Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261018_0600
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 10/18 06Z 0.44 2914  73  60  -4 0.00
Sun 10/18 07Z 0.59 2916  72  61  -4 0.00
Sun 10/18 08Z 0.64 2817  74  64  -3 0.00
Sun 10/18 09Z 0.59 2918  70  72  -2 0.00
Sun 10/18 10Z 0.52 2918  79  76  -2 0.00
Sun 10/18 11Z 0.51 3018  87  75  -1 0.00
Sun 10/18 12Z 0.49 2917  84  70  -1 0.00
Sun 10/18 13Z 0.48 2916  84  61   0 0.00
Sun 10/18 14Z 0.49 2916  85  50   0 0.00
Sun 10/18 15Z 0.47 2814  84  44   0 0.00
Sun 10/18 16Z 0.44 2713  80  42   0 0.00
Sun 10/18 17Z 0.43 2613  70  40   1 0.00
Sun 10/18 18Z 0.40 2513  57  39   2 0.00
Sun 10/18 19Z 0.35 2512  46  35   3 0.00
Sun 10/18 20Z 0.33 2512  42  31   4 0.00
Sun 10/18 21Z 0.33 2513  39  21   5 0.00
Sun 10/18 22Z 0.33 2614  38  13   6 0.00
Sun 10/18 23Z 0.32 2614  36  11   7 0.00
Mon 10/19 00Z 0.31 2614  32  11   8 0.00
Mon 10/19 01Z 0.30 2614  26  11   8 0.00
Mon 10/19 02Z 0.29 2613  20  13   8 0.00
Mon 10/19 03Z 0.29 2613  17  14   8 0.00
Mon 10/19 04Z 0.29 2613  17  16   9 0.00
Mon 10/19 05Z 0.28 2612  18  17   9 0.00
Mon 10/19 06Z 0.28 2512  19  17   9 0.00
Mon 10/19 07Z 0.29 2512  19  18   9 0.00
Mon 10/19 08Z 0.30 2513  18  18   9 0.00
Mon 10/19 09Z 0.31 2613  18  17  10 0.00
Mon 10/19 10Z 0.31 2613  17  17  10 0.00
Mon 10/19 11Z 0.31 2613  17  17  10 0.00
Mon 10/19 12Z 0.31 2713  16  17  10 0.00
Mon 10/19 13Z 0.29 2712  15  17  10 0.00
Mon 10/19 14Z 0.28 2612  15  18  10 0.00
Mon 10/19 15Z 0.27 2611  15  19  10 0.00
Mon 10/19 16Z 0.25 2611  15  19  10 0.00
Mon 10/19 17Z 0.24 2510  14  19  10 0.00
Mon 10/19 18Z 0.25 2610  14  19  10 0.00
Mon 10/19 19Z 0.27 2710  13  19  11 0.00
Mon 10/19 20Z 0.28 2811  14  19  11 0.00
Mon 10/19 21Z 0.29 2911  15  20  10 0.00
Mon 10/19 22Z 0.29 2912  18  20  10 0.00
Mon 10/19 23Z 0.26 3013  21  19  10 0.00
Tue 10/20 00Z 0.21 3113  26  17  10 0.00
Tue 10/20 01Z 0.18 3213  30  15  10 0.00
Tue 10/20 02Z 0.13 3313  35  14  10 0.00
Tue 10/20 03Z 0.10 3312  41  12  10 0.00
Tue 10/20 04Z 0.08 3413  44  11   9 0.00
Tue 10/20 05Z 0.05 3515  42  13   9 0.00
Tue 10/20 06Z 0.02 0017  41  17   9 0.00
Tue 10/20 07Z 0.05 0018  38  17   8 0.00
Tue 10/20 08Z 0.10 0119  35  15   8 0.00
Tue 10/20 09Z 0.11 0119  30  15   8 0.00
Tue 10/20 10Z 0.11 0120  22  13   9 0.00
Tue 10/20 11Z 0.12 0121  19  10   8 0.00
Tue 10/20 12Z 0.13 0121  19   5   8 0.00
Tue 10/20 13Z 0.13 0121  21   2   8 0.00
Tue 10/20 14Z 0.13 0120  24   2   7 0.00
Tue 10/20 15Z 0.14 0219  29   2   7 0.00
Tue 10/20 16Z 0.13 0217  35   3   6 0.00
Tue 10/20 17Z 0.12 0215  40   3   6 0.00

Run total areal avg QPF for the greens is: 0.00 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