Offshore mesovortex affecting the inland penetration of marine stratus along the California coast

June 2nd, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

On 02 June 2014, McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel data (above; click image to play animation) revealed the presence of a cyclonic mesoscale vortex in the vicinity of Point Reyes along the California coast, which appeared to be playing a role in enhancing the inland penetration of marine fog/stratus into areas such as the San Francisco Bay region just south of the mesovortex.

An AWIPS image of 375-meter resolution (projected onto a 1-km AWIPS grid) Suomi NPP VIIRS 0.64 µm visible channel data at 21:07 UTC (below) included overlays of surface station and buoy reports, along with MADIS 1-hour satellite-derived atmospheric motion vectors within the 1050-900 mb layer at 21 UTC. The satellite cloud-tracked winds appeared to be picking up on the cyclonic circulation of the mesovortex. At this particular time, winds at San Francisco (station identifier KSFO) were southwesterly gusting to 23 knots.

Suomi NPP VIIRS 0.64 µm visible channel image, with surface and buoy observations and 1-hour MADIS satellite winds

Suomi NPP VIIRS 0.64 µm visible channel image, with surface and buoy observations and 1-hour MADIS satellite winds

A time series of surface observation at San Francisco International Airport (below) showed the increase in layered stratus clouds (with ceilings of 1000 to 1500 feet) after the southwesterly winds began to increase around 19 UTC.

Time series of surface observations at San Francisco International Airport

Time series of surface observations at San Francisco International Airport

AWIPS images of the GOES-R Cloud Thickness product — with the GOES-R algorithm for Fog and Low Stratus products applied to GOES-15 data — indicated that the thickness of the stratus clouds moving inland across the San Francisco Bay area was only about 500 feet (below; click image to play animation). The thicker stratus clouds with depths of 1000-3000 feet remained off the coast of California.

GOES-15 Cloud Thickness product (click to play animation)

GOES-15 Cloud Thickness product (click to play animation)

The corresponding GOES-15 Marginal Visual Flight Rules (MVFR) product (below; click image to play animation) showed that MVFR probability values were generally below 50-60% in the San Francisco Bay area, with much higher probabilities existing within the offshore marine boundary layer stratus cloud field.

GOES-15 Marginal Visual Flight Rules (MVFR) Probability product (click to play animation)

GOES-15 Marginal Visual Flight Rules (MVFR) Probability product (click to play animation)

GOES-14 SRSOR: from morning fog/stratus to afternoon convection

May 13th, 2014
Suomi NPP VIIRS and POES AVHRR IR brightness temperature difference

Suomi NPP VIIRS and POES AVHRR IR brightness temperature difference “fog/stratus product” images

An AWIPS comparison of nighttime Suomi NPP VIIRS and POES AVHRR IR brightness temperature difference “fog/stratus product” images (above) exhibited signals of fog and/or stratus forming in river valleys straddling the West Virginia and Virginia border on 13 May 2014.

The GOES-14 satellite continued to be operated in Super Rapid Scan Operations for GOES-R (SRSOR) mode, providing images at 1-minute intervals. Early morning 0.63 µm visible channel images (below; click image to play an MP4 animation; also available as a QuickTime movie) showed the narrow fingers of river valley fog/stratus, which began to burn off as heating and mixing increased during the morning hours. There was then a rapid transition to the formation of cumulus clouds across the region, some of which became organized areas of deep convection that produced hail and damaging winds (SPC storm reports).

GOES-14 0.63 µm visible channel images (click to play MP4 animation)

GOES-14 0.63 µm visible channel images (click to play MP4 animation)

A 3-panel comparison showing the difference between standard or routine 15-minute interval, 5-7 minute interval Rapid Scan Operations (RSO), and 1-minute interval SRSO GOES-14 0.63 µm visible channel images (below; click image to play an MP4 animation; also available as a very large Animated GIF) demonstrated the clear advantage of higher temporal resolution for monitoring the rate of dissipation of river valley fog/stratus features, as well as subsequent convective initiation and development.

GOES-14 0.63 µm visible channel images: Standard, RSO, and SRSOR scan strategies (click to play MP4 animation)

GOES-14 0.63 µm visible channel images: Standard, RSO, and SRSOR scan strategies (click to play MP4 animation)

Consecutive overpasses of the Suomi NPP satellite provided a look at the rapid rate of convective cloud development on VIIRS 0.64 µm visible channel images (below).

Suomi NPP VIIRS 0.64 µm visible channel images, with surface observations and frontal boundaries

Suomi NPP VIIRS 0.64 µm visible channel images, with surface observations and frontal boundaries

On a 18:59 UTC MODIS 11.0 µm IR channel image (below), the coldest cloud-top IR brightness temperature was -78º C near the West Virginia/Virginia border.

MODIS 11.0 µm IR channel image

MODIS 11.0 µm IR channel image

GOES-14 SRSOR: severe thunderstorms over the central Plains

May 11th, 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)

The GOES-14 satellite continued to be in Super Rapid Scan Operations for GOES-R (SRSOR) mode on 11 May 2014, capturing the development of thunderstorms along a dryline that stretched from the Texas Panhandle into far southwestern Kansas. As a southward-moving cold front intersected this dryline, 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 movie file) showed that the narrow line of storms later developed into large discrete supercell thunderstorms over Kansas, with widespread reports of tornadoes, large hail, and damaging winds (SPC storm reports).

Farther to the northeast, other large supercell thunderstorms could be seen growing over eastern Nebraska along a warm frontal boundary — these storms exhibited numerous signatures of vigorous overshooting tops. Near the end of the animation, winds gusted to 82 mph at Omaha, Nebraska at 00:51 UTC.

GOES-13 sounder Convective Available Potential Energy (CAPE) derived product imagery (click to play animation)

GOES-13 sounder Convective Available Potential Energy (CAPE) derived product imagery (click to play animation)

AWIPS images of GOES-13 sounder Convective Available Potential Energy or CAPE (above; click image to play animation) and Total Precipitable Water or TPW (below; click image to play animation) with surface frontal analyses revealed the sharp gradient of both instability and moisture across the dryline — just to the east of the dryline, CAPE values exceeded 4000 J per kg (darker purple color enhancement), while TPW values were generally in the 30-40 mm or 1.2-1.6 inch range (shades of yellow). In addition, GOES-13 sounder Lifted Index values were in the -8 to -10º C range across parts of Kansas into southeastern Nebraska prior to convective initiation.

GOES-13 sounder Total Precipitable Water (TPW) derived product imagery (click to play animation)

GOES-13 sounder Total Precipitable Water (TPW) derived product imagery (click to play animation)

A 19:36 UTC Suomi NPP VIIRS 11.45 µm IR channel image (below) showed the early stages of convective development along the dryline in far southwestern Kansas; the coldest cloud-top IR brightness temperature value at that time was -80º C, just west of Dodge City, Kansas KDDC (corresponding GOES-14 visible image).

Suomi NPP VIIRS 11.45 µm IR channel image, with METAR surface reports

Suomi NPP VIIRS 11.45 µm IR channel image, with METAR surface reports

A comparison of POES AVHRRR 12.0 µm IR channel images (below) showed the explosive convective growth over Kansas and Nebraska in the 3-hour period between 19:56 UTC and 22:53 UTC.

POES AVHRR 12.0 µm IR channel images

POES AVHRR 12.0 µm IR channel images

Additional details on this event can be found on the RAMMB GOES-R Proving Ground Blog.

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)