Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 171755
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1255 PM EST Tue Jan 17 2017
The center of a low pressure system is current tracking through SE
MI leading to varying conditions across the region. An occluded warm
front is starting to lift north of the MI/OH border which should
bring improving conditions (MVFR) into the afternoon hours, but IFR
conditions will continue for most locations until then. One question
is, will the boundary lift north of PTK or not? Should be close to
the PTK to PHN line. CIGS look to be locked in around 300-400 feet
for the next few hours under the low but could lift near 1000 ft as
drier air moves in with increasing SW flow. Fog has developed north
of the boundary and should persist through about 20Z. Conditions
will deteriorate again this evening as a secondary wave slides
through the area. Expect mostly IFR conditions through tonight.
For DTW... The occluded front is just south of the terminal which
means fog and LIFR cigs will continue another hour or so. Conditions
may then improve to MVFR for a brief period before IFR returns for
the evening and overnight.
//DTW Threshold Probabilities...
* High for ceiling below 5000 ft through the TAF period.
* Low for ceiling and/or visibility below 200 ft/one half mile.
* High in precip type being all rain today.
Issued at 240 AM EST Tue Jan 17 2017
Latest water vapor imagery shows center of upper level wave over
northeast Illinois, as second sheared out upper wave/trough moving
through Minnesota interacts, scooting our lead wave rather quickly
off to the East along the southern Michigan border this morning. As
of 2 AM, warm front has failed to move into Michigan, but very
impressive warm and moist air in the 925-850 mb level (upper single
numbers for temps and dew pts for that matter) has allowed for just
enough warming at the surface/warmer rain drops to allow for
changeover to rain most locations, despite the backed surface flow
from the East holding temps around freezing, with dew pts in the 31
to 33 range. Even with little or no further ice accumulation
expected, the decision was made earlier to extend headlines to 7 AM,
as untreated secondary roads remain very icy. Temperatures holding
in the 32-34 degree range just not warm enough to fully melt the
Latest model guidance, surface analysis/pressure falls now indicating
surface low tracking farther south, close to I-69 corridor, which
will keep northern half of the CWA on the colder side today, below
40 degrees. Still tough call on how warm to go toward the Ohio
border/Detroit, as high temps really could be anywhere from mid 40s
to mid 50s (see current reading in central Indiana), and will split
the difference and go around 50 degrees. 4Z rap is offering up the
warmest solution, while NAM is one of the coldest.
The farther south low track resulting in weaker pressure gradient
this morning and low level convergence looks to be conducive for
fog developing as moist airmass comes across the cold ground,
but not anticipating dense fog advisory due to lack of snow cover
and upstream obs mostly indicating spotty 1/4 SM visibilities.
Left the chance of thunderstorms in for this morning for
southern half of the CWA, as -21 C cold core at 500 mb tracks
overhead, with pocket of 7 C/km mid level lapse rates. Some
drying out/subsidence this afternoon behind the lead wave, but
Midwest upper level wave moving through Tonight, likely sufficient
to generate some light rain showers/drizzle this evening with
leftover low level moisture/cyclonic flow in place.
Modest low level cold advection through the night (850 mb temps
holding above 0 C), with surface temps dropping off toward freezing.
Expecting precipitation to have shut off before this occurs,
otherwise freezing drizzle could be a concern with possible lack of
ice nucleui as the mid levels dry out late. If there is any
changeover to snow (doubtful) before precip shuts off, would not
expect any accumulation.
Upper level ridging building over the Great Lake region
Wednesday/Thursday providing dry and mild conditations, especially
Thursday with increasing low level southwest flow which should send
temps well into the 40s under mostly sunny skies.
Still watching the closed 500 mb low over the Central Conus for the
end of the work week, with the 00z euro lifting surface low and
rain showers through Lower Michigan on Friday. Meanwhile, the
GFS/Canadian indicating a drier solution as the system shears out
faster, but still worthy of chance pops.
The surface low is forecast to track from far southern Lake Mi early
this morning to the southern Lake Huron basin by late afternoon.
This track will cause an enhancement in the easterly winds across
northern and central Lake Huron today. There will be strong over
lake stability. However, the gradient will still support some gusts
around 25 knots over the open lake. A weakening in the gradient will
occur as the sfc low heads east of the region tonight. This along
with continued strong over-lake stability will support light winds.
This period of light winds will persist into Wednesday before a
modest increase in a southwest gradient ensues.
Based on liquid rainfall totals thus far and the expected additional
rain this morning, 24-hour QPF amounts ending by early this
afternoon between a half and three quarters of an inch seem
reasonable. This will keep river levels in check. There will be some
locally higher rainfall amounts this morning due some potential
convection. If this occurs over the Rouge or Clinton River basins,
there is a chance that these rivers may approach bankfull. Additional
rainfall amounts through the rest of the week are expected to be
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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