Advection fog over Lake Michigan

May 7th, 2009 |
GOES-12 visible images

GOES-12 visible images

GOES-12 visible channel images (above) showed advection fog that developed over Lake Michigan during the day on 07 May 2009. As pointed out on the US Air Quality (aka The Smog Blog) site,  this fog “fooled” the MODIS Aerosol Optical Depth (AOD) algorithm, causing a false signal of very high AOD over Lake Michigan. Also note the appearance of “shock waves” in the fog bank as it encountered obstructions to the southwesterly boundary layer flow in two areas: (1) along the western coastline of Lower Michigan (250-m resolution MODIS true color image), and (2)  some of the larger islands in the northern portion of Lake Michigan (250-m resolution MODIS true color image).

This fog formed as warm and relatively humid air (with dew points in the middle 50s F) moved across the cold waters of Lake Michigan. An AWIPS image of the MODIS Sea Surface Temperature (SST) product (below) indicated that that mid-lake SST values were still in the 37-39º F range — and  this was confirmed by the water temperature values of 37º F and 38º F reported by buoys 45002 and 45007, respectively.

MODIS Sea Surface Temperature product

MODIS Sea Surface Temperature product

The western portion of the advection fog feature was quite thin, so the fog edge was difficult to pick out on the MODIS 11.0 µm “IR window” imagery (below). However, the fog boundaries were quite apparent on the 3.7 µm “shortwave IR” imagery, due to the reflection of solar radiation off the top of the water droplet fog feature (which made the fog appear darker/warmer).

MODIS visible, 11.0 µm IR window, 3.7 µm shortwave IR images

MODIS visible, 11.0 µm IR window, 3.7 µm shortwave IR images

The GOES sounder Cloud Top Height product (below) indicated that the tops of the fog feature over the southern half of Lake Michigan were generally around 2580 feet (darker brown color enhancement).

GOES-12 sounder Cloud Top Height product

GOES-12 sounder Cloud Top Height product

GOES-11 Super Rapid Scan Operations (SRSO) images

May 5th, 2009 |
GOES-11 visible images

GOES-11 visible images

GOES-11 was placed into Super Rapid Scan Operations (SRSO) on 05 May 2009, as a test for support of the upcoming VORTEX2 field experiment. During SRSO, images are available at 1-minute intervals for short periods of time. The GOES-11 visible channel imagery (above) shows severe convection in southwestern Nebraska, which produced hail up to 1.25 inch in diameter (SPC storm reports).

SPC storm reports

SPC storm reports

Long “atmospheric rivers” of moisture

May 5th, 2009 |
MIMIC Total Precipitable Water

MIMIC Total Precipitable Water

AWIPS images of the MIMIC Total Precipitable Water (TPW) product (above) showed the presence of  long, narrow  filaments of moisture (often described as “atmospheric rivers“) that were moving across the North Pacific Ocean and the North Atlantic Ocean during the 04 May – 05 May 2009 period. Studies by Newell and others suggest that these atmospheric rivers can persist for more than 10 days, and are capable of transporting as much water as the Amazon River!
Composite geostationary satellite water vapor imagery (below) showed a similar signature of enhanced clouds and moisture along the axis these two atmospheric rivers — however, the presentation on the water vapor imagery was a bit different in terms of width and location.

Composite of geostationary satellite water vapor images

MIMIC TPW + surface analysis

MIMIC TPW + surface analysis

Note that the surface frontal structure was more closely aligned with the atmospheric rivers seen on the TPW imagery (above), but there was more of a mismatch with the corresponding water vapor image features (below). This is due to the fact that the water vapor imagery is generally sensing a signal from moisture located within a fairly deep layer aloft in the middle to upper troposphere, at a level above which the bulk of the total column precipitable water is located.

Composite water vapor imagery + surface analysis

Composite water vapor imagery + surface analysis

A 4-panel comparison of the MIMIC TPW, the Blended TPW, GOES Imager water vapor channel, and the GOES Sounder TPW products (below) shows that there is good agreement to the general magnitude of the TPW values between the various products. An animation shows the various strengths and weaknesses of each in terms of their utility for tracking atmospheric rivers. The MIMIC and Blended TPW products (top 2 panels) had better  temporal continuity, while the GOES water vapor imagery and the GOES Sounder TPW product (bottom 2 panels) suffered from gaps in coverage due to either Spring eclipse or the variable GOES Sounder scanning strategy.

Comparison of MIMIC TPW, Blended TPW, GOES Sounder TPW, and water vapor imagery

Comparison of MIMIC TPW, Blended TPW, GOES Imager water vapor.  and GOES Sounder TPW imagery

Microburst hits Dallas Cowboys football practice facility

May 2nd, 2009 |
GOES-12 10.7 µm IR images

GOES-12 10.7 µm IR images

AWIPS images of the GOES-12 10.7 µm “IR window” channel (above) showed the development of severe thunderstorms that moved across the Dallas/Fort Worth  metro area in northeast Texas on 02 May 2009. Cloud top temperatures quickly cooled into the -70º to -80º C range (black to light gray color enhancement) as the storms began to produce hail (up to 1.75 inch in diameter), strong surface winds, and a few tornadoes (SPC storm reports). At around 20:30 UTC (3:30 pm local time), strong winds from a microburst caused the collapse of a canopy covering a practice field at the Dallas Cowboys football facility at Valley Ranch (located just to the northeast of Dallas/Fort Worth International Airport, KDFW), with several injuries being reported.

A closer view using a 1-km resolution MODIS 11.0 µm IR window image (below) showed greater detail in the cloud top temperature structure, with some pixels as cold as -84º C (violet color enhancement). Note the sharp “upshear” (western) edge of the storm’s anvil; in addition, there was a subtle “warm trench” signature surrounding the cold cluster of overshooting tops that was located to the southwest of KDFW — this IR storm top signature is sometimes seen with severe thunderstorms.

MODIS 11.0 µm IR image

MODIS 11.0 µm IR image

A comparison of the 4-km resolution GOES-12 10.7 µm IR image with the corresponding 1-km resolution MODIS 11.0 µm IR window image (below) demonstrated the advantage of higher spatial resolution for use in  the detection of severe storm cloud top signatures. The coldest GOES-12 cloud top temperatures were -77º C, about 7º C warmer than the -84º C seen on the MODIS image.

GOES-12 10.7 µm IR + MODIS 11.0 µm IR images

GOES-12 10.7 µm IR + MODIS 11.0 µm IR images

According to the 00:00 UTC rawinsonde report from Dallas/Fort Worth (below), these cold cloud top temperatures associated with the intense overshooting tops were several degree colder than the sounding tropopause temperature of -74º C.

Dallas/Fort Worth TX rawinsonde report

Dallas/Fort Worth TX rawinsonde report