An Evaluation of January Temperature Anomalies in the United States Utilizing a Synoptic Climatologi

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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
• Melissa Malin
• Dr. Katrina Frank
• Steven Quiring
• Dr. Laurence Kalkstein

85th AMS Annual Meeting January 15, 2005
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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

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The Goals Of This Investigation....

• 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

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US Regions
West
Mountain
East
Great Plains
Midwest
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1948 2001 December 1 February 28
Data

• Weather Data
• National Climatic Data Center
• twice daily
• 4 a.m. 4 p.m.
• Air Temperature
• Dew Point Temperature

• Air Mass Data
• Spatial Synoptic Classification
• daily
• Dry Moderate Dry Moderate
• Dry Polar Dry Polar -
• Dry Tropical Moist Polar
• Moist Moderate
• Moist Polar
• Moist Tropical
• Transition

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Methods and Analysis

• standardized using a five-day moving window
• identified by date of the third day

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the identification of singularities
singularity at January 24 -25

• a second-order polynomial curve fit for winter
  trendline
• upper/ lower bounds set at two standard
  deviations

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the identification of singularities
an example of singularities found at a mountain
region station
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synoptic analysis
Three techniques were used to detect changes in
air mass frequency during Thaw and Freeze
events.
Linear Method Second-order Method Mean Method
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linear method

• useful for air masses that exhibit a general
  frequency trend across a season and for stations
  with winter seasons that extend beyond the period
  examined here

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second-order method

• useful for air masses that do not display such
  general, linear frequency tendencies and may be
  less (more) frequent in early and late winter
  though more (less) prominent throughout the
  middle of the season

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mean method
Station Thaw
Observed DM Frequency DM Monthly Mean
Frequency PHL 24 Jan 22.5
21.5 PWM 23 Jan 16.0
14.5 PVD 23 Jan 20.8
19.8 RIC 24 Jan 25.5
26.5 SYR 24 Jan 11.6
10.5

• useful here because singularity windows are
  scrutinized with only frequencies typical of that
  month and seasonal trends do not contribute to
  calculating the strength of that departure

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finding correlations between temperature
differences and frequency differences
Eastern Region Thaws and Linear Method Output
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Results
Inter- and Intra-Regional Variability of the Thaw

• found rather cohesive January thaw signal in
  every region
• appears to move somewhat systematically across
  the country

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found less cohesive January Freeze signal in
western US
Results
Inter- and Intra-Regional Variability of the
Freeze

• appears to also progress somewhat systematically
  eastward

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Results of Synoptic Analysis....
January Thaw
It appears there is no single synoptic
explanation for the Thaw across the country.
East and West .. No Relationships Mountain. Si
gnificantly more frequent warm air masses
(all) Significantly less frequent cold air
masses (L,M) Great Plains. Significantly less
frequent DP- (S) Significantly more frequent
DP (S) Midwest Significantly more
frequent MT (all) Significantly less frequent
DT (all)
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Results of Synoptic Analysis....
January Freeze
It appears there is no single synoptic
explanation for the Freeze across the country.
West . Significantly less frequent warm air
masses (all) Significantly more frequent
MP (L,S) Mountain Significantly more
frequent DP- (L) Significantly more frequent
MP (M) Great Plains Significantly more
frequent DP- (all) Significantly less frequent
DP (all) Significantly more frequent DT (all)
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Conclusions
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
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