MODIS false-color images show areas of flooding in Montana

August 26th, 2014
Before (12 August) and after (26 August) MODIS false-color RGB images

Before (12 August) and after (26 August) MODIS false-color RGB images

Some locations in northeastern Montana received up to 7-8 inches of rainfall over a 5-day period (NWS Glasgow rainfall map), which led to flooding in many areas. A comparison of before (12 August) and after (26 August) 250-meter resolution MODIS false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed the areal extent of flooding (cyan to darker blue areas on the 26 August image). The RGB images use MODIS bands 7/2/1 to help highlight the areas of of floodwater.

The maps below show the total observed rainfall, the departure from normal, and the percent of normal for the 7-day period ending on 26 August.

Observed 7-day rainfall

Observed 7-day rainfall

7-day rainfall departure from normal

7-day rainfall departure from normal

7-day rainfall percent of normal

7-day rainfall percent of normal

Can you use the VIIRS Day/Night Band to know where heavy rain is falling?

August 19th, 2014
Suomi NPP VIIRS Day/Night Band at 0659 UTC and 0838 UTC, 19 August 2014 (click to enlarge)

Suomi NPP VIIRS Day/Night Band at 0659 UTC and 0838 UTC, 19 August 2014 (click to enlarge)

The VIIRS Day/Night Band image toggle above shows nighttime cloud cover over southern Wisconsin associated with a line of deep convection; note how some city lights are not seen (Madison WI KMSN at 0659 UTC, and Milwaukee WI KMKE at 0838 UTC). There are several reasons this may have happened. For example, the convection could have knocked out power over a large region (this did not happen). Scattering associated with the thick convective clouds may have attenuated the city light so much that it could not be detected.

The toggle below of the corresponding VIIRS 11.45 µm Infrared imagery shows very cold cloud tops (-60º to -70º C, near the tropopause) over Madison at 0659 UTC (the observation at 0653 UTC at the Madison airport was Heavy Rain with a Thunderstorm) and over Milwaukee at 0838 UTC (when the Milwaukee airport was having Moderate Rain; they received a half-inch of rain between 0753 and 0853 UTC). The combination of the thick convective cloud and especially the heavy rain is very likely why city lights cannot be seen at certain times, as liquid water is an excellent absorber of visible light. This radar image (from this story) shows the areal extent of the heavy rain at 0745 UTC on 19 August.

Suomi NPP VIIRS 11.45 µm Infrared imagery  at 0659 UTC and 0838 UTC, 19 August 2014 (click to enlarge)

Suomi NPP VIIRS 11.45 µm Infrared imagery at 0659 UTC and 0838 UTC, 19 August 2014 (click to enlarge)

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)