Scientific Forecaster Discussion
fxus63 kdtx 201057
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
657 am EDT Wed Sep 20 2017
The departure of a mid cloud deck overnight with light winds and
abundant low level moisture has led to the development of widespread
fog/low stratus this morning. Taking into consideration a late
September sun angle, it will likely take until late morning or early
afternoon for conditions to improve to MVFR. Afternoon mixing will
attempt to erode the low clouds. Slight warming above the cloud layer
should hold MVFR or low end VFR strato cu in place through the
afternoon. A frontal boundary will stall as it lifts into northwest
lower mi tonight. Mbs will be in fairly close proximity to the
instability axis. This will pose a chance for some late night
convection at mbs, the chances of which remain a bit low to include
in the terminal attm.
For dtw...occasional dense fog is expected to persist through
roughly 13z before daytime mixing starts a steady improving trend.
The onset of daytime heating will lead to widely variable cig/vsby
conditions through the morning.
//Dtw threshold probabilities...
* high for ceilings below 5000 ft through this afternoon. Low
* High in cigs/vsby at or below 200ft/one half mile through roughly
issued at 344 am EDT Wed Sep 20 2017
Upper level low over Ohio is slowly drifting southeast away from lower Michigan
as longwave ridge continues to strengthen overhead. The weakening
low has sent one final moisture surge, located along the 700-850mb
Theta E gradient, northward which is about to pass over Saginaw Bay
as of 07z. This appears to be its last gasp with any lingering
showers more of a mist out of the low stratus and fog due to the
abundant low level moisture in place. The low will fade away through
the day as ridging overtakes it.
Meanwhile further west, a strong shortwave rotating around the
longwave trough will get slung northeastward through the northern
plains into Canada with the aid of a 125+ knot jet. Though this will
be far removed from the Great Lakes, it will pull a warm front north
through lower Michigan today allowing a thermal ridge approaching 17c at
850mb into the state. It will also force a cold front into the
Midwest, draped from the western u.P. Down through WI into Illinois. This
will be the focus for thunderstorm develop today into tonight west
of Southeast Michigan. The warm sector will provide US a fairly Stout cap between
900-700mb which will likely prevent any storms from bleeding east
into our County Warning Area. Models are keying in on a period after 09z
tonight/Thursday morning where a wave tracking along the front
through mid Michigan could bring a period of shower/storms to the Saginaw
region. Then the front will have inched closer to lower Michigan keeping
low chance pops around on Thursday as well. At this point thinking
is it will be difficult for showers to be able to break the cap and
majority of the area will remain dry through the forecast period.
Other main issue will be the heat. Models are being very consistent
with the ridge supporting 850/925mb temps of 17c/+20c respectively.
With dewpoints holding in the 60s limit nocturnal cooling, high temps
should easily make it into the mid 80s and possible upper 80s
Thursday through the weekend. These temps will be nearing 15f above
average for late September. Record highs for all 3 climate sites
(dtw, fnt, mbs) are all around 90f through this stretch. Something
to watch for.
South-southeast winds (generally under 15 knots) will persist across
Lake Huron through the end of the week as high pressure expands from
Quebec into the eastern Great Lakes. The winds across Lake St Clair
and Erie will have a more easterly component, but will be much
lighter. The winds will weaken slightly over the weekend as the high
pressure expands into lower Michigan.
Lake St Clair...none.
Michigan waters of Lake Erie...none.