Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 281428 CCA
AFDDTX

Area Forecast Discussion...CORRECTED
National Weather Service Detroit/Pontiac MI
1011 AM EDT SAT MAY 28 2016

.UPDATE...

An mid level theta e plume lifting northward across the forecast
area this morning initiated some morning convection across the
Saginaw Valley. These thunderstorms have since weakened. Ample
morning sunshine from metro Detroit into the thumb region has
already pushed temps into the low 80s with sfc dewpoints in the
mid 60s, resulting in weak sfc based instability. Based on recent
satellite data, the extensive mid and high level clouds should
take until afternoon before filtering into the ern portions of the
forecast area. This will offer daytime heating the opportunity to
build weak to moderate instability in this region by afternoon.
This suggests possible convective initiation from metro Detroit
across the thumb during the afternoon. Marginal instability, with
0-1km MLCAPE possibly reaching 1500 j/kg from Detroit across the
thumb, and weak deep layer shear will be limiting factors for
severe convection today. Farther east in the forecast area, the
degree of mid and high clouds will limit instability thus reducing
the potential for deep convection. Weak mid level short wave
perturbations embedded within the moist deep layer ssw flow will
still sustain scattered showers and a possible thunderstorm
through the day.

Metro Detroit up through the thumb region should have no problem
reaching highs toward the mid 80s. The early day convection and more
extensive cloud cover farther west may however cause some locals
west of the US23/I-75 corridor to fall short of 80 degrees.
Afternoon temps will be adjusted to reflect these trends.
Also, the strength of the low level sw flow should inhibit an
inland lake breeze push across the thumb region. Thus temps along
the Lake Huron shoreline will be increased.

&&

.PREV DISCUSSION...
Issued at 609 AM EDT Sat May 28 2016

AVIATION...

Low pressure lifting west of the Great Lakes will maintain southerly
flow and warm and humid conditions today and tonight. Axis of mid-
level moisture over the western Great Lakes will pivot into
Southeast Michigan this afternoon as the area of low pressure lifts
from the Central Plains into the Midwest. This should provide BKN
ceilings between 4000-6000 ft, and allow for a better coverage of
showers/thunderstorms this afternoon compared to recent days. Best
chance for thunderstorms will be during peak heating in the
afternoon and evening. Coverage is expected to be high enough to
warrant a mention in area TAFS, with most likely window included as
a TEMPO group. Chances for activity will continue overnight as the
low-level jet axis remains over Lower Michigan, but coverage is
expected to be only isolated to low-end scattered. Winds today will
remain out of the south. May see some gustiness develop with winds
this afternoon (about 20 kts), but cloud cover may limit potential.

//DTW Threshold Probabilities...

* Medium for ceiling at or below 5000 FT during the afternoon and
  early evening.

* Medium for thunderstorms affecting DTW/D21 airspace through
  Saturday evening

PREV DISCUSSION...
Issued at 249 AM EDT Sat May 28 2016

DISCUSSION...

Upper level ridge over the Eastern CONUS will amplify into this
evening as low pressure opens and lift NNE from the central plains
to the upper Mississippi Valley. Heights build slightly over the
region due to this amplification, so expect warm/humid conditions to
persist. High temperatures should reach the mid/upper 80s in most
locations with heat indices a couple of degree warmer than that as
surface dew points hold in the middle 60s throughout the day.

The 00z model consensus suggest there will be a better chance of
showers and thunderstorms across the area from early afternoon into
early this evening. That said, most of the forcing mechanisms
associated with the low pressure system to the west will, indeed,
remain west of the region. This suggests a strong diurnal component
to convective activity, which should be rather disorganized given a
decided lack of any substantial focusing/forcing. This supports a
time window centered on the afternoon hours with a general 40 to 50
percent chance of precipitation as scattered showers/thunderstorms
evolve across lower Michigan with the warm/humid air mass in place.

As this low pressure system continues northeast into the northern
Great Lakes on Sunday, a weak cold front will progress west to east
into the area and provide another chance of scattered to perhaps
numerous showers/thunderstorms during the afternoon/early evening
hours. Activity may be a bit better organized as the cold front
provides additional convergence/lift to focus a moderately unstable
atmosphere. However, bulk shear values remain rather low per model
forecasts (perhaps 20 knots in the 0-6 km layer), so convective
organization may still be rather iffy and generally multi-cellular
in nature. Still, with moderate instability in place and at least
some degree of focus, suspect a few stronger storms will be possible
over lower Michigan even if overall coverage remains AOB 50 percent.

Surface high pressure will build west to east through the area in
the wake of this cold front early next week, providing generally dry
weather. Temperatures will still be on the warm side, 80-85 degrees
away from the immediate Great Lakes shoreline, but lower humidity
values will make for more comfortable conditions and cooler nights
as low temperatures fall into the mid 50s to lower 60s.

Humidity will begin to build again to some extent by the Wednesday
and Thursday time frame as broad southwest flow once again becomes
establish in advance of next organizing low pressure over the plain
states. The chance of scattered showers or thunderstorms will also
return to the area with the approach of this next system with cooler
and drier conditions likely heading into next weekend once this low
pressure system passes to the east/northeast and an amplifying upper
level trough within the northern stream allow a more substantial
surface high pressure system to build SE into the area from Canada.

MARINE...

Areas of dense fog will remain likely over much of Lake Huron
through Saturday night as a warm and humid airmass continues to
reside over the cold lake waters. Otherwise...winds will turn more
southerly and increase slightly today into tonight as low pressure
lifts just west of the Great Lakes. The warm airmass over the area
will continue to support a chance for showers and thunderstorms
through Sunday night. The best coverage of showers and thunderstorms
is expected late Sunday and early Sunday night as a cold front moves
across the region. A few of these storms may be strong or even
severe. Winds will turn westerly behind the cold front for Memorial
Day. A drier airmass should also end the threat for thunderstorms.

&&

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

$$

UPDATE.......SC
AVIATION.....DG
DISCUSSION...DG
MARINE.......HLO


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at www.weather.gov/detroit.



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