Alert archive / Virginia / Mesoscale Discussions in 2018

Mesoscale Discussion 4

January 3, 2018Dorchester County, Somerset County, Wicomico County, Maryland; 20 counties in North Carolina; 28 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Jan 3, 2018, 9:04 PM EST for Dorchester County, Somerset County, Wicomico County, Maryland; 20 counties in North Carolina; 28 counties in Virginia. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Jan 3, 2018, 9:04 PM EST (02:04 UTC)
Expired: Jan 4, 2018, 3:00 AM EST
In force: 6 hr
Issued by: the Storm Prediction Center

All 51 counties

Dorchester County, MD, Somerset County, MD, Wicomico County, MD, Beaufort County, NC, Bertie County, NC, Camden County, NC, Chowan County, NC, Currituck County, NC, Edgecombe County, NC, Gates County, NC, Greene County, NC, Halifax County, NC, Hertford County, NC, Lenoir County, NC, Martin County, NC, Northampton County, NC, Pasquotank County, NC, Perquimans County, NC, Pitt County, NC, Tyrrell County, NC, Washington County, NC, Wayne County, NC, Wilson County, NC, Accomack County, VA, Charles City County, VA, City of Chesapeake, VA, City of Emporia, VA, City of Franklin, VA, City of Hampton, VA, City of Newport News, VA, City of Norfolk, VA, City of Poquoson, VA, City of Portsmouth, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Williamsburg, VA, Gloucester County, VA, Greensville County, VA, Isle of Wight County, VA, James City County, VA, Lancaster County, VA, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Prince George County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 73 km from the middle of the area, began a volume at 02:05 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

Wallops Is Stn, VA (KWAL), launched 00:00Z, 2.1 hours before the alert went out and 113 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 766 m above ground
0-6 km bulk shear: 69 kt
0-1 km storm-relative helicity: 187 m²/s²
0-3 km storm-relative helicity: 273 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

835 
ACUS11 KWNS 040205
SWOMCD
SPC MCD 040204 
MDZ000-DEZ000-VAZ000-NCZ000-040800-

Mesoscale Discussion 0004
NWS Storm Prediction Center Norman OK
0804 PM CST Wed Jan 03 2018

Areas affected...Eastern North Carolina...southeast Virginia
southeast Maryland and southern Delaware

Concerning...Heavy snow 

Valid 040204Z - 040800Z

SUMMARY...Bands of moderate to heavy snow with rates occasionally up
to or exceeding 1 inch per hour are expected to evolve this evening
and continue into the early morning over the coastal Middle
Atlantic.

DISCUSSION...Winter storm affecting eastern NC as of 0130Z this
evening is in the process of reorganizing, with primary snow bands
expected to develop from northeast NC through southeast VA and
southeast MD during the next few hours. An area of pressure falls
persists from far eastern NC into the western Atlantic. The offshore
surface low will undergo significant deepening as it develops
northward along primary baroclinic zone tonight in response to
strong forcing for ascent attending the shortwave trough now
approaching the SC coast. This process will be accompanied by a
corridor of strengthening 850-700 mb frontogenetic forcing northwest
of the surface low and within favored dendrite growth zone,
resulting in moderate to occasionally heavy snow with some of the
bands. Precipitation starting out as rain near the northeast NC and
far southeast VA coasts due to presence of a melting layer should
gradually change to snow this evening as cold advection and melting
lowers the temperature in this layer to sub 0C.

..Dial.. 01/04/2018

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

ATTN...WFO...PHI...AKQ...MHX...LWX...RAH...

LAT...LON   38647523 37807544 36977582 35807585 35297676 35097837
            37427720 38637598 38647523

Nearby

Mesoscale Discussions in Virginia, 2018 Mesoscale Discussions in North Carolina, 2018 Mesoscale Discussions in Maryland, 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.