Tropical Storm Bertha

July 16th, 2008 |

GOES-12 IR image

A GOES-12 IR image from the CIMSS Tropical Cyclones site (above) showed Tropical Storm Bertha continuing to linger over the western Atlantic Ocean on 16 July 2008 — this storm first became “Tropical Depression #2” over the eastern Atlantic, thirteen days earlier (on 03 July).

GOES-12 visible images (Animated GIF)

GOES-12 visible images with an overlay of SeaWinds data from the QuikSCAT satellite (above) revealed that there were still some bursts of convection near the center of the tropical cyclone, and maximum wind speeds remained near 60 knots. Tropical Storm Bertha was in the process of weakening as it began to encounter increasing environmental wind shear. AWIPS images of the GOES-12 water vapor channel (below) showed that the northeastward motion of Bertha was slowing, with a gradual turn toward the southeast as the tropical cyclone began to interact with a mid-latitude low located off to the  east (this middle to upper level low was drifting southwestward across the North Atlantic Ocean).

GOES-12 water vapor images (Animated GIF)

It is interesting to note the large pool of cooler Sea Surface Temperatures (cyan to blue colors) in the wake of slow-moving Bertha (below; sourced from Remote Sensing Systems).

Bertha Sea Surface Temperature image

2 years of MODIS in AWIPS

July 14th, 2008 |

MODIS images in AWIPS (Animated GIF)

July 2008 marks the 2-year anniversary of the beginning of the CIMSS / SSEC effort to provide MODIS imagery and products in AWIPS. Mostly cloud-free conditions over Wisconsin on 14 July 2008 allowed for a nice sample of 12 of these MODIS images and products (above), which are all available to NWS forecast offices to add to their local AWIPS workstations (via Unidata LDM subscription):

  1. 0.6 µm Visible channel (MODIS Band 1)
  2. 1.3 µm Cirrus detection (MODIS Band 26)
  3. 2.1 µm Snow/ice discrimination (MODIS Band 7)
  4. 3.7 µm Shortwave IR (MODIS Band 20)
  5. 6.7 µm Water vapor (MODIS Band 27)
  6. 11.0 µm IR window (MODIS Band 31)
  7. Land Surface Temperature (LST) product
  8. Sea Surface Temperature (SST) product
  9. Normalized Difference Vegetation Index (NDVI) product
  10. Cloud Phase product
  11. Cloud Top Temperature product
  12. Total Precipitable Water (TPW) product

(Note: a MODIS 11.0-3.7 µm Fog/Stratus product is also available on AWIPS; however, this is a night-time only product, so it was not included with the other daytime MODIS images shown above)

These MODIS images and products in AWIPS offer NWS forecasters an opportunity to begin evaluating and using some of the types of data that will be available with the Advanced Baseline Imager (ABI) instrument on the upcoming GOES-R satellite (scheduled to be launched in 2015).

To date, 49 NWS forecast offices have participated in the “MODIS Products in AWIPS” VISIT distance learning lesson (above) that has been offered on the VISIT training calendar since November 2006. As a result, 25 NWS offices have added the CIMSS MODIS imagery and products to their local AWIPS workstations (below), with MODIS being mentioned in 56 NWS Area Forecast Discussions so far.

NWS offices receiving MODIS data

Mesoscale Convective Vortex (MCV) over southeastern Wisconsin

July 11th, 2008 |

AWIPS satellite + radar images (Animated GIF)

A mesoscale convective system (MCS) moved southward across southern Wisconsin during the morning of 11 July 2008, producing a well-defined bowing segment along the southern flank. As the MCS continued to decay into the late morning hours, the signature of a weak Mesoscale Convective Vortex or MCV (see Interesting Clouds on Satellite: “Mesoscale Convective Vortex” from the NWS Milwaukee) became apparent on AWIPS images of the GOES-12 visible and IR channels (above, upper 2 image panels; see also a GOES-12 visible animation from Dave Santek, SSEC). While the presentation of the MCV was fairly impressive on the GOES-12 satellite imagery, this feature was much less obvious on the Milwaukee/Sullivan radar base reflectivity and base velocity data (above, lower 2 image panels).

Northerly winds gusted to 37 mph at the Madison airport KMSN (41 mph on top of the SSEC building in downtown Madison) as the bowing segment convection moved through; however, it is interesting to note that Juneau KUNU later reported a southeasterly wind gust of 43 mph at 17 UTC (Noon local time) as the MCV passed over that area; apparently a boundary layer “wake low” was responsible for producing this brief period of gusty southeasterly winds (which also included gusts to 20 mph at West Bend KETB and 17 mph at Watertown KRYV).

A comparison of MODIS true color and false color images from the SSEC MODIS Today site (below) showed finer detail in the cloud structures of both the leading edge of the convective outflow (the aforementioned bowing segment) and the MCV. The MCV signature was comprised primarily of lower to middle level clouds, and became more obvious as the canopy of high-level cirrus clouds (cyan colors on the MODIS false color image) began to dissipate as the MCS decayed.

MODIS true color + false color images (Animated GIF)

MODIS detects warm cities and cold upwelling

July 10th, 2008 |

MODIS Land Surface Temperature product

Mostly cloud-free skies in the wake of a cold frontal passage (MODIS true color image) allowed some interesting temperature signatures to be observed across the Upper Midwest and western Great Lakes states on 09 July 2008. An AWIPS image of the MODIS Land Surface Temperature (LST) product (above) revealed significantly warmer LST values (90-95º F, red colors) associated with the many cities across the region. The higher density of buildings, roadways, and paved surfaces in cities and urban areas contributes to the markedly higher surface (or “skin”) temperatures observed on satellite imagery — in fact, MODIS LST values were as hot as 101º F in the Chicago area. However, outside of the cities and urban areas, the MODIS LST values were generally in the 70s F, closer to the observed air temperatures (which are usually reported at suburban airports, away from the city centers).

The MODIS Sea Surface Temperature (SST) product (below) revealed a ribbon of significantly colder SST values (around 50º F, cyan colors) in Lake Michigan, along the nearshore waters off eastern Wisconsin. A cold front had moved eastward through the region on the previous day, and post-frontal winds gusting to 20-25 mph helped to aid the process of cold water upwelling immediately off the coast. Mid-lake MODIS SST values were about 10º F warmer (green colors), which was supported by Lake Michigan buoy data.

MODIS sea surface temperature (SST) product