Tracking storm development in MO with Theta-e differentials

On Monday afternoon, a line of storms developed and propagated eastward, essentially bisecting Missouri by late afternoon. Here’s a look at the base reflectivity for the radar at KLSX (St. Louis) at 22Z (about 4pm):

In the same timeframe, the CIMSS NearCast model was projecting a fairly high Theta-e lapse rate.

The box in the top right corner shows this GOES- derived Theta-e difference of around 20-21K in an area west of St. Louis. Interestingly enough, this ΔTheta-e maximum is aligned with the area of convection, seen in the radar imagery above. Will the storm cells continue to propagate eastward and will they actually strengthen as they enter this area of higher instability?

By 23Z, We’re starting to see some individual storm cells develop out ahead of the bow echo.

This would indicate that the area of high instability on the NearCast model is starting to produce some convectively-driven storms. The highest value I found in this image in the newly-formed cells was 56dBZ. So in the near term, it appears the NearCast is correctly predicting convective initiation through the ΔTheta-e product. How about at 0Z itself?

The stronger line behind the pop-up cells has accelerated and swallowed up the smaller individual cells! That is a straight line of storms if I’ve ever seen one. I suppose the ΔTheta-e could be used in this situation to predict that this storm line would evolve in this way. More cases will have to be examined in order to see if this parameter is consistently usable for this purpose!

ProbSevere in Illinois

The NOAA/CIMSS ProbSevere model picked up on some warm sector convection in Illinois (neighboring our operational domain) during the evening of May 12. Figure 1 shows that the storm in the center with the hovering read out had a strong satellite normalized growth rate and strong glaciation rate at 22:15 UTC. The strong growth rates, MESH of 0.92", and large MUCAPE ( > 3000 J/kg) contributed to the probability of severe of 92%. The NWS issued a severe thunderstorm warning (Figure 2) on the center cell at 22:53 UTC (no reports yet received).

Figure 1: Storms developing in northern Illinois exhibit strong satellite growth.

The storm to the west also had a high probability of severe. It too exhibited strong satellite growth rates (though not as strong as the center storm), and MESH over 1". It was never warned on and no reports have been received. There may be some model overforecasting bias in high CAPE / lower shear regimes (as noted in the training), so forecasters should consider this while using ProbSevere guidance during warning operations. One forecaster also noted that the MESH seemed to be overforecasting hail size, based on the reports coming in.

Figure 2: NWS thunderstorm warning issued at 22:53 UTC, shortly after ProbSevere forecasted over 90% probability on this storm.

EDIT

More storms have been warned in northern Illinois. The storm that traveled near Chicago has been highlighted via AWIPS-II readout (see animation below). It had strong satellite growth rates well before a warning was issued (it merged together with other satellite-identified storms objects), which contributed to a high probability of severe. The first probability of severe greater than 50% was forecasted 37 minutes before the first NWS warning. The last image also shows additional NWS severe thunderstorm warnings on storms to the southwest, which also had strong satellite growth rates and probabilities of severe.

-Cintineo

GOES-R Convection Initiation Product Handles Convection Developing in Northern Illinois 5/12

The GOES-R CI product did a fine job depicting convection growing in northern Illinois. The top image at 2145 UTC depicting values around 74% and the second image at 2200 UTC depicting 89%.  The radar images below at 2203, 2222, and 2240 UTC depicted a few developing showers and storms near the CI values below.   The product gave 15-45 minutes of storm lead time.  These storms did not become severe.

Michael Scotten

Value of 1-Minute Satellite Imagery

Monday, May 12, 2014 Mike Smith

Two situations worthy of note:

I “issued” a special weather statement for Winnebago Co. At 2:47pm for 3/4 inch hail and gusts to 40 kts. Using ONLY surface obs and 1-minute satellite data.

At 2:59pm, I issued a severe thunderstorm storm warning for the same county, based on a Fujita U with overshooting then collapsing top in 1-minute data.

NWS issued severe at 2:56pm (unknown to me). Both warnings verified with 1.75” and 2.0” hail reports.

I observed a downburst south of Sullivan, WI and based on the right moving cell, I thought the RFD would intensify at 4:12pm for Walworth Co. Predicted 55 kt and 2” hail. Unknown if it verified.

The right mover got more pronounced and at 4:22pm, I issued a tornado warning for the southeast third of Walworth Co. This was due to the wrapping pattern of the outflow air (into RFD), the 1-minute satellite U and collapsing top, the persistent right movement and high spectrum width in the inflow. NWS issued a tornado warning for the same area at 4:45pm. While a pronounced hook formed, it never quite formed a tight couplet.

ProbSevere highlights strong cored storms. MRMS MESH seems overdone.

The ProbSevere Model is doing a great job highlighting the strongest cells. In this image from 2208z the ProbSevere Model is overlaid on top of the MRMS reflectivity above the -20C isothermal level. The cells annotated with an arrow across eastern IA, southern WI, and north-central IL have 50dBz echoes above the -20C isotherm and the model indicates an 80+% prob of severe.

There were hail reports from three of the four cores highlighted. The lower left produced Quarter sized hail in Henry county IA with the MESH indicating 2.5in, The upper left storm produced reported penny sized hail in Johnson county IA with MESH of 0.89in and the upper right storm produced nickel sized hail in Racine county WI with a MESH of 1.13in. The MESH product is overdone in this example.

Shawn Smith

GOES14-SuperHiResVisible Shows Convective Trends 5/12

The Super Hi-Resolution Visible Satellite Imagery below depicted a differential heating boundary over northern Illinois, denoted by the green line.  Very little cumulus was observed north of the green line where cirrus cloud cover was thicker, while enhanced cumulus congestus was occurring south of the green line.  With low level south to southwest flow, cumulus that developed south of this boundary had a tendency to dissipate when moving north of the green line/boundary. A severe storm denoted by the orange circle in southeast Iowa was moving east northeast and seems to be moving along this boundary.  It will be interesting to see if this storm will continue to be severe over the next few hours.

Michael Scotten

ProbSevere Model Good Lead Time NE Missouri/SE Iowa border – Missing SRSOR Images

The ProbSevere Model indicated an 83% probability of a severe storm within an environment of 2968 J/Kg of MUCAPE and 34.6 kts of EBShear at 2020Z. It also indicated MESH of 1.07inch at this time. The following 2-minute resolution updates continued to show 80+% prob and 1 inch+ MESH as the storm tracked northeast from the NE Missouri/SW Iowa border into SW Iowa except for one frame at 2028z where it showed a 64% prob. WFO DMX issued a SVR at 2037z. ProbSevere may have helped give up to 17 minutes additional lead time if the warning was issued once the ProbSevere crossed above 80%. At the time of this post there were not yet any confirmed hail reports.

Visible satellite data started to show a resemblance of an enhanced updraft on this storm at 2015z with a developing anvil and anvil shadowing at 2025z.  SRSOR VIS data was missing between 2011z and 2030z so had to use conventional visible images for the attached screen captures.

Shawn Smith

EDIT: Missing GOES-14 SRSOR images were due to "daily housekeeping" - BL

NOAA/CIMSS ProbSevere model at Week 2 HWT

The second week of the 2014 HWT is underway, with visiting forecasters evaluating a number of GOES-R products, including the new NOAA/CIMSS ProbSevere model. Forecasters are learning how to use this product today within their warning operations.

The ProbSevere model is probabilistic guidance from a statistical model, which fuses together data from the Rapid Refresh NWP model (RAP), growth rates in GOES-derived cloud products, and Multi-Radar Multi-Sensor (MRMS) Maximum Expected Size of Hail (MESH). Storms are identified and tracked in both satellite and radar imagery. Time trends (normalized vertical growth rate and glaciation rate) are extracted form satellite objects/storms, and shared with overlapping storms, present on radar. The probability of severe in the near future (~0-60 min) is computed using these satellite time trends, the MESH, and MUCAPE and effective bulk shear derived from the RAP.

This storm in south-central Iowa had a 90% probability of severe prior to producing a 64mph wind report. All of the surrounding storms had probabilities generally less than 30%.

A storm that developed in the warm sector also had a strong probability of severe well before 2" hail was reported in north-central Illinois.

With sampling turned on (see image below), we can see the AWIPS-II readout for ProbSevere. The probability of severe is of course displayed, as well as the values of the individual predictors. If the satellite growth rate predictors read 'N/A', that means that the storm is not discernible in satellite imagery, and thus growth rates can't be computed. Work is ongoing to try to associate mature satellite features with individual storms on radar. ProbSevere will still operate with radar+NWP, however, lead time to some severe hazards may not be as great as when the satellite growth rates are incorporated.

-Cintineo

Expanding Overshooting Tops Increase SVR Lead Time in Southern IA

The following images depicted the expansion in overshooting tops depicted by the CIMMS Auto Overshooting Tops Detection Algorithm 2015 to 2045 UTC May 12 across southern Iowa.

The first image had a small red blob in southwest Davis county at 2015 UTC, which greatly enlarged in area by 2025 UTC in the second image.   By 2030 UTC in the third image, the area split up into three blobs.  By 2037 UTC, the fourth image indicated four blobs with the two blobs to the northeast representing the fastest growth and expansion of the storm.  By 2045 UTC, the last image, three blobs were with this storm, possibly indicated that storm was intensifying or at least maintaining intensity.

A SVR was issued for Van Buren county, on the southeast part of the enclosed circular area, with the overshooting tops blobs at 2037 UTC.  A 60 mph gust along with heavy rainfall and low visibility was observed in the warned area at 2127 UTC. The great expansion and splitting of blobs indicated by the Auto Overshooting Top Detection Algorithm could have increased SVR lead time another 10-30 minutes.

Michael Scotten

EWP Status for 12 May 2014: 11:45-7:45 pm Shift

In contrast to last week, the start of this week has come with some very active weather. A fresh batch of forecasters are quickly getting spun up on  all of the experimental products as we look forward to another great week. Today, Shawn Smith (WFO Buffalo) and Michael Scotten (WFO Norman) are forecasting for the Davenport CWA, while Kevin Deitch (WFO Louisville) and Erica Grow (WUSA) are in the St. Louis CWA. Today’s shift will run from 11:45 to 7:45.

Forecasters will have access to a sector of GOES-14 1-minute imagery all week providing feedback on the utility of high temporal resolution imagery in a forecast environment.

- Bill Line, SPC/HWT Satellite Liaison and Week 2 EWP Coordinator