NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260519_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)
=== ===== === ==== ==== === === === ====
Tue 05/19 12Z 0.85 2625  77  52  16 0.00
Tue 05/19 13Z 0.91 2624  76  63  16 0.00
Tue 05/19 14Z 1.13 2625  78  72  15 0.00
Tue 05/19 15Z 1.30 2524  83  86  15 0.01
Tue 05/19 16Z 2.55 2522  86  78  15 0.00
Tue 05/19 17Z 3.37 2420  88  78  15 0.00
Tue 05/19 18Z 4.40 2419  88  81  15 0.00
Tue 05/19 19Z 5.66 2521  86  81  15 0.02
Tue 05/19 20Z 4.70 2622  84  75  15 0.06
Tue 05/19 21Z 2.46 2625  81  66  15 0.08
Tue 05/19 22Z 1.19 2728  81  61  15 0.03
Tue 05/19 23Z 1.04 2729  79  44  16 0.00
Wed 05/20 00Z 1.00 2628  81  43  16 0.00
Wed 05/20 01Z 0.96 2628  76  66  17 0.00
Wed 05/20 02Z 1.04 2631  74  83  17 0.00
Wed 05/20 03Z 1.05 2531  72  74  17 0.00
Wed 05/20 04Z 1.30 2434  80  61  16 0.00
Wed 05/20 05Z 1.49 2438  85  59  16 0.01
Wed 05/20 06Z 1.32 2537  83  60  16 0.00
Wed 05/20 07Z 1.21 2536  86  56  16 0.01
Wed 05/20 08Z 1.12 2533  89  56  15 0.00
Wed 05/20 09Z 1.07 2632  91  55  14 0.00
Wed 05/20 10Z 1.03 2632  95  55  14 0.01
Wed 05/20 11Z 1.05 2631  94  48  13 0.01
Wed 05/20 12Z 1.06 2730  94  48  12 0.01
Wed 05/20 13Z 1.12 2729  96  51  12 0.01
Wed 05/20 14Z 1.32 2727  94  37  11 0.02
Wed 05/20 15Z 1.45 2727  89  32  10 0.02
Wed 05/20 16Z 4.35 2725  83  29  10 0.01
Wed 05/20 17Z 8.42 2824  74  28   9 0.01
Wed 05/20 18Z 9.49 2924  70  15   9 0.00
Wed 05/20 19Z 8.43 2924  72  13   8 0.00
Wed 05/20 20Z 6.20 2923  74  12   7 0.00
Wed 05/20 21Z 4.56 3024  74  11   6 0.00
Wed 05/20 22Z 1.70 3024  78  10   5 0.00
Wed 05/20 23Z 0.94 3025  80  10   4 0.00
Thu 05/21 00Z 0.84 3126  76   8   3 0.00
Thu 05/21 01Z 0.78 3126  74   7   2 0.00
Thu 05/21 02Z 0.82 3126  73   7   2 0.00
Thu 05/21 03Z 0.80 3127  74   6   1 0.00
Thu 05/21 04Z 0.64 3227  75   5   0 0.00
Thu 05/21 05Z 0.49 3226  72   4   0 0.00
Thu 05/21 06Z 0.39 3226  70   4   0 0.00
Thu 05/21 07Z 0.34 3227  65   3   0 0.00
Thu 05/21 08Z 0.29 3327  62   3   0 0.00
Thu 05/21 09Z 0.25 3326  59   4   0 0.00
Thu 05/21 10Z 0.21 3325  56   4   0 0.00
Thu 05/21 11Z 0.17 3323  54   4   0 0.00
Thu 05/21 12Z 0.15 3321  51   4   0 0.00
Thu 05/21 13Z 0.13 3419  50   5   0 0.00
Thu 05/21 14Z 0.14 3316  49   5   0 0.00
Thu 05/21 15Z 0.16 3315  49   5   0 0.00
Thu 05/21 16Z 0.17 3315  49   3   0 0.00
Thu 05/21 17Z 0.27 3314  47   3   0 0.00
Thu 05/21 18Z 0.36 3314  45   3   0 0.00
Thu 05/21 19Z 0.47 3314  42   4   0 0.00
Thu 05/21 20Z 0.44 3315  40   6   0 0.00
Thu 05/21 21Z 0.40 3316  39   8   0 0.00
Thu 05/21 22Z 0.37 3217  38   8   0 0.00
Thu 05/21 23Z 0.33 3318  39   7   1 0.00

Run total areal avg QPF for the greens is: 0.32 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