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FXUS63 KDTX 230011

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
811 PM EDT Thu Jun 22 2017


Cluster of severe thunderstorm activity lifting northward through 
Detroit is being forced along the lead gradient of 850-700mb 
tropical moisture. The thunderstorm activity will continue for the 
first hour or two at Detroit terminals before lifting northward with 
time tonight. There is a high amount of uncertainty with how tonight 
will play out. Hi resolution guidance this afternoon missed 
completely on this warm sector thunderstorm development within 
overwhelmingly anticyclonic flow trajectories. The idea right now is 
that tstorm activity should transition northward to possibly between 
the I 69 corridor to Tri Cities sometime after 02-03Z this evening. 
This activity should then continue (expected to be elevated and 
weaker) throughout much of the night along a slowly sagging cold 

Shower and tstorm potential will then pick up towards daybreak again 
around the Detroit Metro area before transitioning southward over 
portions of Ohio by late morning Friday.


* High for thundestorms early at start of period, low for much of 
  tonight and medium for 09-13Z Friday.

* High confidence in ceilings aob 5kft tonight into Friday Morning.


Issued at 353 PM EDT Thu Jun 22 2017 


Warm and humid southwest flow will be firmly established over lower 
Michigan during late afternoon through tonight. Temperatures will 
come down from highs near 90 and heat index in the mid 90s but it 
will remain warm and muggy through the night. This will leave 
convective trends as the main concern beginning with scattered late 
day/early evening development followed by storms arriving from the 
Midwest frontal system during the night into Friday morning. Passage 
of the front through SE Michigan by early to mid Friday afternoon 
will then bring cooler and less humid air into the region for the 

Afternoon satellite imagery and hourly mesoanalysis/surface 
observations indicate warmer and more humid air moving in through 
the boundary layer in southwest flow over the region. This is 
occuring under a relative theta-e minimum that is a result of both 
warmer air moving in aloft that is not quite as moist and possibly 
some subsidence trailing morning convective activity. The warmer air 
is at least temporarily capping off additional shower/storm 
development through peak heating. There is also observational 
evidence of deeper moisture moving in from the Ohio valley 
associated with the northern fringe of TD Cindy. It is this moisture 
surge that is shown to produce late afternoon/early evening 
convection over northern OH/IN developing into lower Michigan during 
the evening. This activity will occur ahead of the convection 
upstream over the Midwest that is being forced along and ahead of 
the cold front/outflow combination and which is expected to progress 
eastward into SE Michigan during the night. Both rounds of storms 
will share a similar near storm environment. Model derived ML CAPE 
and shear projections best supported by observations are in the 
range of 1000-1500 J/kg along with marginal bulk shear around 30 
knots. This combination will be capable of some multicell structures 
with otherwise moderate mid level wind speed that could produce some 
near severe wind gusts in line with the borderline slight/marginal 
SPC outlook that covers SE Michigan. Locally heavy rainfall will 
likely turn out to be the main concern as PW ramps up to near 2 
inches overnight. Individual convective cells will be moving quickly 
enough but there will be a tendency for some training lines that 
will have localized potential for flooding of prone areas. 

Numerous to widespread showers/storms that spread into the region 
overnight will tend to break up as they will be ahead of the surface 
front and upper level wave toward Friday morning. As this convection 
continues to dissipate during the morning, there will be another 
narrow window of opportunity for new development along the cold 
front before peak heating and before it boundary exits SE Michigan 
during early to mid afternoon. Passage of the front will then open 
the door on cooler and less humid air Friday night into Saturday. 
Some weak instability showers will be possible Saturday afternoon 
and evening but the large scale pattern does not look very 
supportive. Neutral southwest flow aloft downstream of the main 
upper trough and a featureless westerly low level flow might support 
isolated to scattered coverage of light showers during peak heating.

The region will remain in longwave troughing to close out the 
weekend and into the beginning of next week.  This will allow for 
chances for unsettled weather through this time period before things 
start to dry out by the middle of the week.  Longwave ridging starts 
to build in on Tuesday as surface high pressure takes control over 
the Great Lakes region.  As far as temperatures are concerned, highs 
will be noticeably cooler on Sunday and Monday as highs hold around 
70 degrees.  Temps then rebound back towards the upper 70s though 
the end of the extended forecast period.


Warm and moist southerly flow this afternoon, but topping out around 
20 knots for the most part. Scattered showers and thunderstorms 
around late today and this evening, with more solid line of showers 
and embedded thunderstorms later tonight with cold front, which will 
pass through the Central Great Lakes tomorrow. Winds will shift to  
the west-northwest behind the front and remain from that general 
direction through the weekend with wind speeds under 20 knots. An 
unseasonably cold airmass this weekend will bring the chance for 
light showers across most of Lake Huron.


An influx of moisture will trigger scattered showers and 
thunderstorms late today and this evening, with more widespread 
shower and thunder activity with cold front late tonight into early 
tomorrow morning. All told, localized rainfall amounts may reach an 
inch or more, especially from around Flint on north into the Saginaw 
Valley, where storms expected to arrive earlier and are able to 
utilize the waning daytime instability. Urban and small stream 
flooding will be possible with the stronger activity.


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



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