Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20251123_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)
=== ===== === ==== ==== === === === ====
Sun 11/23 18Z 0.23 2209  98  85  -6 0.00
Sun 11/23 19Z 0.23 2209  97  92  -5 0.00
Sun 11/23 20Z 0.23 2209  98  92  -5 0.01
Sun 11/23 21Z 0.26 2309  98  92  -5 0.01
Sun 11/23 22Z 0.26 2309  98  93  -5 0.01
Sun 11/23 23Z 0.25 2508  98  87  -5 0.01
Mon 11/24 00Z 0.26 2608  97  78  -4 0.01
Mon 11/24 01Z 0.25 2708  96  71  -4 0.00
Mon 11/24 02Z 0.27 2809  95  78  -5 0.00
Mon 11/24 03Z 0.32 2810  95  77  -5 0.00
Mon 11/24 04Z 0.34 2911  95  77  -4 0.00
Mon 11/24 05Z 0.36 2912  95  78  -5 0.00
Mon 11/24 06Z 0.42 2913  96  80  -5 0.01
Mon 11/24 07Z 0.50 3015  97  79  -5 0.01
Mon 11/24 08Z 0.53 3017  98  81  -5 0.02
Mon 11/24 09Z 0.54 3018  98  80  -5 0.02
Mon 11/24 10Z 0.56 3120  98  74  -5 0.02
Mon 11/24 11Z 0.61 3122  97  65  -6 0.02
Mon 11/24 12Z 0.64 3123  97  54  -6 0.02
Mon 11/24 13Z 0.66 3123  97  46  -6 0.02
Mon 11/24 14Z 0.66 3123  97  54  -7 0.02
Mon 11/24 15Z 0.55 3122  95  48  -6 0.01
Mon 11/24 16Z 0.54 3120  95  22  -6 0.01
Mon 11/24 17Z 0.53 3018  95   3  -6 0.01
Mon 11/24 18Z 0.48 2917  91   2  -6 0.00
Mon 11/24 19Z 0.41 2917  82   8  -4 0.00
Mon 11/24 20Z 0.39 2918  72  11  -3 0.00
Mon 11/24 21Z 0.32 3018  59  24  -2 0.00
Mon 11/24 22Z 0.31 2918  48  34   0 0.00
Mon 11/24 23Z 0.33 2918  42  62   0 0.00
Tue 11/25 00Z 0.34 2818  35  73   0 0.00
Tue 11/25 01Z 0.36 2817  25  88   0 0.00
Tue 11/25 02Z 0.41 2718  20  91   1 0.00
Tue 11/25 03Z 0.44 2617  20  91   1 0.00
Tue 11/25 04Z 0.43 2518  15  91   1 0.00
Tue 11/25 05Z 0.51 2423  14  92   1 0.00
Tue 11/25 06Z 0.60 2427  14  86   1 0.00
Tue 11/25 07Z 0.67 2529  15  83   2 0.00
Tue 11/25 08Z 0.68 2529  15  83   2 0.00
Tue 11/25 09Z 0.68 2529  16  82   2 0.00
Tue 11/25 10Z 0.66 2627  17  85   2 0.00
Tue 11/25 11Z 0.63 2626  19  83   2 0.00
Tue 11/25 12Z 0.59 2624  25  74   1 0.00
Tue 11/25 13Z 0.52 2622  29  78   2 0.00
Tue 11/25 14Z 0.44 2518  31  85   2 0.00
Tue 11/25 15Z 0.37 2517  35  80   3 0.00
Tue 11/25 16Z 0.34 2417  37  71   3 0.00
Tue 11/25 17Z 0.34 2317  40  67   3 0.00
Tue 11/25 18Z 0.35 2318  42  70   3 0.00
Tue 11/25 19Z 0.33 2318  42  63   3 0.00
Tue 11/25 20Z 0.29 2316  43  58   3 0.00
Tue 11/25 21Z 0.28 2317  47  67   3 0.00
Tue 11/25 22Z 0.30 2317  49  67   3 0.00
Tue 11/25 23Z 0.30 2317  53  70   3 0.00
Wed 11/26 00Z 0.30 2317  61  70   3 0.00
Wed 11/26 01Z 0.30 2317  67  75   3 0.00
Wed 11/26 02Z 0.30 2217  70  91   3 0.01
Wed 11/26 03Z 0.27 2217  75  96   3 0.01
Wed 11/26 04Z 0.23 2116  80  98   3 0.01
Wed 11/26 05Z 0.18 2016  83  98   3 0.01

Run total areal avg QPF for the greens is: 0.28 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