Winter Storm Warning for Today and Tonight

Well, we finally have things narrowed down for the storm this morning, so let’s get down to it.

Winter Storm Warning

...WINTER STORM WARNING REMAINS IN EFFECT FROM 2 PM THIS
AFTERNOON TO 4 AM EST SATURDAY...

* WHAT...Heavy, wet snow expected. Total snow accumulations of 6
  inches or more, with isolated amounts around 10 inches. Winds
  gusting as high as 40 mph.

* WHERE...Portions of south central and southwest Michigan.

* WHEN...From 2 PM this afternoon to 4 AM EST Saturday.

* IMPACTS...Travel could be very difficult. The hazardous
  conditions could impact the evening commute.

Winter Storm Warning

...WINTER STORM WARNING REMAINS IN EFFECT FROM NOON EST /11 AM
CST/ TODAY TO MIDNIGHT EST /11 PM CST/ TONIGHT...

* WHAT...Wet heavy snow expected. Isolated thunderstorms
  possible. Total snow accumulations of 4 to 8 with isolated
  higher amounts around 10 inches. Winds gusting as high as 45
  mph.

* WHERE...Portions of northern Indiana, southwest Michigan and
  northwest Ohio.

* WHEN...From noon EST /11 AM CST/ today to midnight EST /11 PM
  CST/ tonight.

* IMPACTS...Travel could be very difficult. The hazardous
  conditions could impact the evening commute. The combination
  of gusty winds and heavy, wet snow could bring down tree
  branches and lead to power outages.

Winter Storm Warning

...WINTER STORM WARNING REMAINS IN EFFECT FROM 3 PM THIS
AFTERNOON TO 4 AM EST SATURDAY...

* WHAT...Heavy snow expected. Total snow accumulations of 6 to 10
  inches. Winds gust as high as 35 to 45 mph.

* WHERE...Huron, Saginaw, Tuscola, Sanilac, Shiawassee, Genesee
  and Lapeer Counties.

* WHEN...From 3 PM this afternoon to 4 AM EST Saturday.

* IMPACTS...Travel could be very difficult. The hazardous
  conditions could impact the evening commute.

* ADDITIONAL DETAILS...Very heavy snow rates, on the order of 1 to
  2+ inches per hour, are likely over a short three to six hour
  window. These heavy rates are likely mainly late this evening
  into tonight. The peak rates occur this evening followed by
  moderate snow after midnight. Winds gusting to 45 mph may result
  in rapid reductions to visibility and isolated power outages
  will be possible from the cumulative impacts of accumulating wet
  snow and gusty winds.

Winter Storm Warning

...WINTER STORM WARNING REMAINS IN EFFECT FROM 1 PM THIS
AFTERNOON TO 4 AM EST SATURDAY...

* WHAT...Heavy wet snow expected. Total snow accumulations of 6
  to 10 inches. Winds gust as high as 35 to 45 mph.

* WHERE...St. Clair, Livingston, Oakland, Macomb, Washtenaw,
  Wayne, Lenawee and Monroe Counties.

* WHEN...From 1 PM this afternoon to 4 AM EST Saturday.

* IMPACTS...Travel could be very difficult. The hazardous
  conditions could impact the evening commute.

* ADDITIONAL DETAILS... Very heavy snow rates, on the order of 1
  to 2+ inches per hour, are likely over a short three to six hour
  window. The peak rates occur this afternoon into this evening
  followed by moderate snow after midnight. Winds gusting to 45
  mph may result in rapid reductions to visibility and isolated
  power outages will be possible from the cumulative impacts of
  accumulating wet snow and gusty winds. Amounts may be on the
  lower end of the range for Wayne, Lenawee and Monroe counties
  due to intrusion of warmer air resulting in periods of rain.

Winter Weather Advisory

...WINTER WEATHER ADVISORY REMAINS IN EFFECT FROM 2 PM THIS
AFTERNOON TO 4 AM EST SATURDAY...

* WHAT...Snow expected. Total snow accumulations of 2 to 6
  inches. Winds gusting as high as 35 mph.

* WHERE...Mecosta, Isabella, Montcalm, Gratiot, Ottawa and Kent
  counties.

* WHEN...From 2 PM this afternoon to 4 AM EST Saturday.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the evening commute.

Grand Rapids Forecast

Lansing Forecast

Kalamazoo Forecast

Forecast Discussion

-- Impactful accumulating snow today --

A surface low over AR this morning will continue northeastward
today, reaching the vicinity of north-central OH by late this
evening. An associated, negatively tilted mid/upper trough, in
conjunction with a coupled upper-level jet structure, will
facilitate continued deepening of the low later this morning via
strong forcing for ascent and upper-level mass divergence, with
the low likely attaining a SLP of ~975 mb over southern IL this
afternoon. In tandem with the occlusion process, an upper-level "PV
hook" structure will evolve above/adjacent to a developing TROWAL
airstream. Strong QG forcing for ascent within the TROWAL will
maintain a shield of precip as it crosses much of Lower MI
beginning this afternoon. This ascent will be augmented by strong
midlevel frontogenesis that will favor vigorous mesoscale banding.

Forecast confidence remains lower than typical with respect to
snowfall amounts today. The axis of heaviest ensemble-median
snowfall (10:1 SLR) in the EPS has shown continued NW-SE waffling in
recent runs, with a net eastward shift in the past 24 h. However,
the GEFS axis still remains east of the EPS axis. In the
deterministic ECMWF and GFS, the placement of the heavy-snow axis
resembles that of their respective ensemble medians, and the 06z
HRRR is somewhat of an intermediate solution between the GFS and
ECMWF. Not surprisingly, very large ensemble spread in snowfall
still exists at many locations, particularly along the sharp
gradient of accumulation that is situated immediately northwest of
the heaviest median-snowfall axis. At Grand Rapids, for example,
the EPS 25th/75th percentiles (using 10:1 SLR) are approximately
6"/13", with min/max members of 1"/17". This is fairly remarkable
for short-range ensemble spread.

Forecast profiles suggest that rain is possible at the outset, but
low wet-bulb 0C heights should result in a transition to snow as
top-down column saturation and evaporative cooling occur. The DGZ
is somewhat shallow, but is generally situated within weak moist
static stability, and this may facilitate intense snow rates,
especially within mesoscale bands. Below the DGZ, a deep, near-
isothermal layer (warmer than -10C) is present at times and should
favor ice-crystal growth by aggregation, yielding periods with
fluffy snowflake clumps and temporarily higher SLRs.

No changes are planned to the headlines with this update. Across the
Winter Storm Warning area, total snowfall of 6"+ is likely, with isolated
higher amounts (10"+) possible. Snowfall rates may also exceed 1"
per hour. Across the Winter Weather Advisory area, snowfall of
2-5" is expected. Slippery, snow-covered roads are likely to
result in hazardous travel across the warning and advisory area.

-- Slight chance of rain/snow on Sat evening/night --

Models indicate that a shortwave trough will approach the region
late Sat. Lift ahead of this feature may produce light rain or snow
in some areas, with more ensemble members now indicating measurable
precip.

-- Rain/snow likely Sun night and Mon --

Guidance continues to indicate that a modest lee cyclone will
develop over the CO high plains on Sun, then propagate along a
baroclinic zone toward the Great Lakes on Mon. Thermal profiles
suggest predominately rain across the southern forecast area, with
snow possible north.

-- Wed and beyond --

Large forecast uncertainty exists for Wed-Fri of next week. EPS
and GEFS ensemble means differ considerably with respect to the
evolution/placement of large-scale 500-mb height anomalies during
this timeframe. Namely, the EPS mean shifts a longwave trough from
the Rockies on Wed into the central CONUS on Fri, while the GEFS
mean maintains quasi-zonal / less-amplified flow over the CONUS
through Fri.

Regardless of these differences, there is broad consensus in the
ensemble means for a shift in the large-scale regime by next
weekend. In particular, a longwave ridge is likely to become
established near the West Coast next weekend, with a longwave trough
likely over the eastern CONUS. This will favor below-normal temps
for the region, with highs likely remaining in the low 30s next
weekend.