Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 141434
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
934 AM EST Fri Dec 14 2018

.UPDATE...

Rain diminishing in coverage as upper level forcing passes to the
north, with low level moisture axis slowly sliding south through
southeast Michigan this afternoon. Saturated ground and near surface
moisture has lead to fog with calm/nearly calm winds and ill defined
pressure gradient. Fog looks to be the biggest forecast decision
point today and then again tonight, as amount of drying is in
question with the surface ridge axis arriving this evening. Also, not
sure we will get as warm as forecasted today, but will still give
the forecast/December sun a chance to work, as RAP still suggest
maxes will climb into the low/mid 40s. If current fog struggles to
dissipate this afternoon, then it will end up cooler with increased
chance of fog holding/expanding tonight. Will continue to watch
trends, but more than likely will be adding fog to the forecast for
tonight. Amount of high clouds coming up from the south being a
factor as well.

&&

.PREV DISCUSSION...
Issued at 453 AM EST Fri Dec 14 2018

AVIATION...

Widespread IFR will continue through the morning, mainly due to vsby
restriction both within in rain and within the low-level moisture
axis left in its wake. Some window for improvement in cigs,
especially in the Detroit as moisture field pivots, but near-surface
moisture will likely promote IFR vsby regardless. Meanwhile, light
rain will persist within lingering deformation invof KPTK/KFNT
through the morning and possibly early afternoon. Fog potential
tonight remains uncertain, but may warrant eventual introduction
into the forecast conditional on confidence of clearing trends this
evening.

DTW THRESHOLD PROBABILITIES...

* High for ceiling below 5000 ft.

PREV DISCUSSION...
Issued at 315 AM EST Fri Dec 14 2018

DISCUSSION...

Precipitation has overspread most of Se Mi as of 08Z within decent
low to mid level moist isentropic ascent. This moist plume is
associated with the moisture feed ahead of the upper low now
rotating over Texas and has been driven into Srn Mi ahead of a
progressive nrn stream mid level trough now traversing the nrn and
wrn Great Lakes. Ongoing enhanced mid level frontal forcing within
the entrance region of a strengthening upper jet preceding this
trough is supporting more widespread precip from srn Lake Mi into
the Saginaw Valley. This forcing will persist through daybreak. The
mid level frontal structure is then forecast to fracture/weaken in
the 15Z to 18Z time as the main PV anomaly lifts north and east of
the area. This will result in a decrease in both intensity and
coverage of precip late morning through roughly mid afternoon
before it ends completely.

The depth of the warm layer will be great enough to support all rain
from Saginaw to Bad Axe and points south. In fact, low level warm
air advection will lead to slowly rising sfc temps through the
course of the morning. Rap13 soundings across Midland/Bay Counties
indicate a fairly deep isothermal layer centered around 0C, which
may support some snow/sleet during the pre dawn hours. As of 08Z, 2m
temps across most of the Saginaw Valley and thumb region are
hovering around 32 Deg. Road sfc temps are however likely at or just
below freezing. So some icy conditions are likely present on several
paved surfaces across the Tri Cities and northern thumb regions. The
low level thermal advections early this morning across these areas
will be weak, so the rate of rise in sfc temps is likely to be
slower than locals farther south. For this reason, a winter wx
advisory for mixed precip has been issued for Saginaw/Bay/Midland/
Tuscola/Huron counties through 13Z. Locations farther south are
likely to have some paved surface which are icy early this morning,
but the rise in sfc temperatures early this AM should be a little
greater in these areas.

Full to partial clearing will then overspread the area during the
afternoon and evening as rather strong mid level subsidence expands
into srn Mi. This and the remnant low level warm air will boost
afternoon highs into the 40s. Sfc high pressure will then build into
the region from the west tonight. Remnant boundary layer moisture
topped by very dry air does raise concerns for some fog potential
tonight. Surface dry air advection and a strengthening gradient flow
will be limiting factors which support refraining from fog mention
tonight attm.

The aforementioned upper level low will slowly advance from the
southeastern US into the Mid Atlantic over the course of the weekend
while mid level ridging holds across the Great Lakes. This will
support dry and relatively mild conditions across Se Mi through the
weekend. An amplifying northern stream wave is then forecast to clip
the northern Great Lakes late Sun/Sun night. The extent of cold air
in the wake of this system will only bring a modest cooling trend
(Mon highs in the 30s). Building mid level heights will then support
a warming trend heading into mid week. while ample dry air keeps the
area precip free. While medium range model solutions diverge toward
the end of the forecast period, there is at least some agreement
that long wave trough amplification will bring the next chance for
precip on Thursday.

MARINE...

Light to moderate wind will tend to veer around the compass trhough
the weekend as high pressure migrates through the area. Northwest
wind will ramp up behind a cold front early next week potentially
gusting to gales.

HYDROLOGY...

Widespread precipitation will affect southeast Michigan this morning.
Some sleet, snow and freezing rain will occur across the Saginaw
Valley and northern thumb. Total liquid precipitation is expected to
range from a tenth of an inch up to four tenths of an inch.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

UPDATE.......SF
AVIATION.....JVC
DISCUSSION...SC
MARINE.......JVC
HYDROLOGY....JVC


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