Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221749
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1249 PM EST Sun Jan 22 2017

.UPDATE...

An elongated, weak surface trough remains in place over
southeastern Michigan exending from the deepening surface low
pressure system over the southern U.S. northward through the Great
Lakes region and into the southern Canadian prairie provinces. The
air mass within this inverted surface trough can be characterized
as saturated with relative humidity values across the board of
between 95-100 percent. Tough call on what to do with the Dense
Fog Advisory that had been set to expire at noon. The change going
forward is the easterly pressure gradient will increase gradually
in response to cyclogenesis over the Tennessee River Valley.
Therefore, expecting surface visibilities to improve this
afternoon both in response to diurnal heating processes on the
shallow fog and model data support for upwards of +10 knots
1000-950MB geostrophic flow. However, despite the improvement this
afternoon, the concern for tonight turns again to widespread fog
development as higher resolution guidance shows little to no
improvement on surface condensation pressure deficits and no
tangible positive surface pressure tendencies. An inversion is
forecasted in the fcst soundings again overnight, although there
are some differences in surface lapse rate structure. Per
communication and collaboration with surrounding offices, the
decision was made to extend the dense fog advisory through
tonight, ending at 10 AM EST Monday. Again, there will be some
improvement this afternoon but expecting widespread dense fog
redevelopment this evening. Decided to extend the advisory for
both Lenawee and Monroe counties as northern portions of the
counties continue to witness fog. Model data does support some
southward drift and advection of 925 MB moisture to the
Michigan/Ohio stateline rapidly after 21Z.

&&

.PREV DISCUSSION...
Issued at 438 AM EST Sun Jan 22 2017

AVIATION...

Incoming mid-level clouds did an impressively poor job at preventing
vsbys from falling to 0 to 1/4SM early this morning. As a result,
conditions are well below airport minimums areawide. A poor scenario
with regard to recovery today is unfolding. Mid-clouds will be
departing around the 12z diurnal minimum allowing for reinforcement
or further deterioration early in the TAF period. Furthermore,
potential improvement during the diurnal max this aftn will be
hampered, potentially significantly so, by another round of incoming
high clouds. Held on to dense fog at all locations until 17z with
some optimism for improvement to IFR in the afternoon. Fog
redevelops again tonight but increased uncertainty to due
widespread blanket of high cloud.

//DTW Threshold Probabilities...

* High for cigs aob 5kft.

* High for cig and vsby below 200 ft and 1/2sm this morning. Low
  tonight.

PREV DISCUSSION...
Issued at 347 AM EST Sun Jan 22 2017

DISCUSSION...

A very weak and broad trough of low pressure is positioned over
Lower Michigan during the early morning and will remain in place for
much of the day. Within this pattern is a mild and moist boundary
layer that is being increasingly exposed to radiational cooling as
mid and high clouds slide eastward or remain to the south with
convection over Indiana/Ohio. The result is widespread dense fog
that will persist through the morning and then struggle to lift
during the afternoon. Mid and high clouds will begin to thicken
again over the fog layer as the day progresses and inhibit already
weak mid January potential for surface heating. Calm to light and
variable wind is projected to increase from the east around mid
afternoon which should help with some improvement. Given this
favorable environment for persistence, the dense fog advisory will
be extended through noon with updates later in the morning possibly
needed to extend the headline later in the day.

Other than the fog, a stray shower is possible as the mid level
moisture increases over the region during the afternoon. This type
of moisture transport is more effective at generating precipitation
during the night as demonstrated by the showers/storms over Indiana
and Ohio early this morning. The mid level wind field will also
weaken and back toward the east as the Gulf Coast low pressure
system progresses into the Tennessee Valley by evening. The northern
fringes of this system will give us a better chance of showers
tonight, and especially Monday. This is when the upper low will
phase more with the northern stream to produce a deep layer of
deformation of moderate intensity over Lower Michigan. The agreement
among the 00Z model solutions on this scenario is quite good with
all showing a vertically stacked low near the mid Atlantic coast and
an inverted trough extending through the Great Lakes to help focus
moisture and contribute to deeper vertical motion. The GFS is most
bullish on QPF, as usual, but has some merit in this pattern while
the other models all still favor a high POP/lower QPF scenario
which was already built into our going forecast. The good news
here is that precipitation will be all rain Monday into Monday
evening before the temperature profile begins a slow cooling
trend. A short period of rain/snow mix will be possible as the
deformation pattern shifts eastward and precipitation ends by
Tuesday morning.

The break in the action will be short as the next low pressure
system arrives in the Great Lakes Tuesday night. This system will
be feeding off the larger scale upper level trough and powerful
upper jet as it progresses through the Rockies during Tuesday.
Once east of the Rockies, lee side cyclogenesis will take place
and will be enhanced by sharp baroclinicity pre-existing from the
Gulf Coast into the southern/central Plains. Strong deepening of
the system is then likely as the system approaches the Great Lakes
Tuesday night. The individual model solutions from the latest 00Z
cycle offer a wide range of tracks and intensities but the larger
scale pattern favors the stronger GFS/ECMWF on a track through the
central Great Lakes through Wednesday. A brief wintry mix would be
possible in this scenario before changing to all rain for SE
Michigan should the track and timing hold in upcoming forecast
cycles. A cooling trend will then get underway for the end of the
week as this system exits the Great Lakes and pulls in an air mass
more typical for the end of January.

MARINE...

Dense fog advisories remain in effect for marine area through mid-
morning. Winds and waves will remain on the light side through the
forecast period...but easterlies will perk up late tonight through
Monday. Onshore flow may necessitate small craft craft advisories
for ice free areas due to elevated waves on Monday. Marine weather
then remains on the quiet side through midweek.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Dense Fog Advisory until 10 AM EST Monday FOR MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

Lake Huron...Dense Fog Advisory until 10 AM EST Monday FOR LHZ361>363-421-422-
     441>443-462>464.

Lake St Clair...Dense Fog Advisory until 10 AM EST Monday FOR LCZ460.

Michigan waters of Lake Erie...Dense Fog Advisory until 10 AM EST Monday FOR LEZ444.

&&

$$

UPDATE.......CB
AVIATION.....JVC
DISCUSSION...BT
MARINE.......JVC


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