Record rainfall and flooding in Arizona

September 8th, 2014
GOES-15 10.7 µm IR channel images (click to play animation)

GOES-15 10.7 µm IR channel images (click to play animation)

McIDAS images of 4-km resolution GOES-15 10.7 µm IR channel data (above; click image to play animation; also available as an MP4 movie file) showed the merger of two large mesoscale convective systems (MCS) which produced an all-time record maximum calendar day precipitation amount of 3.29 inches at Phoenix Sky Harbor Airport (PHX) on 08 September 2014. Some locations in the Phoenix area received in excess of 5 inches of rainfall (NWS Phoenix event summary).

An AWIPS-II image of 375-meter resolution Suomi NPP VIIRS 11.45 µm IR channel data (below) showed the MCS pair at 09:07 UTC or 3:07 AM local time —  this was prior to the merger, and the southeastern storm exhibited a minimum cloud-top IR brightness temperature of -84º C (purple color enhancement), which was much colder than the -71º C seen with the northwestern storm. At the onset of the heavy thunderstorms at PHX, southerly to southeasterly winds  — likely outflow from the southeastern MCS — gusted as high as 31 knots (36 mph) and visibility was reduced to 0.8 mile (surface reports: text | graph).

Suomi NPP VIIRS 11.45 µm IR channel image

Suomi NPP VIIRS 11.45 µm IR channel image

As the circulation of former-Hurricane Norbert continued to spin over the Pacific Ocean west of Baja California, deep tropical moisture kept working its way farther inland — GOES sounder Total Precipitable Water (TPW) values in excess of 50-60 mm (2.0 to 2.4 inches) were eventually seen across the southwestern half of Arizona (below; click image to play animation).

GOES sounder Total Precipitable Water derived product images (click to play animation)

GOES sounder Total Precipitable Water derived product images (click to play animation)

The Blended Total Precipitable Water product (below; click image to play animation) also showed values of 50-60 mm working their way into southwestern Arizona during the 06-08 September period.

Blended Total Precipitable Water product (click to play animation)

Blended Total Precipitable Water product (click to play animation)

The Percent of Normal TPW product (below; click image to play animation) indicated that these TPW values were in excess of 200% of normal (yellow color enhancement) over large portions of the Desert Southwest. On the morning of 08 September, the TPW value of 2.03 inches derived from rawinsonde data at Tucson, Arizona set a record high for the month of September at that location.

Percent of Normal TPW product (click to play animation)

Percent of Normal TPW product (click to play animation)

GOES-14 SRSOR: Flash flooding in the Las Vegas, Nevada region

August 14th, 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 was placed into Super Rapid Scan Operations for GOES-R (SRSOR) mode on 14 August 2014, providing imagery at 1-minute intervals with the goal of monitoring the western US for convection and/or wildfire activity. McIDAS images of 0.63 µm visible channel data (above; click image to play animation; also available as an MP4 movie file) showed the development of clusters of slow-moving thunderstorms in the Las Vegas, Nevada region. These storms produced strong winds (gusts estimated at 60 mph) and heavy rainfall which caused flash flooding: Boulder City in far southern Nevada (located just east of Henderson, station identifier KHND) received 0.75 inch of rain in only 30 minutes. In addition to the state boundaries and yellow station identifiers, Interstate highways are drawn in red and State highways are cyan.

Another item of interest to note on the GOES-14 visible images: Lake Mead located to the east of Las Vegas was at an all-time record low level (1080.19 feet on 12 August) since it was filled back in the 1930s. The dark blue map outline represents the boundary of the lake as recently as the mid-1990s; the current area occupied by the darker water in Lake Mead’s Overton Arm (which extends northward) is drastically smaller in size, a result of the long-term severe to extreme drought.

AWIPS-2 images of the GOES-15 sounder Total Precipitable Water (TPW) derived product (below; click image to play animation) showed that these thunderstorms developed along a very sharp moisture boundary that was oriented roughly southwest to northeast across the area — TPW values of 30-40 mm (1.2-1.6 inches, yellow to red color enhancement) were seen east of the boundary, with TPW values of 10-20 mm (0.4-0.8 inch, shades of blue) west of the boundary.

GOES-15 sounder Total Precipitable Water derived product images (click to play animation)

GOES-15 sounder Total Precipitable Water derived product images (click to play animation)

Historic Rainfall in Islip, NY

August 13th, 2014
GOES-13 10.7 µm infrared imagery on 13 August 2014; The Islip airport (KISP) is at the violet square (click to animate)

GOES-13 10.7 µm infrared imagery on 13 August 2014; The Islip airport (KISP) is at the violet square (click to animate)

The system that caused flooding in Detroit, MI on 11 August and in Baltimore/Washington on 12 August has moved eastward: Islip, NY, on central Long Island, had historically heavy rainfall early in the morning on 13 August as more than 13″ of rain fell (9.71″ in two hours, and 5.34″ in one hour!!), smashing the New York state record for 24-hour rainfall (Record Event Report).

The GOES-13 animation above shows the satellite presentation of the storms that produced the heavy rainfall (the heaviest rain fell between 0900 and 1100 UTC). It is immediately apparent that the deepest convective clouds were not responsible for the heavy rains: cloud-top IR brightness temperatures over Islip were only near -30º C (per the 1200 UTC OKX sounding, that was around 300 hPa; the tropopause was closer to 150 hPa) and cloud-to-ground lightning was not detected. Winds at the Islip airport shifted from easterly/northeasterly to southeasterly as the heavy rains ended (time series plot of surface weather): an approaching frontal boundary may have helped force the heavy rains.

The animation shows continual cold cloud redevelopment at/near Islip, suggesting that training shower development was an important factor in the flooding.

Although the region was generally cloudy, holes in the cloud cover revealed GOES-13 sounder Total Precipitable Water values (below; click image to play animation) of 45-50 mm or 1.8-2.0 inches over Long Island just ahead of the advancing frontal boundary. The Blended Total Precipitable Water product showed a sudden jump to over 50 mm or 2.0 inches around 10 UTC over Long Island, and these TPW values were around 150% of normal for that location and time of the year.

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

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

The MIMIC Total Precipitable Water product (below) showed a northward surge of tropical moisture into the region on 13 August.

MIMIC Total Precipitable Water (11-13 August)

MIMIC Total Precipitable Water (11-13 August)

Flooding rains over the Chesapeake Basin

August 12th, 2014
MIMIC Total Precipitable Water for the 72 hours ending at 1800 UTC 12 August 2014 (click to enlarge)

MIMIC Total Precipitable Water for the 72 hours ending at 1800 UTC 12 August 2014 (click to enlarge)

Very heavy rain has fallen during the day on August 12th in and around Baltimore (with rainfall rates as high as 2.70″ per hour at KBWI) and Washington DC, with reports of up to 10″. Where has this moisture come from? There are a variety of products available to diagnose total precipitable water in the atmosphere. The animation above, taken from the MIMIC Total Precipitable Water page (link), shows an influx of tropical moisture from the south-southeast has surged northward up to the east coast of Maryland on August 12. A mesoanalysis from SPC also suggests a link to the moisture east and south of Cape Hatteras. The GOES Sounder Total Precipitable Water derived product image at 1800 UTC, below, (from this website) showed very high total precipitable water amounts just south of Baltimore and Washington DC with values exceeding 60 mm or 2.4″. Soundings at 1200 UTC also showed high values of precipitable water: 48.5 mm or 1.90″ at Wallops Island, VA, and 44.7 mm or 1.76″ at Washington Dulles. Finally, the Blended Total Precipitable Water Product from NESDIS showed values around 51 mm or 2″ as well. (Values did not quite reach the 200% of normal threshold, however).

GOES Sounder Total Precipitable Water derived product image at 18 UTC

GOES Sounder Total Precipitable Water derived product image at 18 UTC

The animation of GOES-13 Infrared (10.7 µm) imagery, below, suggests some training was occurring in the thunderstorm development: thunderstorms continually redeveloped and moved over the same region. Training thunderstorms in moisture-rich air is a recipe for flooding.

GOES-13 10.7 µm infrared imagery on 12 August 2014 (click to animate)

GOES-13 10.7 µm infrared imagery on 12 August 2014 (click to animate)

Comparisons of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:16 UTC and 18:54 UTC (below) showed that the convection exhibited cold cloud-top IR brightness temperatures (as cold as -77º C), and subtle shadowing on the visible imagery suggestive of overshooting tops. Using GOES-13 IR imagery,  the CIMSS/NASA Langley Automated Overshooting Tops / Thermal Couplets product displayed one distinct overshooting top (blue square symbol) over the Baltimore area at 18:45 UTC.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:16 UTC

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:16 UTC

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:54 UTC

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:54 UTC