University of Wisconsin-Madison Space Science and Engineering Center

CIMSS Satellite Blog

Freezing fog across the Pacific Northwest

December 10th, 2011

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)

Posted in Fog detection, MODIS, Suomi NPP, VIIRS | No Comments »

Fog and stratus in the Ohio River Valley and central Appalachians

October 5th, 2011

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

Posted in Fog detection, GOES-13, GOES-R, MODIS | No Comments »

River valley fog in Pennsylvania

September 16th, 2011

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.