Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261022_1200
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)
=== ===== === ==== ==== === === === ====
Thu 10/22 12Z 0.06 0018  38  18   6 0.00
Thu 10/22 13Z 0.05 0021  43  18   6 0.00
Thu 10/22 14Z 0.05 0021  51  26   5 0.00
Thu 10/22 15Z 0.05 0020  60  33   5 0.00
Thu 10/22 16Z 0.04 0021  69  45   4 0.00
Thu 10/22 17Z 0.05 3522  77  51   4 0.00
Thu 10/22 18Z 0.08 3523  82  48   3 0.00
Thu 10/22 19Z 0.09 3522  85  34   3 0.00
Thu 10/22 20Z 0.10 3523  88  20   2 0.00
Thu 10/22 21Z 0.08 3526  86  15   1 0.00
Thu 10/22 22Z 0.05 3528  80  12   1 0.00
Thu 10/22 23Z 0.05 0028  73  12   1 0.01
Fri 10/23 00Z 0.07 0028  70  14   1 0.00
Fri 10/23 01Z 0.10 0027  68  19   1 0.00
Fri 10/23 02Z 0.15 0126  65  20   1 0.00
Fri 10/23 03Z 0.18 0126  64  12   0 0.00
Fri 10/23 04Z 0.22 0225  61   2   0 0.00
Fri 10/23 05Z 0.27 0226  54   1   0 0.00
Fri 10/23 06Z 0.28 0225  48   2  -1 0.00
Fri 10/23 07Z 0.27 0224  48   2  -1 0.00
Fri 10/23 08Z 0.23 0223  50   3  -1 0.00
Fri 10/23 09Z 0.21 0224  48   2  -1 0.00
Fri 10/23 10Z 0.21 0224  45   1   0 0.00
Fri 10/23 11Z 0.23 0224  38   1   0 0.00
Fri 10/23 12Z 0.23 0222  33   2   0 0.00
Fri 10/23 13Z 0.21 0221  31   3   0 0.00
Fri 10/23 14Z 0.18 0219  33   4   0 0.00
Fri 10/23 15Z 0.17 0217  36   3   0 0.00
Fri 10/23 16Z 0.16 0215  39   2   0 0.00
Fri 10/23 17Z 0.14 0214  41   1   0 0.00
Fri 10/23 18Z 0.12 0212  40   2   1 0.00
Fri 10/23 19Z 0.11 0211  35   2   2 0.00
Fri 10/23 20Z 0.09 0211  31   2   4 0.00
Fri 10/23 21Z 0.08 0211  28   2   4 0.00
Fri 10/23 22Z 0.08 0210  23   2   4 0.00
Fri 10/23 23Z 0.08 0210  20   1   5 0.00
Sat 10/24 00Z 0.08 0209  17   1   5 0.00
Sat 10/24 01Z 0.05 0207  15   2   5 0.00
Sat 10/24 02Z 0.03 0105  14   2   5 0.00
Sat 10/24 03Z 0.03 0004  12   2   5 0.00
Sat 10/24 04Z 0.02 3504  12   2   5 0.00
Sat 10/24 05Z 0.02 3404  11   2   5 0.00
Sat 10/24 06Z 0.05 3304  10   2   4 0.00
Sat 10/24 07Z 0.07 3105   9   2   4 0.00
Sat 10/24 08Z 0.10 3107   8   2   4 0.00
Sat 10/24 09Z 0.12 3108   8   2   4 0.00
Sat 10/24 10Z 0.14 3210   8   1   4 0.00
Sat 10/24 11Z 0.15 3211   8   1   4 0.00
Sat 10/24 12Z 0.14 3211   9   1   4 0.00
Sat 10/24 13Z 0.12 3311  10   1   4 0.00
Sat 10/24 14Z 0.11 3310  10   1   4 0.00
Sat 10/24 15Z 0.11 3209  11   2   4 0.00
Sat 10/24 16Z 0.10 3208  12   3   4 0.00
Sat 10/24 17Z 0.10 3207  13   5   4 0.00
Sat 10/24 18Z 0.12 3106  14  10   4 0.00
Sat 10/24 19Z 0.15 3008  13  14   4 0.00
Sat 10/24 20Z 0.17 3109  12  16   4 0.00
Sat 10/24 21Z 0.16 3109   9  18   5 0.00
Sat 10/24 22Z 0.16 3109   8  22   5 0.00
Sat 10/24 23Z 0.15 3109   8  29   5 0.00

Run total areal avg QPF for the greens is: 0.01 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