Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260619_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)
=== ===== === ==== ==== === === === ====
Fri 06/19 12Z 1.08 2724  95  65   7 0.00
Fri 06/19 13Z 1.38 2628  95  61   7 0.00
Fri 06/19 14Z 1.85 2629  95  61   8 0.01
Fri 06/19 15Z 2.06 2628  95  64   8 0.01
Fri 06/19 16Z 3.18 2628  94  65   8 0.01
Fri 06/19 17Z 4.81 2628  93  71   8 0.01
Fri 06/19 18Z 7.21 2728  92  67   8 0.01
Fri 06/19 19Z 8.99 2727  90  59   8 0.01
Fri 06/19 20Z 11.35 2726  86  54   9 0.00
Fri 06/19 21Z 11.70 2725  81  50   9 0.00
Fri 06/19 22Z 9.24 2727  82  52   9 0.02
Fri 06/19 23Z 5.43 2727  84  59   9 0.01
Sat 06/20 00Z 2.05 2728  86  72   8 0.02
Sat 06/20 01Z 1.82 2728  88  74   8 0.03
Sat 06/20 02Z 1.59 2728  90  76   8 0.02
Sat 06/20 03Z 1.37 2728  92  76   8 0.03
Sat 06/20 04Z 1.22 2729  93  78   7 0.07
Sat 06/20 05Z 1.06 2828  95  82   7 0.05
Sat 06/20 06Z 0.94 2828  96  92   7 0.08
Sat 06/20 07Z 0.90 2928  97  92   7 0.10
Sat 06/20 08Z 0.85 2927  98  93   7 0.08
Sat 06/20 09Z 0.83 2927  97  90   7 0.07
Sat 06/20 10Z 0.86 3029  97  85   7 0.07
Sat 06/20 11Z 0.82 3029  97  78   7 0.03
Sat 06/20 12Z 0.81 3028  96  74   7 0.03
Sat 06/20 13Z 0.80 3026  96  75   7 0.02
Sat 06/20 14Z 0.85 3023  96  77   7 0.02
Sat 06/20 15Z 1.06 3021  97  75   7 0.03
Sat 06/20 16Z 1.04 2921  97  76   7 0.04
Sat 06/20 17Z 0.94 2921  96  77   8 0.04
Sat 06/20 18Z 1.33 3021  95  72   8 0.04
Sat 06/20 19Z 1.84 3020  94  69   8 0.02
Sat 06/20 20Z 1.71 2919  93  67   8 0.03
Sat 06/20 21Z 1.75 3018  92  63   8 0.03
Sat 06/20 22Z 1.27 3019  93  62   9 0.03
Sat 06/20 23Z 0.73 3018  94  58   9 0.01
Sun 06/21 00Z 0.56 3017  95  64   9 0.01
Sun 06/21 01Z 0.48 3117  96  64   9 0.02
Sun 06/21 02Z 0.43 3117  95  53   9 0.02
Sun 06/21 03Z 0.41 3116  96  50   9 0.01
Sun 06/21 04Z 0.37 3114  96  55   8 0.03
Sun 06/21 05Z 0.32 3113  95  62   8 0.04
Sun 06/21 06Z 0.31 3112  95  63   8 0.02
Sun 06/21 07Z 0.32 3011  96  66   8 0.02
Sun 06/21 08Z 0.31 3010  94  63   8 0.01
Sun 06/21 09Z 0.29 2910  93  59   8 0.01
Sun 06/21 10Z 0.31 2910  93  60   9 0.01
Sun 06/21 11Z 0.30 2810  91  60   9 0.01
Sun 06/21 12Z 0.27 2809  90  61   9 0.01
Sun 06/21 13Z 0.27 2809  91  64   9 0.01
Sun 06/21 14Z 0.30 2709  90  61   9 0.00
Sun 06/21 15Z 0.36 2810  91  63   9 0.00
Sun 06/21 16Z 0.42 2810  91  67   9 0.00
Sun 06/21 17Z 0.68 2909  92  70   9 0.00
Sun 06/21 18Z 0.99 2909  92  71   9 0.00
Sun 06/21 19Z 1.12 2809  91  74   9 0.00
Sun 06/21 20Z 0.89 2909  91  73   9 0.00
Sun 06/21 21Z 0.40 2909  84  73  10 0.03
Sun 06/21 22Z 0.31 3008  81  64  10 0.01
Sun 06/21 23Z 0.37 2809  82  62  10 0.00

Run total areal avg QPF for the greens is: 1.35 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