Strong storm along the East Coast

September 25th, 2015 |
GOES-13 Infrared Water Vapor (6.5 µm) images [click to play animation]

GOES-13 Infrared Water Vapor (6.5 µm) Imagery [click to play animation]

A slowly-moving storm was migrating northeastward along the East Coast of the United States on 25 September 2015. The GOES-13 water vapor animation, above, shows the evolution of this system between 22 and 25 September 2015. The center of circulation in the water vapor imagery has wobbled around the state of Georgia for the past three days as a strong jet along the United States-Canada border has has maintained a series of surface High Pressure systems northeast of the storm, effectively blocking the Low Pressure’s exit from the southeast US.

Moisture available to this storm is depicted in the animation of MIMIC Total Precipitable Water, below. Moisture that moves southwestward towards the southeast US along the Gulf Stream is being joined by moisture moving northward from the tropical Atlantic Ocean.

MIMIC Total Precipitable Water for the 72 hours ending 1400 UTC 25 September [click to enlarge]

MIMIC Total Precipitable Water for the 72 hours ending 1400 UTC 25 September [click to enlarge]

This system has generated flooding rains over South Carolina. The GOES-13 Visible animation from 24 September 2015, below, shows persistent inflow off the Atlantic Ocean. Click here for a media report; Columbia SC reported 2.84″ of rain on 24 September, a record for the date.

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm) Imagery [click to play animation]

The thunderstorms associated with this system also caused a brief EF-2 tornado near Johns Island in Charleston County, SC (SPC Storm Reports). An animation of auto-detected Overshooting Tops, below, captures an overshooting top sequence persisting near Charleston at about the time of the tornado (0445 UTC). The toggle between Terra MODIS (0315 UTC) and Suomi NPP VIIRS (0618 UTC) 11 µm infrared data shows the general northwestward motion of the thunderstorm that produced the tornado (GOES-13 Infrared animation). The coldest cloud-top IR brightness temperature from MODIS was -75º C, with -76º C detected by VIIRS.

Autodetected Overshooting Top from GOES-13 Infrared (10.7 µm) imagery, 0315-0545 UTC [click to enlarge]

Autodetected Overshooting Top from GOES-13 Infrared (10.7 µm) imagery, 0315-0545 UTC [click to enlarge]

Terra MODIS 11.0 µm and Suomi/NPP VIIRS 11.45 µm infrared imagery [click to enlarge]

Terra MODIS 11.0 µm and Suomi/NPP VIIRS 11.45 µm infrared imagery [click to enlarge]

The pressure gradient between the storm over the southeast US and the High Pressure over the Canadian Maritimes had caused long-fetch onshore winds over much of the mid-Atlantic coast. This (and a Full “Super” Moon on Sunday) presages a weekend of coastal flooding. The animation of ASCAT (from METOP-B) winds below, shows 20-25 knot winds over a large region of the Atlantic Ocean between the Gulf Stream and North America. That long fetch will help generate large waves. The surface circulation off the coast of Georgia is also apparent in the 0220 UTC image.

METOP-B ASCAT Scatterometer Winds, 0000-1500 UTC over the western Atlantic [click to enlarge]

METOP-B ASCAT Scatterometer Winds, 0000-1500 UTC over the western Atlantic [click to enlarge]

Semi-Truck/School Bus Collision in Fog in Southeast North Dakota

September 25th, 2015 |
GOES-13 Visible (0.63 µm) imagery and surface observations of visibility; Richland County is outlined [click to play animation]

GOES-13 Visible (0.63 µm) imagery and surface observations of visibility; Richland County is outlined [click to play animation]

Three Semi-Truck/Trailers collided with a school bus in fog in Richland County North Dakota just before 9 AM CDT (1400 UTC) on 25 September 2015. The GOES-13 Visible animation, above, shows an eroding fog bank over southeastern North Dakota. Richland County is outlined in the imagery. The school bus was traveling on Highway 46, which hugs the northern border of Richland County; the accident was about 3 miles west of Interstate 29 (Press Report 1 ; Press Report 2).

Suomi NPP VIIRS "fog/stratus product" IR brightness temperature difference images [click to enlarge]

Suomi NPP VIIRS “fog/stratus product” IR brightness temperature difference images [click to enlarge]

During the preceding nighttime hours, Suomi NPP VIIRS “fog/stratus product” IR brightness temperature difference images at 0756 UTC (2:56 am CDT) and 0937 UTC (4:37 am CDT), above, showed an increasing signal of fog/stratus – yellow to red color  enhancement – over the region during that time period (when surface visibilities also began to rapidly decrease at Wahpeton KBWP, the county seat of Richland County).

GOES-R IFR Probability fields, 1300-1515 UTC on 25 September 2015 [click to play animation]

GOES-R IFR Probability fields, 1300-1515 UTC on 25 September 2015 [click to play animation]

GOES-R IFR Probability fields, above, around the time of the accident, showed a high probability of IFR Conditions over southeast North Dakota. High values were present over the area before sunrise (Sunrise in Fargo on 25 September is at 1318 UTC). Values at 1400 UTC show largest values over northern and western Richland County. The Low IFR Probabilty field for 1400 UTC, below, immediately after the time of the crash, shows a maximum across northern Richland County where the accident occurred.

GOES-R Low IFR Probability field, 1400 UTC on 25 September 2015 [click to enlarge]

GOES-R Low IFR Probability field, 1400 UTC on 25 September 2015 [click to enlarge]