An Evaluation of January Temperature Anomalies in the

United States Utilizing a Synoptic Climatological Approach

Department of Geography, University of Delaware

Center for Climatic ResearchMelissa Malin

Dr. Katrina FrankSteven Quiring

Dr. Laurence Kalkstein

85th AMS Annual MeetingJanuary 15, 2005

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

WestMountain

Great PlainsMidwest

East

Weather DataNational Climatic Data

Center

twice daily4 a.m. & 4 p.m.

Air TemperatureDew Point Temperature

Air Mass DataSpatial Synoptic Classification

daily

Dry Moderate Dry Moderate +

Dry Polar Dry Polar -Dry Tropical Moist Polar

+Moist ModerateMoist Polar Moist TropicalTransition

1948 – 2001December 1 – February 28

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

-1-0.5

00.5

11.5

22.5

33.5

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86Window Number

Ave

rage

Tem

pera

ture

Philadelphia, Pennsylvania

average daily temperatures plotted at each station

-1.5-1

-0.50

0.51

1.52

2.53

3.5

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91

Window Number

Ave

rage

Tem

pera

ture

Philadelphia, Pennsylvania

Winter Trendline

Lower Bound

Upper Bound

the identification of singularities

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

singularity atJanuary 24 -25

the identification of singularities

an example of singularities found at a mountain region station

-4

-3

-2

-1

0

1

2

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86

Window Number

Ave

rage

Tem

pera

ture

Cheyenne, Wyoming

Upper Bound

Winter TrendlineLower Bound

(Thaw)

January 16 - 18

(Freeze)

January 2 - 4

(Thaw)

December 3

Linear MethodSecond-order

MethodMean Method

synoptic analysis

Three techniques were used to detect changes in air mass frequency during Thaw and Freeze events.

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

y = -0.1249x + 22.141R 2 = 0.4111

5

10

15

20

25

30

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85

Window Number

MP+

Fre

quen

cy

Philadelphia, Pennsylvania

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

y = -0.0183x2 + 1.7663x + 1.6291R 2 = 0.6811

0

10

20

30

40

50

60

70

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85

Window Number

DP-

Fre

quen

cy

Philadelphia, Pennsylvania

mean method

•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

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%

finding correlations between temperature differences and frequency differences

Station Window Temp. DM DM+ DP DP- DT MM MP MP+ MT TRProvidence 52 1.16 4.15 -1.14 -17.51 2.32 -0.44 -19.49 1.02 -9.13 -2.39 11.45Portland 52 1.21 2.96 -0.41 -16.57 4.34 -0.62 3.97 6.49 -7.38 -0.04 3.46Syracuse 53 1.61 4.01 -1.05 -11.02 1.10 -0.13 12.71 -0.08 -13.12 6.25 6.09

Providence 53 1.48 5.36 -0.14 -17.51 1.11 -0.46 -21.15 0.00 -9.11 3.61 6.45Richmond 53 1.17 4.33 -3.80 -2.88 -5.52 -2.74 1.83 4.90 -7.06 3.30 8.43

Philadelphia 53 1.11 2.51 -1.24 -14.03 -2.33 6.22 5.07 4.57 -5.52 2.85 8.87Portland 53 1.49 4.04 0.61 -17.53 4.05 -0.60 5.96 4.44 -5.18 1.98 -0.60Syracuse 54 1.54 0.02 -1.03 -9.86 -3.23 -0.13 11.66 5.73 -10.71 6.27 5.04

Providence 54 1.67 2.58 -1.14 -15.50 0.89 -0.47 -24.81 1.99 -7.10 5.71 5.46Richmond 54 1.35 8.47 -0.89 -4.77 -5.61 -2.82 -0.12 1.77 -7.99 4.32 8.42

Philadelphia 54 1.14 2.57 -2.31 -12.88 -3.51 7.28 1.07 5.59 -5.40 4.86 10.86Portland 54 1.56 3.11 0.64 -12.48 0.77 -0.59 7.96 5.40 -5.98 2.01 -2.66

Providence 55 1.35 -2.21 -1.15 -12.50 5.67 0.51 -27.47 1.97 -5.08 3.86 3.47Portland 55 1.35 -3.82 0.66 -7.44 0.48 -0.57 2.95 9.36 -4.78 2.04 -0.72Syracuse 81 1.29 11.28 3.33 -8.56 -22.22 1.93 7.56 -13.39 18.33 8.74 -1.23

Correlation Coefficients -0.09 0.25 -0.12 0.22 -0.42 -0.04 -0.04 -0.23 0.37 -0.44

Eastern Region Thaws and Linear Method Output

Inter- and Intra-Regional Variability of the Thaw

15–17 January

14-16 January 14-17 January

15-17 January26-29 December22-24 January

29 December

24-25 January

23-26 January

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

• found less cohesive January Freeze signal in western US

1 January

4 January3-4 January

2-7 January

28-29 January

(all stations) 5-8 January

26-28 January

Inter- and Intra-Regional Variability of the Freeze

• appears to also progress somewhat systematically eastward

January Thaw

East and West …..No Relationships

Mountain…….Significantly 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)

It appears there is no single

synoptic explanation for the Thaw across

the country.

January Freeze

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)

It appears there is no single

synoptic explanation for

the Freeze across the country.

the Thaw and Freeze are related to variable synoptic conditions rather than a single air

mass typemost conditions observed are generally intuitive

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 relationship between synoptic conditions and singularities is most apparent in the

Central USthe air mass-based methodologies used here did not detect a cause for the Thaw in the East this needs further investigation…