Mesoscale Discussion 22

Issued

Jan 6, 2017, 6:13 PM EST (23:13 UTC)

Expired

Jan 7, 2017, 12:15 AM EST

In force

6 hr

Issued by

the Storm Prediction Center

The Atlanta radar (KFFC), 105 km from the middle of the area, began a volume at 23:16 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

227 
ACUS11 KWNS 062313
SWOMCD
SPC MCD 062313 
SCZ000-GAZ000-NCZ000-TNZ000-ALZ000-070515-

Mesoscale Discussion 0022
NWS Storm Prediction Center Norman OK
0513 PM CST Fri Jan 06 2017

Areas affected...northern GA into far northern SC

Concerning...Winter mixed precipitation 

Valid 062313Z - 070515Z

SUMMARY...Precipitation is expected to transition to snow across far
northern GA and adjacent portions of northern SC over the next
couple of hours as surface temperatures quickly cool. A bit further
south, a wintry mix is expected with freezing rain and sleet,
possibly mixed with snow. This wintry mix will include the greater
Atlanta metro area into the nighttime hours.

DISCUSSION...Surface temperatures across the MCD area ranged from
around 30 to 35 degrees F in GA with 35 to 40 degree temperatures
being reported in adjacent portions of northern SC as of 23z.
Looking at the surface wet-bulb temperatures, many areas across far
northern GA should already be seeing a transition to snow. This is
further supported by radar observations from the KFFC WSR-88D, in
conjunction with latest RAP forecast soundings, indicating any
melting layer aloft is quickly eroding across the far northern MCD
area. Snowfall rates should generally be less than 1 in/hr but some
spotty/brief periods of heavy snow is possible into the nighttime
hours. 

Further south, along a line roughly extending from Polk County GA
east-northeast to Oconee County SC, southward to Heard County GA to
Hart County, GA /red shaded area in the MCD graphic/...mixed
precipitation types are expected. A 21z RAOB from FFC showed a
classic freezing rain sounding with an elevated warm nose around 850
mb of 5.5 deg C. Cold low level advection in conjunction with
wet-bulb temperatures approaching freezing over the next 1-2 hours,
should result in a transition toward sleet and freezing rain...and
possibly some snow mixed in later tonight when the elevated warm
layer erodes /probably not until after 06z/. In fact, an mPING
report was submitted in Cobb County GA at 2250z indicating freezing
rain. This ground truth further supports a transition from rain to
mixed wintry precip types very soon across the southern half of the
MCD area.  Precipitation rates generally should be light, with
periods of moderate to heavy freezing rain at times through this
evening.

..Leitman.. 01/06/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GSP...MRX...FFC...BMX...HUN...

LAT...LON   33548538 34138558 34718564 34998527 35088391 35098334
            34948300 34668297 34508294 33968354 33368471 33318525
            33548538

Mesoscale Discussions in Georgia, 2017Mesoscale Discussions in North Carolina, 2017Mesoscale Discussions in South Carolina, 2017Every mesoscale discussion in 2017

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.