NWS Forecast Discussion

000
FXUS63 KDTX 221826
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
126 PM EST Tue Jan 22 2019


.AVIATION...

A dynamic upper level jet core will bring a wave of low pressure
through Southeast Michigan tonight and Wednesday. Messaging about
the particular storm setup from previous discussion remains valid.
The forecast is calling for a mix of snow, sleet, and freezing rain
to spread into the area from north to south during the course of the
evening and tonight. The precipitation will eventually change over
to all rain for areas along and south of I 69 at daybreak Wednesday.
The main shift to the forecast this issuance was to trend
precipitation type more towards a prevailing freezing rain at the
southern taf sites. Trends still support a predominate all snow
ptype at MBS tonight. Uncertainty exists with the start time of
precipitation at the Detroit and PTK taf sites. Uncertainty also
exists with regards to how far north the warm air will flood in on
Wednesday. The latest RAP solutions are particularly aggressive with
northward push of warm air.

For DTW...Uncertainty does exist with start time of precipitation at
DTW this evening, a consensus suggests around 01Z. A brief period of
snow will be possible at the onset of the event due to wet bulbing.
However, trends mainly support a prevailing freezing rain at DTW as
very cold and dry air will need to be scoured out at the surface. A
steady rise in surface temperatures is expected the latter half of
the night. Questions exist with how fast the surface temperatures
will rise above freezing. Latest indications are by 08Z at DTW. A
warm rain/rain showers is expected until 21Z Wednesday.

.DTW THRESHOLD PROBABILITIES...

*  High in precip type as freezing rain this evening and tonight.
   High in precip type as all rain overnight by Wednesday morning.

*  High for ceilings below 5000 tonight and Wednesday morning.

&&

.PREV DISCUSSION...
Issued at 302 AM EST Tue Jan 22 2019

DISCUSSION...

The arctic high/ridge held on through the evening across southeast
Michigan, allowing temperatures to dip below zero across many
locations once again. The warm start to January is quickly being
erased, and based on the expected much below normal temperatures for
the Weekend, it is apparent the month of January will end up being
normal, if not below normal.

Positive tilted longwave trough tracking through the Rockies this
morning, with good deal of upper level energy/PV rounding the base of
the trough across the northern Mexican border. The consolidated
upper level PV center to eject and track into the Central Plains late
today, and through northern Illinois tomorrow morning and into
northern Lower Michigan Wednesday afternoon.

Waves of isentropic ascent today into tonight over southeast
Michigan, with good moisture advection, as 5 g/kg of specific
humidity in the 850-700 MB layer arrives by Midnight. 00Z NAM has
trended colder/flatter with wave, with areas north of I-69 basically
staying frozen/below freezing through the night, with really a
snow/sleet debate as marginal warm layer sneaks in. The issue is the
850 MB front is lit up along the I-69 corridor as the nose of the 70+
knot translates northeast, so may not be a lot of QPF north of there
if this solution verifies. Also, if the lift is intense enough along
the I-69 corridor, could be looking at precipitation staying mostly
snow/sleet for most of the evening/night. Not an easy forecast, as
regional GEM remains stronger with the surface low (995 MB)/low level
circulation tracking farther north through central Lake Michigan,
which allows the 4 C warm layer at 925 MB to reach Saginaw Bay late
Wednesday morning. FV3-GFS is similar to regional GEM. Even with the
slower/deeper solution, should be good evaporative cooling during the
onset this evening into tonight before the good warm surge arrives
Wednesday morning. All locations in southeast Michigan should start
out as snow/wintry mix before the south to north transition occurs to
rain, but again, north of I-69 there remains a question if a
complete changeover to rain will even occur by 12z Wednesday. After
looking at the latest RAP and Euro as well, planning on going with
winter weather advisory for areas along and north of I-69 for 1-5
inches of snow, higher amounts likely Midland/Bay/Huron counties, but
amount of sleet mixing in could be a factor. South of I-69, favor
little in the way of snow (less than 1 inch), with more of a
sleet/freezing rain mix changing to all rain around or just after
midnight. With the frozen ground and what appears to be at least a
couple hours of freezing rain, have elected to issue winter weather
advisory for freezing rain this evening, with ice accumulations of a
tenth or slightly higher along the higher terrain of
Lenawee/Washtenaw/Livingston/Oakland, with just a glaze of ice for
Wayne/Monroe/Macomb counties.

Mid level dry slot advancing over southeast Michigan during
Wednesday will shut off the rain, as colder/snow deformation looks
to be just north of Tri-cities region. Still may be enough low level
moisture to support drizzle as temps rise to around 40 degrees for
highs.

Strong cold advection in the evening as winds shift to the
west/northwest, and 850 MB temps lower to the negative lower teens
toward midnight. With any lingering moisture on roads, icy spots
could develop.

Per 00z Euro...Another brutal shot of cold air looks to be arriving
to close out the work week, as deep/cold upper level low (490 DAM or
lower at 500 MB) moves over Ontario. 850 MB temps plummeting into the
mid negative 20s again on Friday over southeast Michigan, with
enough wind to support potential wind chills of -15 F or colder once
again. Bitter cold to hang around for the Weekend, with still a few
opportunities for snow into early new week.

MARINE...

Low pressure will lift from the southern plains to northern
Illinois by Wednesday morning. The low will then traverse central
Lower Michigan during the day Wednesday. There will be a
strengthening southerly gradient ahead of this low pressure system.
The winds will actually increase to gale force by late morning and
will persist into early this evening. While probabilities remain
high that gusts will reach 35 knot gales, the probability for gusts
to 40 knots gales is low. The winds will gradually decrease tonight
due both to a subtle weakening of the gradient and low level
warming, thus reducing over-lake mixing depths. Winds will veer to
the west-northwest late Wednesday into Wed night as the surface low
departs east of Lake Huron.

Another intrusion of arctic air is forecast to overspread the Great
Lakes Thurs night into Friday. This will bring another round of
gusty winds (possibly gale force) and high probabilities of heavy
freezing spray.

HYDROLOGY...

There will be an influx of relatively high moisture preceding a low
pressure system that will traverse Lower Michigan on Wednesday
afternoon. The initial surge of moisture will result in a mix of
snow, sleet and freezing rain across the area late this
afternoon/evening before strong warm air advection transitions the
precip over to rain Tues night/Wed morning. The rain will come to an
end Wednesday afternoon. There is a high probability that total
liquid equivalent precipitation totals will range from a half inch
to three quarters of an inch across the area. Probabilities for
precip totals approaching an inch drop off dramatically. If total
precip does approach an inch, there may be some localized flooding
concerns in urban Detroit where warming temps will also result in
some snow melt.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 6 PM to 10 PM EST this evening for
     MIZ060>062.

     Winter Weather Advisory from 2 AM to 5 AM EST Wednesday for
     MIZ060>062.

     Winter Weather Advisory from 7 PM to 10 PM EST this evening for
     MIZ063-068>070-075-076-082-083.

     Winter Weather Advisory from 5 PM this afternoon to 10 PM EST this
     evening for MIZ047>049-053>055.

     Winter Weather Advisory from 2 AM to 8 AM EST Wednesday for
     MIZ047>049-053>055.

Lake Huron...Gale Warning until 10 PM EST this evening for LHZ361>363-441>443-
     462>464.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....CB
DISCUSSION...SF
MARINE.......SC
HYDROLOGY....SC


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NWS DTX Office Area Forecast Discussion