Alert archive / Arkansas / Mesoscale Discussions in 2018

Mesoscale Discussion 21

January 12, 20187 counties in Arkansas; 5 parishes in Louisiana; Issaquena County, Sharkey County, Washington County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Jan 12, 2018, 3:38 AM CST for 7 counties in Arkansas; 5 parishes in Louisiana; Issaquena County, Sharkey County, Washington County, Mississippi. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Jan 12, 2018, 3:38 AM CST (09:38 UTC)
Expired: Jan 12, 2018, 9:45 AM CST
In force: 6 hr
Issued by: the Storm Prediction Center

Counties Ashley County, AR, Bradley County, AR, Calhoun County, AR, Chicot County, AR, Drew County, AR, Ouachita County, AR, Union County, AR, East Carroll Parish, LA, Lincoln Parish, LA, Morehouse Parish, LA, Union Parish, LA, West Carroll Parish, LA, Issaquena County, MS, Sharkey County, MS, Washington County, MS

The radar

The Little Rock radar (KLZK), 195 km from the middle of the area, began a volume at 09:37 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.

The nearest sounding before it

Jackson, MS (KJAN), launched 00:00Z, 9.6 hours before the alert went out and 189 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 136 J/kg
Mixed-layer CIN: -31 J/kg
Mixed-layer LCL: 728 m above ground
0-6 km bulk shear: 62 kt
0-1 km storm-relative helicity: 41 m²/s²
0-3 km storm-relative helicity: 45 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

As transmitted.

043 
ACUS11 KWNS 120938
SWOMCD
SPC MCD 120938 
MSZ000-ARZ000-LAZ000-121545-

Mesoscale Discussion 0021
NWS Storm Prediction Center Norman OK
0338 AM CST Fri Jan 12 2018

Areas affected...Parts of southern AR...northern LA and west-central
MS

Concerning...Winter mixed precipitation 

Valid 120938Z - 121545Z

SUMMARY...A mixture of freezing rain and sleet will continue to
spread eastward during the late overnight into the morning across
south-central and southeast Arkansas, north-central and northeast
Louisiana, and into west-central Mississippi.  Freezing rain rates
should generally be up to 0.05-0.10 inches per 3 hours, though
higher rates (0.10+ inch/hour) associated with a north-south band of
moderate precipitation will remain possible, as this band advances
east.  Locations in south-central Arkansas and north-central
Louisiana should have a decrease in wintry precipitation by 12-13Z.

DISCUSSION...GOES-16 IR imagery indicated a north-south band of
cooling cloud tops moving eastward through south-central AR and
north-central LA early this morning, with surface observations from
KCDH and KELD to KRSN indicating moderate to heavy precipitation
rates since 08-09Z in this band.  These higher rates and cooling
cloud tops are co-located with a compact area of forcing for ascent
attendant to the progressive shortwave trough.  Forecast soundings
suggest cooling of the surface to near-surface air (generally below
900 mb) will occur faster than the lower troposphere from 750-900
mb, such that freezing rain and eventually a mixture of sleet and
freezing rain will occur from west to east across the discussion
area.

..Peters.. 01/12/2018

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

ATTN...WFO...JAN...LZK...SHV...

LAT...LON   32699273 33059299 33619297 33809264 33829190 33739149
            33539090 33279064 33119066 32789074 32529110 32499197
            32529260 32699273

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jan 11, 8:43 PM CST	Mesoscale Discussion	SPC	Clay, Craighead, Fulton, Greene, Independence, Izard and 6 more	6 hr
Jan 12, 2:00 AM CST	Mesoscale Discussion	SPC	Crittenden, Desha, Lee, Mississippi, Phillips, St. Francis	5 hr

Nearby

Mesoscale Discussions in Arkansas, 2018 Mesoscale Discussions in Louisiana, 2018 Mesoscale Discussions in Mississippi, 2018 Every mesoscale discussion in 2018

Sources

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.