Upper Midwest storms and NOAA/CIMSS Prob Severe Model Demonstration

The GOES-R PG CIMSS/MKX shift focused on the Upper Mississippi Valley on Thursday, September 4.  Ongoing convection existed over far northern Wisconsin early in the morning on Tuesday.  The storms were discrete, elevated supercells that eventually congealed into a linear convective system.  While the NOAA/CIMSS ProbSevere model is designed to increase lead-time to the initial severe warning/hazards, this case demonstrates what others have noted during the spring and summer this year, that the ProbSevere model performs well with discrete mature convection.  Figure 1 below is shows the Green Bay 0.5 degree reflectivity with NOAA/CIMSS ProbSevere model output in the shaded contours around storm cells valid at 1452 UTC 4 September 2014.  These two storms with high ProbSevere values (> 90%) produced golf ball sized hail around this time.

Figure 1.  KGRB 0.5 degree reflectivity and NOAA/CIMSS ProbSevere output valid at 1452 UTC 4 September 2014.

Not shown was the progression of these storms across northern Wisconsin in the morning hours on Thursday.  During this time the ProbSevere values were consistently high (> 85%) with sporadic severe reports across the rural Northwoods.

Additional elevated storms developed over western and southwestern Wisconsin during the early afternoon hours, fueled by warm air advection.  These storms struggled to develop as the atmosphere was strongly capped.  The ProbSevere values associated with these storms remained (correctly) quite low over southwestern Wisconsin.  The storms over west-central Wisconsin did exhibit higher probabilities, as much as ~60% (largely due to much higher values of effective bulk shear and MRMS MESH values approaching 0.75"), but as of this writing have yet to produce severe weather.

The strong cap in place is likely to inhibit surfaced based convection along the cold front in Minnesota through the duration of the shift.

-Justin Sieglaff (UW/CIMSS)
-Ben Herzog (NWS MKX)

FROPA convection on the Plains

Strong early September convection fired on a trailing cold front in the late evening and overnight hours in northern OK, southern KS, and southwest MO. The environment near and along the front was characterized by MUCAPE ~2500-4000 J/kg and effective shear ~20-35 kts. The IR-derived satellite growth rates, as captured by the NOAA/CIMSS ProbSevere model were very strong, during this period of GOES-East rapid-scan operation.

GOES-East IR brightness temperature, 5-minute NLDN lightning plot, and METAR station plots.

 The explosive growth rates, along with strong MRMS MESH and a favorable environment, led to very high probabilities of severe (80-100%) before severe weather was reported from many of these storms.

ProbSevere contours overlaid MRMS reflectivity and NWS warnings.

 The first storm to initiate in south-central KS (shown below) went from 10% (22:30Z) to 57% (22:34Z) probability of severe as the observed satellite growth went from moderate/weak to very strong, while the MESH remained constant at 0.25". Six minutes later, the probability of severe was 79% (MESH still < 0.5"). By 22:52Z, the probability of severe exceeded 90%, as the MESH was nearly 0.75". The probability maxed-out at 100% at 23:14Z, when the MESH was 1.47" and the first 1" report was also recorded at this time. This storm would go on to produce a large tornado near the town of Cedar Vale, in Chautauqua county, as well as baseball-sized hail in Winfield, KS.

The storms in the region produced numerous severe weather reports, including hail up to the size of baseballs, wind gusts up to 80 mph, and large tornadoes. The satellite growth rates from the model may increase forecaster confidence in issuing warnings and perhaps increase lead-times to initial severe hazards.

John Cintineo
UW-CIMSS

Severe Hail in Texas Panhandle

All day we were watching weak convection along a cold front in the Central Plains and ProbSevere as expected with these weak storms was no higher than 5 percent. Later in the afternoon, a few isolated cells in the Texas Panhandle rapidly developed. One storm, the Clarendon storm, became severe within an hour of initiation. We utilized ProbSevere as guidance in determining which storms to focus on for potentially severe hail. ProbSevere made it easy to see the evolution and intensification of the individual cells. Eight minutes before the Clarendon warning, ProbSevere was 43%, two minutes later it was up to 72%, another 4 minutes later it was up to 96%. At warning issuance another 2 minutes later it was 98%. ProbSevere performed well with regards to hail size. During this 8 minutes the MESH increased from .71 to 1.8 inches. After the warning was issued, it continued to increase to 2.4 inches. Local storm reports of 1 to 2.5 inch diameter hail were received.

Nearby cells that were developing around this time had a ProbSevere of 80-98%, however none of these cells had a warning except for the Clarendon storm during the initial time period studied. A half hour later the warning over the Clarendon storm was expanded to include most of the nearby cells that ProbSevere had high probabilities for earlier. There were no storm reports issued as of 15 minutes into the warning for the other cells but regardless there was a warning consistent with the ProbSevere guidance.

Sarah Marquardt and Sean Miller
NWS Milwaukee/Sullivan

Crop damage in South Dakota

The morning of August 14th brought a lone hailstorm to central South Dakota. The NOAA/CIMSS ProbSevere model  did not detect cloud growth from satellite, as the convection had been ongoing for some time. The MUCAPE and effective shear of the environment were also rather weak. However, the MRMS MESH product reflected the development of the storm, increasing from 0.71" --> 0.97" --> 1.19" --> 1.69" over the span of 6 minutes (14:50 UTC to 14:56 UTC). The probability of severe increased from 14% to 80% during that short time. The MESH soon after was in the 2-3" range (likely an overestimate, possibly owing to single-radar coverage), and hail of up to 1.25" diameter was reported to damage the local corn crop at 15:05 UTC. The model provided 9 minutes of lead-time to the initial hail reports (measured from the 80% threshold). This example demonstrates how crucial radar detection/diagnosis of storms is in the ProbSevere model, as well as to forecasters.

ProbSevere contours overlaid MRMS Merged Composite Reflectivity, NWS warnings, and local storm reports.

John Cintineo
UW-CIMSS

Satellite growth rate utility in ProbSevere

Convection fired in central Texas along a weak cold front on the afternoon of Monday, August 11th, in an environment characterized by very weak effective bulk shear (< 5 kts) and strong MUCAPE (2800-3600 J/kg).

In the first featured storm, the normalized satellite vertical growth rate went from 'moderate' to 'strong', and the storm-top glaciation rate when form 'weak' to 'moderate' at 17:22 UTC, as the probability of severe jumped from 18% to 61%, with the MESH remaining constant at 0.67 in. The probability then fluctuated between 40% and 60% before the storm was warned at 17:44 UTC with a probability of severe of 58% and MESH = 0.65 in. The fluctuation may have been a result of very low shear and therefore a more "pulse" nature of convection. The satellite growth rates in this storm signaled enhanced probability of severe weather, whereas the shear and MESH were poor to mediocre. This storm was warned again at 18:39 UTC and attained a maximum probability of over 80%. Thus far, there have been no LSRs for this storm, located about 100 miles southeast of Dallas-Fort Worth, TX.

The second featured storm to the southwest had strong normalized satellite vertical growth and glaciation rates at 17:45 UTC. The probability of severe increased from 28% to 72% to 92% from 17:58 UTC -> 18:00 UTC -> 18:08 UTC, as MESH also increased from 0.46 in. to 1.13 in. over that time. This storm was warned at 18:16 UTC and had a severe wind report at 18:18 UTC (trees blocking intersections).

The third storm featured to the northeast of the first storm also had strong satellite growth rates (it was under the same parent satellite cloud-object as the first storm) before rapidly attaining a probability of severe of 86% at 18:56 UTC (MESH = 0.9 in.). It was severe-warned at 19:03 UTC and had a 1 in. hail report at 19:10 UTC.

These examples show how temporal trends in satellite-derived fields can help signal severe potential in slowly developing and more rapidly developing convection. By integrating satellite parameters (when applicable) with radar and NWP fields, we hope to paint a more accurate picture of storm evolution and initial potential severity.

ProbSevere contours around MRMS merged composite reflectivity.

EDIT: Several of these storms did have marginal wind and hail reports.

John Cintineo

UW-CIMSS

ProbSevere in SE Missouri

A high CAPE, low shear environment fueled convective development in southeastern Missouri during the early to mid afternoon on 6 August 2014. Rapid convective development was captured using the ProbSevere function as can be seen in this image.

Convective development over SE MO at 1936Z. ProbSevere values of first warned storm are shown. 0.5 degree reflectivity was captured from KLSX.

This image shows the visible satellite imagery of the same storms in southeastern Missouri. The storm had plenty of lightning associated with it as it tracked to the southeast.

Visible satellite imagery of SE MO. Note the numerous lightning strikes over this area.

At 1936Z, the severe probability was nearly 100% for the northeastern most cell. The MESH value was 1.84. The high CAPE environment allowed these thunderstorms to develop quickly (storms had moderate to strong satellite growth rates), and ProbSevere did a good job in diagnosing the cell as ProbSevere had severe probability values jump from 26% at 1930Z to 81% at 1932Z. Shortly after this spike, the NWS in Paducah issued a Severe Thunderstorm Warning at 1936Z.

At the time of this post, there were no severe storm reports that came out of this cell. This might be contributed to the environment not being as favorable for severe weather (the area was in a See Text severe category from the Storm Prediction Center). SPC did issue an MD for the area for sporadic microbursts shortly after the initial warning, and there were a few penny sized hail reports for a cell that developed over Poplar Bluff. The ProbSevere MESH value for that cell was ~1.14, with a ProbSevere value of 90%. The ProbSevere value was at least 90% for that cell for about five minutes prior to the first report of penny sized hail.

Schultz NWS-MKX
Cintineo UW-CIMSS

ProbSevere in Wisconsin marginal hailers

A departing strong upper-level system over the Great Lakes left an opportunity for storms to develop in a northwest flow regime over northern and central Wisconsin on Thursday, July 31.

Cool air aloft provided good mid-level lapse rates (~ 7 C/km) and associated instability for storms to tap into, coupled with decent low-level lapse rates.

SPC's objective analysis of mid-level lapse rates.

The environment was characterized by ~1500-1900 J/kg of MUCAPE and ~15 kts of effective bulk shear. The AWIPS-II scroll-over readout of the NOAA/CIMSS ProbSevere model contours showed that these storms had strong normalized growth rates and glaciation rates, two or more hours prior. Development on radar lagged the strong growth observed from satellite, in this case. Storms developed MRMS MESH values of 0.7 to 1.15". The MESH, coupled with the satellite and environment information yielded probabilities of severe in the 60-90% range. These storms highlighted below were warned 15-25 minutes after ProbSevere exceeded 50%. The storms in Portage and Barron counties produced 1" hail, while the storms in Burnett and Clark counties had no reported hail. 

While radar is the most valuable stand-alone tool for severe storm analysis, this case highlights the use of the satellite growth rates in the fused product to enhance confidence and lead-time to severe hail. 

ProbSevere contours overlaid MRMS Composite Reflectivity and GOES-East visible imagery.

John Cintineo
UW-CIMSS

ProbSevere MRMS fields vs. Single-source radar fields

NOAA/CIMSS ProbSevere display with kapx 0.5-degree Base Reflectivity, 1744 UTC on 22 July

Note the radar object above, enclosed in purple, from the MRMS (Multi-radar, Multi-sensor) fields, differs from the 0.5 Base Reflectivity field from the Gaylord, MI radar displayed.  This is to be expected because the MRMS is composite reflectivity from a variety of radars (in the case above, likely Gaylord, Marquette (MI) and Green Bay (WI)).  Do not expect a field from a single radar to overlap the MRMS fields.

(Scott Lindstrom, Ben Herzog)

Severe Storms in Northwestern Arkansas

As the CIMSS/MKX GOES-R Proving Ground shift wound down Tuesday afternoon, severe thunderstorms rapidly developed over northwestern Arkansas.  This region was supportive for strong to severe thunderstorms with MUCAPE between 2500 and 3000 J/kg and effective bulk shear 20-30 kts.  Figure 1 below shows the NOAA/CIMSS ProbSevere Model overlaid on MRMS composite reflectivity.  Of note is the rapid increase in the ProbSevere values over the course of 6 minutes between 2032 UTC and 2038 UTC 08 July 2014.  At 2032 UTC the ProbSevere value was 8%, then at 2034 UTC the ProbSevere value jumped to 56%.  This jump was attributed to more intense satellite growth rates (the normalized vertical growth rate went from 1.4%/min (strong) to 2.6%min (quite strong) and the glaciation rate increased from 0.02/min (weak) to 0.06/min (strong)) as well as a jump in the MRMS MESH associated with this storm 0.35" to 0.52".  Another four minutes later at 2038 UTC the probability jumped again to 95% as the MRMS MESH approached 1.00".

Figure 1.  NOAA/CIMSS ProbSevere Model and MRMS Composite Reflectivity over northwestern Arkansas during late afternoon of July 8 2014.

This example illustrates the increase in lead-time to severe hazards as well as severe thunderstorm warning issuance that is possible by quantitatively using satellite growth trends with environmental information and radar observations of a storm's precipitation core.  In this example, the initial severe thunderstorm warning was issued at 2059 UTC--20 to 25 minutes after the significant jumps in the NOAA/CIMSS ProbSevere output.   More storms continued to develop further west during late Tuesday afternoon, most of which became severe thunderstorm warned after reaching high levels of NOAA/CIMSS ProbSevere values.  Only one severe report was received with these thunderstorms, but one wonders if this is more related to the population of very rural northwestern Arkansas--with much of this region covered by state and national parks (Figure 2).

Figure 2.  Google maps showing the one severe hail report received with these storms (green 'H').  The very rural nature to the area inferred by this map makes one wonder if more severe weather occurred than was actually reported.

-Justin Sieglaff, UW/CIMSS
-Steve Hentz, NWS MKX

Low Topped Wisconsin Storms

The synoptic setting for Wisconsin July 7th 2014 featured a small shortwave in a mid level trough over the upper Great Lakes.  MUCAPE values ranged from 300 to 800 j/kg with 0-6 km shear around 25 to 30 kts.  Scattered thunderstorms developed by noon.  SCAN max hail values were from 0.50 inch to 0.75 inch.  The CIMSS probabilities over severe were mainly in the single digit to around 25%, but many storms did have strong vertical and strong glaciation rates.  One storm did approach severe criteria. Using FSI with the Donovan technique a narrow core of 50dbz did just reach severe criteria.  The CIMSS Probability of severe was low at 49% , with the MESH value around 0.50 inch,   giving confidence that the storm was not severe.

-Steve Hentz