Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 242346
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
646 PM EST Fri Jan 24 2020


.AVIATION...

Low level moisture feed is aimed directly at Southeast Michigan this
evening as the center of closed low pressure system is over far
southern Illinois. Models indicate a dry slot will spread due
northward directly through all of the cwa by 06Z this evening. This
will end much of the support for the moderate rain potential. Given
moist low level conditions, expectations are for LIFR cigs, fog and
drizzle to fill in. Uncertainty exists with regards to the overall
potential for VLIFR conditions of cigs 200 ft or less and visbys
less than 1/2SM. Steady low column cold advection will lead to
steepening lapse rates in the boundary layer and help in persistence
for IFR cig heights during the daytime. There is low confidence in
timing of improving cig heights Saturday night.

For DTW...Moist axis directly over DTW and nightfall will promote
lowering cig heights and denser fog development. Uncertainty exists
whether or not VLIFR flight conditions will impact DTW tonight. Cold
advection Saturday will eventually allow some snow flakes to mix in
Saturday afternoon.

DTW THRESHOLD PROBABILITIES...

* High in ceilings below 5000 feet tonight and Saturday.

* High in ptype as rain tonight. Moderate in a rain/wet snow mix
  Saturday afternoon.

* Low to moderate in ceilings and/or visibilities below 1/2SM and/or
  200 feet for a brief time tonight.

&&

.PREV DISCUSSION...
Issued at 337 PM EST Fri Jan 24 2020

DISCUSSION...

Ongoing moisture transport in association with the closed low system
centered over Illinois will continue to fuel light to moderate rain
showers this afternoon and evening before an expansive dry slot
wraps around the low and pushes through SE MI after 00Z. Upper-level
closed low will then continue to slowly meander towards Michigan
tonight, eventually settling over lower Michigan by 18Z Saturday. An
occluded front will draw north with the low late tonight and will
result in the veering of winds from the east to south and eventually
southwest, producing a slight uptick in moisture as overnight lows
and dew points reside in the mid-30s. This set-up will be conducive
for advection fog given the current snowpack, raising concerns for
areas of dense fog overnight. Dense fog has been observed upstream
across MO/IL/IN and increases confidence that this areas of fog will
edge north with the front.

Any fog development will hold on through the late morning/early
afternoon but will lead into another dreary day marked by continuous
overcast skies and on-off drizzle to eventual wintry mix during
daylight hours. Return flow from the departing low will cool the
column throughout the late afternoon and evening, transitioning any
liquid precipitation over to snow. Overall, given the broad scale
and weak forcing with the system, only expected snowfall total
accumulations to peak around a half-inch of slushy accumulation by
Sunday morning. Some models also suggest the stripping of moisture
in the DGZ early Sunday morning, so will need to keep an eye out for
a transition back to drizzle or freezing drizzle.

Westerly flow on Sunday to ensure another overcast day with renewed
rain/snow chances given wrap around moisture from the departing
low/support from PV anomaly, in addition to westerly flow tapping
moisture from Lake Huron. It is not until the passage of a cold
front, forecasted to push through on Monday, that brings the next
potential to see a break from precipitation. Despite the passage of
the prospective front, decent confidence from ensemble members
regarding little fluctuation with temperatures leading into the mid-
week period as highs hold in the mid-30s and gradually warming back
up into the upper-30s later in the week. Thus, high confidence for
above normal temperatures in the extended period.

MARINE...

Easterly winds will slowly start veering to northwesterly late this
evening through Saturday night as the low center crosses the lower
peninsula. This system will bring a mix of rain and snow lasting
through the day Sunday. The low is not particularly strong with a
weaker pressure gradient reducing the overall wind potential. Some
mixing of stronger winds aloft down to the surface could lead to
some gusts around 30kts tonight over northern/central Lake Huron,
but this will only be for a couple hours. There is a small craft
advisory along the Thumb Friday night as southeast flow creates
higher wave action in the nearshore zone.

HYDROLOGY...

Slow moving low pressure system will continue pushing into lower
Michigan late tonight and overnight, however, heaviest of the
rainfall will be observed through the afternoon. Light to moderate
rainfall will taper off late tonight and will transition over to
more of a mist/drizzle leading into Saturday. Storm total
accumulation from this afternoon`s rainfall through tomorrow
afternoon will range between one-quarter inch to one-half inch.
Ponding of water in flood prone areas will be possible with
additional rainfall, but given the longer event duration and lighter
to moderate rainfall intensity, no major flooding concerns expected.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Advisory until 4 AM EST Saturday for MIZ049-055-063.

Lake Huron...Small Craft Advisory until 4 AM EST Saturday for LHZ421-441>443.

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

$$

AVIATION.....CB
DISCUSSION...AM
MARINE.......KK
HYDROLOGY....AM


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