strong satellite growth rates boost ProbSevere value ahead of experimental warning

A storm south of Norman, OK exhibited strong glaciation and normalized satellite growth rates at 19:37Z, provided by GOES-East, to boost the probability of severe to over 60% by 20:34Z. Forecasters in Norman were shown the 2D flash rate/effective bulk shear predictor in ProbSevere, which gave them knowledge that well-sheared storms don't need super high flash rates to contribute postiviely to the overall probability. This knowledge helped forecasters quickly assess the storm and issue a severe thunderstorm warning at 20:41Z. The storm later produced a tornado.

Fig. 1: ProbSevere contours and MRMS MESH.

Utilitly of Prob Severe Combined with Sat Growth Rate and Lightning Flash Rate in Predicting Severe Weather

As storms continue to fire along the dry line in the OUN forecast area, we continue to find utility with the CI and Prob Severe algorithms determining where severe weather is likely. The CI algorithm jumped to 98% at 20Z with with the Severe CI 66% in Stephens County.  They supercell would be the precursor for the Garvin County tornado.

This storm entering Garvin County showed a sharp increase in Prob Severe from 45% at around 20:30Z to 95-100% within 10 minutes. The satellite growth rate was high, and lightning flash rate jumped from minimal to around 50 flashes/minute during this period. The LTG Jump increased from nothing 26 standard deviations above normal at 2035Z about a half an hour before the tornadol

We issued a severe thunderstorm warning based on this information and radar imagery. Within the next half hour, this cell produced a tornado on the ground.

Update 1: This turned out to be a long lived and very strong tornado in Garvin County. 

Update 2: The supercell kept going, and the mesocyclone became broarder.  A decision was made to expand the tornado warning further downstream at 2133Z. It worked out well.

  The hook echo is seen in the reflectivity image.

   At this point the tornadic couplet was well-defined in the polygon.

At 2154Z, another tornado was on the ground with 86 kts of gate to gate rotation with a shear value of 0.0843 s-1.

Reverting back to the CI and Severe-CI products. 

The CI-product peaked at 93% and the SVR-CI 57% at 22Z further depicting the long-lived track of this severe supercell that kept producing tornadoes.


- JP/Yodamaster777

CI good for situational awareness

The CI product alerted me that things may be starting to develop well south of where I had been concentrating my interogation. While storms have been developing across southern OK and near the OK/TX border...A jump in CI much closer to Dallas has shifted my attention southward. When looking at SRS imagery...some development is indeed occurring in this area helping me to become more situationally aware that the entire dry line could become much more active soon.

 

-Jason Bourne

GOES Prob Severe Increased Confidence in Issuing Severe Thunderstorm Warning

We issued a Severe Thunderstorm Warning for 3 counties in NW OK around 20Z.
Using a traditional forecasting methodology of looking for 60dBZ up to the -20C level, we determined that severe hail was becoming a possibility.

The GOES Prob Severe product increased our confidence in making this decision. Around the same 20Z time period, the Prob Severe jumped from around 40% to 75% over a short period of time. We also saw a lighning jump of about 2 sigma during this time as well. These products didn't neccessarily increase our lead time, but increased confidence.

WUUS54 KOUN 092006
SVROUN
OKC003-093-151-092045-
/O.NEW.KOUN.SV.W.0142.160509T2006Z-160509T2045Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE
306 PM CDT MON MAY 9 2016

THE NATIONAL WEATHER SERVICE IN  HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
  SOUTHEASTERN WOODS COUNTY IN NORTHWESTERN OKLAHOMA...
  CENTRAL ALFALFA COUNTY IN NORTHWESTERN OKLAHOMA...
  CENTRAL MAJOR COUNTY IN NORTHWESTERN OKLAHOMA...

* UNTIL 345 PM CDT

* AT 305 PM CDT...DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM
  CAPABLE OF PRODUCING LARGE HAIL UP TO PING PONG BALL SIZE AND
  DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED 7 MILES
  WEST OF ORIENTA...OR 10 MILES NORTHWEST OF FAIRVIEW...AND MOVING
  NORTHEAST AT 65 MPH.

* LOCATIONS IMPACTED INCLUDE...
  CHEROKEE...CARMEN...CLEO SPRINGS...JET...ALINE...LAMBERT...GREAT SALT
  PLAINS LAKE AND ORIENTA.

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 3670 9813 3628 9855 3638 9874 3683 9834
      3697 9812
TIME...MOT...LOC 2005Z 214DEG 58KT 3639 9860

$$


JFP/TAW


- JP/Yodamaster777

GOES CI Useful in Predicting Convective Development on Dryline

GOES CI probabilities proved to be useful in predicting development along the dry line over the NW portion of the OUN CWA.

This image from 18:37Z showed CI values of 80-90%.

One hour later at 19:37Z, significant development is apparent with cloud tops approaching -50C.

-JP/Yodamaster777

DFW Initial Mesoscale Discussion May 9

Started off the day doing a meso analysis of our WFO with my partner for the day.  A prominent dryline is advancing East into a region with high CAPE, lapse rates that have been rapidly steepening, helicity that suggests supercell potential, and plenty of available moisture.  Plenty of signs indicate a potential severe weather outbreak this afternoon.  Isolated tornadoes are possible, but it appears that wind damage and large hail will be the main threats. Right now it's still early.  Decided to give some of the new products a try:

As of this writing the CI and Severe CI probabilities are still quite marginal.









When trying to determine most likely location for storm development, the LAP cape Image shows plenty of high values in our WFO

-Stormfront

There is a race against time with the dynamics of the dryline and the thermodynamics available for storm formation.  The Western portion of our forecast area has already seen the dryline come through.

DFW Mesoscale Discussion May 9

Chance for severe storms increasing across the DFW area ahead of a dryline that is moving into the western portions of the CWA at this time. LAP CAPE and LI is honing in on an area of more favorable instability across the north central counties which is for the most part lining up well with RAP SPC mesoanalysis of ML CAPE and this is confimed by an 18z sounding from Ft. Worth. With fat CAPE in the hail growth zone and very strong mid level lapse rates...large hail should be the biggest threat of the day. With shear values into the 40 kt and above range...convective mode should be supercells. Although large hail will be the primary threat...we are not out of the woods as far as tornadoes are concerned either. The threat for tornadoes will increase in the northeastern portion of the cwa and points north as effective helicity and 0-1 km helicity values are in the 200-300 m2s2 range. LCL values are a little bit higher that ideal for tornadoes so it is possible we see a lot of rotating mesocyclones with few making down to the surface.

As far as low level convergence is concerned along the dryline...Satellite derived winds are not showing as much low level convergence as the RAP mesoscale analysis...shown below.

This makes me think that convective initiation may take a little longer to get going and thus pushing the threat slightly eastward. Fully expect the northeastern quadrant of the cwa to see severe wx but not as confident across the north central near the current position of the dryline. As far as straight line winds are concerned...DCAPE values along the dryline are about 1200 J/kg and observed sounding shows good amount of dry air below 700 mb indicating some downbursts are possible.

Convective initiation values nailed the first radar echos in southern Oklahoma and noted that compared to a fleeting higher CI value, a cluster of high CI and Severe CI values seemed to lend more confidence to the product.

-Jason Bourne

May 9, 2016 Test and First Blog

Focus is on Norman and Dallas Fort-Worth Forecast Areas today...1800 UTC sounding just completed. It is very unstable with supercells possible (0-6 km shear = 43 kts; SBCAPE = 2453) orienting into lines or multiples lines later due to the strong SW flow aloft.

The latest LAP CAPE axis is just west of the I-35 corridor.

LAP Lifted Indices are in the -6C to -8C range along and just west of the I-35 corridor too.  The layered GOES PWAT product shows significant drying aloft in the 700-300 hPa layers (0.10-.19 range) over western and central OK with the layer PWAT in the 0.90-1.25" range.  Thinking is convection will fire west to southwest of OKC and DFW.  The latest CI image shows high chance and likely probabilities west and southwest of OKC. Latest as of 1900 UTC is some 80-90+ probabilities just east of I-44 in OK.

These probabilites will likely continue to increase, and we believe going to warning mode is likely within the next 30-60 mins.  The strong upper level impulse continues to approach from the OK and NW TX panhandles. Will continue to monitor Prob. Severe Model for any new info.

Yodamaster777

Day 1: Monday, May 9 Mesoscale Analysis

Conditions are looking promising for convective development this afternoon. Moist southeasterly flow is currently occurring over the OUN CWA with dewpoints in the mid to upper 60s. Forecast afternoon highs are around 80F. 

Looking at the GOES LAP PWAT values, there is a sharp gradient aloft with a much drier airmass overrunning the moist lower levels. This dry air aloft should contribute to destabilizing the airmass as the afternoon progresses.

 

Based on a supplemental 18Z soundings at OUN, there is a capping inversion present. However, it appears that surface temps are getting close to overcoming the cap and tapping into fairly impressive instability.

The GOES LAP derived imagery from around the same time shows CAPE values around 2000 J/kg centered over the CWA. 

A dry line currently over SE OK will slowly move through the region today. Based on the Super Rapid Scan visible satellite, there is good clearing for daytime heating and cumulus development already beginning to occur ahead of the dry line toward the western end of the sharp CAPE gradient. The GOES-R Convective Initiation (CI) algorithm is suggesting that deeper convection has about a 50-60 % chance of occurring in the next 2 hrs in this area to the SW of the CWA, with one area of clouds at 80-90%. 

 Everything seems to be coming together for convective activity sooner rather than later. -JP

GOES-R/JPSS spring experiment week 4

Our forecasters are starting the week in Dallas/Fort Worth, TX, and Norman, OK, in anticipation of large-scale upper air forcing aiding potential surface development of storms along a dryline.