NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261030_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 10/30 12Z 1.12 2824  87   2   4 0.00
Fri 10/30 13Z 1.23 2826  90   2   3 0.00
Fri 10/30 14Z 1.18 2827  93   9   2 0.01
Fri 10/30 15Z 1.27 2926  96  15   1 0.01
Fri 10/30 16Z 1.54 2926  96  21   0 0.01
Fri 10/30 17Z 1.74 2926  95  23   0 0.01
Fri 10/30 18Z 2.16 2927  94  22  -1 0.01
Fri 10/30 19Z 2.44 2928  94  20  -2 0.00
Fri 10/30 20Z 2.17 2929  93  19  -2 0.00
Fri 10/30 21Z 1.94 3030  93  18  -2 0.01
Fri 10/30 22Z 1.68 3031  94  19  -2 0.01
Fri 10/30 23Z 1.51 3031  96  22  -2 0.01
Sat 10/31 00Z 1.39 3132  96  24  -3 0.01
Sat 10/31 01Z 1.17 3131  96  22  -3 0.01
Sat 10/31 02Z 1.12 3131  97  25  -4 0.01
Sat 10/31 03Z 0.94 3230  96  30  -4 0.01
Sat 10/31 04Z 0.79 3229  95  34  -5 0.01
Sat 10/31 05Z 0.73 3227  95  35  -5 0.01
Sat 10/31 06Z 0.58 3227  93  31  -5 0.01
Sat 10/31 07Z 0.54 3226  92  18  -6 0.01
Sat 10/31 08Z 0.48 3225  91  12  -6 0.01
Sat 10/31 09Z 0.45 3225  90   8  -6 0.01
Sat 10/31 10Z 0.37 3224  87   8  -6 0.01
Sat 10/31 11Z 0.29 3322  80  13  -6 0.00
Sat 10/31 12Z 0.27 3321  77  17  -6 0.00
Sat 10/31 13Z 0.25 3320  74  21  -6 0.00
Sat 10/31 14Z 0.26 3219  72  21  -5 0.00
Sat 10/31 15Z 0.25 3218  68  19  -5 0.00
Sat 10/31 16Z 0.25 3218  64  17  -4 0.00
Sat 10/31 17Z 0.27 3217  63  20  -4 0.00
Sat 10/31 18Z 0.35 3117  65  30  -4 0.00
Sat 10/31 19Z 0.40 3016  66  32  -4 0.00
Sat 10/31 20Z 0.47 3016  71  22  -4 0.00
Sat 10/31 21Z 0.52 2917  72  17  -4 0.00
Sat 10/31 22Z 0.58 2919  71  36  -4 0.00
Sat 10/31 23Z 0.62 2920  70  33  -3 0.00
Sun 11/01 00Z 0.57 3020  68  23  -3 0.00
Sun 11/01 01Z 0.48 3020  66  16  -2 0.00
Sun 11/01 02Z 0.44 3020  66  15  -2 0.00
Sun 11/01 03Z 0.44 3021  66  11  -2 0.00
Sun 11/01 04Z 0.39 3020  64   9  -1 0.00
Sun 11/01 05Z 0.35 3119  61  10  -1 0.00
Sun 11/01 06Z 0.34 3019  58  12   0 0.00
Sun 11/01 07Z 0.35 3019  56  14   0 0.00
Sun 11/01 08Z 0.35 3019  52  15   0 0.00
Sun 11/01 09Z 0.34 3019  48  15   0 0.00
Sun 11/01 10Z 0.34 3019  44  15   0 0.00
Sun 11/01 11Z 0.34 3020  40  16   1 0.00
Sun 11/01 12Z 0.35 3020  38  16   1 0.00
Sun 11/01 13Z 0.37 3021  34  18   1 0.00
Sun 11/01 14Z 0.40 3022  31  14   1 0.00
Sun 11/01 15Z 0.43 3023  29   6   1 0.00
Sun 11/01 16Z 0.44 3124  26   8   2 0.00
Sun 11/01 17Z 0.45 3125  32   7   2 0.00
Sun 11/01 18Z 0.47 3126  61   5   2 0.00
Sun 11/01 19Z 0.52 3125  68  36   2 0.00
Sun 11/01 20Z 0.55 3025  56  34   3 0.00
Sun 11/01 21Z 0.63 2926  60  33   3 0.00
Sun 11/01 22Z 0.70 2928  57  28   3 0.00
Sun 11/01 23Z 0.72 2929  55  21   3 0.00

Run total areal avg QPF for the greens is: 0.19 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