Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 280809
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
409 AM EDT Fri Oct 28 2016
Calm winds, clear skies and moist antecedent ground conditions has
led to the development of fog this morning. Thus far, behavior and
tendencies offered by the surface observations suggests that any
dense fog is not widespread. IR imagery supports that a considerable
amount of high cloud will be overspreading southeastern Michigan
prior to daybreak. With the potential for high cloud to disrupt the
favorable environment for fog development, will address the fog by
including areas of in the morning forecast and handle additional
messaging through Special Weather Statements.
The low level flow will remain decidedly anticyclonic today with
southeasterly 950-850 mb trajectories holding firm right through the
early evening hours. This will be in response to a center of the
surface ridge axis building into portions of northern Ohio and the
central Lake Erie basin. Increased insolation alone will allow
temperatures to moderate back to late October averages with highs
today reaching the lower to middle 50s. An accurate message for
skies today is likely Partly Cloudy.
Low level warm advection will ramp up considerably tonight,
predominately occurring above the base of the subsidence inversion
that will be down to 950mb. Strong low level jet forcing will likely
keep conditions mixed at the surface with southwesterly winds locked
in the 15 to 20 knot range overnight.
The features of interest for the weather Saturday are a cold front
that will be slipping southward from northern Lower Michigan and a
secondary higher theta e gradient that will become organized west to
east across southern sections of the cwa. There is large scale
ridging that is forecasted to hold over the state which will make it
very difficult for precipitation generation through the daylight
hours. Perhaps there will be an isolated light shower possible
across the southern cwa after 21Z as there is some support for the
850mb cold front convergence to accelerate southward and accentuate
some moisture dewpoint gradient aligning over the south.
The item that still needs attention is what sort of surface winds
will be possible Saturday with increased gradient flow in advance of
the front. Specifically, with low level jet overhead what kind of
gust potential will exist during the late morning as PBL deepening
taps into the higher momentum. Right now the forecast is in the 20
to 25 mph range.
The midlevel cold front will become a stationary baroclinic zone
directly over southeastern Michigan early Saturday evening as very
brief upper level jet equilibrium period develops. This will change
during the latter half of Saturday night as enhanced region of upper
level DIV from right entrance region passes overhead of southeastern
Michigan. There is some discussion about a lack of continuity in the
nwp with regards to the upper level dynamics. However, looks like a
prototypical event for a regional stratiform precipitation event.
Given the wavelength of ridge trough couplet and magnitude of
temperature gradient the setup appears favorable for solid 850-700mb
fgen that the NAM does zero in on. Predictability appears high
enough for categorical mention of rain for late Period 2. What is of
lower confidence is what sort of QPF potential exists. The event
will have the potential for the development of mesoscale fgen
banding. With forecasted PWATS of up to 1.40 inches, the potential
for heavy rainfall would exist under such scenario. Something to
watch for in future hi-res solutions. End timing for the event is
also in question but should be done by 15Z Sunday morning.
Strong southerly winds will develop this afternoon as low pressure
tracks north of Lake Superior. A gale watch remains in effect for
the open waters of northern Lake Huron. Sustained near-gales will be
possible at times...but stable southerly flow will limit wind gust
potential. The watch will therefore not be upgraded to a warning at
this time. Gusty fresh northwest winds will build across northern
Lake Huron on Saturday followed by more tranquil conditions into
early next week as high pressure dominates.
Issued at 104 AM EDT Fri Oct 28 2016
Lake effect clouds are rapidly clearing out from NW to SE as
building high pressure disrupts the overlake fetch into SE Michigan.
There is no indication that this trend won`t continue, with the
Detroit area expected to clear out shortly. Areas are showing a
strong tendency to dip to IFR BR within an hour or two of clearing.
However, dense fog is unlikely attm as high clouds are already on
the doorstep and will make maintence of IFR vsby a struggle as they
spread into the area 7-9z. High pressure and a steady south fetch
will ensure VFR through the day today. Aviation concern tonight
becomes strong wind shear as a LLJ folds into the area from the NW.
For DTW...Expect cigs to clear out and remain clear below 5kft
through this evening. The potential exception will be early in the
peak heating period as surface moisture mixes up, potentially
leading to a brief MVFR ceiling before scattering out. For now, will
forgo a mention in the TAF as confidence is low. Wind shear
developing late this evening will be followed by low ceiling
development beneath the attendant inversion toward predawn Saturday
//DTW Threshold Probabilities...
* Low for cig aob 5kft through 18z. Medium after 09z Saturday
Lake Huron...Gale Watch from this evening through late tonight FOR LHZ362-363.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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