Alert archive / Maryland / Severe Thunderstorm Warnings in 2018

Severe Thunderstorm Warning 310, NWS Baltimore/Washington

December 21, 2018Montgomery County, Maryland

NWS Baltimore/Washington issued this severe thunderstorm warning at Dec 21, 2018, 4:29 PM EST for Montgomery County, Maryland. It was in force for 46 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Dec 21, 2018, 4:29 PM EST (21:29 UTC)
Expired: Dec 21, 2018, 5:15 PM EST
In force: 46 min
Issued by: NWS Baltimore/Washington
Area: Storm-based polygon
Hail: 0.75 in
Wind: 60.0 mph

County Montgomery County, MD

The radar

The Sterling radar (KLWX), 32 km from the middle of the area, began a volume at 21:30 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, 9.5 hours before the alert went out and 29 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: 91 J/kg
Mixed-layer CIN: -3 J/kg
Mixed-layer LCL: 533 m above ground
0-6 km bulk shear: 93 kt
0-1 km storm-relative helicity: 224 m²/s²
0-3 km storm-relative helicity: 139 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 1.0

Open this sounding in Storm Lab

The text

As transmitted.

298 
WUUS51 KLWX 212129
SVRLWX
MDC031-212215-
/O.NEW.KLWX.SV.W.0310.181221T2129Z-181221T2215Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
429 PM EST FRI DEC 21 2018

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Montgomery County in central Maryland...

* Until 515 PM EST.

* At 429 PM EST, more severe thunderstorms were located along a line 
  extending from Lansdowne to Reston, moving northeast at 45 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

  IMPACT...Damaging winds will cause some trees and large branches 
           to fall. This could injure those outdoors, as well as 
           damage homes and vehicles. Roadways may become blocked by 
           downed trees. Localized power outages are possible. 
           Unsecured light objects may become projectiles.

* Locations impacted include...
  Germantown, Rockville, Bethesda, Gaithersburg, Olney, Damascus,
  Lansdowne, Lowes Island, Poolesville, Aspen Hill, Potomac, North
  Bethesda, Montgomery Village, North Potomac, Redland, Great Falls,
  Boyds, Rossmoor, Wheaton-Glenmont and Wheaton.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors to protect yourself from wind and lightning. Trees around
you may be downed from damaging winds, so if you are near large
trees, move to an interior room on the lowest floor. Don't drive
underneath trees or in wooded areas until the threat has passed.

&&

LAT...LON 3934 7718 3927 7714 3924 7705 3919 7700
      3917 7701 3916 7698 3897 7719 3898 7724
      3903 7726 3906 7733 3907 7745 3913 7752
      3925 7740 3934 7720
TIME...MOT...LOC 2129Z 220DEG 40KT 3908 7746 3894 7735 

HAIL...<.75IN
WIND...60MPH
 
$$

DHOF

1 follow-up statement

116 
WWUS51 KLWX 212205
SVSLWX

Severe Weather Statement
National Weather Service Baltimore MD/Washington DC
505 PM EST FRI DEC 21 2018

MDC031-212215-
/O.EXP.KLWX.SV.W.0310.000000T0000Z-181221T2215Z/
Montgomery MD-
505 PM EST FRI DEC 21 2018

...THE SEVERE THUNDERSTORM WARNING FOR MONTGOMERY COUNTY WILL EXPIRE
AT 515 PM EST...
    
The storms which prompted the warning have moved out of the area.
Therefore the warning will be allowed to expire.

LAT...LON 3934 7718 3927 7714 3924 7705 3919 7700
      3917 7701 3916 7698 3897 7719 3898 7724
      3903 7726 3906 7733 3907 7745 3913 7752
      3925 7740 3934 7720
TIME...MOT...LOC 2205Z 220DEG 40KT 3938 7713 3924 7702 

$$

DHOF

The office that day

Everything else NWS Baltimore/Washington issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 21, 2:17 AM EST	Coastal Flood Warning	LWX	Anne Arundel, Saint Mary's	25 hr
Dec 21, 3:37 AM EST	Areal Flood Warning	LWX	Baltimore, Harford	5 hr
Dec 21, 1:48 PM EST	Coastal Flood Advisory	LWX	Anne Arundel, Saint Mary's	13 hr
Dec 21, 3:51 PM EST	Severe Thunderstorm Warning	LWX	Howard, Montgomery	24 min
Dec 21, 4:45 PM EST	Severe Thunderstorm Warning	LWX	Baltimore, Carroll, Harford	45 min
Dec 21, 5:01 PM EST	Severe Thunderstorm Warning	LWX	Carroll, Frederick, Howard	29 min

Nearby

Severe Thunderstorm Warnings in Maryland, 2018 Every severe thunderstorm warning 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.