NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260920_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 09/20 18Z 0.25 1920  99  99   7 0.00
Sun 09/20 19Z 0.29 2019  99  99   7 0.06
Sun 09/20 20Z 0.31 2018  99  99   7 0.11
Sun 09/20 21Z 0.29 2116  99  99   7 0.10
Sun 09/20 22Z 0.27 2213  99  99   8 0.06
Sun 09/20 23Z 0.21 2409  99  95   8 0.03
Mon 09/21 00Z 0.12 2905  99  82   8 0.01
Mon 09/21 01Z 0.03 3405  98  64   7 0.00
Mon 09/21 02Z 0.04 0006  97  49   7 0.00
Mon 09/21 03Z 0.07 0008  93  41   7 0.00
Mon 09/21 04Z 0.08 0108  88  32   7 0.00
Mon 09/21 05Z 0.09 0110  81  18   7 0.00
Mon 09/21 06Z 0.09 0011  75   8   7 0.00
Mon 09/21 07Z 0.10 0014  70   2   7 0.00
Mon 09/21 08Z 0.12 0016  68   0   6 0.00
Mon 09/21 09Z 0.14 0017  76   1   6 0.00
Mon 09/21 10Z 0.15 0018  85   2   5 0.00
Mon 09/21 11Z 0.18 0019  88   2   5 0.01
Mon 09/21 12Z 0.20 0118  91   2   4 0.01
Mon 09/21 13Z 0.20 0116  90   2   4 0.01
Mon 09/21 14Z 0.15 0115  85   2   4 0.01
Mon 09/21 15Z 0.15 0114  81   1   5 0.00
Mon 09/21 16Z 0.17 0113  78   1   5 0.00
Mon 09/21 17Z 0.18 0212  75   2   5 0.00
Mon 09/21 18Z 0.21 0212  71   2   5 0.00
Mon 09/21 19Z 0.19 0211  68   2   5 0.00
Mon 09/21 20Z 0.18 0210  66   2   5 0.00
Mon 09/21 21Z 0.18 0211  60   2   5 0.00
Mon 09/21 22Z 0.19 0212  54   2   5 0.00
Mon 09/21 23Z 0.19 0213  50   3   5 0.00
Tue 09/22 00Z 0.20 0313  46   3   5 0.00
Tue 09/22 01Z 0.24 0314  46   3   5 0.00
Tue 09/22 02Z 0.26 0413  49   3   5 0.00
Tue 09/22 03Z 0.26 0513  47   3   5 0.00
Tue 09/22 04Z 0.21 0609  52   3   5 0.00
Tue 09/22 05Z 0.21 0709  56   3   5 0.00
Tue 09/22 06Z 0.18 0707  61   3   4 0.00
Tue 09/22 07Z 0.15 0806  66   3   3 0.00
Tue 09/22 08Z 0.15 0706  68   3   3 0.00
Tue 09/22 09Z 0.15 0805  70   3   3 0.00
Tue 09/22 10Z 0.16 0805  69   3   3 0.00
Tue 09/22 11Z 0.16 0705  68   3   2 0.00
Tue 09/22 12Z 0.17 0606  67   3   2 0.00
Tue 09/22 13Z 0.18 0507  63   3   3 0.00
Tue 09/22 14Z 0.19 0408  62   3   2 0.00
Tue 09/22 15Z 0.23 0409  62   3   3 0.00
Tue 09/22 16Z 0.29 0509  64   3   2 0.00
Tue 09/22 17Z 0.61 0507  68   4   1 0.00
Tue 09/22 18Z 1.39 0507  69   5   1 0.00
Tue 09/22 19Z 1.65 0506  70   7   2 0.00
Tue 09/22 20Z 1.66 0506  71   9   2 0.00
Tue 09/22 21Z 1.43 0406  73  12   2 0.00
Tue 09/22 22Z 0.99 0507  73  14   2 0.00
Tue 09/22 23Z 0.74 0509  73  15   2 0.00
Wed 09/23 00Z 0.66 0610  75  16   2 0.00
Wed 09/23 01Z 0.63 0612  73  19   2 0.00
Wed 09/23 02Z 0.72 0714  69  22   2 0.00
Wed 09/23 03Z 0.81 0816  68  27   2 0.00
Wed 09/23 04Z 0.78 0918  66  28   2 0.00
Wed 09/23 05Z 0.74 0920  62  31   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.41 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