The Variability of Cold Front Precipitation

Abstract

Radar data are utilized to describe the precipitation patterns with 30 summertime cold fronts in the vicinity of Cambridge, Massachusetts. An attempt to relate the precipitation type and coverage to synoptic parameters which can be obtained from the conventional meteorological charts yielded essentially negative results. Possible causes of the precipitation variability are discussed.t Entered as second class matter September 24, 1945, at the Post Office at Lancaster, Pennsylvania, under the Act of August 24, 1912. Acceptance for mailing at special rate of postage provided for in paragraph (d-2), section 34.40, P. L. and R. of 1948, authorized September 24, 1945. Address all business communications, purchase orders and inquiries regarding the Society to the Executive Secretary,

The Distribution and Variability of Cold-Front Precipitation1

“…This investigation has been concerned with the relationship of certain meteorological parameters to the maximum areal coverage of the SCR-615-B and AN/CPS-9 radars and to the average precipitation amounts within the range of such radars during periods of wintertime cold-front activity. As was shown by Austin and Blackmer [ 1 ] and substantiated herein, the synoptic tools available to the forecasters, at least the largescale parameters considered, are inadequated to describe the character and general extent of the cold-front precipitation. This lack of correlation may be due to the difference in size of the synoptic (macro) scale and the radar (meso) scale.…”

“…In a previous investigation by Austin and Blackmer [1], it was found that no strong relationship exists between precipitation estimates of summertime cold fronts and any synoptic parameter tested. The reason for pursuing a similar study with winter cold fronts is that the probability of convective-type precipitation is con- 1 Based on the M.S. Thesis, Dept.…”

“…The cold fronts were classified into three synoptic types after those of Austin and Blackmer [1] : Type A -fronts approach the station from the northwest and are oriented in a northeast-southwest direction ; Type B-fronts are north-south fronts associated with a sharp trough; Type C-fronts are characterized by no northwest flow behind the front.…”

“…1. the sea-level temperature decrease two hours after frontal passage at Boston, 2. the Gardner-Scherhag Instability Index [2] in the warm air prior to front passage, 3. the difference in the 1000-to 500-mb thickness gradient [3] ahead and behind the front at the latitude of Boston, 4. the angle between the orientation of the front and the 700-mb wind [4] at the latitude of Boston, 5. the thermal advection [1] in the warm air, 6. the 850-mb temperature-dew point spread in the warm air, 7. the speed of the front, and 8. average rain-gauge precipitation amounts within radar range of Boston during period of frontal activity. Items 2, 5, and 6 were ascertained from upperair observations taken at Nantucket, Massachusetts prior to but as near the time of frontal passage as possible.…”

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“…(CLEM and MOXON 1950, AUSTIN and BLACKMER 1956, LEACH 1957, many more interesting observations are hidden in scientific progress reports. )…”