Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
127 PM EDT Wednesday Sep 2 2015



Aviation...

Daytime heating is leading to an increasing cumulus field over
southeastern Michigan this afternoon. An unstable and weakly
capped thermal profile will lead to chance of showers and
thunderstorms between 20-02z...over portions of middle
Michigan and the Saginaw Bay region. Questions on coverage
preclude a mention in the taf forecast at this time. Uncertainty with
regards to development is much higher for far Southern Lower
Michigan. Loss of daytime heating will support cloud dissipation
this evening with muggy weather leading to another round of MVFR
visibility restrictions at daybreak Thursday.

At dtw...a low chance for shower and thunderstorm development
exists at the terminal between 20-02z. Very spotty coverage of
potential activity and uncertainty in timing precludes an explicit
mention in the taf forecast.

//Dtw threshold probabilities...

* medium for ceiling at or below 5kft after 18z today

* low for thunderstorms this afternoon and evening.

&&

Previous discussion...issued 1219 PM EDT Wednesday Sep 2 2015

Update...

An isolated coverage of showers and thunderstorms were able to
become rooted this morning along and within an enhanced gradient
of midlevel equivalent potential temperature that washed in from
Wisconsin. Steep 925-850mb lapse rates sampled in 12z kdtx were
enough to aid precipitation loading effects in generating an area
of wind gusts in excess of 50 miles per hour across southern Washtenaw County.
With the activity exiting to the south and east...observational
datasets support a period of quiet weather and insolation through
midday.

The question moving forward centers on precipitation potential
later this afternoon which includes pinning down forcing
mechanisms for additional development. Certainly not a clean
forecast from a Theta-E perspective...with a lack of synoptic
scale frontal boundaries or jet support aloft. The mesoscale convective system system
over portions of northern Wisconsin and the western u.P. Raises
concern but nwp data suggests the trajectory of this forcing will
keep it removed from semich. Cams...and rap/hrrr advertises a
peak heating initiation late this afternoon within a weakly
capped environment to the south of the prior convection. Current
Storm Prediction Center mesoanalysis offers support to this thinking with MLCAPES
already in excess of 2000 j/kg over much of the interior of the
lower peninsula. No tangible edits will be made to the inherited
forecast. Focus will be on initiation of showers and thunderstorms
taking place during the 20-02z timeframe...with possibly a little
better focus north of Interstate 69. Slow storm motion raises a
concern for a heavy rainfall and precipitation loading potential
continues to support an isolated wind gusts threat of 40 miles per hour or
greater.

Previous discussion...issued 336 am EDT Wednesday Sep 2 2015

Short term...today and tonight

The elevated upper height field currently anchored across lower
Michigan will largely hold tight over the next 24 hours...as subtle
height falls tend to only dampen the ridge periphery while streaming
across the northern Great Lakes. This process will eventually ease
a weak low level boundary south and east into the region by late in
the day. This will be accompanied by a slight increase in middle level
Theta-E advection...as the flow veers slightly and deepens from the
southwest. Projected thermodynamic profile for today virtually a
Carbon copy of yesterday...perhaps a touch more mixed. This will
again result in highs of upper 80s/around 90...with an uncomfortable
dewpoint in the vicinity of 70 degrees. This translates into peak
heat indices reaching into the middle 90s. Soundings show a
moderately unstable profile...carrying sufficient middle level lapse
rates but with some capping issues around 700 mb. This indicates at
least a lower end potential for middle afternoon through evening
convective development...fixated along the weak convergence region
accompanying the inbound boundary and perhaps augmented by lake
breeze activity. Background forcing otherwise non-descript limiting
the prospects for a greater coverage.

Another muggy night ahead...with the bottom end of the temperature
spectrum again capped by the elevated dewpoint temperatures. Lows
largely in the upper 60s...lower 70s within the Detroit heat island.
Existing low level gradient casting some doubt in fog potential and
possible coverage during the overnight period /noting a similar
situation currently/. Will hold off a defined mention at this
stage.

Long term...

Still not the best agreement amongst the models...but the general
expectation is the upper wave/energy entering Minnesota early this
morning and additional energy over eastern Montana will slowly work
through lower Michigan on Thursday...and reluctant to exit by
Friday...as it becomes trapped within the backdrop of the building
upper level ridge over Ontario. Moderate to high chance probability of precipitation seems
appropriate on Thursday (especially western areas) as middle level
circulation/cold pool (-10 to -11 c at 500 mb) works through the
area...leading to sufficient destabilization...with MLCAPES climbing
into the 800-1600 j/kg range. High pressure building over eastern
Canada will allow for drier low level easterly flow to attempt to
take hold Thursday night...undercutting the middle level
circulation...and prospects for showers appears to be lower as we
head into Friday. However...the 00z Euro remains most bullish
maintaining shower activity into Friday...and will maintain low
chance probability of precipitation. Expecting highs in the 80s both Thursday/Friday...with
coverage and timing of convective activity determining whether temperatures
will end up in the middle/upper 80s vs lower 80s/near 80...as 850 mb
temperatures hang out in the 15 to 17 c range.

90 degrees looks to be within reach over the second half of the
weekend...as heights resume their upward trajectory. The strong and
large upper level ridge (592+ dam at 500 mb) looks to be centered
over the Middle Atlantic States by Sunday...allowing for strengthening
low level south/southwest flow over lower Michigan...with 850 mb
temperatures reaching and possibly exceeding 18 c.

Marine...

Warm and humid air over the central Great Lakes will promote light
winds and possible fog at times. A weak cold front passing through
Wednesday night will bring the risk of showers and
thunderstorms Wednesday afternoon through Thursday. Light southerly
winds today into tomorrow will shift to a northerly direction behind
the front as we head into Wednesday night...continuing into Thursday.

&&

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

$$

Aviation.....Cb
update.......cb
short term...mr
long term....sf
marine.......sf



You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).

National Weather Service Glossary of Abbreviations