STATION:  SEATTLE-TACOMA INTERNATIONAL AIRPORT (KSEA), WA

CLIMATOLOGICAL SUMMARY.  Period of Record: Jul 1996 to Dec 2008

Summaries based on unedited daily ASOS data.  Errors may be present.

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TEMPERATURE (F)     |   Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov   Dec |   Year
                    |                                                                         |
Avg Max Temp        |  46.5  49.2  52.1  57.6  63.7  68.9  75.7  75.7  69.4  58.6  50.8  45.7 |   59.5
Avg Min Temp        |  36.8  36.7  39.1  41.9  47.4  51.9  56.0  56.0  52.1  45.9  40.1  36.2 |   45.0
Avg Temperature     |  41.6  43.0  45.6  49.7  55.5  60.4  65.8  65.9  60.7  52.2  45.4  40.9 |   52.2
                    |                                                                         |
Extremes:           |                                                                         |
    Extreme Max Temp|    62    62    78    81    90    94    98    92    89    79    65    62 |     98
                    |                                                                         |
    Date of Ext-Day |    19    07    29    16    17    13    11    13    02    09    01    24 |
               -Year|  2005  1998  2004  1999  2008  2002  2007  2002  2006  1996  2008  2005 |
                    |                                                                         |
    Extreme Min Temp|    19    23    28    32    35    42    46    50    42    30    18    14 |     14
                    |                                                                         |
    Date of Ext-Day |    12    18    05    02    07    08    25    31    28    31    28    20 |
               -Year|  2007  2006  1998  1997  2002  2002  2004  1999  1999  2003  2006  2008 |
                    |                                                                         |
Heating Degree Days |   725   622   602   459   299   162    47    35   141   396   587   746 |   4822
Cooling Degree Days |     0     0     0     0     5    23    72    63    13     0     0     0 |    177
                    |                                                                         |
Avg Number of Days: |                                                                         |
    Max Temp >= 90  |   0.0   0.0   0.0   0.0   0.1   0.5   1.2   0.4   0.0   0.0   0.0   0.0 |    2.2
    Max Temp >= 75  |   0.0   0.0   0.1   0.7   2.7   6.3  16.7  16.6   7.3   0.2   0.0   0.0 |   50.5
    Max Temp <= 32  |   0.7   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.1   0.9 |    1.6
                    |                                                                         |
    Min Temp <= 32  |   6.3   5.9   2.3   0.2   0.0   0.0   0.0   0.0   0.0   0.4   3.1   6.7 |   24.9
    Min Temp <= 20  |   0.3   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.2   0.7 |    1.2
    Min Temp  <= 0  |   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0 |    0.0
                    |                                                                         |
Avg Dew Point Temp  |  36.4  35.5  38.4  40.0  45.3  49.2  52.8  53.7  50.8  45.7  40.1  35.8 |   43.6
Avg Wet Bulb Temp   |  39.5  39.7  42.2  44.9  50.0  54.0  58.0  58.5  55.0  48.7  43.0  38.8 |   47.7
                    |                                                                         |
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                    |                                                                         |
Avg Sea Level Pres  | 30.12 30.15 30.10 30.06 30.06 30.05 30.06 30.04 30.03 30.10 30.12 30.16 |  30.09
(Inches of Mercury) |                                                                         |
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                    |                                                                         |
WEATHER             |   Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov   Dec |   Year
See disclaimer below|                                                                         |
                    |                                                                         |
Avg Number of Days: |                                                                         |
    Thunderstorms   |   0.2   0.2   0.7   0.3   0.8   0.8   0.2   0.8   0.1   0.4   0.8   0.2 |    5.5
    Heavy Fog       |   2.8   2.5   0.9   0.4   0.2   0.2   0.4   0.9   2.6   4.4   2.9   4.3 |   22.6
    Fog             |  20.2  14.8  14.4  10.4   9.8   9.2   5.8   7.0  10.7  16.7  16.9  19.2 |  155.0
    Hail            |   0.1   0.3   0.6   0.1   0.1   0.0   0.0   0.0   0.0   0.2   0.5   0.0 |    1.8
                    |                                                                         |
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                    |                                                                         |
PRECIPITATION (In)  |   Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov   Dec |   Year
                    |                                                                         |
Average Monthly     |  6.21  3.05  3.89  2.38  1.77  1.58  0.62  1.06  1.43  3.52  6.74  5.91 |  38.18
                    |                                                                         |
Maximum Daily       |  2.39  1.34  1.86  1.45  0.74  1.16  0.65  1.41  1.19  5.02  3.29  3.77 |   5.02
                    |                                                                         |
    Date of Ext-Day |    17    01    18    13    09    11    16    22    30    20    06    03 |
               -Year|  2005  2000  1997  2002  2000  2001  2001  2001  2007  2003  2006  2007 |
                    |                                                                         |
Avg Number of Days: |                                                                         |
    >= 0.01         |  19.7  15.0  17.9  14.2  12.2  10.4   5.1   5.5   9.1  15.2  18.4  18.5 |  161.1
    >= 0.10         |  14.0   8.2  10.5   7.6   5.6   4.4   2.1   2.7   4.2   7.8  12.5  12.8 |   92.5
    >= 0.25         |   8.4   4.7   5.2   3.0   1.8   2.0   1.1   1.3   1.9   4.9   8.7   7.4 |   50.4
    >= 0.50         |   4.1   1.7   1.8   0.8   0.8   1.0   0.2   0.7   0.6   1.9   4.2   3.5 |   21.3
    >= 1.00         |   0.8   0.2   0.3   0.2   0.0   0.2   0.0   0.2   0.1   0.2   1.5   1.2 |    4.7
                    |                                                                         |
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                    |                                                                         |
WIND (MPH)          |   Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov   Dec |   Year
                    |                                                                         |
Daily Avg Wind Speed|   8.4   8.1   8.3   7.3   7.1   7.0   6.5   6.2   6.2   6.8   7.5   8.4 |    7.3
Daily Avg Max 2-Min |  18.0  17.2  17.9  16.0  14.9  14.5  13.5  13.4  13.7  15.3  16.7  18.3 |   15.8
Daily Avg Peak Gust |  22.4  21.4  22.6  20.0  18.8  18.2  16.8  16.6  17.0  19.1  20.9  23.1 |   19.7
                    |                                                                         |
Maximum Daily Avg   |  17.8  21.4  21.0  16.3  15.2  14.8  12.7  13.3  14.9  17.7  18.6  20.0 |   21.4
                    |                                                                         |
Maximum 2-Minute Avg|    40    39    44    31    30    36    22    24    36    39    37    52 |     52
                    |                                                                         |
Date of Max 2min-Day|    16    07    03    14    18    09    07    29    24    18    24    15 |
               -Year|  2000  2008  1999  2002  2005  2008  1999  2008  1999  2007  1998  2006 |
                    |                                                                         |
Maximum Peak Gust   |    52    53    60    44    40    46    31    29    43    53    48    69 |     69
                    |                                                                         |
Date of Max Gust-Day|    16    07    03    14    18    09    07    09    24    18    24    15 |
               -Year|  2000  2008  1999  2002  2005  2008  1999  2008  1999  2007  1998  2006 |
                    |                                                                         |
Avg Number of Days: |                                                                         |
   Peak Gust >=30   |   6.5   4.6   5.4   2.2   1.2   1.0   0.1   0.0   0.7   3.0   4.8   7.5 |   37.0
   Peak Gust >=40   |   1.2   0.8   1.0   0.3   0.1   0.1   0.0   0.0   0.1   0.4   0.8   1.9 |    6.7
   Peak Gust >=50   |   0.1   0.1   0.3   0.0   0.0   0.0   0.0   0.0   0.0   0.1   0.0   0.2 |    0.8
                    |                                                                         |
   Max 2-Minute >=30|   1.5   1.1   1.0   0.1   0.2   0.1   0.0   0.0   0.1   0.6   1.0   0.0 |    5.6
   Max 2-Minute >=40|   0.1   0.0   0.2   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0 |    0.3
                    |                                                                         |
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Observations of WEATHER may me innacurate due to early ASOS inconsistancies.  Average days
with Thunderstorms may be low due to early mis-detection.

Heavy Fog = Visibility less than or equal to 1/4 mile.
Fog = Visibility greater than 1/4 mile or less than 7 miles.
Peak Gust = Maximum 5-second average.
Snowfall data not observed at ASOS stations.

Copyright ©2009 Western Regional Climate Center - Desert Research Institute - Reno, Nevada.