Daylight Savings storms

As we mindlessly set our clocks ahead one hour, storms raged on in the southern U.S. A shortwave in the polar jet stream plunged southward over the Plains to force strong convection along a 500mb jet streak in eastern Oklahoma and western Arkansas. The NOAA/CIMSS ProbSevere model is moving toward hazard-specific statistical models using MRMS, GOES-ABI series, lightning, and NWP data. ProbHail, ProbWind, and ProbTor will be evaluated for a second year at the NSSL Hazardous Weather Testbed.

This storm northwest of Fort Smith, AR, shot up in ProbSevere value (the probability of severe is simply the maximum of the ProbHail, ProbWind, and ProbTor values) between 21:30Z and 21:40Z, going from 18% to about 50%. Golfball sized hail was recorded at 21:40Z. The increasing MESH (though still less than 1.0") spiked the ProbSevere value, while a jump in the total lightning flash rate increased the ProbSevere value from 65% to over 90% later on (see a time series of this storm's attributes in Fig 2). Interestingly, the 3-6km AzShear was very high before the lightning or MESH really took off, indicating strong mid-level rotation. The storm later recorded 2.0" hail east of Fort Smith. ProbHail had the highest probability for any of the models throughout the duration of the storm.

Fig. 1: ProbSevere contours, MRMS MergedReflectivityComposite for a storm in eastern OK / western AR. NWS severe weather warnings are also plotted.

Fig. 2: Time series of ProbSevere (max of ProbHail, ProbWind, and ProbTor) for the storm in OR/AR, with a subset of contributing predictors.

During the daylight savings time switch, another set of storms forced by a strong subtropical jet stream and moist southerly return flow from the Gulf of Mexico made their way from eastern Texas into Louisiana. The monster supercell in Figures 3 and 4 had a strong normalized satellite growth rate (4.1%/min observed by GOES-16) prior to 03:00Z. The growth rate brought the probability to about 20%, where the MESH and flash rate catapulted the ProbHail value from 20% to 90% in about 20 min. The storm had ProbHail and ProbWind exceeding 85-95%, recording numerous hail and wind reports, while ProbTor peaked at 20% (there were no tornado reports).

Fig. 3: ProbSevere, MRMS MergedReflectivityComposite and associated NWS severe weather warnings for a storm in east TX.

Fig. 4: Time series of ProbSevere (max of ProbHail, ProbWind, and ProbTor) for the supercell in east TX, with a subset of contributing predictors.

Late December storms

A negatively-tilted shortwave brought some low-level moisture return to the gulf states this week, and with the moisture, some scattered severe storms.

A couple tornadic storms affected portions of east Texas. The NOAA/CIMSS ProbSevere model now incorporates the GOES-16 satellite growth rates, and a storm affecting Cherokee Co., TX, had a strong normalized growth well before it produced severe weather.

Figure 1: AWIPS2 screen captures of MRMS MergedReflectivity, ProbSevere contours, and NWS warnings for a storm near Rusk, Texas.

The ProbWind values vacillated largely between 50% and 75% for this storm, before producing a tornado at 00:56 UTC and multiple wind damage reports in the town or Rusk, TX. The strong GOES-16 vertical growth rate, large ENI flash rate (~30-70 fl/min), and stout kinematic fields (eff. bulk shear ~ 45-50 kts; meanwind 700-900mb ~ 35 kts) combined to produce these moderate-strong ProbWind values. The MRMS MESH remained rather low (~ 0.2 - 0.6 in), signaling that this was not a severe hail situation. ProbTor had a maximum value of 12% before the first tornado report.

This storm featured jumps in ProbWind value (one produced by a large increase in flash rate, indicative of a lightning jump), and being an outlier storm amongst its neighbors, in terms of probability value. Both features in ProbSevere objects have been identified by forecasters as indicating possible severe weather.

A second storm formed further south and later in the night, which also produced a damaging tornado, touching down northeast of Beaumont, TX, and later northwest of Lake Charles, LA, blowing off the roof to a restaurant.

Figure 2: AWIPS2 screen captures of MRMS MergedReflectivity, ProbSevere contours, and NWS warnings for storm heading into southwest Louisiana.

The kinematics for this storm were very favorable, with effective bulk shear of 50 kts, meanwind 700-900mb of 45 kts, and 0-1 km storm-relative helicity near 300 J/kg. The first tornado touched down at 07:41 UTC, when ProbTor was about 30%. ProbTor then jumped from 30% to 50% at 08:00 UTC, the time of the second tornado report. This jump in ProbTor value was coincident with an increase in total lightning (a lightning jump) as well as an increase in low-level rotation.

Figure 3: Time series of ProbTor and predictor values for this storm affecting southeast TX and southwest LA.

A tornado warning was issued at 08:10 UTC, when ProbTor had just increased to 90%. The third tornado reported, at 08:20 UTC, was rated EF1 and destroyed the roof of a restaurant in DeQuincy, Louisiana.

Spartanburg, SC Tornadoes

A potent October shortwave traversed the southern U.S. on October 23rd, bringing with it a round of severe weather to the Southeast U.S. The Storm Prediction Center outlook had a 5% contour for tornadoes (Figure 1; probability of a tornado within 25 miles of a given point), citing very strong low-level shear and weak to moderate buoyancy.

Fig.1: SPC tornado outlook issued at 16Z 10/23/2017.

Convection took on a linear storm mode in South Carolina, with a surge in a line heading toward Spartanburg (Figure 2). The NOAA/CIMSS ProbTor model increased to over 80% by 18:20Z, owing to increases in low and mid level azimuthal shear, and a jump in total lightning density, while residing in an environment with excellent 0-1km storm relative helicity (Figure 3).

Fig. 2: ProbSevere (all hazards) contours, NWS warnings, MRMS MergedReflectivity, GOES visible reflectance. The ProbTor was the highest hazard probability for this storm; 88% at this time. 

The first tornado reported was at 18:54Z, coincident with the first NWS tornado warning. The first tornado damaged permanent and mobile homes, downed power lines, and destroyed a horse barn. Later, the storm produced another tornado between downtown Spartanburg and I-26, snapping large trees, as ProbTor was about 45%. After dropping below 20%, ProbTor again increased to 40% at 19:36Z, when another tornado was reported near the North/South Carolina border.

Fig. 3: Time series of ProbTor (thick red line), with constituent predictors. NWS warnings and preliminary LSR reports are on bottom axes.

In this case, ProbTor may have been able to provide an earlier "heads up" to forecasters monitoring the storms for potential tornadic activity. ProbTor is best utilized in conjunction with current warning practices and interrogation of base radar data. If a velocity couplet is outside of the ProbTor object polygon, ProbTor will be underestimated, as may have been the case for a second tornadic storm in North Carolina on this day.

2017 Experiment Complete

The 2017 GOES-R/JPSS Experiment in the HWT is wrapping up today. This has been a great experiment this year with getting to utilize live GOES-16 data in operations here in the testbed. Also we were able to demonstrate GLM lightning data to forecasters for the very first time and have gotten a lot of valuable feedback from forecasters on what they would like to see operationally form the GLM in terms of display capabilities. Feedback from the fourth and final week of the experiment is posted below:

GLM

Get the parallax fixed before fielding

Forecasters will be confused between events, groups, and flashes and what each means and why they are useful

The Stano color curve would be the best default

Being able to monitor trends would be the most useful

A pop up time series like a pop up skew t could be very useful

Training seemed to be pretty good for preparing people

Seeing the spatial extent is a very useful quality of GLM

Another big utility is for monitoring electrification before the other networks can

Don’t see people using it too much if the parallax displacement is still an issue when fielded

NUCAPS

Useful information yesterday out of the gridded products when there was clearing in the area

Obviously most useful for pre-convective environment and getting an early afternoon pass over the area

Overall the experimental product seemed more useful, but there were times that the operational seemed to be a better representation of the environment.

The yellow dots seemed to be somewhat reasonable at times and can have some useful information

As long as people understand how the modifications in the experimental profile are made, they can be extremely useful

Like having both the experimental and the operational soundings to compare the atmospheres

Repeating the latency problem which is the biggest hurdle to operational use

Would be nice to be able to have some automated products produced from NUCAPS profiles

ABI

Understand the RGBs a lot better now than before

Found a couple really useful ones for operations

There were some very useful RGBs for convective applications

RGBs seem to bog systems down in some offices when trying to load

Training should concentrate on best practices and what the colors mean for application

Training needs to be heavily focused on operational benefits

Daytime Cloud Phase RGB seemed to be one that should be introduced first, especially this time of year for convective development

CAPE is still a problem, being consistently too low

Derived Winds should be color coded by pressure level instead of wind speed and steering clear reg, green, yellow type color combinations

ProbSevere

Useful for situational awareness

Good tool for monitoring trends and keeping an eye on storms of interest

ProbTor was useful for seeing storms that were different from any of the other storms

ProbHail was more restrained and seemed to reduce FAR from being too high from relying solely on MESH

Still struggles with wind events and tracking of linear features

-Michael Bowlan

GOES-R Liaison at SPC/HWT

Storms came into NW SD, barely

-tvguy

Line of storms were weaker on the southern half of the line coming in from MT... even though environment indicated some strengthening should occur. Due to 60 dbZ reflectivity at 15Kft, and increase in velocities >30 kt issued SVR for extreme NW corner of Harding Co for low end wind, hail threat. ProbSevere was not impressed, with 11% hail and 9% hail. But I'm not sure this tells the whole story, given strength of storms to the north and potential development of outflow winds as well as elevated reflectivities suggested a greater hail threat than advertised. Chose to discount the negativity of ProbSevere, with additional concern about data quality at such a long distance from the UDX 88D.

As warning about to expire, received LSR of 50 mph. Non-severe. But then velocities really picked up along the line, up to +57 kts. Due to strenthening, reissued along the line for much of that county (Harding).

Even though ProbSevere values were very low... under 10% on all parameters... the storm did produce highway sensor value of 62 mph. Kind of thinking the ProbSevere object is created by reflectivity core, but doesn't consider the stronger wind values created out ahead of that storm -- or, perhaps there are latency issues due to data processing. I don't know.

Finally, saw convergence signature (64 kts) on southern part of line. Upon expiration, reissued farther to the SE for line of windmakers.

ND 1 min imagery

Can see what looks to be lower level inflow into the main area of severe thunderstorms. This indicates to us that the storm is maintaining intensity. This, along with radar and PROBSevere data has led us to continue our warnings

Missing gridded NUCAPS data in complex terrain?

I noticed there were a lot of mixing pixels in the NUCAPS gridded data over the Black Hills despite the fact there was no notable cloud cover. Expanding west, it became apparent this was a common theme across Western Montana into central Idaho as well. Sounding availability overlays show most of these area are considered yellow. It seemed many of these points were areas where there was a gradient between darker forested areas in the terrain, and lower adjacent valley locations. For locations in the west, for this data to be useful and for us to have confidence in using it, we really need a more complete data set. A sounding from the Black Hill is shown at the bottom, which seems meteorologically reasonable.

-64BoggsLites

ND Convection along Warm Front

Finally have CI across the western portion of the CWA. Forcing is largely along the warm frontal boundary at this time, with two notable cells. Still monitoring the potential for initiation along the dryline. Have opted to continue the warning on the cell mentioned in the previous post given a combination of radar, satellite, and environmental data. 1 minute imagery is now in for the area: seeing near steady thick ice in the clouds associated with the isolated cells (which includes the warned cell), but not really beginning to see the cu along the dryline becoming more agitated.

2045Z UNR update - satellite and lightning trends

...update....the cell to the north did in fact product a CG strike per ENTLN data approximately 5-10 minutes after flashes/events where first noted in GLM data.

previous post...

The activity working across south central MT associated with a 500mb speed maxima has continued to develop eastward. Day cloud phase shows an increase in cumulus over far southeast MT over the last hour, and this activity has slowly increased in depth. Meanwhile the cluster of showers just to the west is producing a thicker anvil layer

The Sandwich display shows gradually cooling cloud tops indicating the convective cluster continues to slowly strengthen as it moves into a somewhat more favorable environment.

A 4-panel lightning display shows an increase in lightning trends as well. What's interesting to note (aside from the general increase in lightning trends) is the top left panel is a few flashes and events in a shower to the north of the better convection...an area where cloud to ground lightning has yet to be noted, and max dBz is near 30. Perhaps an indication this cell is strengthening and could produce lightning in the next few minutes.

-64BoggsLites.

Monitering convection along dryline

While storms are initiating near front, have been watching along dry line for new storm development. While that has not yet occurred, did catch a failed attempt at initation.  Visible loop (below) indicates what looks like an orphan anvil develop along the dry line.

In addition, daytime cloud RGB also showed that glaciation started (color becoming more green), it never grew past that initial color and diminished quickly.

-JRM