Experimental Tornado Warning in Hastings, NE

One forecaster in the Hastings, NE WFO issued an experimental tornado warning based on his interrogation of base velocity data at 2137 UTC 01 May 2018.  The forecaster noted the ProbSevere All Hazards probability of tornado was low (9%) at the time he decided to issue the warning (2134 UTC), but then jumped to 40% in the following scan (see Figure 1).  The probability of tornado values continued to increase into the 60% range.  The forecaster commented, he realized the rotation increase he noted in base data took a few minutes to be captured in the MRMS AzShear fields and hence ProbSevere All Hazards.  In this case he said the probability of tornado confirmed his decision to warn and it gave him confidence in the probability of tornado, but to keep aware of the latency in base data into derived products.  This storm did produce a brief tornado shortly after the warning issuance.

Figure 1. KUEX 0.5 degree storm-relative velocity and ProbSevere All Hazards probability of tornado contours over Nebraska 2132-2142 UTC 01 May 2018.

-J. Sieglaff

Convective Initiation in Dodge

Convection initiated along the dry line in northern DDC after 1930 UTC. Referring to the two-panel animation below, initiation is clearly evident in the 1-min visible imagery based on vertical cloud growth and the appearance of a shadow and anvil. Cooling was also obvious in the 1-min IR (not shown). In the bottom panel of the figure is the 5-min convective initiation algorithm overlaid on VIS. The CI algorithm did not successfully capture any of the initiation along the dry line, despite clear skies. In this case, the CI algorithm provided no value.

 

- Bucky

DDC non-warn decision

A group of storms intensified across the southern portion of DDC area. Updrafts weren't terribly organized but near criteria for reflectivity above -20C. ProbSVR exceeded 50% but never topped 70% before decreasing. This agreed well with base data interrogation. GLM Lightning also went to 6 on FED before decreasing again. Similar to what happened with the earlier storm that was severe.

Dodge City, KS Mesoscale Analysis

Today my pair is operating in the Dodge City, KS county warning area which covers roughly the southwest quadrant of Kansas. As of 1900 UTC, GOES-16 visible imagery and surface obs reveal a well-defined dry line stretching southwest to northeast across the CWA. Analyzing the 1-min visible imagery, cumulus clouds are quickly becoming more agitated in time, with towering cu developing all along the dry line.

LAP CAPE field clear sky algorithm highlights the dry line, with CAPE around 1500 j/kg just ahead of the dry line. This is lower than the adjacent GFS first guess pixels, which are between 2000 and 2500 j/kg. A 1900 UTC DDC souding revealed MLCAPE just over 2000 j/kg. So LAP CAPE bringing CAPE values down slightly too low, but capturing the gradient well.

- Bucky

ProbSevere All Hazards Alerts Dodge City Forecaster

One of the forecasters covering the Dodge City, KS noticed a rapidly developing storm just ahead of the main line around 2050 UTC.  The base reflectivity was only near 50 dBZ and MRMS MESH was less than 0.20", but the forecaster noted the appearance of a ProbSevere AllHazards contour of 48% at 2046 UTC.  The ProbSevere All Hazards probability then rapidly increased to 84% only 6 minutes later--due to rapidly increasing total lightning, strong satellite growth rates, and very favorable thermodynamic environment for severe hail (see Figure 1).  The forecaster said, "this caused me to interrogate the storm further using all-tilts and noticed a strengthening trend aloft".  The forecaster added, "ProbSevere All Hazards drew my attention to this storm, that combined with the ProbSevere All Hazards reaching high probabilities with other storms before MRMS MESH was exceeding 1.00" and getting reports of severe hail gave me the confidence to issue an experimental severe thunderstorm warning earlier than I would have using only an all-tilts interrogation of the storm".

Figure 1.  MRMS Composite reflectivity and ProbSevere All Hazards contours 2046 - 2052 UTC 01 May 2018.  The storm of interest AWIPS read-out demonstrates the jumps in probability of severe hail as well as rapidly increasing total lightning flash rates.

-J. Sieglaff

DDC Warning decision

Radar reflectivity increased with more upright updraft over time. Refl values exceeded threshold for warning as ProbSVR increased to 78%. This helped increase warning decision as previous scan was 50%. Lightning FED went from 1 to 6 in 1 min briefly before decreasing again prior to warning issuance.

ProbSevere All Hazards Providing Lead-Time in Kansas

Severe thunderstorms explosively developed along the dry line over central Kansas Tuesday afternoon.  The HWT forecasters are centered on the Hastings, NE and Dodge City, KS WFOs.  Forecasters from both WFOs have noticed ProbSevere All Hazards was exhibiting rapid jumps to to probabilities in excess of 90%, while MRMS MESH values remained in the 0.50" to 0.75" range (see Figures 1 and 2 below).  The forecasters remarked they were pleased with the lead-time ProbSevere All Hazards was providing, despite the MESH still being below severe size (1.00").  The jumps in the probability of hail from ProbSevere All Hazards can be attributed to 1) intense GOES-16 vertical growth rates, 2) rapid increases in total lightning flash rates, and 3) the environmental parameters from Numerical Weather Prediction (NWP) used are extremely favorable for severe hail.

Figure 1.  Storm over Hastings, NE CWA at 2012 UTC 01 May 2018.  Notice ProbSevere All Hazards is 88%, while MRMS is only 0.37".  This example illustrates the power of utilizing other observations of deep convection, specifically satellite derived growth rates and total lightning flash rates, as well as environmental conditions from NWP data.

Figure 2.  Storm over Dodge City, KS CWA at 2014 UTC 01 May 2018.  Notice ProbSevere All Hazards is 95%, while MRMS is only 0.73".  This example also illustrates the power of utilizing other observations of deep convection, specifically satellite derived growth rates and total lightning flash rates, as well as environmental conditions from NWP data.

-J. Sieglaff

DDC ProbSVR

ProbSVR showed a new cell on the back edge of the convection with probs of 85%. This was based on a bad composite MRMS product. The local radar did not support any development in that area.

Preconvective Environment in Wichita

Below you can see VIS imagery of the Wichita CWA (in yellow).  The dry line is clearly seen to the west.

If you look at GOES-East derived CAPE (below), it's missing data over most of KS.  This is to be expected due to the clouds over the central and eastern portion of the state.  But why is the seemingly clear sky western portion of the state missing data?

Looking at the Cirrus band, you see thin high clouds blocking the western portion of the state retrievals.

This missing area is filled in with the AllSkyLAP layer CAPE.

It matches up fairly well with the SPC Mesoscale Analysis MLCAPEs.  The AllSkyLap layer CAPE is only a little underdone.

-Kevin

south side DDC

Looking at southern half of DDC's CWA expecting CI here first along the dryline. Moderate instability exists east of the dryline with deep layer shear sufficient for supercells. Low level winds are veered more than I would like for tornado threat so expect large hail to be the primary threat. Storms are expected to be more isolated as you go south along the dryline further removed from the better forcing. - S Coulomb