Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260130_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 01/30 12Z 0.42 3022  77  78 -25 0.00
Fri 01/30 13Z 0.42 3026  80  81 -23 0.00
Fri 01/30 14Z 0.37 3025  78  83 -22 0.00
Fri 01/30 15Z 0.32 3024  75  81 -20 0.00
Fri 01/30 16Z 0.29 3022  75  78 -19 0.00
Fri 01/30 17Z 0.29 3021  76  75 -19 0.00
Fri 01/30 18Z 0.30 3020  77  72 -18 0.00
Fri 01/30 19Z 0.33 3020  78  69 -18 0.00
Fri 01/30 20Z 0.35 3021  79  67 -19 0.00
Fri 01/30 21Z 0.36 3022  80  65 -18 0.00
Fri 01/30 22Z 0.35 3023  80  63 -18 0.00
Fri 01/30 23Z 0.32 3123  80  61 -17 0.00
Sat 01/31 00Z 0.28 3123  81  61 -16 0.00
Sat 01/31 01Z 0.24 3223  82  59 -16 0.00
Sat 01/31 02Z 0.21 3222  83  53 -15 0.00
Sat 01/31 03Z 0.18 3220  84  51 -15 0.00
Sat 01/31 04Z 0.16 3219  84  48 -14 0.00
Sat 01/31 05Z 0.16 3218  84  46 -14 0.00
Sat 01/31 06Z 0.16 3217  84  44 -14 0.00
Sat 01/31 07Z 0.16 3216  83  42 -14 0.00
Sat 01/31 08Z 0.16 3116  82  41 -14 0.00
Sat 01/31 09Z 0.16 3115  82  39 -14 0.00
Sat 01/31 10Z 0.16 3216  82  37 -14 0.00
Sat 01/31 11Z 0.15 3215  82  35 -14 0.00
Sat 01/31 12Z 0.14 3215  81  34 -14 0.00
Sat 01/31 13Z 0.13 3214  81  34 -14 0.00
Sat 01/31 14Z 0.12 3213  81  34 -14 0.00
Sat 01/31 15Z 0.11 3212  80  34 -14 0.00
Sat 01/31 16Z 0.10 3210  81  34 -14 0.00
Sat 01/31 17Z 0.11 3109  81  34 -14 0.00
Sat 01/31 18Z 0.12 3110  80  33 -14 0.00
Sat 01/31 19Z 0.12 3210  80  32 -14 0.00
Sat 01/31 20Z 0.12 3210  81  32 -14 0.00
Sat 01/31 21Z 0.11 3210  81  31 -14 0.00
Sat 01/31 22Z 0.10 3311  81  30 -14 0.00
Sat 01/31 23Z 0.08 3312  81  29 -13 0.00
Sun 02/01 00Z 0.06 3414  80  27 -12 0.00
Sun 02/01 01Z 0.04 3514  79  25 -12 0.00
Sun 02/01 02Z 0.02 0013  80  24 -12 0.00
Sun 02/01 03Z 0.03 0111  80  26 -12 0.00
Sun 02/01 04Z 0.06 0112  78  22 -11 0.00
Sun 02/01 05Z 0.07 0212  76  22 -10 0.00
Sun 02/01 06Z 0.08 0212  75  21 -10 0.00
Sun 02/01 07Z 0.10 0213  73  19 -10 0.00
Sun 02/01 08Z 0.08 0214  72  18  -9 0.00
Sun 02/01 09Z 0.08 0215  69  16  -9 0.00
Sun 02/01 10Z 0.11 0217  69  14  -9 0.00
Sun 02/01 11Z 0.12 0218  75  15 -10 0.00
Sun 02/01 12Z 0.14 0219  74  17 -10 0.00
Sun 02/01 13Z 0.13 0220  68  15  -8 0.00
Sun 02/01 14Z 0.12 0221  66  11  -8 0.00
Sun 02/01 15Z 0.15 0224  65   9  -7 0.00
Sun 02/01 16Z 0.18 0323  65   9  -8 0.00
Sun 02/01 17Z 0.19 0321  62  10  -8 0.00
Sun 02/01 18Z 0.18 0321  53  11  -8 0.00
Sun 02/01 19Z 0.13 0220  49  12  -7 0.00
Sun 02/01 20Z 0.13 0222  47  13  -7 0.00
Sun 02/01 21Z 0.12 0122  49  14  -7 0.00
Sun 02/01 22Z 0.11 0124  49  15  -7 0.00
Sun 02/01 23Z 0.10 0125  50  14  -7 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