Undular bore approaching Puerto Rico

March 14th, 2013 |
GOES-13 0.63 µm visible channel images (click image to play animation)

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

Hat tip to Luis Rosa at the National Weather Service forecast office at San Juan, who alerted us to the presence of an undular bore that was moving southward toward Puerto Rico on 14 March 2013. The southward propagation of the wave clouds associated with the bore can be seen on McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation). The passage of the bore also seemed to have an effect on the erosion of the marine boundary layer stratocumulus clouds.

An AWIPS image of 1-km resolution POES AVHRR 0.86 µm visible channel data with overlays of surface reports and the surface analysis (below) showed that a cold front was situated about 500 miles northwest of Puerto Rico — so the undular bore was located far in advance of this frontal boundary. As seen on the animation of GOES-13 visible images above, the wave clouds of the bore had dissipated by the time of the AVHRR image (17:38 UTC); at St. Thomas, Virgin Islands (station identifier TIST) the winds briefly shifted to northeasterly at 18-19 UTC, though it is unknown whether this wind shift was related to the arrival of the bore.

POES AVHRRR 0.86 µm visible channel image with surface reports and surface analysis

POES AVHRRR 0.86 µm visible channel image with surface reports and surface analysis

20-year anniversary of the March 1993 “Storm of the Century”

March 13th, 2013 |
Meteosat-3 11.5 µm IR channel images (click image to play animation)

Meteosat-3 11.5 µm IR channel images (click image to play animation)

The 1214 March 1993 “Storm of the Century” (aka “the ’93 Superstorm” or “the Great Blizzard of 1993”) was one of the most significant storms to impact the eastern United States (NWS Wilmington NC summary). McIDAS images of EUMETSAT Meteosat-3 Infrared (11.5 µm) channel images (above) showed the storm as it initially began to experience rapid intensification in the Gulf of Mexico on 12 March. At the time, Meteosat-3 was on loan to the US and serving as the “GOES-East” satellite after the failure of GOES-6 in 1989.

On the following day (13 March), a larger-scale view of Meteosat-3 Infrared (11.5 µm) images (below) revealed the very large size of the storm as it moved along the Eastern Seaboard of the US. Some highlights of the storm included snowfall amounts as high as 56 inches at Mount LeConte in Tennessee, a wind gust to 144 mph at Mount Washington in New Hampshire, a minimum sea level pressure of 28.28 inches at White Plains in New York, and a post-storm record low temperature of -12º F in Burlington, Vermont.

Meteosat-3 11.5 µm IR channel images (click image to play animation)

Meteosat-3 11.5 µm IR channel images (click image to play animation)

The corresponding large-scale view of Meteosat-3 Water Vapor (6.4 µm) images (below) showed the well-defined dry slot and large comma head associated with the storm.

Meteosat-3 6.4 µm water vapor channel images (click image to play animation)

Meteosat-3 6.4 µm water vapor channel images (click image to play animation)

A GOES-7 Visible (0.65 µm) image at 18:01 UTC or 1:01 PM Eastern Time on 13 March (below) showed several interesting aspects of the storm, including widespread stratucumulus cloud streets over the Gulf of Mexico and the Atlantic Ocean (due to cold air advection over warmer waters), and also a large cloud arc in the Pacific Ocean south of Mexico, which was the leading edge of a Tehuano mountain gap wind event (see Schultz, et al, 1997). A rope cloud marked the leading edge of the strong cold front, which at the time of the image had plunged as far southward as Honduras in Central America.

GOES-7 0.65 µm visible channel image

GOES-7 0.65 µm visible channel image (click to enlarge)

Fog and stratus deck over the North Slope region of Alaska

March 11th, 2013 |

The Area Forecast Discussion issued by the National Weather Service forecast office in Fairbanks mentioned the presence of a layer of fog and stratus over parts of the North Slope region of Alaska:

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
1258 PM AKDT MON MAR 11 2013

NORTH SLOPE…THE SUOMI NPP VIIRS SATELLITE FOG PRODUCT WAS INDICATING A DECENT LAYER OF STRATUS ALONG THE NORTH SLOPE. OBSERVATIONS ACROSS THE AREA GENERALLY INDICATED 1 TO 2 MILES IN VISIBILITY WITH FLURRIES AND FOG. THE IFR CONDITIONS ALIGN VERY WELL WITH THE HIGHER PROBABILITIES OF MODIS IFR PRODUCT. THERE ARE SOME VERY ISOLATED POCKETS OF HIGHER PROBABILITIES OF THE MODIS LIFR CONDITIONS. THESE CONDITIONS SHOULD REMAIN THROUGH TUESDAY EVENING OR WEDNESDAY MORNING AS THE SURFACE HIGH PRESSURE REMAINS WITHIN THE AREA. BY WEDNESDAY MORNING THE SURFACE PRESSURE GRADIENT BEGINS TO TIGHTEN…PROVIDING AN INCREASE IN WINDS AND PERHAPS A BREAK IN SOME OF THE FOG.

AWIPS images of the Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” (below) showed the coverage of the fog and stratus over the area.

Suomi NPP VIIRS IR brightness temperature difference "fog/stratus product"

Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product”

The MODIS Instrument Flight Rules (IFR) Probability product (below) exhibited probabilities in excess of 90% (darker red color enhancement) over some areas. As mentioned in the forecast discussion, surface high pressure centered over the region was helping to maintain the presence of fog and stratus.

MODIS Instrument Flight Rules (IFR) Probability product

MODIS Instrument Flight Rules (IFR) Probability product

The corresponding MODIS Low Instrument Flight Rules (LIFR) Probability product (below) had some values greater that 70% (red color enhancement) over the eastern portion of the North Slope. However, you will notice that a large data gap appears in the LIFR product, in an area where IFR probabilities were high. Corey Calvert from CIMSS explained:

“Looks like the issue stems from the RAP model. The max RH in the lowest 1000′ layer is well over 90% for the area being discussed. However, the max RH in the lowest 500′ layer decreases significantly northward toward the water where is terrain is lower. Looks like the RAP is representing an elevated cloud layer with a ceiling between 500′-1000′ above sea level in that area. The high LIFR probs appear to coincide with higher terrain, therefore the lowest 500′ layer is elevated into the RAP cloud layer. The low LIFR probs (the hole in the data) match up with the lower RH values at lower terrain under the RAP cloud layer. The ceiling obs do indicate an elevated cloud layer (one station measuring 300′ and another 700′ in the area), but it’s hard to tell which is right due to the sparsity of obs. If the ceiling truly is hovering around 500′ though then this is believable representation from the products (high prob of IFR but low prob of LIFR)”.

MODIS Low Instrument Flight Rules (LIFR) Probability product

MODIS Low Instrument Flight Rules (LIFR) Probability product

These examples of new satellite products are being evaluated in an operational environment as part of the GOES-R Proving Ground, in an effort to prepare forecasters for the types of satellite data that will be available from the next generation of meteorological satellites (JPSS and GOES-R)

Thunderstorms over Arizona: turbulence, hail, and damaging winds

March 8th, 2013 |
MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images (with CRAS model 500 hPa geopotential height contours)

MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images (with CRAS model 500 hPa geopotential height contours)

AWIPS images of MODIS 0.64 µm visible channel and 6.7 µm water vapor channel images with an overlay of CRAS model 500 hPa geopotential height contours (above) showed an upper-level trough of low pressure that was moving inland across southern California and Arizona on 08 March 2013.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (with surface reports and surface fronts)

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (with surface reports and surface fronts)

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (above) showed that widespread thunderstorms had developed on either side of a cold frontal boundary that was moving eastward across Arizona. The Blended Total Precipitable Water (TPW) product (below) indicated that TPW values were as high as 20 mm or 0.79 inch over much of Arizona, which was in excess of 200% or normal for this time of the year. With unseasonably high moisture in place, these thunderstorms produced a daily record rainfall  of 0.84 inch at Phoenix, with several locations in the Phoenix area receiving over 1 inch of precipitation (Public Information Statement). Hail up to 0.5 inch in diameter was reported — in some cases the hail accumulated to the point of totally covering the ground — and winds gusted to 45-55 mph at several locations.

Blended Total Precipitable Water and Percent of Normal Total Precipitable Water products

Blended Total Precipitable Water and Percent of Normal Total Precipitable Water products

In addition to heavy rainfall, hail, and damaging surface winds, there were several pilot reports of turbulence. Particularly noteworthy were a pilot report of Severe turbulence at an altitude of 28,000 feet, and a pilot report of Severe to Extreme turbulence at an altitude of 11,000 feet. Both of these turbulence reports appeared to be associated with convective cells that were growing rapidly, as seen with GOES-13 10.7 µm IR channel images (below; click image to play animation).

GOES 15/13 10.7 µm IR channel images with pilot reports of turbulence (click image to play animation)

GOES 15/13 10.7 µm IR channel images with pilot reports of turbulence (click image to play animation)