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| Fig. 1: ProbSevere contours, MRMS composite reflectivity, GOES-East visible reflectance, and official NWS severe thunderstorm warnings. |
Thursday, May 12, 2016
Carolina convection
The forecasters are working the Nashville and Huntsville CWAs, but further east in North and South Carolina the surface has reached it's convective temperature, spawning strong thunderstorms. Below shows the NOAA/CIMSS ProbSevere model for several storms in a very unstable and moderately sheared environment. Multiple trees were reported down east of Columbia, SC, at 17:56Z.
NUCAPS Comparison to Radiosonde sounding
We had a 14Z IASI satellite pass this morning. Here is a comparison of a NUCAPS sounding for a point near Nashville to the 12Z Nashville radiosonde launch.
14Z IASI NUCAPS sounding
12Z KOHX radiosonde sounding
The NUCAPS sounding is definitely smoothed compared to the radiosonde sounding, and the airmass is not well-resolved near the surface on the NUCAPS.
However, the NUCAPS sounding does hint at the nearly saturated layer from around 850mb-750mb. The overall instability is fairly similar in both soundings.
- JP
14Z IASI NUCAPS sounding
12Z KOHX radiosonde sounding
The NUCAPS sounding is definitely smoothed compared to the radiosonde sounding, and the airmass is not well-resolved near the surface on the NUCAPS.
However, the NUCAPS sounding does hint at the nearly saturated layer from around 850mb-750mb. The overall instability is fairly similar in both soundings.
- JP
When to ignore PROBSEVERE
-Stormfront
May 12, 2016: 1-min SAT imagery
Cells are rapidly firing across the OHX forecast area, as evident from this loop over the past 20 mins. One can see 4-5 cells rapidly developing with overshooting tops in the central and eastern portion of the forecast area.
-Yodamaster777
-Yodamaster777
FINALLY moving to the Southeast...Day 4 Meso Analysis with NUCAPS Huntsville
We anticipate these airmass thunderstorms to continue for the next couple of hours with a chance for severe storms as a cold front approaches from the NW this afternoon.
LAP data is working again today (YAY!) LAP CAPE has it's typical low bias, not a surprise given the high GFS component this morning. LAP LI values also came in less unstable, but PWAT values are on par with other available information.
May 12, 2016: GOES-R Final Day in Nashville's Forecast Area
The final day features a shift down stream from Norman, OK to Nashville's and Huntsville's forecast areas. Our team is focusing on OHX's forecast area. It is a messier set-up compared to the previous events. Multi-celluar convection continues to fire out ahead of the main cold front. MLCAPE's are generally in the 1000-1500 J/kg range ahead of the line of convection ahead of the front as of 1700 UTC.
The Effective Bulk Shear is generally less than 30 kts at 1700 UTC over most of the forecast area. Though closer to the squall line they are in the 35-45 kt range.
The OHX sounding is fairly unstable if parcels are lifted from 850 hPa. The MUCAPE value off the 12Z sounding is close to 1200 J/kg (see below). The PWAT is close to the RAP analysis at 1.28". The mid-level lapse rates are relatively week in the 6C/km. This may be a day of multi-cells capable of heavy rain until the convective line approaches.
PWAT values are higher than the previous day in the 1.2-1.5" range according to the RAP analysis below.
The LAP data below also shows PWATs in 1.1-1.4" range in the lower right panel. The CAPE analysis looks underdone compared to the RAP data now that the clouds have filled in.
Overall, some marginally large hail and damaging winds are possible. However, these storms look capable of heavy rain ahead of the front. If the line ahead of the cold front intensifies then wind damage would be the main threat.
-Yodamaster777
The Effective Bulk Shear is generally less than 30 kts at 1700 UTC over most of the forecast area. Though closer to the squall line they are in the 35-45 kt range.
The OHX sounding is fairly unstable if parcels are lifted from 850 hPa. The MUCAPE value off the 12Z sounding is close to 1200 J/kg (see below). The PWAT is close to the RAP analysis at 1.28". The mid-level lapse rates are relatively week in the 6C/km. This may be a day of multi-cells capable of heavy rain until the convective line approaches.
Overall, some marginally large hail and damaging winds are possible. However, these storms look capable of heavy rain ahead of the front. If the line ahead of the cold front intensifies then wind damage would be the main threat.
-Yodamaster777
Day 4: Nashville CWA, May 12
Things are developing quickly early this afternoon over the Nashville, TN CWA. A sharp cold front is racing toward the region and will trigger some linear convection over the next couple of hours. Here is the WPC frontal analysis from 18Z.
Out ahead of the front, we have a decently unstable air mass. The 12Z KOHX Nashville sounding showed about 1200 J/kg of Most Unstable CAPE.
The GOES LAP data from 15Z confirmed this pretty well. The LAP was mostly populated with the GFS over our forecast area, but there was an area of cloudy retrieval that indicated 1000-1500 J/kg of CAPE. The GFS values were again much lower.
LAP derived layer precipitable water values of 1.5-1.6 inches moving into the region with the cold front. Given that instability is relatively modest and the shear profile is not all that impressive, we are thinking that the main convective threats today will be heavy rain and straight line winds with the cold front.
- JP
Out ahead of the front, we have a decently unstable air mass. The 12Z KOHX Nashville sounding showed about 1200 J/kg of Most Unstable CAPE.
The GOES LAP data from 15Z confirmed this pretty well. The LAP was mostly populated with the GFS over our forecast area, but there was an area of cloudy retrieval that indicated 1000-1500 J/kg of CAPE. The GFS values were again much lower.
LAP derived layer precipitable water values of 1.5-1.6 inches moving into the region with the cold front. Given that instability is relatively modest and the shear profile is not all that impressive, we are thinking that the main convective threats today will be heavy rain and straight line winds with the cold front.
- JP
Huntsville and Nashville
Our forecasters are beginning the day in Huntsville, AL and Nashville, TN monitoring an eastward moving line of storms and some pop-up convection ahead of it.
Wednesday, May 11, 2016
Daily Summary: Week 4, Day 3 (11 May 2016)
For Wednesday, the groups began operations in the Fort Worth and Pueblo CWAs. It quickly became apparent that Pueblo activity would remain marginal, so that group moved to the Springfield CWA. With convection slow to develop in FWD, that group transitioned to the San Angelo CWA.
LAP
- It showed abundant isntability in central Texas. CAPE, LI, and PW were all on par with what we had expected.
- Looking at layer PW in Pueblo, there was an enhanced area of ll moisture in the SE corner of the state, but activity never made it there to tap into it.
CI
- CI values increase quickly before initiation.
- It was helpful in highlighting development along the outflow boundary, and where along the outflow convection would develop.
- Early on, there were low percentages where nothing happened, so did not see any false alarms.
- It hit on storms in the Midland area where we weren't really expecting any development.
- In Springfield, one cell popped up right on the boundary that eventually produced severe hail near St Louis. It had very high regular CI, and 70 severe CI.
- I noticed regular CI hitting on development south of Pueblo CWA.
ProbSevere
- Our one hail-maker in St Louis made it into the 90s. ProbSevere did well on that cell. Otherwise, we didn't see many storms go over 10, which was good since we didn't have any other severe.
- In Texas, I saw my first 100. Mesh was over 2" We issued a tornado warning on that storm.
SRSOR
- I wrote a blog post on the importance for forecasters to back up and look at the wider view, noting important features. As more OTs develop, one can visualize the linear structure across the region. One could see the evolution of boundaries and their interactions with each other. Inflow into storms from the south was apparent via the movement of low level clouds. While the initial outward expansion of teh anvil was in all directions, it backed up on one side due to the opposing mean flow at that level. Lots of waves were apparent. There are a lot of features and processes that you just cannot see with routine data.
- There was a mature storm with large anvil. New storms formed beneath the anvil along the outflow boundary. We could see the storms mature as they rose through the anvil.
- With a cell in Springfield, the updraft looked vigorous but then died quickly. We could see this in the 1-min imagery as it happened. The 1-min imagery has been helpful for rapidly developing storms, allowing you to see what is happening right away.
SRSOR winds
- In Springfield, as cu developed, winds were available at many levels, allowing us to analyze the presence of directional shear (winds were veering with height). South of our CWA, we saw low level convergence, but in our area, flow was uni-directional. That convergence never made it into Springfield, and the lack of low-level support is likely why convection did not develop.
- In San Angelo, convergence was apparent along the outflow via the satellite-derived wind field.
Lightning Jump
- With storms in Texas, a 3-sigma lightning jump helped me make my warning decision.
NUCAPS
- Pueblo is not an upper air site, so it was helpful there. IASI NUCAPS indicated only weak instability, which made sense given only weak convection/showers. Surface dew point and temperature were very accurate, perhaps because the atmosphere was so dry.
- In Texas, we used NUCAPS in our early analysis which proved to be helpful given sparce UA obs.
- NUCAPS had Wet Bulb Zero heights around 9000 ft, and FL around 12000 ft. Wit the kind o updrafts we had, I am not surprised we had such large hail.
LAP
- It showed abundant isntability in central Texas. CAPE, LI, and PW were all on par with what we had expected.
- Looking at layer PW in Pueblo, there was an enhanced area of ll moisture in the SE corner of the state, but activity never made it there to tap into it.
CI
- CI values increase quickly before initiation.
- It was helpful in highlighting development along the outflow boundary, and where along the outflow convection would develop.
- Early on, there were low percentages where nothing happened, so did not see any false alarms.
- It hit on storms in the Midland area where we weren't really expecting any development.
- In Springfield, one cell popped up right on the boundary that eventually produced severe hail near St Louis. It had very high regular CI, and 70 severe CI.
- I noticed regular CI hitting on development south of Pueblo CWA.
ProbSevere
- Our one hail-maker in St Louis made it into the 90s. ProbSevere did well on that cell. Otherwise, we didn't see many storms go over 10, which was good since we didn't have any other severe.
- In Texas, I saw my first 100. Mesh was over 2" We issued a tornado warning on that storm.
SRSOR
- I wrote a blog post on the importance for forecasters to back up and look at the wider view, noting important features. As more OTs develop, one can visualize the linear structure across the region. One could see the evolution of boundaries and their interactions with each other. Inflow into storms from the south was apparent via the movement of low level clouds. While the initial outward expansion of teh anvil was in all directions, it backed up on one side due to the opposing mean flow at that level. Lots of waves were apparent. There are a lot of features and processes that you just cannot see with routine data.
- There was a mature storm with large anvil. New storms formed beneath the anvil along the outflow boundary. We could see the storms mature as they rose through the anvil.
- With a cell in Springfield, the updraft looked vigorous but then died quickly. We could see this in the 1-min imagery as it happened. The 1-min imagery has been helpful for rapidly developing storms, allowing you to see what is happening right away.
SRSOR winds
- In Springfield, as cu developed, winds were available at many levels, allowing us to analyze the presence of directional shear (winds were veering with height). South of our CWA, we saw low level convergence, but in our area, flow was uni-directional. That convergence never made it into Springfield, and the lack of low-level support is likely why convection did not develop.
- In San Angelo, convergence was apparent along the outflow via the satellite-derived wind field.
Lightning Jump
- With storms in Texas, a 3-sigma lightning jump helped me make my warning decision.
NUCAPS
- Pueblo is not an upper air site, so it was helpful there. IASI NUCAPS indicated only weak instability, which made sense given only weak convection/showers. Surface dew point and temperature were very accurate, perhaps because the atmosphere was so dry.
- In Texas, we used NUCAPS in our early analysis which proved to be helpful given sparce UA obs.
- NUCAPS had Wet Bulb Zero heights around 9000 ft, and FL around 12000 ft. Wit the kind o updrafts we had, I am not surprised we had such large hail.
2330 UTC: SJT Severe Convection
The storms really got rockin' in SJT forecast area. The cell in the northern portion of the forecast area developed a hook echo. At 2330 UTC a distinct jump occurred in the lightning data to +3 sigma. Also, clouds tops continued to rapidly cool.
The hook echo was well-defined at 2333 and it was decided to issue a TOR (see below)
The SRM and Velocity data were very impressive from the KDYX radar. The cursor highlights close to 75 kts on the edge of the old SVR polygon below.
The satellite signatures continued to be impressive in the TOR box (-73C pixel), but new cells began to form further south, and additional SVR's were issued based on the PROB Severe values shooting up to 90-99%, and the overshooting tops in the satellite and IR data (see the 4-panel below).
Overall, it was a great close to a slow starting day.
-Yodamaster777
The hook echo was well-defined at 2333 and it was decided to issue a TOR (see below)
The SRM and Velocity data were very impressive from the KDYX radar. The cursor highlights close to 75 kts on the edge of the old SVR polygon below.
The satellite signatures continued to be impressive in the TOR box (-73C pixel), but new cells began to form further south, and additional SVR's were issued based on the PROB Severe values shooting up to 90-99%, and the overshooting tops in the satellite and IR data (see the 4-panel below).
Overall, it was a great close to a slow starting day.
-Yodamaster777
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