Linear Mesoscale Convective System in the Upper Midwest

August 28th, 2007

GOES-12 visible image

GOES-12 visible channel images (above; Java animation) showed a linear mesoscale convective system developing across parts of Iowa, Minnesota, and Wisconsin on 28 August 2007. Note the picturesque shadows cast by the individual cumulonimbus towers building in northeastern Iowa between 21:00 and 22:00 UTC. The larger cluster of thunderstorms in north-central/northeastern Wisconsin produced several reports of hail (up to 1.0 inch in diameter) and wind gusts of 60-80 mph (SPC storm reports). An AWIPS image of the MODIS 11.0µm IR channel around 19:09 UTC depicted cloud top brightness temperatures as cold as -79º C (-110º F) in north-central Wisconsin, with numerous cloud to ground lightning strikes.

AWIPS GOES-12 sounder Derived Product Images (DPI) of Convective Available Potential Energy (CAPE), Lifted Index (LI), and Total Precipitable Water (TPW) at 17:00 UTC (below) indicated that instability and moisture were increasing within a narrow zone along and just ahead of a wavy frontal boundary that was advancing slowly southeastward through the region. Isolated CAPE values were in excess of 4000 J/kg, LI values were less than -8º C, and TPW values were greater than 50 mm (2.0 inches) in the general area where new convection was seen to develop rapidly in north-central Iowa about 4 hours later on the GOES-12 visible images above.

GOES-12 sounder CAPE

GOES-12 sounder LI

GOES-12 sounder PW

Hurricane Dean remnants affect southern California

August 26th, 2007

GOES-11 water vapor images (Animated GIF)

An animation of GOES-11 water vapor channel images (above) showed that Atlantic Hurricane Dean made landfall in Mexico on 22 August 2007, and eventually emerged into the Pacific basin on 23 August; the middle/upper tropospheric moisture associated with the remnants of Dean then moved slowly northward across the Baja California region toward southern California during the next several days. AWIPS GOES-11 water vapor imagery on 26 August 2007 (below) indicated that a good deal of this moisture had spread across much of the southern half of California — this residual moisture (and vorticity) was responsible for helping to initiate numerous thunderstorms (radar animation), some of which produced flash flooding, record daily rainfall, and even a waterspout in the San Diego area.
AWIPS GOES-11 water vapor images (Animated GIF)

GOES sounder Total Precipitable Water (TPW) derived product imagery (below) revealed PW values as high as 40-50 mm (1.6-2.0 inches) over southern California at 14 UTC on 26 August.

GOES sounder total precipitable water

Since the GOES sounder has 3 separate water vapor channels (6.5 µm, 7.0 µm, and 7.4 µm), the TPW can be partitioned into 3 vertical layers: High Layer PW, Mid Layer PW, and Low Layer PW components (below); on this particular day, the bulk of the TPW across southern California appeared to be in the middle layer, which is generally between 700 and 900 hPa (1-3 km, or 3000-10,000 feet).

GOES sounder PW (high layer)

GOES sounder PW (mid layer)

GOES sounder PW (low layer)

River flooding in southwestern Wisconsin

August 25th, 2007

MODIS true color image (12 August 2007)

Portions of the Upper Mississippi River Valley region received very heavy rainfall during the last half of August 2007 — 10-20 inches (250-500 mm) of rain was observed in a 30-day period across parts of southeastern Minnesota and southwestern Wisconsin, and 30-day precipitation departures there were as much as 300-400% above normal. A MODIS true color image (using the CIMSS/SSEC “MODIS True Color Imagery Viewer” AWIPS application) centered over southwestern Wisconsin on 12 August (above) shows the Mississippi River (flowing north to south) and the Wisconsin River (flowing east to west) several days before the onset of the heavy rain period. Note the appearance of the Mississippi River “flood plains” (the brighter green areas located just downstream of Lock and Dam Number 8 near Genoa, WI and Lock and Dam Number 9 near Harpers Ferry, IA: Google map).

Two weeks later, a corresponding MODIS true color image from 25 August (below) reveals that much of the Mississippi River flood plains had become flooded by water rich with sediment (lighter brown colors). The Wisconsin River also appears notably wider on the 25 August MODIS image, and one of its major tributaries (the Kickapoo River, flowing north to south) is very evident due to an abundance of sediment-laden water. Use this Java applet to interactively fade (or toggle) between the 12 August and 25 August MODIS true color images.

A new record 24-hour precipitation amount for the state of Minnesota was set when 15.10 inches (384 mm) of rain fell on 18-19 August one mile south of Hokah (which is located near the upper left corner of these MODIS images: Google map). In addition, some locations set new records for the highest total precipitation for any calendar month, including 15.18 inches (386 mm) at Madison WI, and 13.75 inches (349 mm) at La Crosse WI.

MODIS true color image (25 August 2007)

Hurricane Dean in the Gulf of Mexico

August 22nd, 2007

GOES-12 10.7µm IR  images (Animated GIF)

After crossing the Yucatan Peninsula of Mexico, Hurricane Dean emerged into the Gulf of Mexico as a Category 1 storm late in the day on 21 August 2007. GOES-12 10.7µm IR imagery (above) shows a ragged eye associated with Dean; also note the burst of convection to the north and northwest of the eye (beginning around 00:45 UTC on 22 August). This area of convection continued to increase in areal coverage, with IR brightness temperatures eventually cooling to -80º C / -112º F (black enhancement).

AWIPS MODIS SST image

An AWIPS image of the MODIS Sea Surface Temperature (SST) product from 20 August (above) reveals a region of warmer SST values in the general area where the convective burst was seen to form on the IR imagery above. SST values were as warm as 86.7º F / 30.4º C (dark red enhancement), and this pocket of deep, warm water may have helped to fuel the burst of convection.

MODIS true color image (before Dean)

MODIS true color imagery of the Yucatan Peninsula before Dean (above) and after Dean (below) show that the hurricane winds increased the levels of turbidity in the waters of the Gulf of Mexico, leading to widespread areas of cyan and milky-colored water off the west coast of the Yucatan (due to a large amount of suspended particulate matter in the water).

MODIS true color image (after Dean)