Binghamton Severe Weather Climatology

WFO Binghamton, New York
Severe Weather Climatology
Joanne M. LaBounty

1. Introduction

The County Warning Area (CWA) of the Binghamton, New York National Weather Service office covers 24 counties in South Central New York and Northeast Pennsylvania. As a result of the modernization of the National Weather Service (NWS), most of the CWAs of Weather Service Offices (WSOs) Syracuse, Binghamton, and Scranton, Pennsylvania were transferred to the Weather Service Forecast Office (WFO) in Binghamton in 1995.

The sensitivity of the NWS to severe weather is correlated well to the radar system available to NWS personnel. Prior to modernization, the weather office in Binghamton used the WSR-74C, which was a local warning radar. The offices in Syracuse and Scranton did not have NWS radars locally, but utilized the RADID system to dial into the surrounding radars.

2. Topography

Most of the region is part of the Appalachian Mountain system (Fig 1). The eastern part of the region is made up of the Catskill and Pocono mountain regions. In the Catskills, the elevations reach about 4,000 feet. The Poconos Mountains are actually a plateau with the average elevation around 2000 feet. Both the Poconos and Catskills are contained in the Delaware River system. West of the Catskills, along the southern tier of New York and northern tier of Pennsylvania, the land is hilly with the average elevation of the valleys ranging from about 700 to 900 feet. Most of the hilltops in this area run from 1000 to 2000 feet. The Susquehanna and Chemung River systems drain most of the land in this area. The Susquehanna and Chemung Rivers merge in Bradford County Pennsylvania and flow southward into the Wyoming Valley of northeast Pennsylvania which encompasses the Scranton-Wilkes Barre area. In the northern part of the region, lies the Finger Lakes which are characterized by deep glaciated valleys, the western Mohawk Valley and southern Tug Hill Plateau.

3. Data

Most of the data used to develop this severe weather climatology was obtained from the National Climatic Data Center database which can be found under NCDC's web site and the home page for the Tornado Project. The NCDC database dates back to 1950 and runs through November 2001.

A number of tornado climatology studies have pointed out that there are a number of limitations to producing a severe weather climatology. Among these limitations are population density, weather sensitivity of the media and the general public, as well as increased efforts from the NWS, local emergency management officials, and spotter groups to seek out severe weather reports. Studies by Ostby (1993) have suggested that a more reliable climatology study may be found by focusing on the most severe events, such as those with F2 tornado intensities or higher. For the purposes of this study, all tornado events were included.

4. Tornadoes

a) yearly frequency

During the period of record (1950-2001), there were a total of 130 tornadoes, 30 of which were category F2 or greater (Fig. 2 ). These tornadoes caused 7 deaths and 74 injuries throughout central New York and Northeast Pennsylvania. At least one tornado has been reported in every county of the CWA with the exception of Seneca County, NY (Fig. 3). Such factors as population bias and increased emphasis on warning verification have influenced the tornado database (Ostby, 1993). The lack of warning verification may explain the lack of tornado reports throughout the CWA from the 1950s through the 1970s since the NWS began its warning verification program in 1980.

b) monthly frequency

Tornadoes have occurred in every month of the year in the CWA with the exception of December and February (Fig 4). The greatest number occur during the late spring and summer warm seasons with the peak occurring in June, a bit later than the May peak shown by national statistics (Grazulis, 1993). This may because warm, unstable air enters New York and Northern Pennsylvania later in the year due to their northern latitude. Studies by Ostby (1993) and Grazulis (1993) have shown that there is a "second season" of tornadoes that occurs in November in many parts of the United States. Only a slight maximum can be seen in the number of November tornadoes that have taken place in the Binghamton CWA.

c) hourly occurrence

Tornadoes were also categorized by their time of occurrence. A pronounced peak in tornado occurrence is during the afternoon and evening hours with a maximum at 6 o'clock (Fig 5). The least likely time for tornadoes is during the overnight hours from midnight through 9 am. The mid to late afternoon hours have been widely recognized as the peak time of most tornadoes in the United States (Grazulis, 1993). Grazulis (1993) has shown that the peak time nationally for all known tornadoes is between 5 and 6 p.m. However, each state has its own unique diurnal distribution.

d) tornado magnitude

The Fujita scale of tornado intensity (Table 1) is derived from the examination of tornado damage. Of all tornadoes in the Binghamton CWA, the vast majority (77%) have been categorized as weak (F0-F1) and 23% were strong (F2-F3). There has never been a violent tornado (F4-F5) observed in Central New York or Northeast Pennsylvania (Fig. 6). Nationally, those figures are 68% weak, 30% strong and 2% violent. However, it has been shown that because of a number of factors (subjective nature of estimating process, surveying techniques), there is about a 50% chance that there is a one category miscalculation in the F scale rating for any F0 through F4 tornado (Ostby, 1993).

Table 1; Source: Fujita (1981)

e) deaths and injuries

Fortunately, there have been very few deaths or injuries from tornadoes in Central New York and Northeast Pennsylvania. In the 51 year period of record (1950-2001), there have been 7 deaths and 74 injuries (Fig. 7). These deaths and injuries were caused by a total of 16 of the 130 tornadoes. This means that for this area, the percentage of tornadoes with deaths or injuries as a percentage of all tornadoes is about 8%. This is probably largely due to the fact that there has never been a violent tornado experienced in this area. Interestingly, none of the deaths or injuries reported were caused by an F0 tornado, even though one-third (33%) of the tornadoes that have occurred in this area have been classified as F0. The F1, F2, and F3 tornadoes that have occurred have caused roughly the same number of deaths and injuries per category, even though 44% of tornadoes have been classified as F1 and only 9% have been F3. This is surely a testament to the strength of a "severe" versus a "moderate" tornado (see Table 1).

5. Hail

a) yearly distribution

Large hail (>3/4 inch diameter) is a fairly common occurrence throughout the CWA, with reports observed in most years since the 1960s and in every county (Fig 8 & Fig. 9). The number of reports has been increasing significantly since the implementation of the NWS warning verification program in 1980. Nationally, a study by Sammler (1993) has shown that hail reports more than doubled in the decade 1981-1990 from the previous decade, due in large part to this verification program.

b) monthly frequency

The climatology for large hail shows a peak frequency in May, a bit earlier than the June tornado maximum (Fig. 10). The number of events rises drastically from April to May, then drops off steadily until the onset of cooler fall weather. Due to the lack of thunderstorms during the cold months in this area, large hail is almost never seen during the late fall through early spring.

c) hourly occurrence

Like tornadoes, the greatest number of hail events occurs during the afternoon through the early evening hours with a slight peak at 4 o'clock (Fig. 11). The least likely time for hail is during the overnight into the mid morning hours.

d) hail size

Table 3 depicts the size estimation guide that the National Weather Service uses to obtain hail size information from spotters, law enforcement, and the public. The NWS uses a hail size of 3/4 inches or greater to verify a severe thunderstorm. As Figure 12 shows, the large majority of the CWA's hail events have been made up of large hail reports (3/4-1.74 inch diameter). The doubling of hail reports in the last decade, as discussed earlier, has been due to a dramatic rise in the smaller hail category (1 inch or less) since 1980. However, the amount of hail reports greater than 1 3/4 inches has remained nearly constant since 1970. While prior to 1983 the highest percentage of hail reports were in the 1 inch to 1 3/4 inch category, since 1983 hail sizes of 1 inch or less have ballooned to where they now account for over 50 percent of all hail reported (Sammler, 1993).

Table 2

6. Damaging Winds

During July, the dominant severe weather type in the CWA shifts to wind damage (Fig. 13). Nationally, the number of severe wind reports peaks in June and July (Doswell, Kelly and Schaefer, 1983). The National Weather Service defines severe thunderstorm winds as those of 50 knots (58 mph) or greater. As is the case with hail, severe thunderstorm winds are not an uncommon occurrence throughout this area and have occurred in every county in the CWA (Fig. 14). The number of reports has increased significantly since the assumption of CWA responsibility by the Binghamton forecast office (Fig.15). Like the verification for tornadoes, the verification for severe thunderstorm winds is quite subjective. Most often, verification is made by reports of damage rather than actual measured wind speeds.

The same pattern holds true for wind damage as with all the other types of severe weather. The greatest number of severe thunderstorm wind events occurs in the afternoon through early evening hours (peak 4 p.m.), while the least number occurs during the overnight hours (Fig. 16).

7. Conclusion

The purpose of this study was to determine the severe weather climatology across the Binghamton, NY CWA. During the past 20 years, a distinct increase in the number of severe weather events has been reported to the NWS. The increase has been most pronounced in the number of severe wind and hail events. This fact is likely attributable to the increased sensitivity of the WSR-88D radar versus the old radar systems, and to the increased awareness of the NWS, local emergency managers, spotters, and the general public to these events.

It was shown that the occurrence of tornadoes and hail is most frequent from the mid spring to the early summer months of May and June, while the peak time for damaging winds occurs during July. The decrease in tornado events during the peak summer months can likely be attributed to the main westerlies shifting north of the area, and thus decreasing the amount of vertical wind shear. The gradual decrease in hail events during the summer can be attributed to the increase in the height of the freezing level, hence making the atmosphere less favorable for hail development.

Severe weather during the heart of summer (July) in this area is most often due to wind damage. This is most often associated with pulse-severe type thunderstorms that produce locally strong microbursts. As expected, the peak time for all types of severe weather occurs during the afternoon through the early evening hours.

It is hoped that this study will give the staff at NWS Binghamton a better understanding of the severe weather that occurs in the Binghamton forecast area. It is hoped that this, along with future study of severe weather events in this area will help improve the forecast and warning program of NWS Binghamton.

References

Doswell III, C.A., D.L, Kelly and J.T. Schaefer: A Preliminary Climatology of Non-Tornadic Severe Thunderstorm Events. Preprints, 13th Conference on Severe Local Storms, St. Louis, Amer. Meteor. Soc., 25-28.

Fujita, T. T., 1981: Tornadoes and downbursts in the context of generalized planetary scales. J. Atmos. Sci., 38, 1511-1534.

Grazulis, Thomas P., 1993: Significant Tornadoes 1680-1991. Environmental Films, 1326pp.

Ostby, Frederick P., 1993: The Changing nature of tornado climatology. Preprints, 17th Conference on Severe Local Storms, St. Louis, MO, Amer. Meteor. Soc., 1-5.

Sammler, William R., 1993: An updated climatology of large hail based on 1970-1990 data. Preprints, 17th Conference on Severe Local Storms, St. Louis, Amer Meteor. Soc., 32-35.