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199904,0.280
199905,0.150
199906,-0.130
199907,0.577
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199910,0.443
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200505,1.103
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200508,0.927
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200511,0.507
200512,0.350
200601,0.567
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200603,0.023
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200608,0.280
200609,-0.610
200610,-0.603
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200701,0.830
200702,0.270
200703,0.447
200704,0.457
200705,0.270
200706,0.590
200707,1.270
200708,2.023
200709,1.470
200710,1.040
200711,0.460
200712,0.170
200801,0.107
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200806,-0.173
200807,-0.310
200808,0.647
200809,0.967
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200811,0.187
200812,0.103
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200903,-0.587
200904,-0.463
200905,-0.007
200906,0.330
200907,0.740
200908,1.053
200909,0.790
200910,0.643
200911,0.327
200912,0.600
201001,0.723
201002,1.283
201003,1.380
201004,0.877
201005,0.137
201006,0.090
201007,0.767
201008,1.280
201009,1.413
201010,0.767
201011,-0.273
201012,-0.443
201101,-0.690
201102,0.133
201103,-0.827
201104,-0.237
201105,-0.393
201106,0.020
201107,0.430
201108,0.217
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201110,-0.193
201111,0.067
201112,0.057
201201,0.570
201202,0.487
201203,0.337
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201206,-0.360
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201208,-0.250
201209,-0.590
201210,-0.900
201211,-1.097
201212,-0.520
201301,-0.003
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201303,-0.357
201304,-0.627
201305,-0.783
201306,-0.367
201307,-0.257
201308,0.067
201309,0.057
201310,-0.327
201311,-0.793
201312,-0.357
201401,-0.280
201402,-0.063
201403,-0.303
201404,-0.240
201405,-0.657
201406,-0.410
201407,0.300
201408,1.117
201409,1.083
201410,0.853
201411,0.747
201412,0.653
201501,0.590
201502,0.193
201503,-0.140
201504,-0.320
201505,-0.170
201506,0.057
201507,0.090
201508,-0.153
201509,0.457
201510,0.373
201511,0.797
201512,0.737
201601,1.363
201602,1.343
201603,0.897
201604,0.053
201605,-0.297
201606,-0.320
201607,-0.340
201608,-0.090
201609,0.243
201610,1.027
201611,0.773
201612,0.167
201701,-0.330
201702,-0.123
201703,0.020
201704,-0.027
201705,0.377
201706,0.773
201707,0.903
201708,0.403
201709,-0.133
201710,-0.860
201711,-0.560
201712,-0.513
201801,-0.410
201802,-0.990
201803,-1.317
201804,-1.123
201805,-0.517
201806,-0.397
201807,0.380
201808,0.547
201809,0.930
201810,0.590
201811,0.390
201812,0.400
201901,-0.25
201902,-0.453
201903,-0.873
201904,-0.353
201905,-0.257
201906,0.230
201907,0.673
201908,1.133
201909,0.603
201910,0.193
201911,-0.387
201912,-0.380
202001,-0.380
202002,-1.143
202003,-1.287
202004,-1.173
202005,-0.083
202006,0.777
202007,1.287
202008,1.200
202009,0.437
202010,-0.093
202011,0.137
202012,0.360
Monthly values for the Pacific-North America Pattern index. During the positive phase, temperatures across the U.S. tend to be sharply split between a warm West and a cool East. In the negative phase, the West is often cooler-than-average while the East is warmer than average.
Air pressure in the lower atmosphere compared to the 1981-2010 average during February 2016 (top), when the PNA was positive, and in February 2019 (bottom), when it was negative. The location of highs and lows and the flow of the jet stream around them often produce a sharp warm-cold split in temperatures in the western and eastern halves of the United States.
Monthly average values for the Pacific-North America Pattern index. During the positive phase, temperatures across the U.S. tend to be sharply split between a warm West and a cool East. In the negative phase, the West is often cooler than average while the East is warmer than average. NOAA Climate.gov image, based on data from NOAA CPC.
The Pacific-North American atmospheric pattern has two phases. The top map shows pressure patterns in February 2016 compared to the 1981-2020 average (positive phase), and the bottom shows February 2019 (negative phase). The location of highs and lows and the flow of the jet stream around them often produce a sharp warm-cold split in temperatures in the western and eastern halves of the United States. The negative phase is also linked to favorable conditions for tornado outbreaks. NOAA Climate.gov, based on data from the Physical Science Lab.