Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260923_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)
=== ===== === ==== ==== === === === ====
Wed 09/23 12Z 0.44 0812  78  15   3 0.00
Wed 09/23 13Z 0.46 0813  76  15   3 0.00
Wed 09/23 14Z 0.47 0813  75  15   3 0.00
Wed 09/23 15Z 0.48 0713  74  15   3 0.00
Wed 09/23 16Z 0.49 0712  70  15   3 0.00
Wed 09/23 17Z 0.52 0710  67  14   4 0.00
Wed 09/23 18Z 0.84 0709  71  14   4 0.00
Wed 09/23 19Z 1.37 0809  73  12   4 0.00
Wed 09/23 20Z 1.84 0808  73  10   4 0.00
Wed 09/23 21Z 1.21 0808  73   9   4 0.00
Wed 09/23 22Z 0.72 0808  72   7   4 0.00
Wed 09/23 23Z 0.56 0808  71   6   4 0.00
Thu 09/24 00Z 0.49 0709  70   4   4 0.00
Thu 09/24 01Z 0.42 0710  65   3   5 0.00
Thu 09/24 02Z 0.35 0711  58   2   5 0.00
Thu 09/24 03Z 0.34 0711  50   2   6 0.00
Thu 09/24 04Z 0.35 0712  44   2   6 0.00
Thu 09/24 05Z 0.34 0712  40   2   6 0.00
Thu 09/24 06Z 0.32 0712  37   2   6 0.00
Thu 09/24 07Z 0.30 0712  34   3   7 0.00
Thu 09/24 08Z 0.28 0711  30   3   7 0.00
Thu 09/24 09Z 0.27 0712  29   3   7 0.00
Thu 09/24 10Z 0.26 0612  29   3   7 0.00
Thu 09/24 11Z 0.24 0612  30   3   7 0.00
Thu 09/24 12Z 0.24 0612  31   4   7 0.00
Thu 09/24 13Z 0.25 0612  32   4   8 0.00
Thu 09/24 14Z 0.23 0611  34   4   8 0.00
Thu 09/24 15Z 0.20 0609  34   5   7 0.00
Thu 09/24 16Z 0.22 0609  35   5   7 0.00
Thu 09/24 17Z 0.21 0608  35   5   7 0.00
Thu 09/24 18Z 0.22 0607  36   5   7 0.00
Thu 09/24 19Z 0.23 0707  38   5   7 0.00
Thu 09/24 20Z 0.23 0607  42   5   7 0.00
Thu 09/24 21Z 0.24 0508  45   5   7 0.00
Thu 09/24 22Z 0.26 0509  49   5   7 0.00
Thu 09/24 23Z 0.30 0511  49   5   8 0.00
Fri 09/25 00Z 0.33 0512  51   5   8 0.00
Fri 09/25 01Z 0.33 0513  53   5   8 0.00
Fri 09/25 02Z 0.35 0615  50   5   9 0.00
Fri 09/25 03Z 0.37 0616  48   5  10 0.00
Fri 09/25 04Z 0.34 0714  46   5   9 0.00
Fri 09/25 05Z 0.33 0614  44   6   9 0.00
Fri 09/25 06Z 0.32 0613  44   6   9 0.00
Fri 09/25 07Z 0.31 0613  44   6   9 0.00
Fri 09/25 08Z 0.30 0513  43   6   9 0.00
Fri 09/25 09Z 0.30 0514  43   6   9 0.00
Fri 09/25 10Z 0.32 0515  45   6   9 0.00
Fri 09/25 11Z 0.34 0515  48   7   8 0.00
Fri 09/25 12Z 0.39 0517  51   7   8 0.00
Fri 09/25 13Z 0.44 0519  53   7   8 0.00
Fri 09/25 14Z 0.47 0619  55   6   8 0.00
Fri 09/25 15Z 0.49 0618  55   7   8 0.00
Fri 09/25 16Z 0.52 0617  53   7   8 0.00
Fri 09/25 17Z 0.49 0515  54   7   9 0.00
Fri 09/25 18Z 0.53 0513  58   7   8 0.00
Fri 09/25 19Z 0.95 0413  62   7   8 0.00
Fri 09/25 20Z 1.34 0313  64   7   8 0.00
Fri 09/25 21Z 0.93 0315  64   8   8 0.00
Fri 09/25 22Z 0.71 0417  64   8   8 0.00
Fri 09/25 23Z 0.66 0419  66   9   9 0.00

Run total areal avg QPF for the 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