NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260920_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 09/20 06Z 0.20 2015  78  16   6 0.00
Sun 09/20 07Z 0.21 2015  81  21   6 0.00
Sun 09/20 08Z 0.18 2015  85  34   6 0.00
Sun 09/20 09Z 0.14 1915  86  62   7 0.00
Sun 09/20 10Z 0.13 1917  89  76   6 0.00
Sun 09/20 11Z 0.14 1918  91  85   6 0.00
Sun 09/20 12Z 0.11 1919  93  92   6 0.01
Sun 09/20 13Z 0.10 1819  94  98   6 0.02
Sun 09/20 14Z 0.09 1818  94  99   6 0.05
Sun 09/20 15Z 0.06 1817  95  99   6 0.06
Sun 09/20 16Z 0.06 1816  97  99   7 0.06
Sun 09/20 17Z 0.08 1916  97  99   7 0.06
Sun 09/20 18Z 0.11 1916  98  99   7 0.05
Sun 09/20 19Z 0.12 1916  98  99   7 0.05
Sun 09/20 20Z 0.12 1916  98  99   8 0.05
Sun 09/20 21Z 0.12 1914  98  92   8 0.05
Sun 09/20 22Z 0.10 1913  98  68   8 0.04
Sun 09/20 23Z 0.11 2011  99  62   7 0.03
Mon 09/21 00Z 0.09 1907  99  58   7 0.02
Mon 09/21 01Z 0.08 2104  99  49   7 0.01
Mon 09/21 02Z 0.06 2801  99  42   6 0.01
Mon 09/21 03Z 0.04 0102  96  43   6 0.00
Mon 09/21 04Z 0.03 0005  95  41   6 0.00
Mon 09/21 05Z 0.04 0008  93  32   6 0.00
Mon 09/21 06Z 0.04 0010  90  18   6 0.00
Mon 09/21 07Z 0.06 0012  89   8   6 0.00
Mon 09/21 08Z 0.06 0013  89   3   5 0.01
Mon 09/21 09Z 0.07 0015  90   2   5 0.01
Mon 09/21 10Z 0.07 0017  90   2   4 0.01
Mon 09/21 11Z 0.09 0018  90   2   4 0.01
Mon 09/21 12Z 0.10 0017  89   2   3 0.00
Mon 09/21 13Z 0.07 0017  86   2   3 0.00
Mon 09/21 14Z 0.04 0016  82   3   3 0.00
Mon 09/21 15Z 0.04 0013  79   2   3 0.00
Mon 09/21 16Z 0.05 0012  72   2   4 0.00
Mon 09/21 17Z 0.06 0112  67   2   4 0.00
Mon 09/21 18Z 0.07 0112  62   1   4 0.00
Mon 09/21 19Z 0.09 0112  56   2   4 0.00
Mon 09/21 20Z 0.10 0212  52   2   5 0.00
Mon 09/21 21Z 0.08 0111  52   2   5 0.00
Mon 09/21 22Z 0.09 0211  51   2   5 0.00
Mon 09/21 23Z 0.13 0311  48   2   5 0.00
Tue 09/22 00Z 0.15 0312  46   2   5 0.00
Tue 09/22 01Z 0.18 0412  43   2   6 0.00
Tue 09/22 02Z 0.20 0412  43   2   5 0.00
Tue 09/22 03Z 0.21 0512  42   2   5 0.00
Tue 09/22 04Z 0.20 0610  44   2   5 0.00
Tue 09/22 05Z 0.18 0708  47   2   4 0.00
Tue 09/22 06Z 0.16 0807  50   2   4 0.00
Tue 09/22 07Z 0.15 0906  52   2   4 0.00
Tue 09/22 08Z 0.13 1105  57   2   3 0.00
Tue 09/22 09Z 0.15 1106  60   3   3 0.00
Tue 09/22 10Z 0.15 1106  63   3   3 0.00
Tue 09/22 11Z 0.13 1105  65   3   2 0.00
Tue 09/22 12Z 0.14 1005  66   3   2 0.00
Tue 09/22 13Z 0.14 0905  66   3   3 0.00
Tue 09/22 14Z 0.17 0806  65   3   3 0.00
Tue 09/22 15Z 0.16 0606  67   3   3 0.00
Tue 09/22 16Z 0.19 0606  70   3   2 0.00
Tue 09/22 17Z 0.25 0506  71   3   2 0.00

Run total areal avg QPF for the greens is: 0.61 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1