Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261017_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)
=== ===== === ==== ==== === === === ====
Sat 10/17 12Z 0.77 3225  98   7  -6 0.00
Sat 10/17 13Z 0.89 3225  97   0  -7 0.01
Sat 10/17 14Z 0.80 3224  96   0  -7 0.01
Sat 10/17 15Z 0.85 3224  95   2  -8 0.01
Sat 10/17 16Z 1.01 3221  90   5  -8 0.00
Sat 10/17 17Z 1.07 3120  88   5  -8 0.00
Sat 10/17 18Z 1.24 3119  83  11  -8 0.00
Sat 10/17 19Z 2.24 3118  76  23  -8 0.00
Sat 10/17 20Z 2.11 3118  73  31  -7 0.00
Sat 10/17 21Z 0.92 3118  70  36  -7 0.00
Sat 10/17 22Z 0.77 3019  66  33  -7 0.00
Sat 10/17 23Z 0.64 3020  59  36  -6 0.00
Sun 10/18 00Z 0.51 3121  51  37  -5 0.00
Sun 10/18 01Z 0.44 3121  48  53  -4 0.00
Sun 10/18 02Z 0.38 3120  46  51  -4 0.00
Sun 10/18 03Z 0.38 3119  46  47  -3 0.00
Sun 10/18 04Z 0.40 3119  48  56  -3 0.00
Sun 10/18 05Z 0.41 3118  52  53  -3 0.00
Sun 10/18 06Z 0.43 3117  55  49  -3 0.00
Sun 10/18 07Z 0.46 3016  57  49  -3 0.00
Sun 10/18 08Z 0.49 3017  59  49  -3 0.00
Sun 10/18 09Z 0.47 3017  69  51  -3 0.00
Sun 10/18 10Z 0.43 3016  74  52  -2 0.00
Sun 10/18 11Z 0.38 2915  76  52  -2 0.00
Sun 10/18 12Z 0.34 2913  76  52  -1 0.00
Sun 10/18 13Z 0.31 2913  74  50   0 0.00
Sun 10/18 14Z 0.30 2913  72  44   0 0.00
Sun 10/18 15Z 0.29 2812  70  39   1 0.00
Sun 10/18 16Z 0.28 2711  67  38   1 0.00
Sun 10/18 17Z 0.31 2712  60  35   2 0.00
Sun 10/18 18Z 0.30 2711  53  33   3 0.00
Sun 10/18 19Z 0.28 2711  44  35   4 0.00
Sun 10/18 20Z 0.27 2611  38  31   5 0.00
Sun 10/18 21Z 0.27 2612  34  21   6 0.00
Sun 10/18 22Z 0.28 2713  29  14   6 0.00
Sun 10/18 23Z 0.30 2713  25  13   7 0.00
Mon 10/19 00Z 0.29 2613  21   9   8 0.00
Mon 10/19 01Z 0.28 2613  17  15   8 0.00
Mon 10/19 02Z 0.28 2512  13  21   8 0.00
Mon 10/19 03Z 0.29 2513  11  28   9 0.00
Mon 10/19 04Z 0.30 2513  11  33   9 0.00
Mon 10/19 05Z 0.31 2514  12  34   9 0.00
Mon 10/19 06Z 0.31 2614  14  31  10 0.00
Mon 10/19 07Z 0.32 2614  16  29  10 0.00
Mon 10/19 08Z 0.32 2614  19  26  10 0.00
Mon 10/19 09Z 0.32 2614  19  24  10 0.00
Mon 10/19 10Z 0.31 2613  19  23  10 0.00
Mon 10/19 11Z 0.31 2713  18  22  10 0.00
Mon 10/19 12Z 0.31 2713  16  22  10 0.00
Mon 10/19 13Z 0.31 2713  16  22  10 0.00
Mon 10/19 14Z 0.29 2712  15  22  10 0.00
Mon 10/19 15Z 0.29 2612  15  21  10 0.00
Mon 10/19 16Z 0.29 2612  14  20  11 0.00
Mon 10/19 17Z 0.29 2712  14  20  11 0.00
Mon 10/19 18Z 0.30 2712  14  19  11 0.00
Mon 10/19 19Z 0.30 2812  14  19  11 0.00
Mon 10/19 20Z 0.29 2912  15  18  11 0.00
Mon 10/19 21Z 0.27 3012  16  17  11 0.00
Mon 10/19 22Z 0.24 3012  19  15  10 0.00
Mon 10/19 23Z 0.20 3111  22  13  10 0.00

Run total areal avg QPF for the greens is: 0.03 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