Even when the atmosphere is supportive of thunderstorms, a source of lift is necessary to provide the upward motion required by a fledgling storm’s updraft. A reliable source of lift is often found near a cold, warm, or stationary front accompanying an approaching low pressure system (figure 1). Terrain or the leading edge of a downdraft from an existing thunderstorm (outflow boundary) can also provide a storm with this all-important ingredient. Continue reading
Introduction Continue reading
On the afternoon on December 10, 2018, an area of what initially appeared to be precipitation (Figure 1) was detected northwest of Evansville, Indiana by the National Weather Service (NWS) Doppler Weather Radar station at Paducah, Kentucky (KPAH). When first detected, the blob was 100 nm northeast of KPAH at an elevation of approximately 12,000 feet. A check of surface weather stations near the blob and visible satellite imagery (Figure 2) indicated that no precipitation was occurring and that skies were clear in the area.
Weather-savvy mariners know the best resource for monitoring the location, size, intensity, and movement of thunderstorms is Doppler Weather Radar from the National Weather Service (NWS). In the first of a two-part series, I’ll explain the basics of radar and introduce the most common types of imagery. Continue reading
A Superstorm Is Born
The remnants of Hurricane Sandy roared ashore near Atlantic City, New Jersey at approximately 7:30 pm on October 29, 2012 with sustained winds of 70 knots and storm surge exceeding 10 feet. Dubbed Superstorm Sandy, it ravaged the coast of New Jersey and New York and produced storm force winds as far west as the Great Lakes.
The weak atmospheric disturbance that would later become Sandy developed over western Africa on October 11. Over the next three weeks, the disturbance slowly strengthened as it travelled west towards the Caribbean. At 8:00 am on October 22, 2012, the National Hurricane Center (NHC) categorized the disturbance as a tropical depression (sustained winds were greater than 34 knots). Remarkably, the storm strengthened from a tropical depression to a tropical storm (sustained winds of 35 – 63 knots) in only six hours. Sandy was declared a hurricane (sustained winds => 64 knots) by the NHC at 8:00 am on October 24, as the storm was approximately 80 nautical miles south of Kingston, Jamaica.