NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260922_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)
=== ===== === ==== ==== === === === ====
Tue 09/22 18Z 0.51 0603  91   4   3 0.00
Tue 09/22 19Z 0.58 0605  91   3   3 0.00
Tue 09/22 20Z 1.17 0706  88   4   3 0.00
Tue 09/22 21Z 0.86 0607  88   5   3 0.00
Tue 09/22 22Z 0.64 0608  90   5   3 0.00
Tue 09/22 23Z 0.58 0610  90   7   3 0.00
Wed 09/23 00Z 0.62 0613  90   8   3 0.00
Wed 09/23 01Z 0.71 0714  90   9   3 0.00
Wed 09/23 02Z 0.79 0815  89   9   3 0.00
Wed 09/23 03Z 0.76 0916  85   9   3 0.00
Wed 09/23 04Z 0.73 0916  83   8   3 0.00
Wed 09/23 05Z 0.68 0917  76   9   3 0.00
Wed 09/23 06Z 0.63 0918  68  11   4 0.00
Wed 09/23 07Z 0.61 0818  64  12   4 0.00
Wed 09/23 08Z 0.57 0818  59  12   4 0.00
Wed 09/23 09Z 0.54 0818  56  13   4 0.00
Wed 09/23 10Z 0.54 0819  54  14   4 0.00
Wed 09/23 11Z 0.55 0819  53  15   4 0.00
Wed 09/23 12Z 0.58 0820  55  17   4 0.00
Wed 09/23 13Z 0.59 0820  59  17   4 0.00
Wed 09/23 14Z 0.57 0920  58  17   4 0.00
Wed 09/23 15Z 0.54 0918  53  16   4 0.00
Wed 09/23 16Z 0.53 0815  56  12   4 0.00
Wed 09/23 17Z 0.56 0814  58  10   4 0.00
Wed 09/23 18Z 0.75 0812  60   9   4 0.00
Wed 09/23 19Z 0.91 0810  64  10   4 0.00
Wed 09/23 20Z 1.02 0810  67  13   4 0.00
Wed 09/23 21Z 0.75 0710  66  13   4 0.00
Wed 09/23 22Z 0.56 0711  64  11   4 0.00
Wed 09/23 23Z 0.52 0712  63   7   4 0.00
Thu 09/24 00Z 0.51 0713  62   5   5 0.00
Thu 09/24 01Z 0.50 0714  61   4   5 0.00
Thu 09/24 02Z 0.46 0715  55   3   5 0.00
Thu 09/24 03Z 0.43 0715  49   3   6 0.00
Thu 09/24 04Z 0.42 0716  44   2   6 0.00
Thu 09/24 05Z 0.39 0716  39   2   7 0.00
Thu 09/24 06Z 0.36 0715  35   2   7 0.00
Thu 09/24 07Z 0.36 0716  31   2   7 0.00
Thu 09/24 08Z 0.35 0716  31   2   7 0.00
Thu 09/24 09Z 0.33 0715  33   2   7 0.00
Thu 09/24 10Z 0.31 0715  32   2   7 0.00
Thu 09/24 11Z 0.31 0715  28   2   8 0.00
Thu 09/24 12Z 0.32 0715  27   2   8 0.00
Thu 09/24 13Z 0.33 0715  26   2   8 0.00
Thu 09/24 14Z 0.32 0715  24   3   8 0.00
Thu 09/24 15Z 0.31 0814  26   2   8 0.00
Thu 09/24 16Z 0.30 0712  27   2   8 0.00
Thu 09/24 17Z 0.31 0711  28   2   8 0.00
Thu 09/24 18Z 0.33 0711  31   2   8 0.00
Thu 09/24 19Z 0.36 0711  34   2   8 0.00
Thu 09/24 20Z 0.37 0711  39   1   8 0.00
Thu 09/24 21Z 0.37 0711  42   2   8 0.00
Thu 09/24 22Z 0.41 0613  43   1   8 0.00
Thu 09/24 23Z 0.43 0514  46   1   7 0.00
Fri 09/25 00Z 0.42 0515  46   1   8 0.00
Fri 09/25 01Z 0.40 0516  40   2   9 0.00
Fri 09/25 02Z 0.43 0618  35   2   9 0.00
Fri 09/25 03Z 0.43 0618  31   2   9 0.00
Fri 09/25 04Z 0.40 0618  22   2  10 0.00
Fri 09/25 05Z 0.38 0618  16   2  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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