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Soil Table 3: Mean Earth Temperatures, 
Annual Soil Swing, and Phase Constants for U.S. Cities*

Note: The 'Phase Constant' represents the coldest day of the year. 
The warmest day of the year is approximately 6 months (~182 days) after To. 


 
State
City Tm (oC) As(oC) Coldest
Day of Year
To(Days)
Warmest
Day of Year
T1(Days)
AL
Birmingham
18.3
10.6
31
213
  Montgomery
19.4
10.0
31
213
     
AR
Little Rock
17.8
11.7
32
214
AZ
Phoenix
22.8
12.8
33
215
  Tucson
21.1
10.0
34
216
 
 
 
 
 
 
CA
Los Angeles
17.8
3.9
54
 236
 
Merced
20.0
13.9
33
 215
 
San Diego
17.8
3.9
54
 236
 
 
 
 
 
 
CO
Colorado Springs
10.6
11.7
36
 218
 
Denver
11.1
12.2
37
 219
 
Grand Junction
12/8
13.9
32
 214
 
 
 
 
 
 
DC
Washington
13.9
12.2
36
218
 
 
 
 
 
 
FL
Appalachio.
21.1
8.3
36
218
  Jacksonville
21.7
7.8
32
214
 
 
 
 
 
 
GA
Atlanta
16.7
10.6
32
214
 
Augusta
18.3
10.0
30
212
 
Macon
19.4
9.4
33
215
 
 
 
 
 
 
IA
Des Moines
11.1
15.6
35
217
  Sioux City
10.6
16.1
34
216
           
ID
Boise
11.7
11.7
34
216
  Idaho Falls
7.8
12.8
34
216
 
 
 
 
 
 
IL
Chicago
10.6
13.9
37
219
 
E. St. Louis
13.9
13.3
34
216
 
Urbana
11.7
14.4
35
217
 
 
 
 
 
 
IN
Ft. Wayne
11.7
13.3
35
217
 
Indianapolis
12.8
13.3
34
216
 
South Bend
11.1
13.9
37
219
 
 
 
 
 
 
KS
Dodge City
13.9
13.9
35
217
 
Topeka
13.3
14.4
35
217
 
 
 
 
 
 
KY
Louisville
15.6
12.2
33
215

 
State
City Tm (oF) As(oF) Coldest
Day of Year
To(Days)
Warmest
Day of Year
T1(Days)
LA
Lake Charles
21.1
8.9
32
214
  New Orleans
21.1
8.3
32
214
  Shreveport
18.9
10.6
32
214
MA
Portland
8.9
12.2
39
221
  Plymouth
10.6
11.7
43
225
 
 
 
 
 
 
MI
Battle Creek
10.0
13.3
35
217
 
Detroit
10.0
13.9
39
221
 
Sau St. Marie
5.6
14.4
40
222
 
 
 
 
 
 
MN
Duluth
5.0
15.6
37
219
 
Int. Fals
3.9
17.2
34
216
 
Minneapolis
8.3
16.1
35
217
 
 
 
 
 
 
MO
Columbia
13.9
13.3
35
217
Kansas City
14.4
14.4
35
217
Springfield
14.4
12.8
34
216
MS
Biloxi
21.1
9.4
32
214
 
Columbus
18.3
10.6
32
214
Jackson
19.4
10.0
31
213
MT
Billings
9.4
12.8
37
219
 
Great Falls
8.9
12.8
36
218
 
Missoula
7.8
11.7
35
217
 
 
 
 
 
 
NB
Grand Junction
11.1
15.0
35
217
  Lincoln
11.7
15.6
34
216
N. Platte
10.6
14.4
35
217
NC
New Bern
18.3
9.4
35
217
  Greensboro
15.6
11.1
31
213
           
ND
Bismark
6.7
17.2
33
215
  Grand Forks
5.6
18.3
35
217
  Williston
7.2
16.1
34
216
           
 NJ
Trenton
12.8
12.2
38
220
 
 
 
 
 
 
 NM
Albuquerque
15.0
12.2
31
213
 
Roswell
17.2
12.2
30
212
 
 
 
 
 
 
 NY
Albany
10.0
13.9
38
220
 
Binghamton
8.9
13.3
38
220
Niagra Falls
10.0
13.3
24
216
Syracuse
10.0
13.3
38
220
NV
Ely
8.3
12.2
35
217
  Las Vegas
20.6
12.8
32
214
  Winnemucca
11.1
12.2
33
215

 
 
State
City Tm (oF) As(oF) Coldest
Day of Year
To(Days)
Warmest
Day of Year
T1(Days)
OH
Akron
11.1
12.8
37
219
 
Columbus
12.8
12.2
34
216
 
Dayton
13.3
13.3
40
222
 
Toledo
10.6
13.9
36 
218
OK
Altus
18.3
13.3
33
215
 
Oklahoma City
16.7
12.8
34
216
 
Tulsa
16.7
12.8
34
216
 
 
 
 
 
 
OR
Astoria
11.7
5.0
45
227
 
Medford
12.8
9.4
34
216
Portland
12.2
7.2
37
219
PA
Middletown
12.8
12.8
35
217
  Philadelphia
12.8
12.2
34
216
 
Pittsburg
11.1
12.8
36
218
Wilkes-Barre
11.1
12.8
36
218
SC
Charleston
18.9
8.9
32
214
 
Greenville
16.7
10.6
33
215
 
Sumpter
18.3
10.0
32
214
 
 
 
 
 
 
SD
Huron
8.3
16.7
35
217
  Rapid City
10.0
13.9
38
220
           
TN
Bristol
15.0
11.1
32
214
  Knoxville
16.1
11.7
31
213
 
Memphis
17.2
11.7
32
214
Nashville
15.6
11.7
32
214
TX
El Paso
18.9
11.1
28
210
 
Ft. Worth
20.0
11.7
34
216
  Houston
21.7
8.9
33
215
 
San Antonio
22.2
8.9
32
214
 
 
 
 
 
 
UT
Salt Lake City
11.7
13.3
35
217 
VA
Norfolk
16.1
11.1
37
219
Richmond
15.6
10.6
33
215
Roanoke
15.0
11.1
33
215
VT
Burlington
7.8
14.4
37
219
WA
Moses Lake
11.7
12.8
29
211
Seattle
11.7
6.7
36
218
  Spokane
9.4
11.7
32
214
           
WI
Green Bay
7.8
14.4
37
219
  Madison
9.4
15.0
36
218
           
WV
Charleston
14.4
11.1
33
215
  Elkins
11.1
11.1
32
214
           
WY
Casper
9.4
13.3
37
219
  Cheyenne
8.9
11.7
39
221
  Lander
7.8
13.3
38
220
  Sheridan
8.9
13.3
35
217

 
*Adapted from Closed-Loop/Ground-Source Heat Pump Systems Installation Guide.  NRECA Research Project 86-1.  Oklahoma State University.  1988. and Perry, Robert H. and Chilton, Cecil H. Chemical Engineer's Handbook. 5th Ed. New York, McGraw Hill Book Company, 1973.

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