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Humidity & snowmelt increasing

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  • patneuman2000 <npat1@juno.com>
    Humidity and snowmelt rates are increasing 1) Average humidity (dewpoint deg. F) Midwest & Great Plains 1948-1997 __ 1998-2002 _ Diff. __ 39.1 _______ 41.5
    Message 1 of 1 , Feb 21, 2003
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      Humidity and snowmelt rates are increasing

      1) Average humidity (dewpoint deg. F)
      Midwest & Great Plains

      1948-1997 __ 1998-2002 _ Diff.
      __ 39.1 _______ 41.5 ____ 2.4 __ CHICAGO1958
      __ 39.5 _______ 42.5 ____ 3.0 __ MOLINE 1948
      __ 40.9 _______ 43.7 ____ 2.8 __ PEORIA 1948
      __ 42.6 _______ 44.4 ____ 1.8 __ SPRINGF1948

      __ 45.5 _______ 47.4 ____ 1.9 __ EVANSV 1948
      __ 40.6 _______ 42.8 ____ 2.2 __ FORTWA 1948
      __ 42.7 _______ 44.7 ____ 2.0 __ INDIAN 1948
      __ 40.4 _______ 41.9 ____ 1.5 __ SOUTHB 1948

      __ 39.0 _______ 41.4 ____ 2.4 __ DESMOi 1945
      __ 37.3 _______ 40.2 ____ 2.8 __ DUBUQu 1951
      __ 36.4 _______ 38.9 ____ 2.5 __ MASONC 1948
      __ 37.6 _______ 40.1 ____ 2.5 __ SIOUXC 1948

      __ 42.9 _______ 45.0 ____ 2.1 __ COVING 1948
      __ 43.9 _______ 46.2 ____ 2.3 __ LEXINGT1948
      __ 45.3 _______ 47.6 ____ 2.3 __ LOUISV 1948

      __ 34.5 _______ 37.0 ____ 2.5 __ ALPENA 1959
      __ 38.9 _______ 40.5 ____ 1.6 __ DETROI 1948
      __ 38.2 _______ 41.0 ____ 2.8 __ FLINT 1948
      __ 38.5 _______ 41.2 ____ 2.7 __ MUSKEG 1948
      __ 36.2 _______ 38.5 ____ 2.3 __ TRAVEC 1948

      __ 29.4 _______ 31.9 ____ 2.5 __ DULUTH 1948
      __ 27.8 _______ 31.6 ____ 3.8 __ INTERF 1948
      __ 34.2 _______ 37.3 ____ 3.1 __ MINNEA 1945

      __ 43.2 _______ 45.7 ____ 2.5 __ COLUMB 1948
      __ 44.7 _______ 46.7 ____ 2.0 __ SPR MO 1948
      __ 44.3 _______ 46.6 ____ 2.3 __ ST_LOU 1945

      __ 39.6 _______ 42.4 ____ 2.8 __ OMAHA_ 1948

      __ 31.6 _______ 34.2 ____ 2.6 __ FARGO_ 1948

      __ 40.5 _______ 43.1 ____ 2.6 __ CLEVEL 1948
      __ 41.8 _______ 43.0 ____ 1.2 __ COLUMB 1948
      __ 41.5 _______ 43.0 ____ 1.5 __ DAYTON 1948
      __ 39.9 _______ 41.8 ____ 2.1 __ TOLEDO 1946

      __ 39.7 _______ 41.7 ____ 2.0 __ PITTSB 1945

      __ 34.8 _______ 37.7 ____ 2.9 __ SIOUXF 1948

      __ 45.3 _______ 46.2 ____ 0.9 __ BRISTOL
      __ 50.0 _______ 51.3 ____ 1.3 __ MEMPHI 1948
      __ 48.3 _______ 49.1 ____ 0.8 __ NASHVI 1948

      __ 43.9 _______ 46.0 ____ 2.1 __ CHARLE 1949

      __ 34.0 _______ 36.7 ____ 2.7 __ EAU_CL 1949
      __ 35.4 _______ 38.3 ____ 2.9 __ GREENB 1949
      __ 36.5 _______ 38.9 ____ 2.4 __ LA_CRO 1948
      __ 36.7 _______ 39.2 ____ 2.5 __ MADISO 1948
      __ 37.6 _______ 40.1 ____ 2.5 __ MILWAU 1948

      Average Difference(Diff) 2.4 43 stations
      (15 states)

      Data obtained from the Midwest Climate Center (MCC)
      Beginning date after station name, 1995 msg at Pittsburgh

      Dewpoints have been increasing as air temperatures warm.
      On average, dewpoints in the Midwest increased 2.7 deg.F
      for the last five year period (1998-2002) versus a 50 year
      average basic period (1948-1997).
      Pat Neuman 2/21/2003

      2) Snowmelt rate increases as humidity increases

      Even if there were no change in the measured air temperatures
      at a location, the rate of snowmelt can increase as the
      humidity (dewpoint) increases at that location.

      For example, assume two separate days each with the same
      snow pack at isothermal conditions at 32 deg. F., each day
      having a mean temperature of 40 deg. F. Holding everything
      else but dewpoint the same, a day with a mean dewpoint of
      30 deg. F. would have at least double the melt versus a
      different day with a mean dewpoint of 26 deg. F.(melt would
      be .24 in. versus .10 in., according to the formula and table
      given below.

      Table showing effect of dewpoint change on rate of snowmelt

      _Td__ 26 __ 30 __ 34 __ 38
      Ta
      40 __.10 __.24 __.38 __.52
      48 __.42 __.56 __.70 __.84

      Ta = air temperature F
      Td = dewpoint F
      M = snowmelt, in./day (in body of table shown above)

      Equation for rate of snowmelt:
      * M = 0.074 (0.53Ta' + 0.47Td'):
      Ta' = difference: Ta at 10ft & snow surface temperature.
      Td' = difference: Td at 10ft & snow surface dewpoint.
      Ta' & Td are mean daily temperatures.

      Assumptions:
      _ Heavily forested area (> 80 percent cover).
      _ Snow pack assumed to be isothermal at 32 deg. F
      _ Snow pack has 3 per cent free-water content.
      _ Loss by forest transpiration = short-wave radiation melt

      * From: Ven Te Chow, Handbook of Applied Hydrology,
      1964, 10-40, Ref. 23, Runoff from Snowmelt", U.S. Army
      Corps of Engineers, Engineering and Design Manuals,
      EM 1110-2-1406, Jan. 5, 1960.

      Pat Neuman (Self)
      Chanhassen, MN
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