GOES-13 fog/stratus product (click image to play animation)

AWIPS images of the 4-km resolution GOES-13 10.7 µm – 3.9 µm “fog/stratus product” (above; click image to play animation) showed a large area of fog and/or stratus (yellow to orange color enhancement) that was increasing in areal coverage during the pre-dawn hours on 06 February 2012. Although the fog/stratus product is useful for locating the presence and temporal trends of such features, it does not offer any reliable indication of whether it is fog on the ground or stratus cloud aloft.

One product that attempts to give the forecaster some quantitative information is the GOES Low CLoud Base (LCB) prodcut (below; click image to play animation), which attempts to blend surface observations with satellite data to indicate whether the cloud base is above or below the threshold of 1000 feet.

GOES-13 Low Cloud Base product (click image o play animation)

With 1-km resolution data, the MODIS instrument aboard the polar-orbiting Terra and Aqua satellites offers a similar “fog/stratus product” (below) that provides better clarity, especially regarding the exact location of the edges of the fog and/or stratus.

MODIS fog/stratus product images

In this particular case, a number of locations beneath the western and southern edge of the fog/stratus feature were expereincing freezing fog (below) and visibilities of 1/4 mile or less, which was creating hazardous road conditions and prompting the issuance of Freezing Fog Advisories.

MODIS fog/stratus product with METAR surface reports

As part of CIMSS participation in GOES-R Proving Ground activities, products are being developed which can provide more quantitative information about such parameters as Fog Depth and the Probability of Marginal Visual Flight Rules (MVFR) or Instrument Flight Rules (IFR) conditions (below). In this case, across the southwestern part of Iowa (where widespread freezing fog was being reported), the fog depth was as high as 1400-1500 feet, with probabilities of MVFR and IFR conditions as high as 75-90% and 60-75%, respectively.

MODIS Fog Depth, MVFR Probability, and IFR Probability products

Shortly after sunrise, it is interesting to note that a comparison of 1-km resolution POES AVHRR 0.63 µm visible channel, 3.74 µm “shortwave IR” channel, and 10.8 µm channel “IR window” channel images (below) revealed that part of the swath of fresh snow cover (as deep as 4-6 inches) across western Iowa could be seen through the translucent western edge of the fog/stratus deck that was beginning to burn off during the morning hours. The fog/stratus deck appears warmer (darker gray enhancement) om the 3.74 µm image, due to the sensitivity of that channel to the reflection of solar radiation off the tops of supercooled water droplet clouds.

Farther to the south, note the presence of narrow fingers of valley fog in the Ozark Mountains and surrounding regions in Oklahoma, Arkansas, and Missouri.

POES AVHRR 0.63 µm visible, 3.74 µm "shortwave IR", and 10.8 µm "IR window" images

Aqua MODIS: 11.0 µm IR images (grayscale, and color-enhanced) + "Fog/stratus product"

A comparison of AWIPS images of 1-km resolution Aqua MODIS 11.0 µm “IR Window” channel data (both grayscale, and color-enhanced) and the corresponding MODIS “Fog/stratus product” (above) showed some areas of fog and/or stratus cloud over the eastern half of Hudson Bay, Canada on 26 January 2012. On the fog/stratus product, low clouds and/or fog appear as the yellow-to-red enhanced features, while cirrus cloud features appear darker black.

The primary feature of interest here is the very thin – almost “translucent” – patch of fog/stratus located in the upper center portion of the image, to the west of Akulivik (station identifier CYKO) and Povungnituq (station identifier CYPX). The exact edges of this feature were difficult to identify in either the grayscale or the color-enhanced IR images — but the conventional “Fog/stratus product” (simply the difference in IR brightness temperature between the 11.0 µm and 3.7 µm channel data) allowed unambiguous identification of the edges.

About 45 minutes earlier, a similar comparison using McIDAS images of of 375-meter resolution Suomi NPP VIIRS 11.450 µm IR data (both grayscale, and color-enhanced) and the corresponding VIIRS “Fog/stratus product” (below) showed much more detail associated with this particular thin fog/stratus feature. The higher spatial resolution allowed many more of the  ice leads to be seen — even some of the larger ones that were located below the thin fog/stratus feature.

Suomi NPP VIIRS: 11.450 µm IR (grayscale, and color-enhanced) + "Fog/stratus product"

1-km resolution MODIS vs 4-km resolution GOES-13 fog/stratus product images

The National Weather Service forecast office in Mobile, Alabama mentoned their use of the MODIS fog/stratus product during the pre-dawn hours on 14 December 2011:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOBILE AL
1140 PM CST TUE DEC 13 2011

.AVIATION UPDATE (14/06Z ISSUANCE)…LOW CIG AND VSBY CONDITIONS CONTINUE. GOES IMAGER 11-3.9 AND MODIS POLAR ORBITER CONTINUE TO INDICATE A LOW STRATUS DECK WITH LOW VISIBILITY IN A LAYER WHOSE EDGE OVERLAYS A LINE FROM NEAR FOLEY TO BAY MINETTE AND ON UP TO CAMDEN. POINTS WEST OF SAID LINE ARE PRETTY WELL SOCKED IN AND PRETTY CLEAR ELSEWHERE. HAVE THEREFORE KEPT REDUCED PREVAILING GROUP TO A QUARTER MILE AND VV001 FOR BFM AND MOB.

A comparison of AWIPS images of the 1-km resolution MODIS vs the corresponding 4-km resolution GOES-13 fog/stratus product (above) demonstrated the advantage of using higher spatial resolution data to more accurately locate the eastern edge of the fog.

MODIS fog/stratus product + METAR surface reports

AWIPS images of the 1-km resolution MODIS fog/stratus product (above) showed areas of freezing fog that were persisting across parts of the Pacific Northwest region of the US during the pre-dawn hours on 10 December 2011. This freezing fog was causing a few traffic accidents on roadways across the region.

On the previous day (09 December), an NPP VIIRS true color image (below; courtesy of Liam Gumley, CIMSS) showed the daytime coverage of the fog and stratus features that were trapped beneath a strong temperature inversion with stagnant high pressure in place over the region.

NPP VIIRS true color image (courtesy of Liam Gumley, CIMSS)

MODIS and GOES-13 fog/stratus product images

Strong nocturnal radiational cooling beneath a large area of high pressure centered over the Ohio River Valley led to the formation of widespread areas of fog and stratus on 05 October 2011. AWIPS image comparisons of the 1-km resolution MODIS and the 4-km resolution GOES-13 fog/stratus products at 03:30 UTC or 11:30 pm local time (above) and 07:45 UTC  or 3:45 am local time (below) demonstrated the clear advantage of having improved spatial resolution to detect the more subtle features such as river valley fog.

MODIS and GOES-13 fog/stratus product images

To compliment the improved fog/stratus detection capabilities offered by higher spatial resolution, other products are being developed (as part of the CIMSS participation in GOES-R Proving Ground activities) that provide more quantitative information about areas of fog and/or low cloud: for example, Fog Depth, Marginal Visual Flight Rules (MVFR) Probability, and Instrument Flight Rules (IFR) Probability (below). In this case, the 07:45 UTC products indicated that the Fog Depth values were as high as 1231 feet (cyan color enhancement) over parts of northern West Virginia, where there were also MVFR Probabilities greater than 90% and IFR Probabilities greater than 75% (brighter red color enhancement).

GOES-13 fog/stratus product, Fog Depth, MVFR Probability, and IFR Probability

1-km resolution MODIS fog product + 4-km resolution GOES-13 fog product

The early morning area forecast discussion issued by the National Weather service office at State College, Pennsylvania mentioned that river valley fog was being detected by the MODIS fog/stratus product:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
526 AM EDT FRI SEP 16 2011

.SYNOPSIS...
A LARGE HIGH PRESSURE SYSTEM OVER THE GREAT LAKES WILL BUILD SLOWLY EAST TO NEW ENGLAND BY SUNDAY AND MONDAY. A DYING COLD FRONT WILL LIKELY PUSH INTO THE REGION LATE MONDAY OR TUESDAY. A DIGGING TROF AND ASSOCIATED SLOW MOVING COLD FRONT COULD AFFECT THE REGION BY LATE NEXT WEEK.

.NEAR TERM /UNTIL 6 PM THIS EVENING/... EARLY AM MODIS 11-3.7UM IMAGERY SHOWING DENDRITIC PATTERN OF FOG IN THE DEEP RIVER VALLEYS OF THE ALLEGHENY MTNS.

A comparison of AWIPS images of the 1-km resolution MODIS fog/stratus product with the corresponding 4-km resolution GOES-13 fog/stratus product (above) demonstrated the advantage of higher spatial resolution for detecting such small-scale features. A subtle fog signal was beginning to show up at this time in the GOES-13 fog/stratus product image, but it was difficult to tell whether it was due to noise or actual fog features.

About an hour and 15 minutes later, a similar comparison using a 1-km resolution POES AVHRR fog/stratus image and the corresponding 4-km resolution GOES-13 fog/stratus product image (below) showed that while the fog signal had become better defined by this time on the GOES-13 image, the POES AVHRR image again showed the river valley fog features with much greater clarity.

1-km resolution POES AVHRR fog product + 4-km resolution GOES-13 fog product

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
523 AM EDT FRI AUG 12 2011

.NEAR TERM /UNTIL 6 PM THIS EVENING/…
HIGH PRESSURE AND ASSOCIATED DRY AIR MASS PRODUCING A NEARLY CLOUDLESS MORNING OVER CENTRAL PA. 07Z MODIS 11-3.7UM IMAGERY SHOWS FOG HAS DEVELOPED IN THE VALLEYS OF WESTERN PA…WHERE COOL AIR IN CONTACT WITH RELATIVELY WARMER RIVER/STREAM WATER. ANY FOG SHOULD BURN OFF BY 8-9AM.

AWIPS images of the 1-km resolution MODIS fog/stratus product along with the corresponding 4-km resolution GOES fog/stratus product image (below) demonstrated the improvement in river valley fog detection that is possible with higher spatial resolution. Note the river valley fog on the MODIS image that was mentioned across western Pennsylvania, as well as other areas of river valley fog across parts of southern New York and northern West Virginia.

1-km resolution MODIS and 4-km resolution GOES fog/stratus product images

About 3 hours later, a similar comparison of 1-km resolution POES AVHRR and 4-km resolution GOES fog/stratus product images (below) show that river valley fog had increased across parts of western and northern Pennsylvania. The large amount of noise on the GOES fog/stratus product made it difficult to accurately locate where river valley fog features had formed.

1-km resolution POES AVHRR and 4-km resolution GOES fog/stratus product images

CIMSS participation in GOES-R Proving Ground activities includes making a variety of POES AVHRR and MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

The VISIT training lessons “POES and AVHRR Satellite Products in AWIPS” and “MODIS Products in AWIPS” are available to help users understand these products and their applications to weather analysis and forecasting.

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.

POES AVHRR 3.7 µm shortwave IR image

An AWIPS image of POES AVHRR 3.7 µm shortwave IR data (above) revealed a large number of fire “hot spots” (black to red to yellow pixels) across much of eastern Kansas on 12 April 2011. The majority of these were grassland fires.

On the following day (13 April 2011), a well-defined area of dense smoke aloft could be seen stretching from Missouri into southwestwen Iowa on a MODIS 0.65 µm visible channel image (below).

MODIS 6.5 µm visible channel image

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GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible images (above; click image to play animation) showed that the dense smoke feature moved very little during the day. An overlay of NAM12 850 mb winds (below) indicated that light southwesterly winds in the morning transitioned to a more organized southeasterly flow as a low-level cyclonic circulation moved southward across Nebraska into Kansas.

GOES-13 visible images + NAM12 850 mb winds

A MODIS true color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below; displayed using Google Earth) provided a better view of the smoke pall aloft as the northern end wrapped around the low-level cyclonic circulation.

MODIS true color RGB image (displayed using Google Earth)

MODIS Aerosol Optical Depth (AOD) products from the IDEA site (below) showed very high ADO values  (orange to red color enhancement) associated with this smoke feature.

MODIS Aerosol Optical Depth (AOD) products

GOES-11 0.65 µm visible image (click to play animation)

McIDAS images of GOES-11 0.65 µm visible channel data (above) showed a persistent Tule fog event across much of the Central Valley of California on 05 January 2011. The northern portion of the fog eventually began to erode into the afternoon hours, but the remainder of the fog feature showed little change. A 1-km resolution MODIS Red/Green/Blue (RGB) true color image from the SSEC MODIS Today site (below) offered another view of the fog. The snow-covered Sierra Nevada Range can be seen to the east of the Central Valley.

MODIS true color Red/Green/Blue (RGB) image (viewed using Google Earth)

Before the areal extent of the fog could be monitored using daytime visible images, a comparison of AWIPS images of the 1-km resolution MODIS fog/stratus product and the corresponding 4-km resolution GOES-11 fog/stratus product (below) demonstrated the clear advantage of improved spatial resolution for detecting the location of the fog edges. In addition, the portions of the fog that were deeper in vertical extent were highlighted with an orange to red color enhancement.

1-km resolution MODIS and 4-km resolution GOES-11 fog/stratus product images

The MODIS Cloud Top Temperature (CTT) product (below) depicted CTT values of +1 to +4º C (lighter red color enhancement) across the fog feature. Note that the CTT product incorrectly identified the cold, snow-covered Sierra Nevada mountains as cloud, with CTT values between 0 and -25º C (yellow to blue color enhancement).

MODIS Cloud Top Temperature product