Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 170740
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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
Issued at 1203 AM EST Tue Jan 17 2017
Decreased coverage of heavier precipitation will allow surface
temperature to creep a little more above freezing in those trouble
spots north of DTW but it will take a couple more hours from
issuance time for that to occur. A transition to all rain will then
spread from the DTW area northward along with the next round of
heavier showers. Upstream thunderstorm coverage has been too low to
mention at any one of the terminal sites but expect at least a round
of heavy rainfall to move in from Illinois/Indiana during
the night through about mid morning.
In addition to precipitation type challenges, ceiling and visibility
will continue the downward trend into LIFR as the surface low and
warm front approach and move through SE Michigan. The latest
projections take the low center toward FNT by late morning with low
ceiling and fog breaking out along and ahead of the track over all
of SE Michigan. This will also be accompanied by fog reducing
visibility down to 1/2-1/4SM in classic warm frontal fashion. Any
breaks of improvement in the warm sector will be short-lived as the
trailing cold front moves through the region with IFR ceiling later
in the afternoon through Tuesday evening.
For DTW... Surface temperature is expected to continue gaining
ground above freezing during the night and as the next round of
heavier rain showers moves into the region. Ceiling and visibility
will also continue to fall into LIFR through most of the morning.
Prospect for thunder looks slim based on upstream observations.
//DTW Threshold Probabilities...
* High for ceiling 5000 ft or less tonight through Tuesday evening.
* Moderate ceiling and/or visibility below 200 ft/one half mile
through the morning.
* Low for thunderstorms through the morning.
MI...Winter Weather Advisory until 7 AM EST this morning FOR MIZ047>049-
Freezing Rain Advisory until 7 AM EST this morning FOR MIZ060>063-
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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