University of Wisconsin-Madison Space Science and Engineering Center

CIMSS Satellite Blog

Historic heavy rainfall event at Nashville, Tennessee

May 2nd, 2010

GOES-13 10.7 µm IR images

During 01 May – 02 May 2010 the 2-day total precipitation at Nashville, Tennessee was 13.57 inches — by far the wettest 2-day period on record for that location (the old record was 6.68 inches on 13-14 September 1979, in association with Hurricane Fredrick). With 7.25 inches falling on 02 May (5.57 inches of that in just 6 hours!), this also set a record for the wettest calendar day on record. And, remarkably, only 2 days into the month May 2010 is already the wettest May on record for Nashville. An animation of 24-hour observed precipitation can be seen here.

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (above) showed several rounds of deep convection moving northeastward across the region during the period, with some cells exhibiting IR cloud top brightness temperatures as cold as -74º C. This convection was developing along and ahead of a slow-moving cold frontal boundary.

Images of 1-km resolution MODIS 11.0 µm IR data (below) revealed even colder cloud top IR brightness temperature values of -82º C with some of the stronger convection developing over far western Tennessee. The 1-km resolution AVHRR Cloud Top Temperature (CTT) product also indicated CTT values as low as -80º C for some of the stronger thunderstorms.

MODIS 11.0 µm IR image

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Blended Total Precipitable Water (TPW) product

However, more important than the cold convective cloud top temperatures was the plume of rich moisture that was feeding northward across the Gulf of Mexico and into the Tennessee Valley region. The Blended Total Precipitable Water (TPW) product (above) showed that TPW values began to exceed 50 mm across the Lower Mississippi River Valley region late in the day on 01 May, with TPW within the moisture plume reaching 75 mm over the Gulf of Mexico late in the day on 02 May. TPW values were greater than 200% of normal across most of the Mississippi and Tennessee Valley regions, as well as within the northward-moving moisture plume.

With the greater areal coverage on AWIPS of the MIMIC TPW product (below), it could be seen that the plume of moisture moving meridionally (northward) across the Gulf of Mexico actually originated from the zonal band of deep moisture associated with the Inter-Tropical Convergence Zone (ITCZ) that was located between the Equator and 10º N latitude over the far eastern Pacific Ocean. MIMIC TPW values over the Gulf of Mexico became greater than 60 mm late in the day on 02 May; GOES-13 Sounder TPW values were also as high as 66 mm over the Gulf of Mexico on 02 May.

Incidentally, this case also serves as a great example of why you can’t always identify and track important TPW plumes on standard water vapor imagery — the water vapor channel is often sensing radiation from a layer that is above that of the bulk of the TPW plume (comparison of GOES water vapor image and MIMIC TPW image).

MIMIC Total Precipitable Water (TPW) product

Rawinsonde data from Nashville (below) generally revealed a very moist atmosphere throughout much of the troposphere during the period, with TPW values as high as 2.00 inches at 00 UTC on 02 May.

Nashville, Tennessee rawinsonde data

===== 03 MAY UPDATE =====

Before (29 April) and after (03 May) MODIS false color RGB images

A comparison of before (29 April 2010) and after (03 May 2010) 250-meter resolution MODIS Red/Green/Blue (RGB) false color images (above) from the SSEC MODIS Today site shows dramatic changes in some of the smaller rivers across western and central Tennessee following the record-setting rainfall that occurred on 01-02 May. On the false color images (created using MODIS bands 7/2/1 as the R/G/B channels), water appears as varying shades of blue, while dense vegetation appears as brighter shades of green.

On the corresponding set of before/after MODIS true color images (created using MODIS bands 1/4/3 as the R/G/B channels), increased river water turbidity (varying shades of light brown) can be seen — a result of high amounts of sediment transport (below).

Before (29 April) and after (03 May) MODIS true color images

Before (29 April) and after (03 May) MODIS true color RGB images

AWIPS images of the MODIS 0.645 µm visible channel and the 2.1 µm near-IR “snow/ice channel” data (below) demonstrate how the 2.1 µm imagery can be used to better identify flooded areas that do not show up as well on the visible channel imagery. Water (like snow and ice) is a strong absorber at the 2.1 µm wavelength, and thus appears very dark on the “snow/ice” image.

MODIS 0.645 µm visible channel and 2.1 µm near-IR "snow/ice" channel images

CIMSS has been supplying a variety of MODIS images and products in AWIPS (some of which are displayed on this page) to a number of NWS forecast offices as a part of the GOES-R Proving Ground effort.

===== 05 MAY UPDATE =====

MODIS false color images from 03, 04, and 05 April 2010

MODIS false color images from 03, 04, and 05 May 2010

A comparison of 250-meter resolution MODIS false color images from 03 May, 40 May, and 05 May 2010 (above) showed that while some of the smaller rivers and tributaries appeared to be receding somewhat, a number of the larger rivers did appear to remain swollen, with many areas still inundated with flood waters.

Posted in AVHRR, GOES sounder, GOES-13, GOES-R, Heavy rain / flooding, MODIS, POES, Red/Green/Blue (RGB) images, Severe convection, Synthetic satellite imagery | No Comments »

Convection Returns to the southern Plains

April 23rd, 2010

Spring convection and associated severe weather returned to the southern Plains on April 22nd. Did predictors of convection do a good job in locating the severe cells?

CIMSS has recently started to produce synthetic satellite imagery from the Weather Research and Forecasting (WRF) model run at the National Severe Storms Laboratory (NSSL). Output from daily runs at 00 UTC is produced for 9 infrared bands that correspond to those of the Advanced Baseline Imager (ABI) that will fly on GOES-R. The hourly loop of the 11.2-micrometer channel, above, for the period between 1800 UTC 22 April and 00 UTC 23 April, shows convection initially forming along the dryline in the Texas Panhandle between 1900 and 2000 UTC before progessing northeastward into Oklahoma and Kansas. Synthetic imagery of the middle of 3 ABI water vapor channels (6.95 microns), show a similar story. Model predictions give clues on where to look for convective development. How did real-time predictors of convective development perform?

The UW Convective Initiation algorithm combines observations of 10.8-micron cooling (from GOES-13) with cloud phase changes. When cooling occurs as cloud phase is changing (suggesting growing cumulus towers that are glaciating), GOES-13 pixels are flagged as showing convective initiation. Depending on the cloud phase — all water, mixed water and ice, or all ice, the initiation is flagged in the screengrabs from N-AWIPS above as pre-CI cloud growth (blue), CI likely (green), or CI occurring (yellow). Once glaciation has occurred, CI detection turns off. A previous blog entry on this method is here.

UWCI does flag individual cells that subsequently develop, ignoring adjacent towering cumulus. Thus, it can draw forecaster attention to the updrafts that, for whatever reason, are the most vigorous. For example, the image at 1701 UTC show convective initiation indicated in one spot along the dryline in west Texas. By 1745 UTC, convection has developed. Shortly after 1800 UTC, UWCI identifies individual cells along a line from the extreme western portion of the Oklahoma panhandle northward into east central Colorado. These cells subsequently spawn severe weather. UWCI also flags nascent convective development for cells that eventually develop into an arc of convection over central Kansas at 2301 UTC. Note also that UWCI flags specific convective towers within a large cumulus field over the southern Panhandle. (Consider the three images at 2131 UTC and 2145 UTC and at 2231 UTC; convection initiation flagged at the earlier two images develops most vigorously as shown in the final image). This can focus forecaster attention to the clouds that are growing most rapidly.

The two images above show where convective initiation was diagnosed to be ongoing at some time on 22 April, as well as a preliminary Storm Report from the Storm Prediction Center. Note the good general overlap of UWCI points over the High Plains and storm reports. That more Storm reports exist than UWCI points reflects the UWCI philosophy of keeping the false alarm rate low, perhaps at the expense of detection.

There are several UWCI hits over the northeast on 22 April as well. There, cold air at upper levels promoted self-destructing sunshine and shower and thunderstorm development. Clear skies early in the day (1431 UTC) gave way to cumuliform development. The strongest updrafts likely yield the strongest cloud-top-cooling signal (as shown in this loop) and evolve into the most vigorous shower or thundershower. Even though severe weather was not reported with these cells, lightning was produced, starting around 1900 UTC as shown here. Cloud-top cooling can give a forecaster a head’s up that a particular cell might become vigorous enough to electrify.

(Note: this post has been corrected to remove images from before 1645 UTC on 22 April that may have included mis-navigated regions of convective initiation).

Posted in Convective Initiation, GOES-13, GOES-R, Synthetic satellite imagery | No Comments »

Yet another East Coast winter storm

February 6th, 2010

GOES-11/GOES-12 water vapor composite images

The Winter of 2009/2010 has brought a number of significant snowfall events to parts of the US East Coast — and another powerful storm affected that region on 05 February – 06 February 2010. The highest storm total snowfall reported was 40.0 inches at Colesville in Maryland. Washington Dulles International Airport received 32.4 inches of snow (their largest 2-day snowfall on record), and Baltimore-Washington International Airport received 24.8 inches of snow (their second-largest 2-day snowfall on record). So far, this is Philadelphia’s 2nd-snowiest winter on record (56.3 inches) and Washington DC’s 3rd-snowiest winter on record (44.9 inches).

AWIPS images of 3-hourly composites of the GOES-11 and GOES-12 water vapor channel data (above) showed a strong disturbance originating over the Pacific Ocean that was progressing eastward across the southwestern US and northern Mexico during the days leading up to the storm. There was also evidence of a plume of subtropical moisture seen on the water vapor imagery.

The presence of this moisture plume was confirmed on MIMIC Total Precipitable Water (TPW) images (below), which revealed a clear linkage to the rich moisture source within the Inter-Tropical Convergence Zone (ITCZ) over the eastern equatorial Pacific Ocean. MIMIC TPW values were in the 50-60 mm (2.0 – 2.4 inch) range within this moisture plume as it was being drawn northeastward across the Gulf of Mexico — and the Blended Total Precipitable Water product showed a large area of TPW values exceeding 200% of normal from the Gulf of Mexico to the mid-Atlantic states.

MIMIC Total Precipitable Water

4-km resolution GOES-12 water vapor images with an overlay of cloud-to-ground lightning strikes (below) showed 3 important phases of the storm: (1) a expansive area of cold cloud tops associated with the initial round of heavy snowfall later in the day on 05 February; (2) the penetration of a broad dry slot, which helped to release convective instability along it’s leading edge that led to periods of thunder and lightning (especially during the 08-10 UTC time period), and (3) a well-defined deformation zone where additional snowfall banding developed during the final hours of the storm.

GOES-12 6.5 µm water vapor images + cloud-to-ground ligtning strikes

A series of 1-km resolution AVHRR Cloud Top Temperature product images and MODIS 11.0 µm IR images (below) showed greater detail of some of the banding structures during different phases of the storm.

AVHRR Cloud Top Temperature and MODIS 11.0 µm IR images

1-km resolution AVHRR visible images (below) displayed the cloud features as the surface low was rapidly deepening just offshore during the day on 06 February.

AVHRR 0.86 µm visible images + surface analyses

MetOp ASCAT scatterometer winds at 14:05 UTC on 06 February (below) indicated that surface winds were generally in the 30-40 knot range, which were in agreement with offshore buoys which were reporting wind gusts 31-43 knots at 15 UTC. The highest reported gust was 61 mph at Lewes, Delaware during the pre-dawn hours on 06 February.

AVHRR 0.86 µm visible image + ASCAT scatterometer winds

===== 07 FEBRUARY UPDATE =====

A comparison of a 1-km resolution MODIS visible channel image and a false-color Red/Green/Blue (RGB) image (below) shows the extent of the snow cover on the morning of 07 February. On the RGB image, snow appears as varying shades of red, in contrast to supercooled water droplet clouds (which appear as brighter features). Even after compaction of the heavy snowfall, there were still a number of sites reporting snow depths in excess of 30 inches that morning. Additional MODIS true color and false color imagery — at resolutions up to 250 meters — can be seen at the SSEC MODIS Today and the SSEC MODIS Direct Broadcast web sites.

MODIS visible + MODIS fasle-color Red/Green/Blue (RGB) image

MODIS true color images from the SSEC MODIS Today site can also be displayed using Google Earth (below). The location of 40.0 inch snowfall report (at Colesville, Maryland) is also noted on the image.