Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261024_1800
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)
=== ===== === ==== ==== === === === ====
Sat 10/24 18Z 0.13 3106  36   2   5 0.00
Sat 10/24 19Z 0.11 3206  38   3   5 0.00
Sat 10/24 20Z 0.10 3206  37   3   5 0.00
Sat 10/24 21Z 0.12 3106  35   5   5 0.00
Sat 10/24 22Z 0.15 3007  33   6   6 0.00
Sat 10/24 23Z 0.17 3008  32   7   6 0.00
Sun 10/25 00Z 0.18 3008  33   8   6 0.00
Sun 10/25 01Z 0.15 3007  33   8   6 0.00
Sun 10/25 02Z 0.14 3007  32   9   6 0.00
Sun 10/25 03Z 0.13 3006  30   9   7 0.00
Sun 10/25 04Z 0.12 2905  28  10   7 0.00
Sun 10/25 05Z 0.13 2806  25   9   7 0.00
Sun 10/25 06Z 0.15 2806  20   9   7 0.00
Sun 10/25 07Z 0.14 2806  17  10   8 0.00
Sun 10/25 08Z 0.15 2807  15  10   8 0.00
Sun 10/25 09Z 0.15 2706  15  11   8 0.00
Sun 10/25 10Z 0.15 2706  15  12   8 0.00
Sun 10/25 11Z 0.18 2708  16  14   8 0.00
Sun 10/25 12Z 0.20 2709  18  16   8 0.00
Sun 10/25 13Z 0.21 2709  16  18   8 0.00
Sun 10/25 14Z 0.19 2709  13  18   8 0.00
Sun 10/25 15Z 0.18 2608  12  17   9 0.00
Sun 10/25 16Z 0.19 2609  13  16   9 0.00
Sun 10/25 17Z 0.20 2609  15  14   9 0.00
Sun 10/25 18Z 0.22 2610  15  16   9 0.00
Sun 10/25 19Z 0.24 2510  14  16   9 0.00
Sun 10/25 20Z 0.24 2511  13  14   9 0.00
Sun 10/25 21Z 0.26 2512  15  14  10 0.00
Sun 10/25 22Z 0.29 2613  18  14  10 0.00
Sun 10/25 23Z 0.30 2614  20  15  10 0.00
Mon 10/26 00Z 0.31 2614  20  16  11 0.00
Mon 10/26 01Z 0.32 2615  20  15  11 0.00
Mon 10/26 02Z 0.34 2616  17  15  11 0.00
Mon 10/26 03Z 0.35 2617  13  15  11 0.00
Mon 10/26 04Z 0.38 2618  11  14  11 0.00
Mon 10/26 05Z 0.40 2619  14  13  10 0.00
Mon 10/26 06Z 0.40 2720  18  12  10 0.00
Mon 10/26 07Z 0.39 2719  21  13  10 0.00
Mon 10/26 08Z 0.41 2819  25  12  10 0.00
Mon 10/26 09Z 0.44 2820  30  15  10 0.00
Mon 10/26 10Z 0.47 2821  39  24   9 0.00
Mon 10/26 11Z 0.46 2821  46  26   9 0.00
Mon 10/26 12Z 0.49 2822  55  41   9 0.00
Mon 10/26 13Z 0.53 2823  63  54   9 0.00
Mon 10/26 14Z 0.55 2824  75  70   8 0.01
Mon 10/26 15Z 0.52 2924  89  77   8 0.03
Mon 10/26 16Z 0.54 3023  90  87   6 0.03
Mon 10/26 17Z 0.53 3023  86  91   6 0.01
Mon 10/26 18Z 0.54 3023  86  86   5 0.01
Mon 10/26 19Z 0.56 3022  87  78   4 0.01
Mon 10/26 20Z 0.55 3122  86  68   3 0.02
Mon 10/26 21Z 0.51 3121  86  51   2 0.01
Mon 10/26 22Z 0.47 3223  88  28   1 0.02
Mon 10/26 23Z 0.42 3224  91  21   0 0.01
Tue 10/27 00Z 0.33 3323  87  21   0 0.01
Tue 10/27 01Z 0.27 3323  84  19  -1 0.00
Tue 10/27 02Z 0.21 3423  79  14  -2 0.00
Tue 10/27 03Z 0.17 3422  78  12  -3 0.00
Tue 10/27 04Z 0.15 3422  75  12  -3 0.00
Tue 10/27 05Z 0.15 3423  71  11  -3 0.00

Run total areal avg QPF for the greens is: 0.17 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