Hail-Producing storm over the Texas Hill Country

May 9th, 2014 |
ProbSevere_09May2014_1400

AWIPS-2 display of a strong thunderstorm over Texas, including ProbSevere Readouts at 1400 UTC

A hail-producing storm (cick here for Storm reports from SPC) moved through Edwards, Real and Bandera counties of Texas after sunrise on May 9th. This storm gives a nice opportunity to compare ProbSevere and GOES-14 SRSO-R depictions of a severe storm. The 1400 UTC image, above, shows ProbSevere > 95%, with a MESH just over 1″. Within the next 10 minutes, MESH increased to 1.48″ at 1406 UTC (when ProbSevere was 96%), and to 1.92″ at 1408 UTC (see image below, when ProbSevere was 99%). A Severe Thunderstorm Warning was issued at 1408 UTC.

ProbSevere_09May2014_1408

AWIPS-2 display of a strong thunderstorm over Texas, including ProbSevere Readouts at 1408 UTC

The storm maintained its strength over the following half hour. Imagery from 1436 shows MESH values near 1.50″ and ProbSevere is at 99%. At 1442 UTC, the radar shapefile vanishes from the display, a result of processing errors, but it is back at 1444 UTC. Note that the Satellite Predictors have flipped at 1444 UTC from values derived at 1015 UTC to ‘Mature Storm‘ (this change has nothing to do with the missed processing at 1442 UTC). Recall that ProbSevere is designed to probabilistically determine whether or not a storm will produce severe weather in the next 60 minutes. ‘Mature Storm’ designations serve as a reminder that Probabilities have been elevated for a long period of time.

At 1458 UTC, below, near the end of the Severe Thunderstorm warning, the MESH value that is incorporated into the ProbSevere computation has decreased to 1.17″, and ProbSevere has dropped to “only” 97%. At 1502 UTC, however, MESH has started to increase again, to 1.21″ (and ProbSevere remains high); a second severe thunderstorm warning is issued at 1504 UTC when MESH is at 1.53″ (and ProbSevere is at 99% again). ProbSevere remains high through 1530 UTC.

ProbSevere_09May2014_1458

AWIPS-2 display of a strong thunderstorm over Texas, including ProbSevere Readouts at 1458 UTC

GOES-14 was in SRSO-R mode during this hail event, allowing an opportunity to see the storm evolution at very high temporal resolution. (The storm initially was right at the edge of the domain). The animation below shows cloud-tops warming around 1440 UTC, before cooling again, consistent with changing updraft speeds that can be inferred by changes in MESH. Cold temperatures occurred at 1501 UTC, 209.1 K. Temperatures were cooler than 210 K only at 1500 and 1501 UTC — that is, for two minutes — demonstrating the importance of 1-minute imagery in resolving without aliasing the coldest features at cirrus level. A second very cold event occurred between 1507 and 1509 UTC (brightness temperatures were cooler than 208 K); it was gone by 1511 UTC (when brightness temperatures were all warmer than 211 K). One-minute imagery is necessary to resolve these very rapid changes at cirrus level.

ProbSevere_09May2014_1458

GOES-14 Visible (0.62 µm) (top) and GOES-14 IR (10.7 µm) (bottom) from 1401 UTC through 1530 UTC on 9 May. Edwards, Real and Bandera Counties are highlighted

The plot below shows the coldest IR Brightness Temperature observed in the GOES-14 10.7 µm channel over the hail-producing storm. Tic-marks along the x-axis are at 5-minute intervals, and there are large differences that occur with time-scales shorter than 5 minutes. This is consistent with the findings of Cintineo et al. in the September 2013 issue of Journal of Applied Meteorology and Climatology (link).

BT_CloudTop_SRSO

Minimum cloud-top IR Brightness Temperature over hail-producing storm, from 1411-1530 UTC. Tic marks on x-axis every 5 minutes.

During the following hours, 1-minute interval GOES-14 0.63 µm visible channel images (below; click image to play animation; also available as an MP4 movie file) showed other areas of convection which produced damaging winds across parts of southeastern Texas.

GOES-14 0.63 µm visible channel images (click to play animation)

GOES-14 0.63 µm visible channel images (click to play animation)

GOES-14 Super Rapid Scan Operations for GOES-R (SRSOR) 1-minute interval imagery

May 8th, 2014 |
GOES-14 0.63 µm visible channel images (click to play animation)

GOES-14 0.63 µm visible channel images (click to play animation)

Another period of activating GOES-14 for Super Rapid Scan Operations for GOES-R (SRSOR) began on 08 May 2014. One area of severe thunderstorms began to develop over the South Dakota/Nebraska/Minnesota/Iowa region, as see on McIDAS images of 1-minute interval GOES-14 0.63 µm visible channel data (above; click image to play animation; also available as an MP4 file).

An AWIPS image of GOES-13 0.63 µm visible channel data at 15:15 UTC with overlays of METAR surface observations and fronts/pressure analysis (below) showed that a well-defined warm frontal boundary was in place across the region at 15 UTC, which helped to act as a focus for convective development as it moved northward during the morning and afternoon hours. The Storm Prediction Center had outlined a Moderate Risk for severe thunderstorms over this area, and later issued a Tornado Watch at 17:50 UTC. The first report of hail from these storms was at 17:03 UTC over far western Minnesota (SPC storm reports).

GOES-13 0.63 µm visible channel image with METAR surface reports and surface front and pressure analyses

GOES-13 0.63 µm visible channel image with METAR surface reports and surface front and pressure analyses

SRSOR mode provides the opportunity to compare satellite scanning strategies. The animation below (also available as an MP4 movie file) shows

GOES-13 0.63 um visible channel images: Standard 15-minute interval (left), RSO (center), and SRSOR (right) [click image to play animation]

GOES-13 0.63 um visible channel images: Standard 15-minute interval (left), RSO (center), and SRSOR (right) [click image to play animation]

Another comparison of SRSOR vs RSO vs Standard image scan modes is shown below, focusing on convection farther south over the Kansas / Oklahoma / Texas region (click image to play very large animated GIF file; click here for the same animation on YouTube; an MP4 version is also available here).

GOES14_1655_8May2014_Center_OKC

GOES-13 0.63 µm visible channel imagery in SRSO mode (left), in RSO mode (center) and in Standard mode (right) (click to animate very large file)

Tropical Invest 90E in the eastern Pacific Ocean

May 7th, 2014 |
MIMIC Total Precipitable Water product (click to play animation)

MIMIC Total Precipitable Water product (click to play animation)

AWIPS images of the MIMIC Total Precipitable Water product (above; click image to play animation) showed the well-defined cyclonic circulation associated with Tropical Invest 90E in the Eastern Pacific Ocean during the 06 May – 07 May 2014 period.

Overlays of the tropical surface analysis at 6-hour intervals (below) indicted that the area of low pressure formed in the region of a fracture in the InterTropical Convergence Zone (ITCZ) / Monsoon Trough off the southwest coast of Mexico.

MIMIC TPW product with tropical surface analyses

MIMIC TPW product with tropical surface analyses

An overpass of a polar-orbiting Metop satellite provided ASCAT surface scatterometer winds at 16:41 UTC (below). The strongest winds were generally in the 20-30 knot range.

MIMIC TPW product with Metop ASCAT winds

MIMIC TPW product with Metop ASCAT winds

Near the end of the day, the lowering sun angle helped to highlight shadowing on GOES-15 0.63 µm visible channel images (below; click to play animation) associated with overshooting tops in the eastern quadrant of the low; the Tropical Overshooting Tops product helped to unambiguously highlight the location of these overshooting top features.

GOES-15 0.63 µm visible channel images, with Tropical Overshooting Tops product (click to play animation

GOES-15 0.63 µm visible channel images, with Tropical Overshooting Tops product (click to play animation)

Severe Storms over Wisconsin

May 7th, 2014 |

Convection developed along the edge of warm air moving northward into Wisconsin early in the morning on May 7th. The Day 1 Outlook from the Storm Prediction Center showed the region to be in a Slight Risk.

The NOAA/CIMSS ProbSevere model, which fuses together information from GOES-derived cloud products, Multi-Radar Multi-Sensor (MRMS) data, and Rapid Refresh (RAP) NWP data, picked up on these convective storms on the north side of a baroclinic zone. The environment was characterized by 1000-2000 J kg-1 of MUCAPE and adequate effective bulk shear (~30-40 kts). The instability was elevated, as the surface airmass reflected a cool easterly flow. (Click here to see the DVN and GRB soundings from 1200 UTC 7 May)

Very early Wednesday morning (1000-1100 UTC), a storm developed in west-central Wisconsin moving eastward. ProbSevere pegged the storm at 25% probability of producing severe weather, given the environment, strong normalized vertical growth rate (inferred from IR-derived data), and moderate maximum expected size of hail (MESH). As the MESH increased over 1.0”, ProbSevere increased to about 70%. By 1026 UTC, the probability was 74%, and 1 minute later the National Weather Service (NWS) issued a severe thunderstorm warning. The warning was issued 5 minutes after ProbSevere’s first probability > 50%. This storm later weakened and decreased in probability, but then picked up again and produced 1.0” hail in Clark county at 1218 UTC, all the while maintaining a warning.

westcentral_WI_20140507

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

Other storms developed near Richland County in Wisconsin around 1400 UTC. A strong satellite vertical growth signal could not be computed for these storms because of thick cirrus overhead from decaying convection to the north. ProbSevere nevertheless had high probabilities (due to a favorable environment and large MESH) prior to these storms being warned. The eastern of the two storms showed a ProbSevere value exceeding 50% thirteen minutes before the first NWS warning; ProbSevere for the western storm exceeded 50% 26 minutes before the first NWS warning. Both storms dropped severe hail in Richland county (Storm Report) — 1.25″ diameter hail at 1443 UTC for the eastern storm (4 minutes after the NWS warning), 2.0″ diameter hail at 1442 UTC with the western storm (coincident with its first warning). A storm southeast of these two in Sauk county had a high probability of severe (> 70%) by 1442 UTC, also because of large MESH, good MUCAPE and effective shear, but it was never warned and never produced any severe reports (until it coalesced later with the other storms into a convective line)

southwest_WI_20140507

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

Lastly, a storm west of Milkwaukee quickly developed and was monitored by ProbSevere. By 1454 UTC, the storm’s probability of severe jumped from 7% to 24% (at the start of the animation) because its normalized vertical growth rate became very strong (see the visible and IR loops).

Milwaukee_20140507

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

AWIPS 10.7 µm imagery,below, shows the evolution of the storms as viewed from GOES-East. The first storm, over central WI at 1030 UTC, shows considerable electrical activity but overshooting tops are not detected. The storms over Richland/Sauk Counties around 1400 UTC, and near Milwaukee around 1500 UTC do show overshooting tops.

Reg_IR_Sat_20140507loop

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

VIIRS and AVHRR both overflew these systems around 0730 UTC. The toggle of imagery below shows the great detail in the cloud-top that is available with 1-km resolution as from VIIRS and AVHRR. In addition, the Day/Night band can be used at night (especially when the lunar illumination is low, as was the case on 7 May) to detect lightning, characterized as streaks of white in the Day/Night band imagery. One such streak is visible near Manitowoc, WI.

POES_VIIRS_GOES_20140507_0745

POES AVHRR 10.7 µm imagery at 0736 UTC, Suomi/NPP VIIRS imagery (11.0 µm and Day/Night Band) at 0746 UTC, and GOES-East 10.7 µm imagery at 0745 UTC (Click to enlarge)

The NOAA/CIMSS ProbSevere product is being evaluated at the Hazardous Weather Testbed. Additional examples can be found at the HWT Blog.