NWS Forecast Discussion
FXUS63 KDTX 211442
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
942 AM EST Sun Jan 21 2018
Dense fog has drifted northward to the I-96 corridor resulting in
locations dropping to one quarter of a mile or less. A Dense Fog
Advisory is now in effect through at least 1 pm this afternoon.
Patchy dense fog is present over much of the area to the north of
I-96, especially across the Tri-Cities and Thumb where transient
visibility reduction to one mile or less is being observed. Will be
monitoring the possible expansion of the Dense Fog Advisory northward
or extension of current Advisory passed 1 pm.
Issued at 535 AM EST Sun Jan 21 2018
A warm front currently draped along the Ohio River Valley will
slowly strengthen as it lifts toward southern MI by tonight.
Southerly winds will usher in several rounds of moisture up into the
area through the period. This will lead to deteriorating conditions
early in the taf which should then hold through the forecast. Look
for IFR conditions with both CIGS and VSBYS today and tonight, with
some potential for LIFR with some obs upstream supporting this. Will
amend as needed to account for this. Fog will be prevalent today
with some drizzle possible at times. Rain will arrive late tonight
into Monday morning.
For DTW... IFR stratus and fog over the terminal should hold through
the forecast with some risk of LIFR at times. Today should be mostly
dry with only the risk of some drizzle at times. Rain will move in
around 09Z tonight with best chances occuring on Monday.
/DTW THRESHOLD PROBABILITIES...
* High for ceiling 5000 ft or less through Monday.
* 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...high for rain late
Issued at 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
MI...Dense Fog Advisory until 1 PM EST this afternoon for MIZ075-076-082-
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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