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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
745 am EDT Tuesday may 26 2015



Aviation...

Fog and low stratus is beginning to lift northward into Michigan and
should influence the terminals until late morning when mixing
commences and scatters skies out. Surface observation show this stratus to
be fairly extensive to our south though cirrus debris is hiding it
in satellite imagery. VFR conditions through the afternoon until
convection begins to develop around 22z. Coverage will peak around
00-03z this evening so will include this period for thunderstorms and rain. Some
lingering showers will continue into the overnight before we see a
transition back to a low stratus deck.

For dtw...mainly MVFR stratus field lifting north toward the
terminal should affect the terminal through about 15-16z. Ceilings will
scatter out this afternoon before showers and thunderstorms develop
late this afternoon and evening. A stray shower/tstorm cannot be
ruled out between 21-00z but the better coverage looks to fall
between 00-03z this evening.

//Dtw threshold probabilities...

* medium in ceilings below 5000 feet this morning...and again this evening
through the overnight.

* Low in thunderstorms late this afternoon...medium this evening.

&&

Previous discussion...issued 349 am EDT Tuesday may 26 2015

Short term...today and tonight

The overall longwave setup has not changed over the last several
days with the slowly drifting trough engulfing much of the
west/central Continental U.S. While ridge over the East Coast holds strong.
This has lead to Southeast Michigan being located in between the two dominate
features with persistent swerly flow keeping a warm and humid
airmass in place. Today will be slightly different in the sense that
the trough will become a little more progressive with the strong
vorticity maximum...now an open wave...moving from NE to MN/WI. This mean the
next shortwave tracking up through the trough will track through the
western Great Lakes. This will help provide a bit stronger forcing
over the area than we have seen with the shortwaves the previous
couple days. Additionally...models are advertising this wave to be a
bit stronger than yesterdays wave which resulted in a few isolated
thunderstorms and winds gusts 50 to 60 miles per hour.

Current ridging aloft will remain overhead through this afternoon
before the middle level shortwave begins to swing up into southern Michigan.
Most of the day will feature only cirrus clouds filling the sky as
the middle levels are quite dry and mixing will limit the cumulus field until
the afternoon. The wave will lift through the area late this
afternoon through the evening hours...between about 22-04z. An
enhanced band of Theta-E with decent isentropic ascent between 305-
310k will lift northward providing the focus for the storms.
Slightly better conditions should exist today for storm development
with the closer proximity to the wave and favorable timing of
convective initiation occurring during peak heating. Models are all
in the ballpark of around 500 j/kg with the NAM coming in a few
hundred higher which is typical. Lapse rates have struggled the last
few days but appear to be favorable up to around 750mb today which
should help storms get going. A ll jet will nose up into the area in
the evening resulting in deep layer wind speeds around 40 knots. Br
shear values will increase to around 30 knots. All in all it looks
like we will see a line/band of showers and thunderstorms lift north
this evening with the possibility of some storms reaching severe
limits while traveling NE at 35 miles per hour. Primary threat appears to be
damaging wind with lesser threats being hail and tornados. Brief
heavy downpours and localized flooding will also be possible as
precipitable waters rise to near 1.75 inches. Storm Prediction Center has upgraded all of lower Michigan
from marginal to slight risk.

Some showers and thunderstorms may linger through the overnight as
it appears the upper low will try to pull another weaker lobe of
vorticity through the region while the middle level cool pool slides
through northern lower. Temperatures will stay mild in the middle 60s
as SW flow continues ahead of the cold front located up through the
Midwest.

Long term...

Above normal temperatures and a couple more rounds of organized
activity through the end of the week as southeastern Michigan
remains under elevated heights/upper level ridge. Pattern breaking
cold front to push through next weekend.

Wednesday...numerical output has converged over the past 24 hours in
advertising a solution for a stronger surface low center tracking
through the northern Great Lakes on Wednesday. The difference stems
from more efficient phasing of Southern Plains and Central Plains
vorticity anomalies...and associated jet entrance region. This jet
entrance region and southern tail of vorticity anomaly will drag
through southeastern Michigan on Wednesday providing synoptic scale
support to the County Warning Area. Persistence in thermodynamic profile suggests
similar cape values Wednesday with as much as 1000-1200 j/kg of
SBCAPE/MLCAPE possible. Surface trough/Theta-E gradient/weak cold
front is expected to push into southeastern Michigan during the
afternoon providing a focusing mechanism. Timing of this feature is
important for the forecast...with quicker timing negating any
potential for instability during the afternoon. Even in slower
solution...richest equivalent potential temperature is forecasted to
reside immediately south and east of lower Michigan. Expectations
are for showers and thunderstorms to become scattered coverage Post
18z...with an isolated shower scenario prior to 18z. The deeper wind
field will have stripped out by Wednesday...with 0-6 km bulk shear
ranging 15-25 knots. The conditional uncertainty of instability
combined with marginal deep layer shear supports messaging of just a
Standard thunderstorm risk for Wednesday. Latest swody2 keeps
marginal designation to the south and east of Michigan...tied to
Richer Theta-E content.

Thursday...downstream ridging will expand eastward across the
central Great Lakes on Thursday. Very weak surface riding is
expected to build into the state...with models indicating the low
level anticyclonic circulation tracking locally...seeking out the
Lake Huron/Erie aggregate. Gone dry Thursday...with warm air
advection and low sky fraction allowing temperatures to push into
the lower 80s.

Friday...will be watching the next day or so how the models handle
the amplification of the ridge over sections of northern Canada.
It remains possible quicker strengthening of the ridge could occur
and serve as blocking for the developing cold front and forcing.
For now...precipitation chances start early on Friday...but this
very well could be pushed back with time. Additionally...a slower
solution would support higher temperatures than what is already in the
grids. Middle to possibly upper 80s could be in play.

Marine...

Southwesterly flow will remain in place over the Great Lakes region
through midweek. Winds today are expected to range 10 to 15 knots
with gusts to 20 knots this afternoon. Winds are forecasted to
increase on Wednesday...with frequent gusts ranging 20 to 25 knots.
The chance of showers and thunderstorms will increase late this
afternoon and evening...lingering into Wednesday. A weak surface
trough will pass through the state late Wednesday. Dry conditions
are the expected Thursday and much of Friday.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....Drk
short term...drk
long term....cb
marine.......cb



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