A quick update, one of our forecast groups is moving to the Brownsville WFO in the anticipation of convective development and potential severe weather.
-Sieglaff
Monday, April 18, 2016
As of 2015z
As of 2015z:
Also, special 18z KCRP sounding quite instructive. Strong cap in place near 850 mb, with most of the steep lapse rates and deeper shear in the mid-levels above this feature. This substantiates our earlier notion that tornadic/wind producing storms are less likely, with hail the main threat. Stronger/potential severe storms in the NW portion of the forecast area at this time are seemingly not surface-based.
Are the weaker lapse-rates/shear in the surface-850 mb layer biasing CI-severe downward? ;)
Also, special 18z KCRP sounding quite instructive. Strong cap in place near 850 mb, with most of the steep lapse rates and deeper shear in the mid-levels above this feature. This substantiates our earlier notion that tornadic/wind producing storms are less likely, with hail the main threat. Stronger/potential severe storms in the NW portion of the forecast area at this time are seemingly not surface-based.
Are the weaker lapse-rates/shear in the surface-850 mb layer biasing CI-severe downward? ;)
Updated Mesoanalysis
18z special sounding from CRP has arrived with well-pronounced capping noted near the 850-hPa level. Radar and satellite trends continue to show severe convection north of the now stalled outflow induced frontal boundary. Considering the 18z sounding, along with observed radar and satellite trends, all severe convection so far this afternoon appears to be non-surface based convection. As a result, svr hail remains the main concern.
torman1
torman1
Prob Severe in Complex Convection
This may be a rarely small percentage of cases, and probably more common in high CAPE / low shear environments where multicell storm structures dominate. But, in the case of the cells in western Webb County we have noticed two distinct cores on radar. Prob Severe tracks these distinctly to start and gives useful values for the southernmost storm, but then merges the two later before splitting again. This leads to inconsistency in the lightning flash rate values. When the two cells are merged, lightning flash rates are combined and much higher. When they split, the lightning flash rates are separated and lower. Obviously there are limitations in how the algorithm can identify separate cells in these complex environments, but it is something the user should be aware of.
-dryadiabat
-dryadiabat
20z update
As of 20z:
Additional severe thunderstorm warning issued for flanking line developing SW of initial storm in Northern Webb county, TX. Large hail is again quite probable, with deep, tall core through the mid-levels.
Interestingly, severe CI has seemingly remained fairly low with this storm, while ProbSevere has elevated values.
Suggestion for CI probability: Have the algorithm mark a particular cloud element as "already convected" (or some other wording to that effect), in order to let the user know this particular cell/cloud element is no longer being sampled by the algorithm. - J-Money
Additional severe thunderstorm warning issued for flanking line developing SW of initial storm in Northern Webb county, TX. Large hail is again quite probable, with deep, tall core through the mid-levels.
Interestingly, severe CI has seemingly remained fairly low with this storm, while ProbSevere has elevated values.
Suggestion for CI probability: Have the algorithm mark a particular cloud element as "already convected" (or some other wording to that effect), in order to let the user know this particular cell/cloud element is no longer being sampled by the algorithm. - J-Money
20Z Radar Update...
Initial cell as weakened below severe limits with a secondary storm strengthening directly to its south. Overall thoughts on PROBSvr remain unchanged as it seems to lag behind observed radar trends. Traditional radar interrogation methods (50 dBZ core above the -20C line) continue to provide greater lead-time for warning decisions.
Convective initiation algorithem actually did hint at general region of southern TX for new storm development over 1-hr in advance of new storms forming. Once storms form, is there something that could be displayed to show that the CI algorithem is no longer tracking the area?
torman1
Convective initiation algorithem actually did hint at general region of southern TX for new storm development over 1-hr in advance of new storms forming. Once storms form, is there something that could be displayed to show that the CI algorithem is no longer tracking the area?
torman1
Storm moving into KCRP WFO
Both forecaster groups are setup in the Corpus Christie, TX WFO. Thus far the only storm of interest was over Webb County near the Rio Grande river. The forecaster groups found ProbSevere to confirm what they had observed in their all-tilts radar analysis--a strengthening storm in the 1850 to 1900 UTC time frame (Figure 1). The ProbSevere information helped increase confidence, but did not much provide lead-time since the forecasters said, "...we were already on this storm, examining all-tilts". They speculated ProbSevere output would be even more useful in a region with multiple storms that require interrogation and a warn/no-warn decision.
As of this writing no reports have been received from this storm. We've had some conversations related to the difficulty in validating storms in very rural regions.
-Sieglaff
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| Figure 1. NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 1846 - 1900 UTC 18 April 2016. |
-Sieglaff
CI signature good at showing big convection in West Texas
Analysis of the CI and CI severe shows 80% and a drop back down to 75% (for CI) before convection developed. Storm is displaying strong hail signatures. We have extended warning for webb county.
Interesting to see that at the same time we are watching a big line of convection south of the Corpus Christi radar that may be dumping heavy rain but, not looking severe.
Webb County, TX Storm Update
Overall, PROBSvr continues to show high probabilities of severe hail. So far no reports have been received at the WFO, not surprising considering the low population density in this part of TX. Otherwise, Lightning Jump data showed a 2 sigma increase approximately 20 minutues before warning went out the door. Finding little utility with the Convective Initiation products so far.
torman1
Latest update
As of about 19z:
Severe thunderstorm warning issued for large hail in the NW edge of the CWA, just south of KCZT. Strong deep-layered shear (0-6 km layer), versus weaker 0-1 km values argues for hail producing supercells and possibly isolated downburst winds, versus tornadic storms. Reflectivity jumps in the mid-levels on the KDRT radar seemed to portend a near-future jump in ProbSevere values for this storm.
A collision of a northward moving convergence boundary with the southward moving synoptic boundary at the eastern end of the CWA has touched off additional convection. This is near a gradient zone in stability/shear. Lightning flash rates/overshooting tops are not overly impressive, as of yet. We'll continue to monitor. - J-money
Severe thunderstorm warning issued for large hail in the NW edge of the CWA, just south of KCZT. Strong deep-layered shear (0-6 km layer), versus weaker 0-1 km values argues for hail producing supercells and possibly isolated downburst winds, versus tornadic storms. Reflectivity jumps in the mid-levels on the KDRT radar seemed to portend a near-future jump in ProbSevere values for this storm.
A collision of a northward moving convergence boundary with the southward moving synoptic boundary at the eastern end of the CWA has touched off additional convection. This is near a gradient zone in stability/shear. Lightning flash rates/overshooting tops are not overly impressive, as of yet. We'll continue to monitor. - J-money
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