Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 300700
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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 CWA
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
Issued at 1157 PM EDT Mon AUG 29 2016
Evening persistence of high clouds from upstream has not inspired
much confidence as a negative factor for fog development. This was
being relied on to maintain VFR through the night which remains
possible at FNT and MBS. The DTW corridor will likely see at least
MVFR restriction before sunrise through about mid morning. This is
where the westward extension of high pressure will remain from the
primary center over Lake Erie and Ontario with a position capable of
directing lake moisture toward DTW. MVFR visibility will then give
way to light southwest wind that will become steadier through the
day and bring a renewed moisture return. This could generate some
showers late in the day into Tuesday evening, especially with the
help of daytime heating.
//DTW Threshold Probabilities...
* Moderate for ceiling 5000 ft or less during late afternoon into
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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