Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260703_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)
=== ===== === ==== ==== === === === ====
Fri 07/03 06Z 0.68 3023  87  55  18 0.00
Fri 07/03 07Z 0.76 3025  87  58  17 0.00
Fri 07/03 08Z 0.74 3024  85  56  17 0.00
Fri 07/03 09Z 0.72 3023  84  49  17 0.00
Fri 07/03 10Z 0.63 3022  79  40  17 0.00
Fri 07/03 11Z 0.59 3023  75  30  17 0.00
Fri 07/03 12Z 0.55 3021  73  25  17 0.00
Fri 07/03 13Z 0.56 2920  73  22  17 0.00
Fri 07/03 14Z 0.61 2919  72  20  17 0.00
Fri 07/03 15Z 0.69 2919  73  23  17 0.00
Fri 07/03 16Z 0.85 2917  74  29  17 0.00
Fri 07/03 17Z 1.96 2816  76  38  17 0.00
Fri 07/03 18Z 6.01 2716  79  48  17 0.00
Fri 07/03 19Z 8.77 2716  74  53  17 0.00
Fri 07/03 20Z 9.39 2718  69  61  18 0.00
Fri 07/03 21Z 6.40 2818  69  64  18 0.00
Fri 07/03 22Z 2.74 2818  70  65  18 0.00
Fri 07/03 23Z 1.44 2818  72  60  17 0.00
Sat 07/04 00Z 1.17 2918  72  63  17 0.00
Sat 07/04 01Z 1.06 2918  74  63  17 0.00
Sat 07/04 02Z 0.98 2919  78  62  17 0.00
Sat 07/04 03Z 0.82 2920  77  62  17 0.02
Sat 07/04 04Z 0.81 2921  77  63  17 0.00
Sat 07/04 05Z 0.68 3023  81  61  16 0.00
Sat 07/04 06Z 0.60 3122  83  58  16 0.01
Sat 07/04 07Z 0.58 3122  86  58  16 0.00
Sat 07/04 08Z 0.56 3121  90  62  15 0.00
Sat 07/04 09Z 0.58 3022  91  60  15 0.01
Sat 07/04 10Z 0.56 3021  90  59  15 0.01
Sat 07/04 11Z 0.60 3022  93  66  14 0.01
Sat 07/04 12Z 0.58 3121  94  66  14 0.01
Sat 07/04 13Z 0.57 3121  94  60  13 0.01
Sat 07/04 14Z 0.54 3121  92  54  13 0.01
Sat 07/04 15Z 0.53 3119  88  50  13 0.01
Sat 07/04 16Z 0.59 3119  86  54  12 0.01
Sat 07/04 17Z 0.90 3018  84  42  12 0.01
Sat 07/04 18Z 1.15 3117  81  33  12 0.00
Sat 07/04 19Z 1.25 3117  80  24  12 0.00
Sat 07/04 20Z 1.30 3117  76  17  12 0.00
Sat 07/04 21Z 1.46 3117  73  13  12 0.00
Sat 07/04 22Z 1.34 3116  70  10  12 0.00
Sat 07/04 23Z 0.83 3216  67   6  12 0.00
Sun 07/05 00Z 0.53 3216  66   5  12 0.00
Sun 07/05 01Z 0.51 3316  65   4  12 0.00
Sun 07/05 02Z 0.43 3315  65   5  12 0.00
Sun 07/05 03Z 0.27 3414  63   5  12 0.00
Sun 07/05 04Z 0.16 3411  62   5  12 0.00
Sun 07/05 05Z 0.14 3410  62   6  12 0.00
Sun 07/05 06Z 0.09 3508  61   7  12 0.00
Sun 07/05 07Z 0.08 0006  61   7  12 0.00
Sun 07/05 08Z 0.07 0104  61   7  11 0.00
Sun 07/05 09Z 0.07 0302  61   7  11 0.00
Sun 07/05 10Z 0.06 0701  60   7  11 0.00
Sun 07/05 11Z 0.06 1301  60   7  11 0.00
Sun 07/05 12Z 0.05 1702  59  10  12 0.00
Sun 07/05 13Z 0.05 1702  60  14  11 0.00
Sun 07/05 14Z 0.07 1401  63  12  11 0.00
Sun 07/05 15Z 0.18 1402  69   8  11 0.00
Sun 07/05 16Z 0.29 1401  73   7  11 0.00
Sun 07/05 17Z 0.37 1300  75   7  11 0.00

Run total areal avg QPF for the greens is: 0.12 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