Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 271934
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
334 PM EDT Sun May 27 2018

.DISCUSSION...

Changes to the forecast include increased PoPs today for the
northern CWA with likely Pops for the Thumb between 21-02Z.
Messaging to include conditional risk for strong to severe
thunderstorms this evening north of I 69 with wind gusts to 60mph
and 1 inch diameter hail possible. The area was upgraded earlier to
a marginal designation for severe weather in midday Swody1
update.

Noisy forecast again today with Southeast Michigan directly within
the dirty summertime ridge. Difference today has been the
development of CIN between 3.5-7.0 kft agl in response to a 825-
700mb anticyclone center pushing across far southern Lower Michigan.
Satellite trends have supported this capping layer with very little
cumulus development to this point. The anticyclone center is one of
a very shortwavelength and presents an issue as midlevel theta e is
progged to wash back in along the northern flank of the anticyclone
center west to east directly into Saginaw Bay region yet this
afternoon. The theta e axis is resolved by the NAM to be respectably
deep from 900 to 700mb. This midlevel moisture in combination with
strong late May insolation and an atmosphere preconditioned for deep
mixing will likely lead to convective initiation in the higher
terrain north of Saginaw Bay. Storm movement will be to the
southeast at approximately 30 mph. Consensus of CAMS and high
updraft probabilities in HREF output supports an increased
confidence in thunderstorm activity from Saginaw Bay southeastward
to Port Huron in the 21-02Z time window. Data supports a steeping of
a convergence axis directly over northern cwa in response to slow to
move deep ridging to the southeast. Uncertainty does with regards to
magnitude of MLCAPES with model resolution/gradient issues in the
northern Thumb. Current thinking is based on model soundings and RAP
based mesoanalysis that at least 1500 J/kg MLCAPE will be available
for thunderstorms this afternoon. 0-6km bulk shear of approximately
25 knots in vicinity of Lake Huron will be more than sufficient for
storm organization. Thunderstorm activity this afternoon will be
capable of wind gusts to 60 mph and hail to 1 inch.

Farther south, including metro Detroit, models keep just enough
CIN/capping to inhibit convective development. Some question with
small amount of capping as skin layer dewpoints in the soundings do
not invoke a lot of confidence. Certainly possible for thunderstorm
activity over the southern cwa with the amount of instability within
the column. Introduced entry level chance PoPs this evening,
however, current data suggests thunderstorms will remain to the
northeast of metro Detroit.

A hot and muggy Memorial Day as the upper level ridge is forecasted
to shear to some extent across the central Great Lakes. Yet again,
forecast is all about the details with models now showing less
focused anticyclonic vorticity advection for the state early in the
day. To what extent is questionable as there is differences between
Euro and NAM. Euro does show some AVA during the late day period.
Regardless, will honor long days and maintain highs in the lower
90s. Question is again on thunderstorm potential as some CAM output
is suggesting convective initiation over the higher terrain of Lower
Michigan, pushing southward into the Saginaw Bay region. Overall
pattern will be conducive for increasing low level deformation and
backdoor front as likelihood for organized northeasterly
anticyclonic flow increases during the evening. Given this potential
trigger, and what should be steep low level lapse rates over the
landmass of Lower Michigan continuing chance PoPs over the northern
cwa. Low certainty in CAPEs with poor surface parameterizations, but
the idea is for less instability on Monday given stronger background
ridging signal.

Backdoor front off of the lake is expected to become quasi
stationary over portions of the cwa Tuesday. Net result is for
cooler temperatures over the north half of the cwa with highs still
expected to reach the upper 80s south of I 69. Relief from the muggy
dewpoints will not arrive until a nocturnal release of the Lake
Huron marine layer occurs Tuesday evening.

Abundant tropical moisture associated with the remnants of Alberto
will overspread the region on Wednesday. A cloudy morning will be
followed by an increasing chance for showers and eventually more
steady rainfall through the day and Thursday as PWAT values
gradually rise to above 2 inches. Prolonged rainfall with periods of
heavier rates expected with occasional embedded thunder possible.
Highs will hold in the low 80s through both days. Widespread rain
will be on the way out Thursday evening before potent upper energy
(presently in the form of a cutoff low over the southwest CONUS)
brings in another round of rainfall Friday. As this trough exits
toward the Mid-Atlantic region, a cooler, drier, and more seasonable
air mass will be ushered into SE Michigan for the weekend.

&&

.MARINE...

Winds will remain out of the south and light across the lakes today
as a weak low pressure drops south out of northern Michigan and
washes out. This will bring an associated frontal boundary across
Lake Huron and shift winds out of northwest tonight and into
tomorrow morning. Winds continue to remain light with favorable
boating conditions for the most part today with the exception of
decreasing areas of fog across inner Lake Huron and widely scattered
storms this afternoon that may develop across west central Lake
Huron down towards Saginaw Bay this afternoon. Mostly favorable
boating conditions remain for the majority of Memorial Day as high
pressure builds with a return to light southerly winds. Though,
Memorial Day evening may see some scattered thunderstorms again as a
frontal boundary drops southward. Weather conditions deteriorate
midweek remnants of Subtropical Storm Alberto move towards the
region.

&&

.CLIMATE...

Here is a list of record high temperatures for
this holiday weekend.

Monday, May 28th:

Detroit                95 (set in 2012)
Flint                  93 (set in 2012)
Saginaw/Tri-Cities     92 (set in 1977)

&&

.PREV DISCUSSION...
Issued at 206 PM EDT Sun May 27 2018

AVIATION...

VFR conditions will prevail for most terminals today. Mostly clear
conditions to start this TAF period with some diurnally driven
scattered Cu developing. Plenty of moisture and instability
throughout the day with a boundary bisecting southeast Michigan will
allow for a chance of storms that develop off of the higher terrain
of northern lower Michigan and move southeast along the boundary
towards MBS and possibly into FNT/PTK. Have added tempo group to MBS
as it have the highest probability to see storms between 20/24Z. Have
included VCTS for potential at FNT/PTK. Capping across the south
will likely limit thunderstorm potential. Will leave any mention of
thundestorms out with low confidence across the south. Flow will
likely remain light at 5-10 kts out of the south/southwest with calm
conditions overnight.

For DTW...Capping across lower Michigan will be limiting convective
potential later this afternoon. Some diurnal Cu may develop below
5,000 ft, but remain scattered.

DTW THRESHOLD PROBABILITIES...

* Low for CIGs at or below 5,000 ft.


&&

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

$$

DISCUSSION...CB/TF
MARINE.......AA
CLIMATE......CB
AVIATION.....AA


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