Upstate NY popcorn storms

In the evening of May 13, single-cell convection developed over western NY. We can see from the ProbSevere contours (figure 1), one storm stands out above the rest. This storm, residing in a weakly-sheared environment, had strong satellite growth rates (at 23:00 UTC and 23:25 UTC) and MESH of approximately 1" at 7pm (00Z May 14). The probability of severe was 76% at this time. Six minutes later the NWS issued a severe thunderstorm warning (figure 2). This example exemplifies what some forecasters have been saying, that ProbSevere can help pick out the right storm(s) to pay closer attention to.

Figure 1: ProbSevere contours at 00:00 UTC on May 14.

Figure 2: NWS warning issued at 00:06 UTC May 14.

-Cintineo

Overshooting Top Detection – Mid Atlantic Region

The Overshooting Top Detection algorithm seemed to be poorly observing overshooting tops with pulse convection over the Mid-Atlantic States.  From both images (one at 2245 UTC and 2300 UTC), no overshooting tops were observed by the algorithm with the convection in western Maryland and northern Virginia.  A few tops were observed over West Virginia.

EDIT:
I made it clear to the forecasters that even though these storms had cold tops (or may have appeared to have overshoots in the vis), that does not mean there is an overshooting top. In this case, there was not likely a detectable minimum within the cloud shield. When training forecasters to use this type of product, it is important to make these types of aspects of the products clear.

ProbSevere Overdone in WV – 2308Z

Convection through the day in West Virginia has been strong, perhaps marginally severe at times but no reports have yet been received.  However, I noticed the probsevere tool began to struggle once this convection congealed into a linear segment.  The highest probs appear to be driven by a falsely high MESH value, which was at 1.41 inches at this time.  There was no satellite data going into the probsevere tool at this time.  Looking at reflectivity data, the bulk of the reflectivity (60+ dBz echoes) were below the freezing level, so I’m not quite sure why the MESH was so high.  But this tool was definitely overdone in this instance.

-Deitsch

More convection in Indiana

A few late afternoon/evening storms have fired up again in southern Indiana, but only one is standing out. In the animation below, the ProbSevere model showed a jump in the probability of severe from 8% to 33% with the inclusion of moderate and strong satellite growth rates in a modest environment with about 1500 J/kg of MUCAPE and 30 kts of effective shear. As the MESH began to increase, so did the probability of severe. ProbSevere had a forecast of 63% at 21:44 UTC, 19 minutes prior to a severe thunderstorm warning being issued by the NWS (figure 2). No reports have been recorded, however. Forecasters this week have noted how ProbSevere can help identify the storms most important to watch or interrogate further.

Figure 2: NWS warning on southern Indiana storm.

-Cintineo

ProbSevere Model Error

In this image from 2158z over southern South Carolina the ProbSevere model highlighted an area where there was hardly a cloud in the sky. The readout shows a 78% prob of severe storm with 1600 J/kg MUCAPE, 2.1kts of EBShear and MRMS MESH of 2.08 inches.

Talking with the developer of this model, he indicated this is a known problem associated with QC of the MRMS MESH data.

Shawn Smith

Convective Initiation Product over eastern West Virginia

Click the image for an animated loop of GOES East visible imagery between 16z and 1745z along with the Convective Initiation product.

The color scale on the convective initiation product has been adjusted to three colors to simplify identification of the various probabilities. Blue is a 0-30% probability, Yellow is a 31-70% Probability and Red is 70% to 100%. I feel this helps to show increasing probabilities better than the standard multi-color scale. In the looping image notice the outlined area over eastern W. Virginia to the west of the Shenandoah Valley. Watch how the CI product shows increasing probs starting at 1615z along a ridge top 30 to 45 minutes before a line of thunderstorms exploded along the ridgeline. This product also highlighted these storms about 3 hours before a Satellite Precipitation Estimate message was issued by NESDIS. (1907z)

Shawn Smith

Tuesday 2030Z – NearCast Analysis

This post shows how the Nearcast model did well in depicting a weak north/northwest moving boundary that initiated convection in southwestern WV.  In a rather “pulsey” environment, the ability to pick out this boundary aided in confidence as to where convection was going to form.  Definitely a good tool to use in conditions where forcing is subtle and there is uncertainty on location on CI.

-Deitsch

Here is the 2030Z forecast from the 20z Nearcast model. White line represents a weak boundary

Here is the same image with current radar overlaid.

Appalachian pulse storms

ProbSevere has picked up on pulse convection in West Virginia (figure 1). A storm in a very weakly-sheared environment in eastern WV exhibited strong and moderate satellite growth rates and increasing MESH. It had a probability of severe of 70% by 1:30pm, about 25 minutes before the first NWS warning was issued. The storm later produced 1.75" diameter hail at 2:11pm.

Figure 1: Pulse convection in WV.

On the east slope of Tennessee, three storms that had moderate to strong satellite growth rates and MESH around 0.5 to 1.5" also had strong probabilities of severe (> 60%) prior to being warned. So far, the northernmost and southernmost storms were reported to have 1" hail.

Figure 2: Pulse storms in eastern TN.

-Cintineo/Sieglaff

NearCast – Decreasing 780 mb Theta E = Weakening Storms in NW OH

CIMMS NearCast 780mb Theta E product depicted decreasing values from 15 UTC (first image – around 329 K in NW OH) to 19 UTC (second image – around 327 K in NW OH)  on May 13.  Storms seemed to decrease in coverage and intensity 18-20 UTC in NW OH.  The decrease in mid level moisture around 780 mb may have caused the decrease in storm coverage and intensity.

The GOES Vertical Theta-e Differential Mid-Low product showed an increase 15 to 19 UTC from -5 K to +1 K, which may have helped to cause the decrease in storm coverage and intensity.

Michael Scotten

Convection in the Hoosier state

During day 2 of the HWT this week, the forecasters are tracking a line of storms heading through Michigan. Further south, however, storms fired along the cold front prior to our shift (~11:00am on May 13) in Indiana. In figure 1, we see part of the line with an elevated probability of severe (from the NOAA/CIMSS ProbSevere model). A strong satellite normalized vertical growth rate and moderate glaciation rate contributed to probabilities in the 45-55% range. The environment was marginal, and the MRMS MESH started to increase in the 0.6-0.7" range. When the NWS issued a severe thunderstorm warning, the MESH spiked to 1.84" and the probability increased to 96%. This storm later produced wind damage in northern Indiana.

Figure 1: Early convection over northern Indiana.

Further south, more storms developed on or ahead of the cold front. You can see that for the featured storm in eastern Indiana (figure 2), the strong satellite growth rates jumped the ProbSevere probability from 4% to 51%. MESH was only around 0.3". The NWS did issue a warning on this storm at 2:30pm (figure 3), 16 minutes after the first probability of over 50%. No reports have been recorded yet.

Figure 2: Convection in eastern IN. Satellite growth rates contribute to elevated probability of severe prior to NWS warning. MESH was very marginal.

Figure 3: NWS warning that came out at 2:30 PM.

-Cintineo/Sieglaff