Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260703_0000
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 00Z 1.02 2621  76  63  20 0.00
Fri 07/03 01Z 1.17 2725  75  64  20 0.00
Fri 07/03 02Z 1.23 2827  82  70  19 0.00
Fri 07/03 03Z 1.03 2826  86  65  19 0.00
Fri 07/03 04Z 0.84 2925  86  72  19 0.01
Fri 07/03 05Z 0.84 2926  88  57  18 0.02
Fri 07/03 06Z 0.86 3025  89  45  18 0.00
Fri 07/03 07Z 0.81 3024  88  37  17 0.00
Fri 07/03 08Z 0.82 3023  87  24  17 0.00
Fri 07/03 09Z 0.79 3023  86  17  17 0.00
Fri 07/03 10Z 0.67 3023  82  13  17 0.00
Fri 07/03 11Z 0.54 3022  75  11  17 0.00
Fri 07/03 12Z 0.46 3120  73  16  17 0.00
Fri 07/03 13Z 0.43 3018  70  19  18 0.00
Fri 07/03 14Z 0.45 3016  68  19  17 0.00
Fri 07/03 15Z 0.55 2915  69  34  17 0.00
Fri 07/03 16Z 0.72 2816  69  54  18 0.00
Fri 07/03 17Z 1.47 2817  74  47  17 0.00
Fri 07/03 18Z 7.55 2718  74  52  17 0.00
Fri 07/03 19Z 8.27 2818  67  55  18 0.00
Fri 07/03 20Z 8.14 2817  64  62  18 0.00
Fri 07/03 21Z 6.62 2817  65  68  18 0.00
Fri 07/03 22Z 2.44 2716  68  74  18 0.00
Fri 07/03 23Z 1.77 2718  71  83  18 0.00
Sat 07/04 00Z 1.22 2720  79  79  18 0.04
Sat 07/04 01Z 1.04 2618  82  85  17 0.00
Sat 07/04 02Z 0.85 2720  87  90  17 0.05
Sat 07/04 03Z 0.81 2721  92  84  16 0.01
Sat 07/04 04Z 0.61 2820  93  74  17 0.02
Sat 07/04 05Z 0.54 2920  88  74  17 0.01
Sat 07/04 06Z 0.53 3022  87  69  16 0.01
Sat 07/04 07Z 0.51 3122  87  55  16 0.01
Sat 07/04 08Z 0.54 3022  89  47  15 0.01
Sat 07/04 09Z 0.55 3123  89  47  15 0.01
Sat 07/04 10Z 0.52 3124  89  44  15 0.01
Sat 07/04 11Z 0.54 3125  90  53  14 0.01
Sat 07/04 12Z 0.53 3125  89  47  14 0.01
Sat 07/04 13Z 0.53 3123  85  40  13 0.01
Sat 07/04 14Z 0.57 3123  84  36  13 0.00
Sat 07/04 15Z 0.53 3220  82  26  12 0.00
Sat 07/04 16Z 0.60 3220  81  27  12 0.00
Sat 07/04 17Z 0.88 3217  75  24  12 0.00
Sat 07/04 18Z 2.24 3217  71  18  12 0.00
Sat 07/04 19Z 2.60 3116  73  16  12 0.00
Sat 07/04 20Z 2.96 3115  74  13  12 0.00
Sat 07/04 21Z 2.22 3114  75  13  12 0.00
Sat 07/04 22Z 2.04 3115  73  11  12 0.00
Sat 07/04 23Z 1.25 3116  69  12  12 0.00
Sun 07/05 00Z 1.13 3117  66  13  12 0.00
Sun 07/05 01Z 1.07 3118  65  13  12 0.00
Sun 07/05 02Z 1.09 3218  64  10  12 0.00
Sun 07/05 03Z 0.96 3217  65   9  12 0.00
Sun 07/05 04Z 0.61 3216  64   8  11 0.00
Sun 07/05 05Z 0.39 3315  59   6  12 0.00
Sun 07/05 06Z 0.27 3313  54   5  12 0.00
Sun 07/05 07Z 0.22 3311  52   5  12 0.00
Sun 07/05 08Z 0.14 3309  50   4  12 0.00
Sun 07/05 09Z 0.14 3307  47   3  12 0.00
Sun 07/05 10Z 0.20 3207  47   3  12 0.00
Sun 07/05 11Z 0.23 3207  47   4  11 0.00

Run total areal avg QPF for the greens is: 0.24 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