Mt. Whitney Portal Store & Hostel Forums General Mt. Whitney Portal Store Message Board A Test of Temp Forecast Near Whitney Zone

I was curious about how reliable the National Weather Service (NWS) forecast is for forecasting temperatures in the Whitney Zone so I decided to make a test. It involves comparing the NWS forecasted temperatures with the temperatures that are measured by the California Department of Water Resources at one of their automated stations. Although there isn't a station in the Whitney Zone, there is one in the Cottonwood Lakes area which is nearby, about 14 miles south of Mt. Whitney.

The table below contains the NWS forecast for lat 36.483, long -118.177 (i.e. for the Cottonwood Lakes Station) that was last updated 3:43 am PDT Tues Aug 21, 2007, and the Cottonwood Lakes station (CWD) temperature measurements that were taken afterwards.

                   high,ºF          low,ºF      
                NWS  CWD  dev    NWS  CWD  dev

Tue 8-21-07     69   73    -4    47   48    -1         
                          
Wed 8-22-07     69   75    -4    45   43    +2
     
Thu 8-23-07     67   69    -2    42   40    +2
     
Fri 8-24-07     71   73    -2    47   40    +7
     
Sat 8-25-07     71   71     0    48   39    +9
      
Sun 8-26-07     71   61   +10    48   46    +2
      
Mon 8-27-07     69   63    +6                                  

The "low" column is the overnight low that occurs from sunset of the given date to sunrise of the next morning.
The "dev" columns are the deviations of the forecast from the measured temp, i.e. dev = NWS - CWD .

The altitude of 10,430' for the NWS forecast is a little higher than the altitude of 10,150' of the Cottonwood Lakes Station. This may contribute a slight error to the NWS forecast that would tend to underestimate the temperature by roughly 1ºF.

NWS forecast last updated 3:19 am PDT Sun Sep 2, 2007:

                   high,ºF          low,ºF      
                NWS  CWD  dev    NWS  CWD  dev

Sun 9-2-07      73   70    +3    47   39    +8               
                          
Mon 9-3-07      72   69    +3    44   46    -2      
     
Tue 9-4-07      70   69    +1    40   32    +8 
     
Wed 9-5-07      64   63    +1    39   34    +5      
     
Thu 9-6-07      65   65     0    41   35    +6
      
Fri 9-7-07      64   68    -4    42   36    +6     
      
Sat 9-8-07      65   63    +2                                   

NWS forecast last updated 8:47 pm PDT Thu Sep 13, 2007:

                   high,ºF          low,ºF      
                NWS  CWD  dev    NWS  CWD  dev

Fri 9-14-07     66   59    +7    31   27    +4                      
                          
Sat 9-15-07     60   61    -1    34   26    +8         
     
Sun 9-16-07     55   58    -3    36   25   +11     
     
Mon 9-17-07     55   52    +3    39   25   +14           
     
Tue 9-18-07     57   59    -2    40   39    +1   
      
Wed 9-19-07     56   49    +7    34   22   +12          
      
Thu 9-20-07     53   33   +20                                                  

================================================================

              SUMMARY OF THE THREE SETS OF DATA

                        largest |dev|'s

                   high,ºF          low,ºF      
     day        NWS  CWD  dev    NWS  CWD  dev

     one        66   59    +7    47   39    +8               
                          
     two        69   75    -4    34   26    +8      
     
     three      55   58    -3    36   25   +11 
     
     four       55   52    +3    39   25   +14      
     
     five       57   59    -2    48   39    +9
      
     six        71   61   +10    34   22   +12    
      
     seven      53   33   +20                                   

Some personal observations:

1) Note that in general, the more days into the future the forecast, the less accurate it is expected to be. This isn't obvious from a cursory look at the data.

2) For the worst case in the first 2 days, the temperature was 8ºF colder than forecasted. For the worst case in days 3-4, the temperature was 14ºF colder than forecasted. For the worst case in days 5-7, the temperature was 20ºF colder than forecasted.