Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261025_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 10/25 06Z 0.13 2906  22  17   7 0.00
Sun 10/25 07Z 0.15 2906  20  18   7 0.00
Sun 10/25 08Z 0.16 2807  19  19   8 0.00
Sun 10/25 09Z 0.17 2808  17  21   8 0.00
Sun 10/25 10Z 0.18 2808  16  21   8 0.00
Sun 10/25 11Z 0.19 2808  16  22   8 0.00
Sun 10/25 12Z 0.19 2808  16  21   8 0.00
Sun 10/25 13Z 0.19 2809  16  20   8 0.00
Sun 10/25 14Z 0.18 2808  15  19   9 0.00
Sun 10/25 15Z 0.18 2708  15  18   9 0.00
Sun 10/25 16Z 0.19 2708  15  17   9 0.00
Sun 10/25 17Z 0.20 2609  16  18   9 0.00
Sun 10/25 18Z 0.22 2610  16  18   9 0.00
Sun 10/25 19Z 0.23 2610  14  18  10 0.00
Sun 10/25 20Z 0.24 2610  14  18  10 0.00
Sun 10/25 21Z 0.27 2611  13  17  10 0.00
Sun 10/25 22Z 0.28 2712  14  17  10 0.00
Sun 10/25 23Z 0.29 2713  15  17  10 0.00
Mon 10/26 00Z 0.29 2713  14  17  11 0.00
Mon 10/26 01Z 0.30 2613  14  16  11 0.00
Mon 10/26 02Z 0.32 2615  14  15  11 0.00
Mon 10/26 03Z 0.33 2615  13  15  11 0.00
Mon 10/26 04Z 0.34 2616  10  15  11 0.00
Mon 10/26 05Z 0.35 2716   9  15  10 0.00
Mon 10/26 06Z 0.35 2716  11  13  10 0.00
Mon 10/26 07Z 0.36 2716  13  13  10 0.00
Mon 10/26 08Z 0.41 2818  18  17  10 0.00
Mon 10/26 09Z 0.42 2819  23  21  10 0.00
Mon 10/26 10Z 0.46 2821  31  30   9 0.00
Mon 10/26 11Z 0.48 2922  42  47   9 0.00
Mon 10/26 12Z 0.50 2922  56  44   8 0.00
Mon 10/26 13Z 0.49 2923  66  65   8 0.00
Mon 10/26 14Z 0.50 2923  75  78   8 0.01
Mon 10/26 15Z 0.51 2924  84  84   8 0.01
Mon 10/26 16Z 0.50 2923  88  82   7 0.02
Mon 10/26 17Z 0.51 2923  89  88   6 0.02
Mon 10/26 18Z 0.50 2922  88  91   6 0.02
Mon 10/26 19Z 0.50 3021  86  91   5 0.02
Mon 10/26 20Z 0.52 3021  82  94   4 0.01
Mon 10/26 21Z 0.58 3022  82  91   3 0.02
Mon 10/26 22Z 0.54 3023  77  84   2 0.02
Mon 10/26 23Z 0.51 3123  78  68   2 0.01
Tue 10/27 00Z 0.43 3224  81  68   1 0.01
Tue 10/27 01Z 0.35 3323  84  59   0 0.01
Tue 10/27 02Z 0.28 3322  83  46   0 0.01
Tue 10/27 03Z 0.23 3321  81  37  -1 0.00
Tue 10/27 04Z 0.20 3320  81  29  -2 0.00
Tue 10/27 05Z 0.18 3420  79  21  -3 0.00
Tue 10/27 06Z 0.14 3420  75  18  -3 0.00
Tue 10/27 07Z 0.11 3420  70  15  -3 0.00
Tue 10/27 08Z 0.10 3419  66  11  -2 0.00
Tue 10/27 09Z 0.09 3419  62   6  -2 0.00
Tue 10/27 10Z 0.08 3418  57   4  -2 0.00
Tue 10/27 11Z 0.08 3419  51   6  -1 0.00
Tue 10/27 12Z 0.08 3418  47   8  -1 0.00
Tue 10/27 13Z 0.06 3417  42   9  -1 0.00
Tue 10/27 14Z 0.05 3416  40  10  -1 0.00
Tue 10/27 15Z 0.06 3414  39  10  -1 0.00
Tue 10/27 16Z 0.06 3413  39  10  -1 0.00
Tue 10/27 17Z 0.06 3411  40   9  -1 0.00

Run total areal avg QPF for the greens is: 0.19 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