Prob severe...a suggestion

While tracking the 35 dBZ echo is good with developing convection, the example image below shows where this methodology fails.  Note the new discrete storm that has developed to the north of the mature supercell (dropping hen egg size hail).  The prob severe model contouring provides no usefull information for the storm to the north as it is unduly influenced by the storm to the south.

Perhaps as storms mature, a new inner contour based on 50 dBZ would provide storm specific information for the northernmost cell?

Tornadotod

Eastern Pittsylvania County Severe Thunderstorm Warning - Prob Severe Jump Slow With Cirrus Canopy

I issued a Severe Thunderstorm Warning for Eastern Pittsylvania County (and others) at 2209 UTC, due to a combination of increasing high reflectivity aloft via all tilts, and a quick jump in Prob Severe model values. These values increased from 11% and 52% (two cells within a cluster of cells) at 2159 UTC to 88% (all cells in cluster) at 2201 UTC. There was a 4 sigma lightning jump with that storm as well at 2202 UTC. There was a delayed report of 1.00" hail at 2145 UTC in Pittsylvania County. There was also 1.00" hail at 2205 UTC in that county. Perhaps issuing the warning right after the jump in Prob Severe may have lead to lead time on the second 1.00" hail report. JJW

Eastern Botetourt County Severe Thunderstorm Warning - Prob Severe Steadily Increases.

I issued a Severe Thunderstorm Warning for Eastern Botetourt County (and others), due to a combination of a 1.00" hail report at 2136 UTC, as well as increasing high reflectivity aloft with all tilts and steadily increasing values of Prob Severe. The Prob Severe values gradually increased through the 70s and 80s percent range in the time leading up to the warning (2146 UTC). The storm continues to increase in strength. Update: 1.00" hail in Rockbridge County at 2200 UTC. JJW

Loads of data...

A picture is worth a thousand words

GOES visible imagery overlaid with CI probability and satellite derived winds.
Blue color denote lower level winds while red colors indicated high level winds.
No doubt convection will develop in and around the DC area shortly.

Tornadotod

Update: a little more than an hour later...success!

Stokes County NC Severe Thunderstorm Warning - Prob Severe Values Jump, But Were Delayed.

I issued a Severe Thunderstorm Warning for Stokes County NC at 2126 UTC, due to a combination of high reflectivity aloft via all tilts, and a jump in the Prob Severe model from 24% at 2119 UTC to 72% at 2122 UTC. The Prob Severe remained around 75% for a few scans afterwards. The cirrus canopy prevented any data on growth rates with the Prob Severe model, which perhaps delayed the jump in values. Update: Half dollar size hail in Stokes County at 2125 UTC, so no lead time. Again, Prob Severe may have shown the jump in Prob Severe sooner without the cirrus canopy overhead. JJW

CI versus Severe CI

Well...the first warning has just been issued for the Sterling CWA in Nelson county, VA. Looking back at the Severe CI verses the CI Probability...both indicated convective initiation at least 1 hour prior to the warning being issued. Severe CI algorithm only showed 1% probability 2 hours prior to the warning whereas the CI algorithm showed 60% probability 1 hr and 15 minutes prior to the warning.

Severe CI Algorithm

CI Algorithm

The warning was issued at 2100Z. The first report of nickel size hail came in at 2104Z with a penny size hail report at 2115Z...both in Nelson county. Both CI Algorithms proved valuable because it gave us an area to focus on for convective development. UPDATE: Golf ball size hail reported at 2115Z (with 15 minutes lead time).

Testing NUCAPS (JPSS) over the RNK CWA

After testing out some of the GOES-R products that will be included later when it goes live, we decided to test out the NUCAPS feature which is currently on the active JPSS satellite.

I first plotted the special 18z RNK sounding and it showed PW at 0.85 and the CAPE at 2290. The profile also shows a pronounced dry layer around 6km.

I then brought in the NUCAPS below, which showed some similar features including the dry layer around 6km and also the PW around 1. It was very impressive with a similar CAPE value of 2236. However, with NUCAPS, I had to adjust the dewpoint and temperature at the surface based off of interpolation of nearby station data. This is somewhat time consuming when in a severe coverage mode and needs to be looked at to see if there is an easier way to make adjustments to the sounding.

-BW

Eastern Franklin County Severe Thunderstorm Warning - High Prob Severe Values Help!

I issued another Severe Thunderstorm Warning for Eastern Fraklin County, based on a combination of continued high reflectivity aloft from the all tilts product, and the high Prob Severe values of 90% or higher. There was some low level rotation with this cell, but not strong or persistent enough for a tornado warning to be issued. Update: 1.00" hail in Franklin County at 2015 UTC. JJW

Warning Operations Have Commenced

As expected, convection now developing in earnest over southwestern portions of the CWA.  Based on rapid increase in both prob severe and lightning jump data to 5 sigma, issued for Nelson county.

Update: golfball size hail reported in Nelson county at 2115Z.

BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE BALTIMORE-WASHINGTON
459 PM EDT MON MAY 2 2016

THE NATIONAL WEATHER SERVICE IN STERLING VIRGINIA HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
  CENTRAL NELSON COUNTY IN CENTRAL VIRGINIA...

* UNTIL 545 PM EDT

* AT 459 PM EDT...DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM
  CAPABLE OF PRODUCING QUARTER SIZE HAIL. THIS STORM WAS LOCATED NEAR
  SHIPMAN...OR 8 MILES NORTHEAST OF CLIFFORD...AND MOVING NORTHEAST AT
  30 MPH.

* THIS SEVERE THUNDERSTORM WILL BE NEAR...
  SHIPMAN AROUND 505 PM EDT.
  WINTERGREEN AROUND 515 PM EDT.
  SCHUYLER AROUND 525 PM EDT.

OTHER LOCATIONS IMPACTED BY THIS SEVERE THUNDERSTORM INCLUDE
ROCKFISH...BRYANT...LOVINGSTON...ELMA...GREENFIELD...JONESBORO...FABER...
ROSELAND...NELLYSFORD AND MASSIES MILL.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

SEVERE THUNDERSTORMS PRODUCE DAMAGING WINDS...DESTRUCTIVE HAIL...DEADLY
LIGHTNING AND VERY HEAVY RAIN. FOR YOUR PROTECTION...MOVE TO AN
INTERIOR ROOM ON THE LOWEST FLOOR OF YOUR HOME OR BUSINESS. HEAVY
RAINS FLOOD ROADS QUICKLY SO DO NOT DRIVE INTO AREAS WHERE WATER
COVERS THE ROAD.

&&

LAT...LON 3773 7904 3797 7884 3779 7869 3778 7869
      3777 7868 3768 7895
TIME...MOT...LOC 2059Z 229DEG 25KT 3775 7894

$$

TORNADOTOD

NUCAPS Soundings

Both the 17Z and 18Z NUCAPS Soundings crossed through the Sterling CWA this afternoon giving us a glimpse at quickly evolving pre-convective environment.

17Z NUCAPS crossed the Eastern portion of KLWX. 18Z NUCAPS crossed the Western portion of KLWX.

17Z NUCAPS Sounding (near Leesburg, VA)

18Z NUCAPS Sounding (near Romney, WV)

Between 17 and 18Z...the surface temperature warmed and low to mid level moisture increased. This in turn increased the CAPE from roughly 900 J/kg to over 3000 J/kg. One minor downfall to the NUCAPS soundings that were sampled was that they required data editing to better represent surface observations. In this example...both the temperature and dew point temperatures were 5 to 10 degrees too cool. Modifying the sounding can very subjective so improvements need to be made to better reflect actual observations.

~Lilly Miller~