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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
1055 am EDT Tuesday Aug 30 2016

made slight adjustment to pops into the afternoon hours to account
for current radar trends. Some isolated showers have been drifting
eastward along the I-69 corridor this morning. Appears to be just
enough convergence at 850mb on the nose of the deeper moisture
plume to weaken the cap and allow these showers to persist farther
east than previously anticipated. Though radar trends have been
diminishing, there is enough activity continuing to pop up to keep
the slight chance mention going. Will address evening and
overnight potential with the afternoon forecast package.


Previous discussion...
issued at 648 am EDT Tue Aug 30 2016


Clusters of thunderstorms across nrn Illinois and SW lower mi have
developed within a plume of mid level moisture and elevated
instability. This moisture and instability axis will lift into the
Saginaw Valley this morning. Increasing daytime destabilization
within this moist axis will target the mbs region for better chances
for afternoon convection. A cold front moving down from the north
will increase the chances late in the day. This front will slowly
push south toward Metro Detroit late tonight, providing better
chances for thunderstorms farther south overnight. The approach of
the front combined with ample low level moisture will support low
stratus development overnight.

For dtw...a pool of relatively stable air is expected to remain over
Detroit as the instability plume remains west of north into the
evening. So the prospects for convection prior to 00z is rather low.
Gradual moisture advection will support at least some scattered
clouds based below 5000 ft late morning and early afternoon.

//Dtw threshold probabilities...

* low in ceilings at or below 5000 ft today and this evening.
Moderate overnight.

* Low in thunderstorms this afternoon and evening. Moderate

Previous discussion...
issued at 300 am EDT Tue Aug 30 2016


Large upper level circulation/low over northern Manitoba early this
morning tracking into northern Ontario today and into southern
Quebec on Wednesday, allowing for much cooler Canadian air to filter
into Great Lakes region, as additional upper level energy tracking
through central Canada helps carve out the positively tilted
eastern United States trough by Thursday. Pronounced upper level
ridge already building into lower Michigan on Friday, assuring a
dry and sunny Saturday.

Upper level forcing with cold front slowly tracking through lower
Michigan this afternoon/tonight is weak, and 500 mb temps are
actually warming a bit compared to the current -11 c over the u.P.
Looking at two distinct moisture axises, one with the actual
front which is very narrow, and the second/deeper moisture axis over
Chicago area which attempts to spill over east into the County Warning Area
during the day. None-the-less, forecasted 850 mb temps are fairly
warm (17 c), warm enough to provide a cap through most of the day.
Weak 0-6 km bulk shear (20 knots) and corresponding weak low level
convergence as well. None-the-less...MLCAPES advertised to reach
between 1000-1500 j/kg across northern third of the cwa based on
maxes in the mid 80s, and any outflow boundaries could help
overcome the weakening low level cap. Latest hrrr (4z) indicating
a fairly good coverage of activity rolling through late in the day
in this moisture rich environment, however, preference is still
toward a bit more muted/isolated-scattered pop forecast in line
with Canadian/Euro solutions.

Loss of daytime heating will allow MLCAPES to slip below 1000 j/kg
as cold front slowly tracks through Southern Lower Michigan
tonight/tomorrow morning. On flip side, it looks like we may get
into right entrance forcing of upper level jet late tonight into
Wednesday morning, worthy of maintaining low chance pops, despite
the weak mid level lapse rates, 5.7-6.1 c/km from 700-500 mb.

Cold pool/trough axis will be moving through on Thursday, with 850
mb temps still progged to be 7-8 c, and could see some isolated Lake
Huron enhanced showers around eastern thumb region. Regardless,
with steep low level lapse rates, expecting at least partly
cloudy skies, holding temps in the low to mid 70s.

Increasing diurnal temperature swings Friday-Saturday as ridging at
all levels settles over the central Great Lakes leading to general
subsidence and clear skies. Localized fog potential near warm
Inland Lakes as min temperatures likely reach around 50 degrees.


South winds this morning will veer toward the southwest by afternoon
ahead of a cold front advancing across Upper Michigan. There will
only be a slight increase in wind speeds ahead of the front due to
warm air advection and strengthening stability across the lakes. The
front will move south across Lake Huron this afternoon and tonight,
providing a chance for thunderstorms. It will then slowly push into
Lake Erie on Wednesday, sustaining the chance for thunderstorms
across lakes St Clair and Erie into Wednesday afternoon.

Post frontal cold air advection under strengthening northwest winds
will support gusty winds on Lake Huron Wednesday through Thursday,
and lakes St Clair and Erie Wednesday night and Thursday. Small
Craft Advisory conditions are likely during this period, especially
on Lake Huron as the flow veers toward the north (onshore) by
Thursday morning. There is a high probability that wind gusts across
Southern Lake Huron will be in the 25 to 30 knot range during this


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



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