An Evaluation of January Temperature Anomalies in the United States Utilizing a Synoptic Climatological Approach. Department of Geography, University of Delaware Center for Climatic Research Melissa Malin Dr. Katrina Frank Steven Quiring Dr. Laurence Kalkstein. 85 th AMS Annual Meeting
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An Evaluation of January Temperature Anomalies in the United States Utilizing a Synoptic Climatological Approach
Department of Geography, University of Delaware
Center for Climatic Research
Dr. Katrina Frank
Dr. Laurence Kalkstein
85th AMS Annual Meeting
January 15, 2005
The January Thaw
has roots in New England weather folklore
“…a characteristic meteorological condition that tends to occur on or near a specific calendar date.” -American Meteorological Society
an anomalous warm spell invading during the coldest time of year
i. identification of a January Thaw signal across the United States
ii. assess the inter- and intra- regional variability of the January Thaw
Can the Thaw be explained synoptically? …through an assessment of air mass frequency
The Goals Of This Investigation....
National Climatic Data Center
4 a.m. & 4 p.m.
Dew Point Temperature
Air Mass Data
Spatial Synoptic Classification
Dry Moderate Dry Moderate +
Dry Polar Dry Polar -
Dry Tropical Moist Polar +
1948 – 2001
December 1 – February 28
average daily temperatures plotted at each station
Methods and Analysis
January 24 -25
January 16 - 18
January 2 - 4
the identification of singularities
an example of singularities found at a mountain region station
Three techniques were used to detect changes in air mass frequency during Thaw and Freeze events.
Station Thaw Observed DM Frequency DM Monthly Mean Frequency
PHL 24 Jan22.5% 21.5%
PWM 23 Jan16.0% 14.5%
PVD 23 Jan20.8% 19.8%
RIC 24 Jan25.5% 26.5%
SYR 24 Jan11.6% 10.5%
Eastern Region Thaws and Linear Method Output
Inter- and Intra-Regional Variability of the Thaw
Inter- and Intra-Regional Variability of the Freeze
Results of Synoptic Analysis....
It appears there is no single synoptic explanation for the Thaw across the country.
East and West …..
Significantly more frequent warm air masses (all)
Significantly less frequent cold air masses(L,M)
Significantly less frequent DP- (S)
Significantly more frequent DP (S)
Significantly more frequent MT (all)
Significantly less frequent DT (all)
Results of Synoptic Analysis....
It appears there is no single synoptic explanation for the Freeze across the country.
Significantly less frequent warm air masses(all)
Significantly more frequent MP(L,S)
Significantly more frequent DP-(L)
Significantly more frequent MP(M)
Significantly more frequent DP-(all)
Significantly less frequent DP(all)
Significantly more frequent DT*(all)
this research provides evidence for the existence of a regionally coherent January Thaw and January Freeze
both show signs of west- east advancement across the US
The Freeze often occurs just prior to the Thaw
the Thaw and Freeze are related to variable synoptic conditions rather than a single air mass type
most conditions observed are generally intuitive
the relationship between synoptic conditions and singularities is most apparent in the Central US
the air mass-based methodologies used here did not detect a cause for the Thaw in the East
this needs further investigation…