Alert archive / Maryland / Mesoscale Discussions in 2012

Mesoscale Discussion 40

January 21, 2012New Castle County, Delaware; 4 counties in Maryland; Chester County, Delaware County, Philadelphia County, Pennsylvania

The Storm Prediction Center issued this mesoscale discussion at Jan 21, 2012, 7:07 AM EST for New Castle County, Delaware; 4 counties in Maryland; Chester County, Delaware County, Philadelphia County, Pennsylvania. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Jan 21, 2012, 7:07 AM EST (12:07 UTC)
Expired: Jan 21, 2012, 10:00 AM EST
In force: 3 hr
Issued by: the Storm Prediction Center

Counties New Castle County, DE, Baltimore County, MD, Cecil County, MD, City of Baltimore, MD, Harford County, MD, Chester County, PA, Delaware County, PA, Philadelphia County, PA

The radar

The Dover AFB radar (KDOX), 106 km from the middle of the area, began a volume at 12:11 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

Washington/Dulle, VA (KIAD), launched 12:00Z, 0.1 hours before the alert went out and 152 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: 1 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 473 m above ground
0-6 km bulk shear: 69 kt
0-1 km storm-relative helicity: 595 m²/s²
0-3 km storm-relative helicity: 779 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

219 
ACUS11 KWNS 211207
SWOMCD
SPC MCD 211207 
NJZ000-PAZ000-DEZ000-MDZ000-211500-

MESOSCALE DISCUSSION 0040
NWS STORM PREDICTION CENTER NORMAN OK
0607 AM CST SAT JAN 21 2012

AREAS AFFECTED...NERN MD / NRN DE / SERN PA / WRN NJ

CONCERNING...FREEZING RAIN 

VALID 211207Z - 211500Z

AN INCREASE IN PRECIPITATION RATES /PRIMARILY FREEZING RAIN/ IS
EXPECTED TO OCCUR DURING THE 12-15Z PERIOD OVER PORTIONS OF THE
UPPER CHESAPEAKE BAY AND LOWER DE RIVER VALLEY REGION.  FREEZING
RAIN WILL BE THE PRIMARY P-TYPE INVOF THE BALTIMORE METRO WITH A
CHANGEOVER FROM SNOW TO SLEET AND FREEZING RAIN FARTHER NE NEAR AND
N OF THE GREATER PHILADELPHIA AREA.

RECENT SURFACE ANALYSIS SHOWS THE 32 DEG F ISOTHERM EXTENDING IN A
SW-NE ORIENTATION FROM NEAR THE MOUTH OF THE POTOMAC NEWD IN A WAVY
FASHION INTO SRN NJ.  SURFACE OBS THE PAST 3 HRS SHOW TEMPS WARMING
1-2 DEG F OVER THE MCD AREA.  A CONCENTRATED ZONE OF PRESSURE FALLS
IS EVIDENT OFF THE NJ/DE COAST WHERE AN ELY FETCH FROM THE
RELATIVELY WARMER SHELF WATERS HAS LED TO A 5-10 DEG WARMING THE
PAST FEW HRS NEAR THE IMMEDIATE MD/DE/NJ COAST.  RADAR MOSAIC SHOWS
A DISJOINTED PRECIP PLUME BEGINNING TO SPREAD EWD E OF THE FALL LINE
AND THIS WILL OVERSPREAD THE REGION THE NEXT FEW HOURS.

LATEST MODEL GUIDANCE SHOWS THE TERMINUS OF A 50 KT LLJ SHIFTING NE
AND AWAY FROM THE REGION --IN CONJUNCTION WITH A DEVELOPING SURFACE
LOW OFF THE NJ COAST-- BETWEEN 12Z-18Z AS AN ELONGATED SHORTWAVE
TROUGH APPROACHES FROM THE W.  AS THIS OCCURS...AN INCREASINGLY
MOIST AIRMASS /CHARACTERIZED BY PW NEAR 0.75 INCH/ ATOP A
SUBFREEZING LAYER...AND INCREASING LARGE SCALE LIFT WILL FAVOR
PRECIPITATION RATES 0.05-0.10 INCH/3 HRS.  FORECAST SOUNDINGS NEAR
THE PHILADELPHIA METRO SHOW A GRADUAL TRANSITION IN P-TYPE FROM SNOW
TO A MIX OF SLEET/FREEZING RAIN BY MID MORNING.  FARTHER S NEAR
BALTIMORE...A MORE PRONOUNCED WARM NOSE WILL FAVOR PRIMARILY
FREEZING RAIN.

..SMITH.. 01/21/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...PHI...CTP...LWX...

LAT...LON   39417693 39597670 40187526 40287481 40167464 40007468
            39117654 39177681 39417693

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jan 21, 12:59 AM EST	Mesoscale Discussion	SPC	Adams, Allegheny, Armstrong, Bedford, Berks, Blair and 29 more	4 hr

Nearby

Mesoscale Discussions in Maryland, 2012 Mesoscale Discussions in Pennsylvania, 2012 Mesoscale Discussions in Delaware, 2012 Every mesoscale discussion in 2012

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.