Tropical Storm Ida has formed in the southwestern Caribbean Sea. Strong convection near the center is evident in the visible image, above, as well as suggestion of a banded feature northeast of the center. The southwestern Caribbean Sea is a region where tropical cyclogenesis can still occur at this time of year because of the combination of two things: (1) still-warm ocean waters (see an analysis of sea surface temperatures from CIMSS here; and (2) small values of vertical wind shear, as shown here. Microwave estimates of Precipitable water (using MIMIC) show that Ida formed in a region of enhanced precipitable water.

Ida is forecast to take a path over Nicaragua and Honduras (the path is depicted in the image of SSTs above (and here) before re-emerging over the still-warm waters of the far western Caribbean.

Update, 5 November. Visible imagery from the morning of 5 November, above, show upgraded Hurricane Ida on the coast of Nicaragua. The visible image shows banded structures over the Caribbean that speak to the increased organization to the system. However, its motion over the rugged terrain of Central America should cause weakening. Torrential rains over the mountains of Nicaragua and Honduras will accompany the storm.

Loops (Visible and Infrared) taken from the CIMSS tropical webpage show the evolution of Ida after landfall. Ida quickly lost intensity to depression status late on the 6th. The storm is forecast to be over the northwest Caribbean, where waters are very warm, over the weekend, so re-intensification is possible.

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The long nights of November allow ample cooling in clear airmasses, and fog is a frequent occurrence over rivers that are still relatively warm compared to the surrounding land. In these near-water locations, cooling to the dewpoint, and resultant saturation, allows fog to form in and along River valleys as shown in the above visible image from GOES-12. The Ohio River and its many tributaries in Pennsylvania, West Virginia and Kentucky are plainly visible.

Detection of fog at night occurs by comparing observed brightness temperatures at about 11 microns and about 3.9 microns. Small water droplets in fog are not effective emitters of radiation at 3.7 or 3.9 microns — that is, they do not emit like blackbodies — but the water droplets are effective emitters of radiation at 11 microns. Thus, the temperature inferred by the satellite (that assumes all bodies are emitting like blackbodies) is cooler for the 3.9-channel than for the 11-micron channel. A difference between the two temperatures, then, can be used to highlight fog.

The MODIS Fog product image, above, from AWIPS, shows the channel difference at 0736 UTC on 2 November, and it suggests ongoing fog in river valleys from New York State southwestward to Kentucky. The nearly simultaneous GOES image (from 0730 UTC) is below. The degraded resolution of the GOES infrared sensor over the Ohio Valley (about 5-km pixels, vs. 1-km pixels for MODIS) means that developing fog, by its nature at very small horizontal scales, is not initially detected. The finer-resolution detector on the MODIS instrument provides earlier warning of developing fog.

Fog in the river valleys is more obvious in the GOES Fog Product image from 1030 UTC, three hours later. However, the pixel footprint of GOES IR sensor means a less defined horizontal mapping of the true fog locations. The higher resolution MODIS instrument gives earlier detection and better horizontal delineation of fog events.

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The Halloween Blizzard of 1991 was an early-season storm that moved north from the Gulf of Mexico to the upper Great Lakes. Unseasonably cold air allowed the rich moisture-laden airmass to deposit a long band of snow from the Panhandle of Texas northeastward to western Lake Superior. Many early-season snow total records were broken, and single-storm records fell at Minneapolis (28.4″) and Duluth (36.9″) Typically storms from the Gulf of Mexico do not move due north; however, eastward motion of this system was blocked by a large nor’easter off the coast of New England (the so-called “Perfect Storm”).

In the visible loop above, notice the rapid melting of snow deposited by the system in the Texas Panhandle, despite record cold (30 and 31 October 1991 are the only October days in Amarillo history when the surface temperature stayed below 30 F all day). Snowcover in South Dakota (the Missouri River stands out) also speaks to the chill in the airmass on the cold side of the storm. A larger-scale visible animation is available here.

Update

The 1991 “Halloween” storm is the “single storm record for the metropolitan (Twin Cities)” area. A comparison of a GOES-7 Infrared and visible image on November 1, 1991 at 21 UTC.

H/T

These NOAA GOES-7 data was accessed via the University of Wisconsin-Madison SSEC Data Services, using the McIDAS-X software.

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AWIPS images of the MODIS visible and 2.1 µm near-IR “snow/ice” channels (above) showed areas of snow cover across parts of eastern Colorado, far northwestern Kansas, and Nebraska on 23 October 2009. Snow is a strong absorber at the 2.1 µm wavelength, so it appears very dark on the snow/ice channel image.

The corresponding MODIS Land Surface Temperature product (below) revealed significantly colder LST values in the middle to upper 30s F (darker green colors) where the snow cover was deeper. There was a lack of surface reports in the exact areas of deeper snow cover, except for Limon in eastern Colorado (station identifier KLIC), which was reporting a surface air temperature of 39º F at the time.

Snowfall amounts from this particular storm (which moved through the region on 22 October) included 15 inches at Elizabeth, Colorado, 12 inches at Brady, Nebraska, and 4 inches at Saint Francis, Kansas. These locations are marked on a MODIS Red/Green/Blue (RGB) true color image from the SSEC MODIS Today site (below, displayed using Google Earth).

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