Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260130_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)
=== ===== === ==== ==== === === === ====
Fri 01/30 06Z 0.75 2927  81  45 -24 0.00
Fri 01/30 07Z 0.76 2931  82  46 -24 0.00
Fri 01/30 08Z 0.66 3031  80  50 -24 0.00
Fri 01/30 09Z 0.58 3031  80  55 -23 0.00
Fri 01/30 10Z 0.52 3030  82  60 -23 0.00
Fri 01/30 11Z 0.45 3029  82  67 -22 0.00
Fri 01/30 12Z 0.43 3029  81  72 -22 0.00
Fri 01/30 13Z 0.40 3029  81  76 -21 0.00
Fri 01/30 14Z 0.36 3027  82  77 -21 0.00
Fri 01/30 15Z 0.33 3025  83  76 -20 0.00
Fri 01/30 17Z 0.30 3021  83  72 -18 0.00
Fri 01/30 18Z 0.31 3021  83  69 -18 0.00
Fri 01/30 19Z 0.35 3022  84  67 -18 0.00
Fri 01/30 20Z 0.36 3022  84  66 -18 0.00
Fri 01/30 21Z 0.36 3022  84  64 -17 0.00
Fri 01/30 22Z 0.34 3022  85  63 -17 0.00
Fri 01/30 23Z 0.31 3022  85  64 -16 0.00
Sat 01/31 00Z 0.28 3123  86  63 -16 0.00
Sat 01/31 01Z 0.25 3223  87  62 -16 0.00
Sat 01/31 02Z 0.22 3222  86  59 -16 0.00
Sat 01/31 03Z 0.20 3220  86  55 -15 0.00
Sat 01/31 04Z 0.19 3219  85  51 -15 0.00
Sat 01/31 05Z 0.18 3218  84  47 -14 0.00
Sat 01/31 06Z 0.18 3117  83  45 -14 0.00
Sat 01/31 07Z 0.18 3117  83  44 -14 0.00
Sat 01/31 09Z 0.19 3117  84  44 -15 0.00
Sat 01/31 10Z 0.19 3117  84  43 -15 0.00
Sat 01/31 12Z 0.17 3116  84  42 -15 0.00
Sat 01/31 13Z 0.16 3115  84  41 -15 0.00
Sat 01/31 14Z 0.15 3114  84  40 -15 0.00
Sat 01/31 15Z 0.15 3113  84  39 -15 0.00
Sat 01/31 16Z 0.15 3113  84  38 -15 0.00
Sat 01/31 17Z 0.15 3112  84  38 -15 0.00
Sat 01/31 18Z 0.14 3212  84  38 -15 0.00
Sat 01/31 19Z 0.13 3212  83  36 -14 0.00
Sat 01/31 20Z 0.12 3312  84  36 -14 0.00
Sat 01/31 21Z 0.10 3311  84  38 -14 0.00
Sat 01/31 22Z 0.10 3313  83  38 -14 0.00
Sat 01/31 23Z 0.09 3315  83  38 -14 0.00
Sun 02/01 00Z 0.04 3514  83  37 -13 0.00
Sun 02/01 01Z 0.03 3512  84  39 -14 0.00
Sun 02/01 02Z 0.03 3511  82  38 -13 0.00
Sun 02/01 03Z 0.03 0011  77  36 -12 0.00
Sun 02/01 04Z 0.03 0011  75  35 -12 0.00
Sun 02/01 05Z 0.05 0112  73  31 -11 0.00
Sun 02/01 06Z 0.05 0114  69  29 -10 0.00
Sun 02/01 07Z 0.06 0114  66  28 -10 0.00
Sun 02/01 08Z 0.10 0214  64  29 -11 0.00
Sun 02/01 09Z 0.10 0215  61  29 -10 0.00
Sun 02/01 10Z 0.07 0116  58  27 -10 0.00
Sun 02/01 11Z 0.08 0117  56  23  -9 0.00
Sun 02/01 12Z 0.11 0219  58  22 -10 0.00
Sun 02/01 13Z 0.13 0219  58  21 -10 0.00
Sun 02/01 14Z 0.12 0218  56  18  -9 0.00
Sun 02/01 15Z 0.11 0218  53  16  -9 0.00
Sun 02/01 16Z 0.12 0219  51  15  -8 0.00
Sun 02/01 17Z 0.10 0219  52  13  -8 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