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

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

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)

View only this post Read Less

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.

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)

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).

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.

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 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.

View only this post Read Less

An optimization to the GOES-13 scanning schedule (discussed here) that provides, among other things, better coverage of the Caribbean Sea, became operation at 1600 UTC on May 6, 2014. Half-hourly imagery (in this case, 10.7 µm) from before the switch show intermittent coverage over the Caribbean Sea (at :15 and :45 minutes after the hour); CONUS imagery at :02 and :32, however, only extended to 14 N and to 63 W.

GOES-13 Infrared (10.7 µm) Imagery, times as indicated, before the switch to an Optimized Schedule (click to enlarge)

GOES-13 schedule optimization allows the :00 and :30 (note the slight shift in nominal time) images to scan to 5 N. (and also east to 54 W) Thus, an animation with 15-minute imagery (below) shows more complete coverage over the Caribbean.

GOES-13 Infrared (10.7 µm) Imagery, times as indicated, after the switch to an Optimized Schedule (click to enlarge)

View only this post Read Less

NOAA/CIMSS ProbSevere superimposed on MRMS radar display over southeastern Virginia. Times as indicated. (Click to enlarge)

The Hazardous Weather Testbed (HWT) exercise (Click here for the HWT blog) is ongoing at the Storm Prediction Center.  One of the new products being tested by forecasters is the NOAA/CIMSS ProbSevere product. ProbSevere in the animation above highlighted a cell that produced hail. The AWIPS-2 readout suggests strong vertical growth, and strong glaciation, at 0215 UTC. (The HWT Blog entry on this storm is here) What did the satellite view?

GOES-13 Visible Imagery (0.63 µm), times as indicated. (Click to enlarge)

Visible imagery, above, from just before sunset, shows nascent convective development east of Lynchburg over southeastern Virginia, and also older convection over the Chesapeake Bay and Delmarva Peninsula. The infrared imagery (10.7 µm), below, shows rapid development of convection over southeastern Virginia after 0000 UTC. The first convective cell, which cell is east of the Outer Banks of North Carolina at 0315 UTC, had cloud-tops that cooled about 12 C in 17 minutes (between 0115 and 0132 UTC); the storm that produced hail, and was warned, had cloud-tops that cooled 20 C in 13 minutes, between 0202 UTC and 0215 UTC. This strong vertical growth contributes to a big increase in the ProbSevere value.

GOES-13 Infrared Imagery (10.7 µm), times as indicated. (Click to enlarge)

When interpreting the radar and satellite imagery, be aware of the effects of parallax on the satellite imagery. GOES-13 imagery displayed here is not corrected for parallax. GOES-13 data are parallax-corrected when used in ProbSevere computations, of course.

View only this post Read Less