Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210840

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
340 AM EST Sun Jan 21 2018


Closed mid level circulation centered over the southern Rockies
early this morning projected to lift into the plains today.
Subsequent strong dynamic response will commence immediately
downstream of the pending height falls, sustaining a broad corridor
of moist isentropic ascent within an increasing low level southwest
flow. Early stages of this low level moistening process now underway
locally, as a lead wing of higher 925 mb relative humidity
translates into an extensive stratus canopy. More pronounced
reduction in ceiling heights looming over Indiana indicative of the
pending greater moisture advection yet to come, focused along an
organizing warm frontal structure that eventually migrates into the
region late today and tonight. The existing moist/mild environment
still generally characterized by a lack of ascent through the
column, suggesting that any light precipitation production will
remain in the form of drizzle today. Given the milder start but
higher cloud coverage, highs of lower 40s remain reasonable.

Little variation in conditions through tonight. Synoptic forcing
tied to the inbound mid latitude cyclone will hold off until Monday
morning. This will simply favor the perpetuation of drizzle or light
rain within areas of fog for a bulk of the overnight period.
Potential for some locally dense fog to emerge post-sunset, focused
along and north of the advancing warm front. Very small window for
possible freezing drizzle/rain across northern Midland/Bay counties
and the northern thumb early Monday morning as temperatures flirt
with the freezing mark for a time.

A period of robust dynamic ascent anchored by solid low level jet
forcing, upper diffluence and theta-e advection situated at the edge
of a pronounced upper height fall gradient will support widespread
rainfall during the Monday period. Convective element to this
environment could lead to some heavier rainfall at times, with the
possibility for a few rumbles of thunder. Precipitation chances will
briefly diminish as the mid level dry slot punches in late Monday
into early Monday night. This may allow an already mild resident
airmass to witness some late day recovery, so highs well into the
40s certainly look attainable.

Sizable upper low will pivot across the region Monday night and
Tuesday. Lead cold frontal boundary anchoring the edge of the
inbound upper height fall gradient will sweep through late Monday
night. The associated increase in cva and frontal convergence will
support an uptick in precipitation coverage by Tuesday morning.
Unsettled conditions throughout Tuesday will maintain the potential
for showers. Only weak cold air advection will ensue with this
initial frontal passage, so boundary layer conditions may remain too
warm to support snow outside of the heaviest bursts. Forecast will
continue to simply call for a rain/snow mix on Tuesday, with
temperatures slowly falling through the upper and middle 30s during
the day.  Best shot of accumulating snow, albeit brief, comes late
Tuesday or early Tuesday night as the secondary stronger cold front
sweeps through.  Highest potential would be focused toward the north
/Saginaw valley and thumb region/.



A weak cold front has dropped into northern Lake Huron and will
stall there today. An approaching low pressure system over the
Plains will lift a warm front into the southern Lakes late this
evening which will bring mild air in from the Ohio valley over all
other marine areas with steady southerly flow. The low will
strengthen today while lifting slowly toward southern Lake MI,
eventually passing eastward through the region Monday night and
Tuesday. This system will produce widespread coverage of
precipitation, primarily rain from Saginaw Bay southward and a
wintry mix to the north. The position of the low over central Lake
Huron will result in increased easterly flow over the north half of
the lake on Monday. A gale watch remains in effect for this briefly
higher period of winds. The wind will weaken and then shift
northwest in the wake of the low on Tuesday. Northwest wind trailing
the system could approach gales briefly Tuesday night into



A large low pressure system will continue to bring very mild air
into the region through Monday. This will result in additional
melting snow followed by increasing coverage of rain showers tonight
which will become widespread Monday. The snow will melt but the
ground will not thaw fast enough to prevent runoff from both the
snow and rainfall. This could result in ponding of water on roads
and other prone areas. Creeks and streams around the region could
also become elevated due to runoff. Total rainfall is expected to be
around 1 inch between tonight and Monday night with most falling
during Monday.


Issued at 1151 PM EST Sat Jan 20 2018


Warm front will become increasingly organized as it lifts northward
into the forecast area later tonight. Outstanding, synoptic scale
forcing will aid in the development of the boundary and provide what
should be a fair amount of overrunning and isentropic ascent with
time. MVFR stratus deck largely arrived on time. Question now
becomes whether or not the cloud line remains progressive and moves
northward. Model data is suggesting that it may have trouble now
that its in place over metro Detroit. Regardless, first push of 300K
isentropic ascent will arrive over the Detroit terminals after 09Z
which should allow for onset of IFR. A secondary cloud line has
emerged on satellite upstream and times very well to 09Z IFR onset.
Given the lack of deep saturation in the forecast soundings,
especially in ARW and RAP soundings, continue to favor a -dz
mention.  High confidence in surface air temperatures above
freezing. Widespread rain is expected to hold off until around
daybreak Monday.

For DTW... VFR will lower to MVFR in stratus during the evening, and
then down to IFR/LIFR in stratus and fog overnight. Temperatures are
expected to be above freezing before the greatest potential for
drizzle develops Sunday morning.


* High for ceiling 5000 ft or less tonight through Sunday.

* Low confidence in visibilities less than 1/2 mile.

* Low confidence in ceiling heights at or less than 200 feet.

* High for drizzle as precipitation type Sunday morning.


Lake Huron...Gale Watch from Monday morning through Monday evening for

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



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