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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MODIS 3.7 µm shortwave IR images

AWIPS images of 1-km resolution MODIS 3.7 µm shortwave IR data (above) revealed a large number of “hot spots” (black to red to yellow color enhancement) due to wildfires that were burning across parts of western Ontario, Canada on 17 July – 18 July 2011.

McIDAS images of GOES-13 0.63 µm visible channel data (below) showed the unusually dense smoke plume resulting from these wildfires. Over Ontario, most of the smoke was located aloft (see the US Air Quality Smog Blog for more details), but surface visibilities were still being restricted to 2-5 miles at some locations. Farther away from the source region, the leading edge of the smoke moving over portions of New England and the Canadian Maritime Provinces exhibited significantly less optical thickness.

GOES-13 0.63 µm visible channel images

The hazy extent of the smoke plume could be more readily seen on a MODIS “true color” Red/Green/Blue (RGB) image from the SSEC MODIS Direct Broadcast site (below). As an aside, note that there are still some large ice floes in the open water of Hudson Bay.

MODIS true color Red/Green/Blue (RGB) image

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GOES-13 0.65 µm visible channel images (click image to play animation)

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed the cyclonic circulation of clouds and the convective bursts associated with the development of Tropical Storm Bret in the western Atlantic Ocean north of the Bahamas on 17 July 2011.

A morning AWIPS image of MODIS 11.0 µm IR channel data with an overlay of MetOp Advanced Scatterometer (ASCAT) surface winds (below) indicated a broad cyclonic flow with maximum velocities around 22 knots at 14:23 UTC.

MODIS 11.0 µm IR image + ASCAT surface scatterometer winds

Later in the day, a DMSP-18 SSMIS 85 GHz microwave image from the CIMSS Tropical Cyclones site (below) showed that the deep convection was limited to the eastern semicircle of the tropical cyclone at that time, due to the presence of some westerly wind shear.

DMSP-18 SSMIS 85 GHz microwave image + deep layer wind shear

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