Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260129_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)
=== ===== === ==== ==== === === === ====
Thu 01/29 18Z 2.70 2911  86  67 -19 0.00
Thu 01/29 19Z 2.01 2914  89  62 -19 0.00
Thu 01/29 20Z 1.32 2816  92  56 -19 0.00
Thu 01/29 21Z 1.10 2818  95  53 -19 0.00
Thu 01/29 22Z 1.27 2920  94  51 -19 0.01
Thu 01/29 23Z 1.45 2924  92  46 -20 0.01
Fri 01/30 00Z 1.23 3026  90  41 -20 0.01
Fri 01/30 01Z 0.85 3026  88  39 -21 0.00
Fri 01/30 02Z 0.81 3026  87  41 -22 0.00
Fri 01/30 03Z 0.83 2927  86  37 -22 0.00
Fri 01/30 04Z 0.80 2928  84  33 -23 0.00
Fri 01/30 05Z 0.72 2928  80  33 -23 0.00
Fri 01/30 06Z 0.65 2929  75  36 -23 0.00
Fri 01/30 07Z 0.58 2929  71  39 -23 0.00
Fri 01/30 10Z 0.48 2929  69  53 -22 0.00
Fri 01/30 11Z 0.46 3029  70  63 -22 0.00
Fri 01/30 12Z 0.43 3028  73  73 -22 0.00
Fri 01/30 13Z 0.40 3028  77  79 -21 0.00
Fri 01/30 14Z 0.38 3027  80  80 -21 0.00
Fri 01/30 15Z 0.37 3025  82  77 -21 0.00
Fri 01/30 16Z 0.36 3023  82  74 -20 0.00
Fri 01/30 17Z 0.35 3022  83  69 -20 0.00
Fri 01/30 18Z 0.37 3021  83  64 -20 0.00
Fri 01/30 19Z 0.40 2921  83  63 -20 0.00
Fri 01/30 20Z 0.42 2921  84  62 -19 0.00
Fri 01/30 21Z 0.42 2921  84  61 -19 0.00
Fri 01/30 22Z 0.39 3022  84  60 -18 0.00
Fri 01/30 23Z 0.33 3022  84  60 -17 0.00
Sat 01/31 00Z 0.28 3122  84  60 -16 0.00
Sat 01/31 01Z 0.23 3122  85  59 -16 0.00
Sat 01/31 02Z 0.21 3221  85  58 -15 0.00
Sat 01/31 03Z 0.19 3220  85  56 -15 0.00
Sat 01/31 04Z 0.18 3219  85  55 -14 0.00
Sat 01/31 05Z 0.18 3219  85  55 -14 0.00
Sat 01/31 06Z 0.19 3219  84  52 -14 0.00
Sat 01/31 07Z 0.19 3119  83  48 -14 0.00
Sat 01/31 08Z 0.20 3119  83  45 -14 0.00
Sat 01/31 09Z 0.21 3119  83  42 -14 0.00
Sat 01/31 10Z 0.21 3119  82  41 -14 0.00
Sat 01/31 11Z 0.20 3119  81  41 -14 0.00
Sat 01/31 12Z 0.19 3119  80  42 -14 0.00
Sat 01/31 13Z 0.18 3118  79  43 -14 0.00
Sat 01/31 14Z 0.17 3116  79  46 -14 0.00
Sat 01/31 15Z 0.16 3114  77  43 -14 0.00
Sat 01/31 16Z 0.16 3113  75  39 -14 0.00
Sat 01/31 17Z 0.16 3113  75  35 -14 0.00
Sat 01/31 18Z 0.16 3112  76  29 -14 0.00
Sat 01/31 19Z 0.16 3112  77  26 -14 0.00
Sat 01/31 20Z 0.15 3111  79  25 -14 0.00
Sat 01/31 21Z 0.14 3111  80  27 -15 0.00
Sat 01/31 22Z 0.15 3112  80  29 -15 0.00
Sat 01/31 23Z 0.14 3213  79  32 -14 0.00
Sun 02/01 00Z 0.11 3313  76  36 -14 0.00
Sun 02/01 01Z 0.07 3312  75  38 -14 0.00
Sun 02/01 02Z 0.04 3411  73  40 -14 0.00
Sun 02/01 03Z 0.02 3510  70  40 -13 0.00
Sun 02/01 04Z 0.02 0011  66  39 -12 0.00
Sun 02/01 05Z 0.02 0011  62  37 -11 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