Fall severe weather outbreak over the Southern Plains

A strong, negatively tilted, diffluent short wave trough forced severe thunderstorms in the Southern Plains ahead of and along a potent cold front yesterday. Figure 1 shows a high-level evolution of the storms and ProbSevere v2 (PSv2) from discrete to more linear storm modes as the event proceeds.

Fig. 1: GOES-16 IR, MRMS MergedRef, ProbSevere storm contours, and NWS warnings.

One supercell that traveled through downtown Dallas, TX dropped a strong, EF3 tornado which produced much damage, which an NWS survey marked 01:58 UTC as the initial touchdown time. The storm went on to produce an EF1 tornado, starting at 02:36 UTC.


This storm was the right moving supercell after a left split (see Figure 2). Figure 3 shows the time series of PSv2 model output before the split, while Figure 4 shows the time series after the split, including NWS warnings and preliminary storm reports. The storm initially exhibited a strong satellite growth rate and a spike in MRMS MESH, which contributed to the rapid increase in ProbHail and ProbWind.

Fig. 2: ProbSevere, MRMS MergedRef, and NWS severe weather warnings in AWIPS2, depicting the storms affecting the DFW metro area.

You may find the time series of PSv2 model predictors for Figure 2 here and Figure 3 here. 

Fig. 3: Time series of ProbSevere models for a tornadic storm prior to it splitting. NWS warnings and preliminary storm reports are on the lower axis.

Fig. 4: Time series of ProbSevere models for a tornadic right-moving supercell after it split. NWS warnings and preliminary storm reports are on the lower axis (EDIT: tornado report times are the start times of tornadoes from an NWS survey).

An experimental convolutional neural network, which uses ABI channels 02 and 13, as well as flash extent density from the Geostationary Lightning Mapper, was deployed on this scene. The model produces an "Intense Convection Probability" (ICP). The 50% and 90% contours correspond well with robust satellite signatures, such as overshooting tops and enhanced-Vs. While there is also good correspondence with reports, probabilities of < 25% are present for some hail reports early in the event and some wind reports late in the event, showing that all severe weather is difficult to detect with a satellite-only approach. Regardless, such a model may be able to enhance ProbSevere, especially in regions with no radar coverage. See this CIMSS blog post for more information and examples from this model.

Convective Intensity Continues to Diminish in Eastern, ID

The Day Convection RGB generally shows weak to moderate convection persisting over eastern, ID.  There are occasional new updrafts that develop, but are short-lived.  Combining the satellite trends with radar reflectivity generally depict that the severe threat has become isolated over eastern, ID.

Day Convection RGB loop.

Convective Intensity Waning across Eastern, ID?

The Day Cloud Convection RGB still shows updrafts persisting over eastern, ID.  However, the anvils of the existing convection are spreading over the area and potentially inhibiting afternoon surface heating.  GLM data has also showed a diminishing trend in activity.   Note, the GLM data did not load for the last few frames.

Flash extent density overlayed on Day Cloud Convection RGB.

Tall cell in western GGW's area

Strong updraft in western GGW showed the red colors going over to greens...likely the updraft getting into the warmer stratosphere.
Day cloud phase distinction loop over the area shows a continued strong updraft with gravity waves radiating outward.



Quite a bit of flashes in that cell in GGW.

Charley

Storms Continue to track Northeast in Eastern, ID

The latest mesoanalysis shows values around 500 J/kg in portions of eastern, ID.  However, the NUCAPS modified sounding suggests that this could actually be in excess of 1600 J/kg by sampling a point in southern Fremont county.  Therefore, vigorous updrafts are expected to continue as these storms continue to track northeast this afternoon.


Latest SPC mesoanalysis of MLCAPE.


NUCAPS modified sounding.

Stronger Core

Continuing the SVR downstream, as yet another strong core pops up.  Colder cloud on IR and now prob severe is starting to jump up.  Blue color showing ProbHail and ProbWind in the 30s.
Cell also showing more signs of organization in the SRM...better chances for hail.



Also getting a pickup from the DMD (latency issue still for NMDA).



Charley

Two Severes ongoing Fergus County

IR imagery from GOES-West shows good updrafts continuing to radiated waves outward from warned storms in Fergus County.



...but ProbSevere continues to run cold.  Unfortunately it will be very tough to verify my warning given the rural nature of the area.



MESH tracks followed nicely the cells in the warning...though primary thought was these were wind producers.  Still seeing very bright TOE on GOES-West with these cells.

Charley

MESH high ProbHail Moderate

At 2120z SFX radar depcited a potentially severe thunderstorm located SW of Pocatello.  At this time, nearly 50 dBZ returns were observed in excess of 35kft.  The -20C level was approximately 17kft.  The MESH readout in ProbSevere showed 1.59".  However, ProbHail was only 55%.  This appears to be a case where the ProbHail algorithm was reducing the probability based on the environment despite several aspects that support issuing in warning for severe hail.  A warning was issued for this storm at 2101z.

2120z SFX 0.5 radar.

EWX ProbHail Case

Had an interesting opportunity to watch a quickly intensifying cell relatively close to the radar.  While ProbHail did a decent job monitoring the trend in this cell, its (2 to 4 minute) latency in an environment conducive of rapidly intensifying cell could possibly lead to a reduction in Lead Time. By monitoring the cell via All-Tilts BR/BV/CC/ZDR and GOES-East Satellite Imagery via Mesosector, I was able to get roughly 5 additional minutes of lead time on my warning (ProbHail was less than 45% by warning issuance). A good reminder as to how the ProbSevere suite is best utilized as an additional tool, and not necessarily the deciding factor in warning ops, especially in freshly forming cells.



Quick update: The earlier warning did verify with quarter-sized hail. I did find some utility with the ProbHail when it came to making the decision to re-issue the warning or not, especially as the storm began to near the "cone of silence." Accessing the time series  which continued to show >95% ProbHail and a quick glance at a neighboring radar, I had enough forecasting confidence to continue the warning downstream.
---------------------------------------------------------------------------------------------------- Mountain Bone

Modified NUCAPS Sounding

Point in eastern TFX area shows higher CAPE on the latest RAP sounding from SPC, compared to the modified NUCAPS sounding. That area is popping now with new cells.

Charley