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.

GOES-R CI Across Far Western Texas

051413 1945 UTC GOES-R CI

Shown above is the 1945Z GOES-R CI. Note the two red values of 90% or greater within the panhandle of far western Texas.

051413 1941 UTC Base Reflectivity

051413 1956 UTC Base Reflectivity

Both of the red areas, especially the southeast one, depicted an increase in 0.5 Degree reflectivity indicating developing convection. This product seems to be doing a good job with new developing convection, though much of this convection would not sustain itself likely due to a weakly sheared environment. I would like to see how this product responds to a more strongly sheared environment. 

Scotten

14May2013 Mesoscale Discussion: W Great Lakes

Monitoring the potential for convective development across W Minnesota / SE South Dakota, and across central Nebraska.

Shortwave trough currently progressing east across S Saskatchewan into E Ontario providing support for some initial development across the Canadian provinces, as seen in IR / VIS / CTC data. Large-scale lift aloft, in association with eastward progressing frontal boundary is supporting a line of agitated cumulus extending south into NW Minnesota. Nearcast difference CAPE product indicates an axis of weak-to-moderate instability (500-1000 J/kg) in front of this boundary extending south into NE and IA. WRF simulated IR fails to develop much of any activity across N Minnesota, keeping all activity developing after dark across the UP of Michigan. Farther south and west, it shows better development across Iowa and Nebraska around 00Z. However, considering best large-scale forcing exists closer to the Canadian border, and model fields were generally overestimating surface dew points farther south (forecast >60 versus AOB lower 50s being observed), thought is that best potential may exist closer to the international border over the next few hours.

If storms can develop, dry low levels and steep lapse rates support a high wind threat from higher based storms. Better wind fields farther north (0-6 km shear >50 kts) and slightly cooler temps also support an enhanced threat for marginal severe hail closer to the Canadian border.

Picca

Daily debrief: 5/14/13

Yesterday was a very quiet day in regard to convection, ending with only one issued warning for the entire shift. However this gave forecasters the chance to explore and familiarize themselves with each experimental product, and through this they were able to provide some good feedback. Comments are shown below:

- 'Cloud Top Cooling had a good day and seemed to hit most of the good storms.'
- 'The only warned storm wasn't caught by the Cloud Top Cooling due to cirrus, but it did catch the earlier ones.'
- 'The GOES-R CI was very confetti like and too noisy.'
- 'The synthetic imagery did a pretty good job of tracking the short wave on shore [in the NW US]. It was slightly faster, but really keyed in on the development of the first storm in NE Oregon.'
- 'It did a good job translating that shortwave further inland and keyed in on the other storms initializing further east.'
- 'Despite the fact that [the convective activity] was pretty unorganized, the synthetic imagery did capture the initial storm and also the second round.'
- 'Combining the forecast from the synthetic imagery with what the Nearcasting was showing gave us a pretty good idea of where to key in on.'
- 'The Theta-E difference [from the Nearcast] showed unstable air over Montana. When storms entered this unstable air they did strengthen quite a bit, several becoming severe.'

Today looks to be pretty quiet as well and in an effort to maximize our evaluations we'll be splitting our forecasters up between Texas and the western Great Lakes. Down in Texas our experimental warning operations will focus on the Midland and San Angelo CWAs, while in the western Great Lakes they will, for now, be focused on a mesoscale outlook.

GOES-R CTC Training Comments...

Location: Montana. Threat: severe hail/high winds. Soundings suggest potential for thermodynamically-driven downbursts over mountainous terrain. Question: will cloud dtop cooling (CTC) rate be applicable to hail cores that could generate wet/dry microbursts?

CTC rates have been noted to have problems in mountainous regions such as the Rockies and even Appalachians. The rates were at or below 10C/15 minutes on the first few updrafts and only one storm briefly (one volume scan) reached 50 dbz through 20UTC. A storm entering Idaho County showed cooling rates of 12.6C/15 minutes at 2015 UTC, but this storm did not intensify until after 2130 UTC. This storm was not assigned a CTC rate after 2015 UTC because of masking by cirrus blowoff. Another storm that formed on the forward flank of this storm became marginally severe but was also never identified due to cirrus.

Possible sampling issues were noted in the MRMS sfc height of 60 dbz above -20C. The levels showed big scan to scan variability which may have been a function of distance from KMSO and sparse coverage of surrounding radars. As this storm got closer to the RDA, the scan to scan variability decreased.

SPC issued a severe thunderstorm watch at 21UTC with the main threats being large hail and high winds, with a secondary threat of a tornado.

-Ostuno