Bay Effect and Ocean Effect Snows in Virginia and North Carolina

January 5th, 2016 |
GOES-13 Visible (0.65 µm) Imagery, 1300-2045 UTC on 5 January 2015 [click to animate]

GOES-13 Visible (0.65 µm) Imagery, 1300-2045 UTC on 5 January 2015 [click to animate]

As a Low pressure center moved away from the coast, and a High pressure system approached from the west (link), cold air swept south along the east coast of the United States and produced light snow/flurries over Tidewater Virginia and the Outer Banks of North Carolina on Tuesday, 5 January 2016. The animation above, of the GOES-13 Visible Imagery, shows a band of cloudiness originating over the northern Chesapeake Bay that widened as it moved south. By the time it reached southern Virginia, it was producing snow. Conditions over the Outer Banks of North Carolina were very icy, as shown in this Video, courtesy of Sam Walker. The snow closed schools in Dare County. The 1300 UTC observations, below, in a toggle with 2100 UTC observations, showed morning snow over the Tidewater region and over extreme eastern North Carolina with strong north-northwest winds (gusting to 30 knots at Norfolk Naval Air Station). By 2100 UTC, winds had shifted and weakened and snow was no longer reported (an intermediate 1754 UTC MODIS image showed the cloud bands 1 hour after reports of snow had ended). It was still cold however: the sub-freezing daytime high in Norfolk VA was the first of the winter and the coldest day since late February 2015 (Temperatures did rise above freezing after sunset, however, to 35 at 11:59 PM on the 5th).

GOES-13 Visible (0.65 µm) Imagery, 1300 and 2045 UTC on 5 January 2015, with surface weather observations and wind barbs [click to enlarge]

GOES-13 Visible (0.65 µm) Imagery, 1300 and 2045 UTC on 5 January 2015, with surface weather observations and wind barbs [click to enlarge]

The cold air aloft necessary for Bay Effect (or Ocean Effect) snows was present in the 1200 UTC Sounding at Wallops Island, Virginia (or click to compare Stuve and Skew-T plots from this site). Temperatures 1 km above the surface were at -15.7ºC, with 850-mb temperatures near -10ºC. NOAA’s NAM and GFS Numerical Models indicated 850-mb temperatures cooler than -10ºC near Chesapeake Bay. That cold air in combination with warm sea-surface temperatures at or above +10ºC, at least as forecast (source) or as recently observed from satellite (AVHRR: 30 December and 27 December) [source], and MODIS: 02 January) or observed from buoys, easily met the 13ºC temperature difference threshold commonly cited to support lake effect snows.

In the preceding nighttime hours before visible imagery was available, long and well-defined bay effect and ocean effect cloud bands were evident on 1-km resolution Terra and Aqua MODIS 11.0-3.7 µm IR brightness temperature difference (legacy “fog/stratus product”) images, below. One cloud band was slowly moving westward over time toward the Outer Banks of North Carolina; at 07 UTC, Kill Devil Hills (located just north of Manteo, station identifier KMQI on the images) was reporting moderate snow reducing the surface visibility to 1/2 mile.

MODIS 11.0-3.7 µm IR brightness temperature difference images [click to enlarge]

MODIS 11.0-3.7 µm IR brightness temperature difference images [click to enlarge]

Flooding in the Missouri/Mississippi/Ohio River basins

January 2nd, 2016 |

Aqua MODIS false-color RGB images on 19 December 2015 and 02 January 2016 [click to enlarge]

Aqua MODIS false-color RGB images on 19 December 2015 and 02 January 2016 [click to enlarge]

A comparison of 250-meter resolution Aqua MODIS false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site on 19 December 2015 and 02 January 2016 (above) showed large increases in the width of portions of the Missouri/Mississippi/Ohio Rivers (as well as many of their tributaries and surrounding lakes) during that 14-day period. These false-color images use MODIS bands 7/2/1 as the R/G/B components — water appears as varying shades of darker blue. Some light snow cover (shades of cyan) can also be seen in the upper left corner of the 02 January image.

A comparison of Aqua MODIS true-color (created using bands 1/4/3) and false-color (created using bands 7/2/1) RGB images on 02 January (below) demonstrated the advantage of the false-color imagery for detection of the extent of river and lake flooding. The high sediment content of the area lakes and rivers made them appear as varying shades of tan to brown on the true-color image, making their boundaries more difficult to distinguish from the similar shades of the surrounding bare ground surfaces. (Note: when GOES-R is launched in late 2016, similar spectral bands on the ABI instrument will allow the creation of these types of true-color and false-color RGB images)

Aqua MODIS true-color and false-color RGB images on 02 January 2016 [click to enlarge]

Aqua MODIS true-color and false-color RGB images on 02 January 2016 [click to enlarge]

A more detailed view of flooding across the eastern portion of the MODIS images (in southern Indiana and northern Kentucky) was provided by 30-meter resolution Landsat-8 false-color imagery, as visualized using RealEarth (below). A magnified view of the Evansville, Indiana / Owensboro, Kentucky area can be seen here.

Landsat-8 false-color image [click to enlarge]

Landsat-8 false-color image [click to enlarge]

Maps of total observed precipitation and departure from normal (below) during the same 14-day period as the 2 MODIS false-color images shown at the top of the blog post revealed that widespread areas received upwards of 8-10 inches of rainfall, which was 6-8 inches above normal for that 2-week period of time.

19 December 2015 to 02 January 2016 total precipitation and departure from normal [click to enlarge]

19 December 2015 to 02 January 2016 total precipitation and departure from normal [click to enlarge]

As a result of water runoff from the heavy precipitation, new records for maximum river gauge height were set for the Mississippi River at Cape Girardeau, Missouri and Thebes, Illinois (below).

River gauge plot for the Mississippi River at Cape Girardeau, Missouri [click to enlarge]

River gauge plot for the Mississippi River at Cape Girardeau, Missouri [click to enlarge]

River gauge for the Mississippi River at Thebes, Illinois [click to enlarge]

River gauge for the Mississippi River at Thebes, Illinois [click to enlarge]

Additional information is available from the NWS Paducah.

GOES Water Vapor Animations for 2015

January 1st, 2016 |

The GOES-13 and GOES-15 Imager provides routine observations at five wavelengths, including 6.5 µm, a wavelength that is sensitive to water vapor absorption (SHyMet lesson). The YouTube animations below show full-disk GOES-13 (GOES-East) and GOES-15 (GOES-West) water vapor images at 3-hour intervals for every day during 2015. GOES-15 shows the remarkable tropical cyclone activity that occurred as a result of warmer-than-normal sea surface temperatures over the central Pacific. Much less hurricane activity occurred in the Atlantic.

Once GOES-R is launched in late 2016, the ABI instrument will provide full-disk images at 5-minute intervals, rather than the 3-hour intervals shown here. The animations from GOES-R will contain 288 images per day rather than 8.



GOES Infrared Animations for 2015

January 1st, 2016 |

The 10.7 micrometer infrared window channel on GOES-13 and GOES-15 helps monitor the state of the atmosphere and surface. The animations below, from GOES-13 (top) and GOES-15 (bottom), similar to the GOES Water Vapor Animations, show active tropical convection over the Pacific, relatively fewer tropical systems over the Atlantic, an active winter season storm pattern up the US East Coast at the start of the animation, and an active pattern along the US West Coast at the end.