ProbSevere products for a storm in North Carolina

A storm in North Carolina produced 75-mph microburst wind gusts, downing many trees and overturning a pick-up truck. It also produced 1.5"-diameter hail.

Early on, ProbSevere LightningCast produced high probabilities of lightning well ahead of the first flashes (see Figure 1). LightningCast uses GOES-R ABI channels to predict next-hour lightning occurrence. For the  storm that produced severe weather (in eastern NC), LightningCast had 60 minutes of lead-time to the first flashes, measured from the 50% threshold. LightningCast often produces 20-30 minutes of lead-time to the first flash (see Figure 2).

Figure 1: LightningCast contours, GOES-16 ABI visible channel imagery, and GOES-16 GLM flash-extent density over the Carolinas.

Figure 2: Varying lead-times to initial GLM-observed flashes in coastal Carolina storms, measured from certain LightningCast probability thresholds.

ProbSevere version 3 (PSv3), which fuses radar, satellite, lightning, and NWP data to predict next-hour severe-weather probabilities, had an elevated probability of severe on the storm in eastern North Carolina before severe weather was reported. PSv3 was much higher than ProbSevere v2 (PSv2) early on. For instance, at 18:04 UTC, 21 minutes before the 75-mph wind gust, PSv3 was 39% and PSv2 was 2%. The 0-3 km lapse rate and MRMS MESH were the highest-contributing predictors, with the ENI lightning density and GOES-R satellite growth rate also contributing to the 39% probability of severe.

Figure 3: ProbSevere contours, MRMS MergedReflectivity, and NWS severe-weather warnings for storms in eastern North Carolina

Figure 4: The soon-to-be-severe North Carolina storm at 18:04 UTC, comparing PSv3 and PSv2.

Figure 5: Time series of ProbSevere v3 and ProbSevere v2 probabilities for the early portion of the severe storm in eastern North Carolina.

ProbSevere time series tool

At the 2021 HWT, forecasters will be able to use a new feature of the ProbSevere AWIPS plug-in: a time series tool. Forecasters from previous HWTs have consistently given positive feedback on a web-based meteogram tool, and so we have implemented something similar in AWIPS. 

To use it, you simply double-click on a ProbSevere object, and a window opens up with the time series of ProbHail, ProbWind, ProbTor, and ProbSevere (prob. of any hazard) for the given storm. We hope this will help forecasters better monitor the trends in hazard probabilities.

Figure 1: A severe-hail-producing storm in northeastern North Carolina, and the associated history of its ProbSevere probabilities in a time series window (ProbSevere was equal to ProbHail for this storm).

ProbSevere v3 will also be demonstrated at this year's HWT. PSv3 is driven by a new statistical model (gradient-boosted decision trees) and incorporates new MRMS, ABI, GLM, and SPC mesoanalysis data. This storm was warned at 17:31 UTC, and produced 1-inch hail at 17:38 UTC. At 17:26 UTC, ProbHail v3 jumped to 25%, whereas v2 was only 4%. ProbHail v3 might have been able to highlight this strengthening storm to the forecaster, whereas version 2 did not. A predictor importance analysis of ProbHail v3 for this storm at 17:26 UTC revealed that the highest contributing predictors were:

1. MRMS reflectivity at -20C (52 dBZ)

2. Eff. bulk shear (40 kt)

3. MRMS composite reflectivity (66 dBZ)

4. MRMS MESH (0.55 in)

5. Wet-bulb 0C height (7180 ft)

We expect that ProbSevere v3 will be more accurate and better calibrated than ProbSevere v2, meaning the probabilities more closely match severe report occurrence.