MIMIC TPW

Microwave estimates of total precipitable water (from the CIMSS MIMIC website), above, from 24-27 July 2011, show the progression of a tropical wave through the northwest Caribbean Sea into the southern Gulf of Mexico. Late in the day on 27 July, Air Force Reconaissance found a closed circulation with winds that were strong enough to earn the system a tropical storm designation.

GOES 15 Visible Image 2245 UTC 27 July

Visible imagery from late in the day (above) on the 27th shows extensive convection, with some overshooting tops over the Yucatan Channel and over the adjacent landmass. Forecasts are for Don to strengthen slowly as it moves towards the west-northwest. Oceanic heat content estimates from RSMAS as displayed at the CIMSS Tropical Weather website show a region of high heat content (associated with the Loop Current in the Gulf of Mexico) north of the projected path of Don. Intensification of Don could be more rapid if the storm moves farther to the north, over the region of higher heat content.

Shear values around Don are low. That and the warm sea surface temperatures over the Gulf argue for slow intensification.

Don’s projected path into south Texas takes it to a region suffering from extreme drought, as shown here.

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GOES 15/GOES 13 Sounder loop

The earth-viewing instruments on the GOES-15 spacecraft, which is above 90 W longitude, were turned on July 25th, and will be sending Imager and Sounder data for the next two weeks. Satellites in storage are periodically awakened to test functionality. GOES-West, currently GOES-11, will be retired at the end of the year and GOES-15 is a candidate to replace that Geostationary Satellite at 135 W Longitude.

The above loop shows Sounder data from GOES-15 and GOES-13, both remapped to the same projection, for 1746 UTC on July 27th. Note that the most bands of the Sounder imagery from GOES-15 shows cleaner signals; colder detectors onboard GOES-15 (because GOES-15 has a different configuration than GOES-13) mean that the same signal has less noise.

Visible imagery from GOES-15 and GOES-13 gives similar views of the developing tropical system off the coast of Yucatan, in part because the satellites are only separated by 15 degrees of longitude (GOES-13 sits on the Equator at 75 degrees West Longitude)

GOES-15 imager data differs from GOES-11. Whereas GOES-11 has a 12.0 micrometer channel, which is useful for observations of dust and ash (when used in conjunction with the 10.7 micrometer channel), GOES-15 has a 13.3 micron channel, which data are useful for cloud-top properties.

GOES 15/GOES 13 Imager Water Vapor loop

The GOES-15 Imager water vapor channel has 4-km resolution versus 8-km resolution on GOES-11. In the loop above, note the better depiction of gradients (despite the vastly different view angles) and the better depiction of the mid-level vortex at the southwest edge of the image.

Another comparison of 8-km resolution GOES-11 6.7 µm water vapor images with corresponding 4-km resolution GOES-15 6.5 µm water vapor images can be seen below, viewing a lobe of middle-tropospheric vorticity that was moving southeastward over Nunavut, Canada (GOES water vapor image with an overlay of GFS 500 hPa vorticity). Again, the satellite viewing angles are different, but the features and gradients (even at the high latitude of 65 degrees North) are much clearer on the GOES-15 water vapor images.

GOES-11 6.7 µm (top panels) and GOES-15 6.5 µm water vapor channel images (bottom panels)

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POES AVHRR visible image + surface analysis

Accurately diagnosing cloud properties can be a challenge, especially over regions such as the panhandle of southeastern Alaska where upstream upper air report information is sparse. New satellite products such as those derived using POES AVHRR and MODIS spectral bands (channels) can be helpful in such situations. On 22 July 2011, the Area Forecast Discussion issued by the National Weather Service forecast office at Juneau, Alaska included the following:

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
529 AM AKDT FRI JUL 22 2011

.SHORT TERM…A LOW OVER THE SW GULF WILL MOVE TO THE S-CNTRL GULF BY LATE AFTERNOON…THEN BEGIN TO TURN SE TONIGHT. ASSOCIATED OCCLUDED FRONT WILL MOVE INTO THE SERN GULF BY LATE THIS AFTERNOON…THEN SLOWLY WEAKEN AS IT NEARS THE SRN OUTER COAST TONIGHT. USED A BLEND OF THE 00Z GFS AND ECMWF FOR THE SHORT TERM PERIOD.

OTHERWISE CLOUDS WILL BE A TRICKY CALL AS THERE WILL LIKELY BE SEVERAL AREAS OF THIN MID-LEVEL CLOUDS ALONG WITH SOME LOWER CLOUDS ALONG THE COAST AND WRN PARTS OF INNER CHANNELS. THINK A LOT OF THE LOWER CLOUDS WILL BREAK UP TODAY AS FLOW TURNS MORE ELY AHEAD OF APPROACHING FRONT. THE MID-LEVEL BANDS WILL BE A TRICKIER ISSUE…AND THINK A BAND WILL HANG ALONG THE COAST MTNS FROM THE PAJN AREA SEWD…BUT BE THIN AND BROKEN ENOUGH TO ALLOW SUNSHINE TO PEEK THROUGH MUCH OF THE TIME.

AWIPS images of the 1-km resolution POES AVHRR visible channel (above) and corresponding 1-km resoltion POES AVHRR IR channel (below) showed the cloud band associated with the occluded front as it approached the Alaska Panhandle.

POES AVHR IR image + surface analysis

A comparison of the 1-km resolution POES AVHRR Cloud Type, Cloud Top Temperature, and Cloud Height products (below) offered a bit more information about the composition and properties of various parts of this cloud band. The coldest cloud top temperature value within the cloud band was -54ºC, and the highest cloud top heights were 11 km.

POES AVHRR Cloud Type, Cloud Top Temperature, and Cloud Height products

Taking a closer look at the far southern Alaska Panhandle region using a comparison of the 1-km resolution MODIS Fog Depth, MODIS MVFR Probability, and MODIS IFR Probability products (below) indicated a number of localized ares where the fog depth was higher, and higher probabilities of Marginal Visual Flight Rules (MVFR) and Instrument Flight Rules (IFR) conditions existed.

MODIS Fog Depth, MVFR Probability, and IFR Probability products

CIMSS participation in GOES-R Proving Ground activities includes the development and testing of these types of products, along with their dissemination to select NWS offices for evaluation and feedback.

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GOES-13 fog/stratus product + GOES-13 visible channel images

AWIPS images of the 4-km resolution GOES-13 “fog/stratus product” at night followed by 1-km resolution GOES-13 0.63 µm visible channel data (above) showed that there was a great deal of river valley fog along the portion of the Mississippi River where Wisconsin borders Minnesota and Iowa, as well as some of the tributaries across southwestern Wisconsin on the morning of 19 July 2011. Not surprisingly, much more detail in the fog structure was evident in the higher spatial resolution visible images after sunrise, compared to that seen using the night-time 2-channel IR brightness temperature difference employed to create the standard operational fog-stratus product.

Another example showing how improved spatial resolution aids in river valley fog detection could be seen below with a comparison of the 1-km resolution MODIS fog/stratus product with the 4-km resolution GOES-13 fog/stratus product images around 07:30 UTC (2:30 am local time). Along the Wisconsin River Valley at that particular time, Lone Rock (station identifier KLNR) and Boscobel (station identifier KOVS) were both reporting surface visibilities restricted to 0.25 mile with fog.

GOES-13 fog/stratus product + MODIS fog/stratus product images

More quantitative information about the fog features is available using products such as the Fog Depth and Marginal Visual Flight Rules (MVFR) Probability products (below), which blend model fields with satellite imagery. Fog depth values along the Mississippi River were greater than 700 feet (blue color enhancement), and MVFR Probability was near 50% (lighter green color enhancement) at 09:15 UTC (4:15 am local time). CIMSS participation in the GOES-R Proving Ground includes the distribution of these types of products to select NWS forecast offices for testing and evaluation.

GOES-13 Fog/Stratus product, Fog Depth product, and MVFR Probability product

McIDAS images of GOES-13 0.63 µm visible channel data (below) offered a slightly clearer view of the river valley fog dissipation during the morning hours.

GOES-13 0.63 µm visible channel images

Farther to the east, there was extensive fog/stratus over southern Lake Michigan, which was discussed on the GOES-R Proving Ground Hazardous Weather Testbed blog.

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