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

Simulated Imagery and CI/CTC in Northern Mesoscale Discussion

Two areas seem to be possible for convection near and west of the Great Lakes. The first is across northern Iowa as an outflow boundary and sfc trough are providing strong sfc convergence in an area of higher sfc dew points in the 50s. Limited instability and shear in this area would limit organization of storms. Main threat here would be dry/wet microbursts as hail/rain cores descend into deep dry layer below cloud base. Stronger shear is present in the second area of concern, ahead of northern stream shortwave trough in northeast Minnesota and Upper Peninsula of Michigan. CTC rates of -15C/15 min noted along a sfc front/convergence zone just north of the Canadian border at 1945 UTC and this area extends south into northern Minnesota.

The CIRA Simulated IR satellite shows storms initiating in both of these areas by 01 UTC. (see image). This was the general area stroms did form although the simulation was about an hour or two slower than reality (see IR satellite image from 2345 UTC).

Top image is the CIRA/NSSL WRF simulation 10.4um IR for 01Z Wed MAY 14th, showing some convective initiation across the Upper Peninsula of Michigan and some bigger storms across northern Iowa and eastern Nebraska. Bottom image is the actual 2345 UTC IR satellite image.

As of 20 UTC, the GOES-R CI Sfc convective initiation shows the highest percentages (around 77%) in southern MN and western WI. By 21 UTC the highest percentages (up to 90%) were across Nebraska. CTC cooling rates were 5-15C/15minutes in these stronger updrafts, which were small and isolated, stretching from CO to WI. The line of higher convective initiation decreased as the storms initiated, then were followed by individual storm cloud-cooling tops identified by the CTC. See following images.

GOES-R CI at 2015 UTC

10km Radar Coded Message at 2119 UTC showing the line of showers and thunderstorms.

CIMSS Cloud top cooling – Instantaneous image at 2130 UTC. Max values around -15C/15 minutes, that spiked up to -40C/15 min by 22Z UTC from NE Iowa to SE Minnesota. Severe microburst winds hit Mason City, Iowa around 2150 UTC. The storm showed a CTC cooling rate of -25C/15 min at 2132 UTC. The algorithm gave a value of -70C/15 min for one storm, which was probably a misinterpretation caused by anvil blowoff from a previous updraft.

Ostuno

Nearcast CAPE Too High Across N TX/W OK

The CIMSS-NRE 780-500mb CAPE image above overestimated CAPE values in this layer. The LAPS SBCAPE image below was more accurate, which can be confirmed by the 00 UTC local soundings. I wonder if missing data over west Texas degraded the CIMSS-NRE 780-500 mb CAPE image. 

Scotten

14May2013 0000Z San Angelo Nearcast

Currently monitoring strong to at times severe storms on the western boundary of the SJT CWA. Thermodynamic environment still appears supportive of marginally severe hail and occasional high wind gusts, based upon the continued movement of cells (generally NE) into a region of 800-1000 J/kg according to the Nearcast product. Do not expect sustained severe, considering the lack of a more organized / stronger wind field, but continued pulse severe events seem likely.

051413 23:30 UTC Nearcast CAPE and Reflectivity

Picca

RGB Shows Airmass Changes and Extent of Convective Development

When you want a visual depiction of what the airmass structure looks like, the GOES Sounder RGB product can fill the bill. The image below is that product at 22Z, along with RAP13 500 mb winds to show the airmass movement. You can clearly see the airmass difference along the Red River. The bluer colors are more typical of midlatitude airmasses, while the greenish red area is associated with a subtropical airmass. There is even a wind shift line in the RAP 500 mb winds, showing the airmass boundary. The convection over west Texas shows up clearly as the white areas. These storms are feeding off the better instability and moisture provided from the south.

We think that the increasing midlevel flow provided by the advancing subtropical airmass will help to sustain the Texas convection and allow it to organize into an MCS structure over the next few hours.

051413 2200 UTC RGB Airmass and 500mb winds

CL

Simulated IR/WV Verifies Well

051413 2200 UTC Simulated IR Imagery 

051413 2201 UTC IR Imagery

The first image is a GOESR CIRA CIMSS Simulated IR image from sometime 15-18 UTC for 22 UTC on May 14, 2013, while the second image is the actual IR image
at 2201 UTC. Overall, the simulated IR image did a great job capturing colder cloud tops from convection in west Texas as well as isolated convection over New Mexico. In addition, warmer cloud tops across south Texas were handled well. This product may be helpful for importing into GFE/IFPS for forecast updates as well as short range (3-6 hr) public and aviation forecasts.

051413 2200 UTC Simulated WV Imagery

051413 2201 UTC WV Imagery

The third image is the simulated water vapor image from 15-18 UTC for 22 UTC, while the fourth image is the actual water vapor image for 22 UTC. The results were favorable with the simulated WV performing well with convection over west Texas. The ribbon of drier mid/upper level air from the Texas Panhandle to Oklahoma is reasonably well depicted though the simulated image was a bit too far south compared to the actual. The simulated image in New Mexico verified very well showing convection mainly along the higher terrain across the central part of the state.

Scotten

Consistent CTC Allows for 90 minutes of Lead Time

051413 1915 UTC Cloud Top Cooling

051413 1945 UTC Cloud Top Cooling

051413 2002 UTC Cloud Top Cooling

051413 2015 UTC Cloud Top Cooling

051413 2115 UTC Cloud Top Cooling and warning polygon

The sequence of images depicts a consistent area of cloud top cooling (at least -10C/15 minutes) that occurred about 90 minutes prior to the issuance of SVRs with large hail
likely with MESH values above 1 inch. If a consistent CI signature occurs, this may significantly increase lead time for severe thunderstorms.