Rutgers Weather and Climate Monitoring and Weather Forecasting SystemProgram Justification
Dr. David A. Robinson and Dr. Richard H. Dunk31 May 2002
19 April 2002: “Severe Local Storms”
This case study provides strong evidence of the accurate observation, timing, placement, and severity of the extreme heat and severe storms reflected in both the RAMS output and the NJWxNet products. The ETA output has a spatial and temporal resolution (32km grid every 12 hours) too coarse to recognize the existence of local severe storms during the afternoon. However, RAMS was configured for local convection with a spatial and temporal resolution (2km grid every hour) refined enough to recognize individual severe storms.
The 8pm 18 April 2002 RAMS output recognized individual thunderstorms in northern NJ and a powerful squall line by Philadelphia the afternoon of 19 April, as verified by the 5pm radar image. RAMS also recognized the potential for locally severe winds associated with the storms. Newark Airport reported a wind gust of 74mph as the storms moved through the area. The RAMS model accurately depicted the spatial extent and severity of the 19 April 2002 storms 24 hours in advance, with the timing of the event approximately one hour behind the observed storms. For this case the RAMS run clearly captured the fast-moving nature of the convection and resultant high winds as well as reasonably forecasting the local amounts and locations of the scattered precipitation. (Fig. 1 and 2) The corresponding ETA forecast did not forecast the localized convection (and associated high winds) through northern New Jersey for this case. (Fig. 3)
The NJWxNet maps for this case study were constructed using approximately 50 stations including the 10 NWS stations. The local temperature differences would not have been recognized at a county level by the existing NWS stations, especially the central NJ corridor and the coastal zone. Precipitation and wind measurements are known to vary even more than temperature from location to location, especially during extreme events, hence the need for a dense network of stations for monitoring purposes. RAMS forecast the temperatures to drop 20 degrees in one hour with the passage of the storms, which is clearly shown in comparison with the observed NJWxNet temperature values. (Fig. 4)
The NWS could not foresee the localized severe storm potential using the ETA model and only ten stations, as reflected in their forecasts. (Fig. 5) The NJWxNet provided a more accurate depiction of hourly surface conditions resulting from the additional data points. The RAMS model has been reconfigured further since the 4-6 March 2001 event to account for NJ-area characteristics. RAMS predicted the 19 April 2002 severe storm event with a greater precision and accuracy in terms of time, space, and severity than the other two cases. Further improvements in RAMS forecast precision and accuracy are expected with further configuration refinements for the NJ-area and the inclusion of NJWxNet data.
Figures
Figure 1: a) 5pm 19 April 2002 Base Reflectivity radar image, b) 5pm NJWxNet temperatures, note the cooler sea breeze along the coast and cooler values after the storms in NW NJ, and c), d), and e) show the 22-24-hour RAMS forecasts for hourly precipitation rates for 6pm - 8pm 19 April 2002. Note the similarity between the squall line and scattered northern NJ convection in c) the 6pm forecast versus a) the 5pm radar, as well as the quick pace of the storms between c), d) and e).
Figures
Figure 2: 23-hour RAMS forecast wind speed for 7pm 19 April 2002 in a close-up over the northern New Jersey region. This wind pattern indicates strong winds (red = 40+ mph) associated with a thunderstorm pushing through the Newark/New York City area. A 74mph wind gust from a thunderstorm was reported at Newark Airport around 6pm 19 April 2002.
Figures
Figure 3: a) 22-24-hour ETA forecast precipitation for 6pm-8pm 19 April 2002 in a close-up over the Mid-Atlantic region. This rainfall pattern indicates light rain (under 0.10 inches) in northern NJ and the Delaware River valley. b) 24-hr ETA wind forecast for 8pm 19 April 2002 in a close-up view over the Mid-Atlantic region. This wind pattern indicates weak winds (dark blue = under 10 mph) throughout the New Jersey area. A 74mph wind gust from a thunderstorm was reported at Newark Airport around 6pm 19 April 2002.
Figures
Figures
Figure 5: NWS Forecasts issued 19 April 2001 for the evening for selected areas of the state, notice only NE NJ zones called for anything aside from a chance of storms:
NJZ009 - 010 - 012 - 201000 -
HUNTERDON NJ - MIDDLESEX NJ - SOMERSET NJ -
500 PM EDT FRI APR 19 2002
.TONIGHT...A CHANCE OF SHOWERS AND THUNDERSTORMS THIS EVENING... OTHERWISE PARTLY CLOUDY. LOWS IN THE UPPER 50S. SOUTHWEST WINDS 10 TO 15 MPH BECOMING NORTH LATE THIS EVENING. CHANCE OF RAIN 30 PERCENT.
PAZ067>071 - NJZ013 - 015>020 - DEZ001 - MDZ008 - 201000 -
BUCKS PA - BURLINGTON NJ - CAMDEN NJ - CECIL MD - CHESTER PA - DELAWARE PA - GLOUCESTER NJ - MERCER NJ - MONTGOMERY PA - NEW CASTLE DE - OCEAN NJ - PHILADELPHIA PA - SALEM NJ - WESTERN MONMOUTH NJ -
500 PM EDT FRI APR 19 2002
.TONIGHT...PARTLY CLOUDY. A CHANCE OF SHOWERS AND THUNDERSTORMS UNTIL LATE IN THE EVENING OR AROUND MIDNIGHT. LOWS AROUND 60. SOUTHWEST WINDS 10 TO 15 MPH BECOMING NORTH AFTER MIDNIGHT. CHANCE OF RAIN 30 PERCENT.
NJZ005 - 011 - 200950 -
ESSEX - UNION -
350 PM EDT FRI APR 19 2002
.REST OF TODAY...PARTLY CLOUDY. CHANCE OF SHOWERS AND THUNDERSTORMS UNTIL
SUNSET. SOME STORMS MAY CONTAIN SMALL HAIL AND GUSTY WINDS. .TONIGHT...PARTLY CLOUDY. LOWS 55 TO 60. WEST WIND 5 TO 10 MPH BECOMING NORTH.
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