the area, but
flooding is not expected due to the long duration and intermittent
nature of the rainfall. Runoff from the rainfall will increase flow
rates and water levels in local streams and rivers.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 6 AM to 8 PM EDT Saturday for LHZ422.

     Small Craft Advisory from 6 AM Saturday to 4 AM EDT Sunday for
     LHZ421-441.

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

$$

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


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