Alert archive / Pennsylvania / Mesoscale Discussions in 2011

Mesoscale Discussion 29

January 18, 20114 states

The Storm Prediction Center issued this mesoscale discussion at Jan 18, 2011, 12:29 AM EST for 4 states. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued
Jan 18, 2011, 12:29 AM EST (05:29 UTC)
Expired
Jan 18, 2011, 6:30 AM EST
In force
6 hr
Issued by
the Storm Prediction Center
All 23 counties

New Castle County, DE, Cecil County, MD, Harford County, MD, Camden County, NJ, Gloucester County, NJ, Hunterdon County, NJ, Mercer County, NJ, Somerset County, NJ, Warren County, NJ, Berks County, PA, Bucks County, PA, Carbon County, PA, Chester County, PA, Dauphin County, PA, Delaware County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Montgomery County, PA, Northampton County, PA, Philadelphia County, PA, Schuylkill County, PA, York County, PA

The radar

The Philadelphia radar (KDIX), 113 km from the middle of the area, began a volume at 05:28 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 00:00Z, 5.5 hours before the alert went out and 194 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-pSkew-T log-p diagram, Washington/Dulle, VA at 00:00Z on 2011-01-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 00:00Z on 2011-01-18The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 234 square meters per square second.1939587897117Sfc1 km3 km6 km9 kmRMLM
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
1527 m above ground
0-6 km bulk shear
53 kt
0-1 km storm-relative helicity
234 m²/s²
0-3 km storm-relative helicity
306 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.

080 
ACUS11 KWNS 180529
SWOMCD
SPC MCD 180529 
NJZ000-PAZ000-DEZ000-MDZ000-181130-

MESOSCALE DISCUSSION 0029
NWS STORM PREDICTION CENTER NORMAN OK
1129 PM CST MON JAN 17 2011

AREAS AFFECTED...LOWER DELAWARE RIVER VALLEY...SERN PA

CONCERNING...FREEZING RAIN 

VALID 180529Z - 181130Z

PRECIPITATION RATES ARE EXPECTED TO INCREASE AFTER 06Z ACROSS SERN
PA AND THE LOWER DELAWARE RIVER VALLEY...INCLUDING THE PHILADELPHIA
METRO AREA. P-TYPE WILL TRANSITION FROM SNOW TO FZRA BY EARLY
MORNING...WITH LIQUID PRECIPITATION RATES OF 0.05-0.10 IN/HR.

A SWATH OF WINTRY-MIXED PRECIPITATION OVER DELMARVA WILL CONTINUE
EXPANDING NWD INTO THE LOWER DELAWARE RIVER VALLEY AND SERN PA. 05Z
SFC OBJECTIVE ANALYSIS INDICATES THE SFC FREEZING LINE IS POSITIONED
FROM 15 NE ACY TO 30 SSW DOV...WITH LIGHT-MODERATE SNOW ALREADY
BEING OBSERVED OVER MUCH OF NJ AND SERN PA. AN EVENTUAL TRANSITION
TO FZRA IS EXPECTED TO OCCUR BY 06Z AS LOW-LEVEL WAA STRENGTHENS
ATOP SUB-FREEZING SFC TEMPERATURES. STRONG ISENTROPIC ASCENT WITH
40-50 KT LOW-LEVEL WINDS WILL YIELD INCREASING PRECIPITATION RATES
OVER THE AREA. WITH TIME...THE SFC FREEZING LINE IS EXPECTED TO
SHIFT SLIGHTLY NWD...WITH A TRANSITION TO RAIN FORECAST TO OCCUR
OVER NJ...NRN DEL...AND PORTIONS OF SERN PA BY 12Z.

..ROGERS.. 01/18/2011

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

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

LAT...LON   39687511 39507572 39517621 39667688 39957734 40497690
            40967560 40977504 40717457 40207444 39687511

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Jan 17, 7:44 PM ESTMesoscale DiscussionSPCAnne Arundel, Baltimore, Charles, Howard, Montgomery, Prince George's and 1 more6 hr
Jan 18, 3:33 AM ESTMesoscale DiscussionSPCBergen, Essex, Hudson, Morris, Passaic, Sussex and 2 more6 hr
Jan 18, 8:01 AM ESTMesoscale DiscussionSPCBergen, Essex, Hunterdon, Morris, Passaic, Somerset and 2 more4 hr

Nearby

Mesoscale Discussions in Pennsylvania, 2011Mesoscale Discussions in New Jersey, 2011Mesoscale Discussions in Maryland, 2011Every mesoscale discussion in 2011

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.