GOES-R CI Confirms Severe Thunderstorm Initiation near Red River

051513 2045 UTC GOES-R CI and Reflectivity

The GOES CI product detected a 60% yellow area at 2045 UTC. By 2115 UTC, a thunderstorm had developed in this yellow area. This storm strengthened and prompted the issuance of a Severe Thunderstorm Warning by 2205 UTC. Baseball hail was reported by this storm at 2212 UTC, and a tornado was observed around 2242 UTC. The CI product gave about 20-30 minute lead time for storm development, 75-90 minute for severe weather, and nearly 120 minutes of lead time for the weak tornado.

051513 2115 UTC GOES-R CI and Reflectivity

051513 2045 UTC GOES-R CI and Reflectivty

Scotten

Simulated IR Underestimates Cloud Cover over Okahoma

The top image is CIRA/NSSL WRF Simulated IR while the bottom image is observed IR around 22 UTC. The simulated IR underestimated cloud cover over Oklahoma where a mid/upper low was centered. The convection over the Rockies in Colorado and New Mexico as well as cooler cloud tops over eastern Texas and Louisiana were handled well by the simulated IR. The convection near Lubbock, Texas was captured very well.

051513 2200 UTC Simulated IR

051513 2145 UTC IR Imagery

Helge

Using CTC to issue 2116 UTC Comanche Country SVR

Based upon CTC rates around -20 to -25 C and initiation within a LAPS-analyzed region of approx. 2500 J/kg of CAPE, we warned on a cell that was developing around the Brown/Comanche/Mills intersection, expecting that strong cooling rates within an axis of (model-represented) good instability would at least result in a hail threat. However, the cell quickly weakened as it moved into the FWD CWA. Based upon recent sounding from MPEX in Seymour, TX, current atmospheric column across central TX may be too dry, resulting in growing updrafts entraining too much dry air and dissipating from negative buoyancy.

CTC Rate (SW portion of CWA) at 2045 UTC

LAPS analyzed instability and reflectivity at 2115 UTC

PGLM Flash Extent Density Comparison with MRMS Data

A lightning jump of 18 Flash/Min to 40 Flash/Min between 1908 and 1909Z with a second jump to 51 Flash/Min at 1912Z preceded a rapid increase in vertically integrated ice, MESH, and reflectivity at the -10C isotherm. A 1″ hail report was then acquired at 1926Z in Ratliff City.

The following plot shows the flash extent density trace for the storm approaching Ratliff City, OK. Focus on the timeframe between roughly 1900Z and 1930Z. Notice the strong jump between 1908Z and 1909Z.

MESH jumped from 0.63in (1910Z) to 1.10in (1912Z) to 1.26in (1914Z) with the last detection of 1.02in (1924Z) before dropping off thereafter. The following images show the jump from 1910Z to 1912Z.

051513 1910 UTC MESH

051513 1912 UTC MESH

Looking at the vertically integrated ice product…there was an increase in values from 14 kg/m2 (1908Z) to 20 kg/m2 (1910Z) to 32 kg/m2 (1912Z) with consistently high values above 30 kg/m2 through 1924Z. See the images below as the storm approached Ratliff City.

051513 1902 VIL

0501513 1910 VIL

051513 1912 VIL

Regarding reflectivity at the -10C isotherm…there was an increase to 59dBZ by 1912Z then 61dBZ at 1914Z (not shown).

Again, the 1″ hail report was acquired in Ratliff City at 1926Z which gives the lightning flash extent density tool a 17min lead time to the 1″ hail report.

RJM

RGB Depicts Shortwave and Developing Convection in W TX

051513 1901 UTC RGB Airmass

051513 2001 UTC RGB Airmass and 500mb Heights

The images at 19 and 20 UTC respectively depicted an area of drier air, most likely associated with a short wave on the back side of a mid/upper low over southwest Oklahoma. This wave seems to be enhancing cloud top cooling and convection generation over west Texas, near Lubbock. We will keep a close eye on this feature to see if this wave will allow for explosive convection 22-01UTC near a dryline from near Childress to San Angelo with very unstable (2000-3000 J/kg) air near and east of the dryline.

Scotten

Nearcasting and the Slow Low Moving over OUN

An healthy looking low pressure area has moved towards SW OK with lots of convection already ongoing.

051513 1930 UTC Vertical Theta-E Difference (top left), Sustained Convection Index (top right), CAPE (lower left), and Visible Imagery (lower right)

The main swath of unstable air is visualized nicely with that product, showing a tongue of very unstable air expanding from the far W-Gulf coast towards S-Oklahoma. The ‘sustained convection index’ highlights that area, where strong and longer lived updrafts might evolve betimes (and given agitate Cu field development, it won’t take that long for that). NRE CAPE field has 1500 J/kg just south of OK and with ongoing diabatic heating, we expect a further increase during the following hours. So, using the NRE product the focus for strong/sustained convection clearly shifts in the Dallas/Fort Worth area and south.
Also using the theta-e diff low-mid product, conditions for at least isolated to scattered initiation towards the Lubbock area seems to be plausible, given westward expanding plume of unstable air and interaction with others mesoscale features at the surface. In fact, there currently evolves an east-west aligned theta-e tongue just south of Lubbock, which overlaps nicely with evolving showers and thunderstorms. 

 Helge

Using the RGB Airmass around DFW

We are setting up in the Dallas/Fort Worth CWA today, and expect some busy weather in a few hours. So, I’ve been scanning the various products to get a general overview. The SPoRT GOES RGB product is good to get a general sense of the airmass structure. Decided to do a second post on it today to start off.

In the image below, the greenish yellow colors represent the more humid subtropical airmass, while the blue to red color is the drier, more continental airmass. You can see the approximate position of the dryline at the interface of these colors. Of course, the sounder is sampling the upper mid levels here (400-500mb) and doesn’t exactly correspond to the surface dryline…you can see this in the overlaid obs. Still, this is a product that can give you a quick idea of the general airmass setup.

051513 1800 UTC RGB Airmass and Surface Observations/Winds

CL

Comparison of IR and Simulated IR Imagery

As part of the Nowcast / Warning desk for FWD, it’ll be interesting to watch initiation along the northern portions of the tightening dryline this afternoon.

When comparing the simulated IR with the actual IR at 19Z, it appears the simulated is underdoing cloud-cover on the backside of the upper low (across NW TX / W OK). It then initiates convection across NW TX around 21-23Z. The possibility exists that across the northern portion of this region, around the Red River or so, heating might be overdone on the model, resulting in initiation too early / too widespread. It will be interesting to see how initiation occurs along the dryline today.

19Z Actual IR

19Z Simulated IR

23Z Simulated IR

Daily Debrief: 5/15/13

After a quiet start yesterday forecasters did get some weather to work with later in the evening, mostly out in Texas but were also watching some clusters of storms up the western Great Lakes. Check out the feedback below:

- 'The CI product was more in its element yesterday because [we were watching] a nice, defined band of cumuls and it was easier to see the trend in the signals.'
- 'The CI product was much more accurate in Western Texas then it had been previously in the NW US.'
- 'The CI did well showing the trend on the line in Western TX.'
- 'The CTC did well in storms with strong updrafts, but got fooled by cirrus blow off on several occasions.'
- 'There were several instances where there were no CTC detections at all but you could see the storms developing beneath the cirrus shield.'
- 'Despite being about an hour off, the simulated IR did very in showing where the severe storms were in NE Iowa.'
- '[The Simulated Imagery] was really good. It showed the cluster in Iowa and also downplayed what we though would happen further north.'
- 'The RGB was a really neat tool and showed the various airmass boundaries in SW Texas.'

Today we'll doing a 1-9pm shift and are already seeing some convection right over our heads here in Norman. Focus areas today will be the DFW CWA where there is a slight risk and also, with the chance (finally) for some lightning activity, the OUN CWA.

CTC Struggles in Areas of Broad Ice Clouds

The CTC algorithm missed a developing storm that went on to become a robust storm and prompted an experimental severe thunderstorm warning. The storm in question is highlighted below within the red hatching at 2114Z when visually it was very apparent the storm was rapidly intensifying.

The algorithm “missed” this developing storm mainly due to the algorithm defining the cloud type in the vicinity of the developing storm as thick ice and cirrus at 2032Z and 2045Z. This storm was likely within the thick ice and cirrus definition…and therefore was included in the ice cloud exclusion zone and not given a CTC rate.

This example merely illustrates that not all developing storms will be captured by the algorithm even if visually it looks to be clearly intensifying. This is especially the case in a situation where multiple storms are in one area.

RJM