Initial severe thunderstorm warning issued for Webb County in southern Texas @ 1859 UTC. MRMS reflectivity at -20C now peaking at 61 dBZ with PROBSvr quickly increasing the probability of severe hail. DFX radar currently in SAILS mode and additional volume scans provided little added value due to hail being the primary concern, at least initially. That said, PROBSvr probability of severe seemed to be playing catchup as forecast decision to issue warning occurred prior to probabilities increasing significantly.
torman1
Monday, April 18, 2016
Environmental Analysis for Hail
Our initial assessment of the hail threat was from the 12z Corpus Christi sounding. We used it to assess hail growth zone height by sampling the -10C, -20C, and -30C heights AGL (this is approximately between 300mb and 500mb). The problem is this data is now 7 hours old and there are spatial limitations too, since this observation was taken almost 200 miles away from the storm we are particularly interested in. NUCAPS soundings would improve our assessment spatially since there is no sounding sight near our area of interest today. Also, the satellite pass that would provide NUCAPS data is timely, since it falls between radiosonde observation times. 300mb to 500mb is also the portion of the atmosphere that NUCAPS performs the best due to higher information content. This is very important in rapidly changing environments.
-dryadiabat
-dryadiabat
Prob Severe Compared to Reflectivity
Comparing the prob severe to radar reflectivity over time. We noticed the prob severe ramped up to 86% and then dropped back down to 31. Using some common radar analysis techniques this correlated well. The radar reflectivity jumped to over 50 dbz and then dropped down to 46 dbz.
Thunder
Thunder
Initial blog post
Initial blog post:
Today's focus will be over extreme southern Texas as an outflow induced frontal boundary continues to sag south across the Corpus Christi and Brownsville CWAs. Ahead of this boundary, ample amounts of low-level moisture are in place with early afternoon dewpoints hovering in the lower to middle 70s. Latest 1-km SRSOR visible imagery from GOES-14 indicates plenty of low-level CU in place south of the boundary, however SPC mesoanalysis is already showing a moderately unstable airmass with MLCAPE values currently exceeding 2000 J/kg is some locations across far southern Texas. So far, convection has been slow to kickoff in the unstable airmass south of the boundary, with the only notable convection of interest located along the Texas/Mexico border where the outflow induced front appeared to begin interacting with elevated terrain just west of the Rio Grande River. That said, PROBSvr has been tracking this cell quite well so far, however probabilities for severe remain low at this time. Also of interest is a northward moving outflow/differential heating boundary which will continue tracking north this early afternoon, before eventually colliding with the outflow induced frontal boundary approching from the north. As these two boundaries collide, expect developing/strengtheing convection as the airmass largerly remains uncapped per latest SPC mesoanalysis grapics. Effective bulk shear of 40-45 kts remains more than supportive for severe development, however deep layered shear vector orientation along the effective outflow boundary may keep developing convection in linear segments. Of interest however, Rapid-Refresh soundings from south-central Texas show deep inflow directly from the east with quick veering with height above 900-hPa. As a result...cannot rule out an isolated tornado or two, however very dry air aloft along with steep mid-level lapse rates will likely keep large hail and damaging winds the primary focus of severe weather concerns.
torman1
Today's focus will be over extreme southern Texas as an outflow induced frontal boundary continues to sag south across the Corpus Christi and Brownsville CWAs. Ahead of this boundary, ample amounts of low-level moisture are in place with early afternoon dewpoints hovering in the lower to middle 70s. Latest 1-km SRSOR visible imagery from GOES-14 indicates plenty of low-level CU in place south of the boundary, however SPC mesoanalysis is already showing a moderately unstable airmass with MLCAPE values currently exceeding 2000 J/kg is some locations across far southern Texas. So far, convection has been slow to kickoff in the unstable airmass south of the boundary, with the only notable convection of interest located along the Texas/Mexico border where the outflow induced front appeared to begin interacting with elevated terrain just west of the Rio Grande River. That said, PROBSvr has been tracking this cell quite well so far, however probabilities for severe remain low at this time. Also of interest is a northward moving outflow/differential heating boundary which will continue tracking north this early afternoon, before eventually colliding with the outflow induced frontal boundary approching from the north. As these two boundaries collide, expect developing/strengtheing convection as the airmass largerly remains uncapped per latest SPC mesoanalysis grapics. Effective bulk shear of 40-45 kts remains more than supportive for severe development, however deep layered shear vector orientation along the effective outflow boundary may keep developing convection in linear segments. Of interest however, Rapid-Refresh soundings from south-central Texas show deep inflow directly from the east with quick veering with height above 900-hPa. As a result...cannot rule out an isolated tornado or two, however very dry air aloft along with steep mid-level lapse rates will likely keep large hail and damaging winds the primary focus of severe weather concerns.
torman1
Value of Parallax Correction
We just got started setting up our procedures in AWIPS II and got caught up in a discussion of the value of parallax correction. It is very obvious when you toggle between the two. The correction is very evident in the mid and especially the higher clouds. We're currently looking at thunderstorm anvils in the western part of Corpus Christi's forecast area. The correction removes some of the shadowing from these anvils that were projected onto the lower clouds. Also, we looked outside of the area we were focused in, up further north. The edge of the cirrus across portions of Iowa and Missouri shifted significantly between the standard visible image without correction, and the parallax corrected image. We can see where this would be most valuable with the derived products and ensuring their placement is accurate and lines up well with radar data.
In the above images, corrected is on the top and uncorrected is on the bottom.
-dryadiabat
In the above images, corrected is on the top and uncorrected is on the bottom.
-dryadiabat
The Experimental Warning Program at the Hazardous Weather Testbed Begins
The 2016 Experimental Warning Program at the Hazardous Weather Testbed begins today and will run through the week of May 9, 2016. The weather this week looks to be dominated by a cutoff upper level low over the Rocky Mountains into the western Central Plains, so much of the week will be spent in Texas. Both groups of forecasters today are beginning their shifts in the Corpus Christie, TX WFO. One group may move to Brownsville WFO if it looks like capping will be overcome/a forcing mechanism becomes apparent or to the San Antonio WFO if elevated convection looks to become more intense. I will be supporting the NOAA/CIMSS ProbSevere product and my posts will focus on ProbSevere.
-Sieglaff
-Sieglaff
HWT 2016 GOES-R/JPSS Spring Experiment Begins Today!
The HWT 2016 GOES-R/JPSS Spring Experiment in Norman, OK begins today, 18 April, and will run through 13 May. Three NWS Forecasters and one Broadcast Meteorologist will participate in the GOES-R and JPSS product evaluations each week. Participants will utilize the experimental satellite-based products in a real-time AWIPS-II to issue experimental mesoscale forecast updates and severe thunderstorm and tornado warnings.
Products to be evaluated include:
You can follow this blog for live updates and forecaster posts from within the HWT.
Bill Line, SPC/HWT Satellite Liaison
Products to be evaluated include:
- GOES-R Legacy Atmospheric Profile (LAP) All-sky Thermodynamic Products
- GOES-R Convective Initiation and Severe Convective Initiation
- Probability of Severe Model
- GOES-14 Super Rapid Scan Operations for GOES-R (SRSOR) 1-min imagery
- Atmospheric motion vectors (updating every 10 minutes)
- Parallax-corrected 1-min imagery
- Total Lightning using PGLM (in LMA networks)
- Lightning Jump Algorithm (using ENI)
- NUCAPS Temperature and Moisture Profiles (JPSS)
You can follow this blog for live updates and forecaster posts from within the HWT.
Bill Line, SPC/HWT Satellite Liaison
Thursday, March 31, 2016
Tulsa-Claremore, OK Tornado
Most likely the strongest tornado of the day occurred just northeast of downtown Tulsa, Oklahoma, and moved east-northeastward toward Claremore and Justice, OK.
A strong GOES-derived normalized satellite growth rate, along with an increase in total flash rate from 22 to 35 flashes/min, increased the probability of severe to 84% at 22:42Z, in this high MUCAPE, high effective bulk shear environment, despite MRMS MESH only being 0.61 in. Fourteen minutes later (22:56Z), the probability increased to 95%, while MESH decreased to 0.56 in., and the flash rate increased to 84 fl/min. The probability generally stayed over 90% until the storm's demise. The first severe thunderstorm warning was issued at 23:35Z, about 40 min after the storm attained a >90% value from the ProbSevere model.
A tornadic debris ball signature was evident from KINX radar at 00:17Z, manifest in the base radar fields: a 'hook' signature in the reflectivity, strong velocity couplet, low correlation coefficient, and near zero or varying differential reflectivity; all coincident features are an indication that a tornado is creating and lifting debris. The storm also produced golfball-sized hail.
Future development of the ProbSevere model will investigate radar velocity products and dual-pol fields to give more accurate and hazard specific probabilities of severe (e.g., hail, wind, tornado).
A strong GOES-derived normalized satellite growth rate, along with an increase in total flash rate from 22 to 35 flashes/min, increased the probability of severe to 84% at 22:42Z, in this high MUCAPE, high effective bulk shear environment, despite MRMS MESH only being 0.61 in. Fourteen minutes later (22:56Z), the probability increased to 95%, while MESH decreased to 0.56 in., and the flash rate increased to 84 fl/min. The probability generally stayed over 90% until the storm's demise. The first severe thunderstorm warning was issued at 23:35Z, about 40 min after the storm attained a >90% value from the ProbSevere model.
A tornadic debris ball signature was evident from KINX radar at 00:17Z, manifest in the base radar fields: a 'hook' signature in the reflectivity, strong velocity couplet, low correlation coefficient, and near zero or varying differential reflectivity; all coincident features are an indication that a tornado is creating and lifting debris. The storm also produced golfball-sized hail.
Future development of the ProbSevere model will investigate radar velocity products and dual-pol fields to give more accurate and hazard specific probabilities of severe (e.g., hail, wind, tornado).
 |
| KINX low-level scan ~00:17Z March 31, 2016. Images are from social media. The coincident signatures indicate a tornadic debris ball. Top-left: hook signature in horizontal reflectivity; top-right: strong inbound-outbound velocity couplet; bottom-left: a 'hole' of low correlation coefficient; bottom-right: near-zero differential reflectivity. |
Fast moving storms and MRMS MESH
A fast moving storm in west-central Illinois yesterday produced hail much larger than the expected maximum size, depicted by the MRMS MESH, part of the ProbSevere model. Though it might not look like it from the animation below, the storm was pegged moving NE at 50 mph.
In cases like these, a fast-moving storm that is also perhaps shallow can result in an underestimate of MESH, since the storm may move a non-negligible amount in between consecutive radar elevation scans, resulting in a storm that appears to have a 'tilted' core, but is really just a result of storm motion. A 'tilted' or legitimately tilted core can result in a lower than normal MESH since MESH is based off of vertical integration of reflectivity.
Despite a strong satellite growth rate, the weak MESH, weak total lightning flash rate, and weak-moderate shear only resulted in a probability of severe of 9% when a 1" hail report was received (18:35Z, 4 min before the warning was issued), and maximum probability of 27%. In this case, ProbSevere would not have been useful to highlight the hail potential, thus forecasters should bear in mind many other environmental factors as well as the limitations of observations.
In cases like these, a fast-moving storm that is also perhaps shallow can result in an underestimate of MESH, since the storm may move a non-negligible amount in between consecutive radar elevation scans, resulting in a storm that appears to have a 'tilted' core, but is really just a result of storm motion. A 'tilted' or legitimately tilted core can result in a lower than normal MESH since MESH is based off of vertical integration of reflectivity.
Despite a strong satellite growth rate, the weak MESH, weak total lightning flash rate, and weak-moderate shear only resulted in a probability of severe of 9% when a 1" hail report was received (18:35Z, 4 min before the warning was issued), and maximum probability of 27%. In this case, ProbSevere would not have been useful to highlight the hail potential, thus forecasters should bear in mind many other environmental factors as well as the limitations of observations.
Late March warm frontal convection in Iowa
A strong system brought severe storms to many parts of the U.S. yesterday, including a few riding along a warm front in Iowa.
The NOAA/CIMSS ProbSevere model was recently updated to include total lightning data. The total flash rate (flashes/min) is coupled with the RAP effective bulk shear to form a two-dimensional predictor. The RAP MUCAPE, MRMS MESH, and GOES-derived satellite growth rates are also still predictors in ProbSevere (see how the MUCAPE and effective bulk shear are used in ProbSevere) .
In this case, the total lightning / effective shear predictor helped contribute to over 60 min of lead-time from the 60% threshold.
As this storm was diminishing, a conglomerate of convection erupted just to its east, producing wind and hail reports in the Des Moines metro.
The NOAA/CIMSS ProbSevere model was recently updated to include total lightning data. The total flash rate (flashes/min) is coupled with the RAP effective bulk shear to form a two-dimensional predictor. The RAP MUCAPE, MRMS MESH, and GOES-derived satellite growth rates are also still predictors in ProbSevere (see how the MUCAPE and effective bulk shear are used in ProbSevere) .
The highlighted storm in central IA developed in an environment with decreasing MUCAPE (1000 J/kg --> 600 J/kg) but excellent shear (~45-50 kts). The strong total flash rate (~35-70 fl/min) with the strong shear, as well as an observed moderate normalized growth rate, helped elevate the probability despite modest MESH (0.45-0.75 in). The probabilities ranged from 60% to 85% (mainly > 70%) before the first severe thunderstorm warning was issued, at 23:58Z, which was 5 min before the first 1" hail report.
In this case, the total lightning / effective shear predictor helped contribute to over 60 min of lead-time from the 60% threshold.
As this storm was diminishing, a conglomerate of convection erupted just to its east, producing wind and hail reports in the Des Moines metro.
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