Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 252316
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
716 PM EDT WED MAY 25 2016


.AVIATION...

Continuation of a stable environment through at least the first half
of the night will again leave all SE Michigan terminals under simply
some degree of high cloud /above 6000 ft/.  Loss of heating will
prompt the reduction in wind speed magnitude through the latter half
of the evening.  There remains the potential for ongoing convective
activity now over Chicago to expand eastward overnight, reaching SE
Michigan during the early-mid morning hours /08z-13z/.  Any activity
likely arrives locally in a much weaker state, diminishing the
likelihood for a greater coverage of thunder.  This will continue
to preclude any mention at this time.

FOR DTW...Quiet conditions through 08z, window for showers
thereafter through 12z.  Very low probability for a thunderstorm to
emerge in the vicinity of the terminal during that time.  Will
refrain from a defined mention at this stage, allowing subsequent
trends upstream dictate the need for a specific inclusion.

//DTW Threshold Probabilities...

* Low for ceiling 5000 FT or less late tonight and Thursday.

* Low for thunderstorms affecting DTW/D21 air space late tonight and
  Thursday.

&&

.PREV DISCUSSION...
Issued at 351 PM EDT Wed May 25 2016

DISCUSSION...

Persistent upper level ridging along with another day of dry and
modest surface dewpoints has resulted in an overachievement of
surface temperatures across much of the southern 2/3rds to 3/4ths of
the cwa. Afternoon temperatures easily reached into the middle 80s.
A rather weak frontal boundary has become increasingly organized
over far northern portions of the cwa generally along and north of
the M 46 corridor. This feature resides in a zone of soft lower
tropospheric confluence or shearing deformation. The vertical
circulation tied to the boundary has been deep enough to aid in some
isolated elevated convective showers. Explicit hi-res model output
suggests a duration of continued shower development along this
frontal boundary into the afternoon, potentially as late as the 01z
timeframe. Could also see the activity focus west of the Tri Cities
region with time, possibly over sections of far western lower
Michigan. Surface observations near the boundary are still reporting
some 60 degree dewpoints. Forecast sounding analysis along with with
SPC mesoanalysis suggests that around 750 J/kg of MLCAPE will be the
high water mark or CAPE ceiling the environment will be up against
for the remainder of this afternoon and evening. No strong or severe
thunderstorms are expected with the marginal instability and lack of
shear.

Model data is also suggesting that rogue shower activity may
be possible across the far southern CWA south of Detroit as very
weak dcva will lift northward. The very weak midlevel convective
activity that has been on regional mosaic over Ohio is associated
with this forcing. Cannot rule it out the showers completely, but
not giving it much credence either because of the strength of the
upper level riding aloft.

Flow trajectories are forecasted to turn cyclonic for a time tonight
and tomorrow over portions of the upper Midwest as a deep midlevel
trough lifts into the Northern Plains. This inflection point in the
flow will be tied to the entrance region of a new upper level
jetstreak and will harbor a respectable arc of shortwave energy. It
is along this arc of cyclonic vorticity that models have been
supporting old convective showers remnants to push ahead of the cva
and through the CWA between 9-14Z. The forecast item for late
tonight is what sort of coverage of showers and possible
thunderstorms will exist as this forcing enter southeastern
Michigan. The forecast is now muddied as some various solutions are
suggesting a break point or precipitation void over southeastern
Michigan with the early Thursday activity. Have to say the signs
for widespread precipitation is not overly convincing with an overall
lack of big picture forcing. Semich will reside in an unfavorable
right exit region to the upper level jet, while really remaining
more tucked under the upper level ridge and higher geopotential
heights. The bottomline is that any showers, thunderstorms or old MCS
complex that arrives will be weakening. The solution space is
literally all over the map with POPs, anywhere from low chance pops
to categoricals. Decided to maintain much of the inherited forecast
and continue the likely pops. No strong or severe weather is
expected through Thursday morning.

Latest model data suggests some potential exists for severe weather
Thursday afternoon and evening conditional to storm development.
Main support for vigorous updrafts is on the thermodynamic side as
forecast soundings show a legitimate chance for SBCAPE and MLCAPE in
excess of 2000 j/kg by late Thursday afternoon. The CAPE profile
looks contingent on mid 60s dewpoints. Given a reasonable proximity
of mid 60s dewpoints upstream today and the higher likelihood for
early day precipitation and potential moistening of near surface
layer, 2000 J/kg seems reasonable. The main limitation for severe
weather in the short term remains the weak environmental wind
profile and weak shear. The forecasted 0-6km bulk shear is expected
to b 20 knots to possibly as high as 30 knots particularly north of
the M 46 corridor. Combine all of these factors and the idea is that
if storms do develop, severe wind gusts and large hail will be
possible. Soundings do show some capping issues at roughly 5000 ft
agl to contend with. As far as what sort of trigger or focusing
mechanism exists, that remains a good question as there really is
not one. The nam is suggesting that midlevel convective development
may occur in and along the Saginaw Bay region Thursday evening (Fri
00/03Z) as a tail of convergence or cyclonic vorticity settles
southward off of the U.P. of Michigan and Lake Superior shortwave.
In these high cape scenarios all bets are off when a perturbation
is introduced. A very interesting setup and worth monitoring.

Another old nocturnal low level jet cycle is forecasted to lift into
southeastern Michigan on Friday. The overall wind profile is not
expected to change much which really holds things down as a
persistence forecast. Model data continues to suggest some remnant
MCS system could slide across souther lower Michigan on Friday.
Maintainted much of the inherited forecast with likely POPs for
showers and thunderstorms Friday afternoon and Friday evening.
However, predictability and forecast confidence is low on basin
average QPF, liquid amounts.

The pattern will remain active for the start of the weekend and
possibly for the beginning of Memorial Day as Southeast Michigan
remains between troughing to the north and ridging from high
pressure to the south.  A couple of waves riding through the flow
will allow for continued rain/storm chances both Saturday and
Sunday, especially in the afternoons as the diurnal component kicks
in.  Depending on the timing of ridging building in over the area on
Monday, the day may remain dry although at this current time slight
chances for showers are still in the forecast.  Chances decrease
going through Memorial Day and conditions should quiet down Monday
night into Tuesday as upper level ridging builds in.

MARINE...

A stationary front across southern Lake Huron is spawning a few
showers/thunderstorms.  This front will begin lifting north
overnight then become semi stationary through the weekend. For all
marine areas a southerly component to the flow will persist through
the weekend with periodic disturbances producing shower and
thunderstorm chances.  Some fog is possible again tonight across
northern Lake Huron as dew points in the 50s continue to advect over
the colder water.

&&

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

$$

AVIATION.....MR
DISCUSSION...CB/SS
MARINE.......DRC


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