NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260519_0000
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)
=== ===== === ==== ==== === === === ====
Tue 05/19 00Z 0.60 2219  63  32  18 0.00
Tue 05/19 01Z 0.69 2319  61  28  18 0.00
Tue 05/19 02Z 0.74 2220  62  28  18 0.00
Tue 05/19 03Z 0.67 2222  64  27  18 0.00
Tue 05/19 04Z 0.69 2225  64  48  18 0.00
Tue 05/19 05Z 0.92 2331  63  41  18 0.00
Tue 05/19 06Z 1.48 2441  66  70  18 0.00
Tue 05/19 07Z 1.15 2635  73  59  16 0.09
Tue 05/19 08Z 1.15 2630  70  42  16 0.00
Tue 05/19 09Z 1.21 2630  71  47  16 0.00
Tue 05/19 10Z 1.27 2531  73  29  16 0.00
Tue 05/19 11Z 1.29 2533  77  31  15 0.00
Tue 05/19 12Z 1.24 2533  78  41  15 0.00
Tue 05/19 13Z 1.21 2632  81  56  15 0.00
Tue 05/19 14Z 1.06 2529  80  58  15 0.01
Tue 05/19 15Z 1.15 2526  81  54  15 0.00
Tue 05/19 16Z 2.42 2423  83  68  15 0.00
Tue 05/19 17Z 2.75 2425  87  80  15 0.01
Tue 05/19 18Z 7.15 2525  86  72  15 0.02
Tue 05/19 19Z 5.78 2525  84  79  15 0.01
Tue 05/19 20Z 6.16 2526  81  85  15 0.00
Tue 05/19 21Z 4.91 2624  80  72  15 0.00
Tue 05/19 22Z 3.37 2623  82  60  15 0.00
Tue 05/19 23Z 2.12 2523  83  59  15 0.00
Wed 05/20 00Z 1.16 2425  86  56  15 0.01
Wed 05/20 01Z 1.02 2527  77  51  16 0.00
Wed 05/20 02Z 0.97 2629  74  53  16 0.00
Wed 05/20 03Z 1.08 2532  73  62  16 0.00
Wed 05/20 04Z 1.43 2537  84  74  15 0.00
Wed 05/20 05Z 1.35 2538  88  71  15 0.00
Wed 05/20 06Z 1.24 2537  89  63  16 0.00
Wed 05/20 07Z 1.04 2535  84  54  16 0.00
Wed 05/20 08Z 1.19 2536  91  55  15 0.00
Wed 05/20 09Z 1.24 2635  95  58  14 0.01
Wed 05/20 10Z 1.18 2735  95  43  14 0.01
Wed 05/20 11Z 1.13 2734  95  40  13 0.02
Wed 05/20 12Z 1.11 2733  93  37  12 0.01
Wed 05/20 13Z 1.15 2731  89  30  12 0.01
Wed 05/20 14Z 1.48 2728  85  49  11 0.01
Wed 05/20 15Z 3.47 2726  80  54  10 0.01
Wed 05/20 16Z 7.33 2723  76  67   9 0.00
Wed 05/20 17Z 8.02 2822  72  42   9 0.00
Wed 05/20 18Z 10.72 2823  69  40   9 0.00
Wed 05/20 19Z 8.95 2823  71  24   8 0.00
Wed 05/20 20Z 7.01 2923  72  15   7 0.00
Wed 05/20 21Z 5.03 2923  75  18   6 0.00
Wed 05/20 22Z 1.95 3023  79  17   5 0.00
Wed 05/20 23Z 0.98 3024  82  16   4 0.00
Thu 05/21 00Z 0.89 3124  82  10   3 0.00
Thu 05/21 01Z 0.85 3125  79   5   2 0.00
Thu 05/21 02Z 0.89 3126  75   3   1 0.00
Thu 05/21 03Z 0.87 3127  73   2   0 0.00
Thu 05/21 04Z 0.69 3229  74   2   0 0.00
Thu 05/21 05Z 0.53 3228  75   2   0 0.00
Thu 05/21 06Z 0.41 3228  71   2   0 0.00
Thu 05/21 07Z 0.34 3328  65   2   0 0.00
Thu 05/21 08Z 0.31 3329  61   2  -1 0.00
Thu 05/21 09Z 0.24 3328  58   3   0 0.00
Thu 05/21 10Z 0.19 3327  55   4   0 0.00
Thu 05/21 11Z 0.14 3425  53   4   0 0.00

Run total areal avg QPF for the greens is: 0.23 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