NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260520_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)
=== ===== === ==== ==== === === === ====
Wed 05/20 00Z 1.07 2617  74  38  16 0.00
Wed 05/20 01Z 1.14 2520  72  43  16 0.00
Wed 05/20 02Z 1.22 2525  69  50  16 0.00
Wed 05/20 03Z 1.35 2530  67  62  16 0.00
Wed 05/20 04Z 1.54 2533  71  80  16 0.00
Wed 05/20 05Z 1.66 2436  74  67  17 0.00
Wed 05/20 06Z 1.86 2540  80  70  16 0.01
Wed 05/20 07Z 1.49 2637  83  63  15 0.08
Wed 05/20 08Z 1.36 2637  84  80  15 0.00
Wed 05/20 09Z 1.28 2634  84  77  15 0.00
Wed 05/20 10Z 1.22 2631  89  68  15 0.00
Wed 05/20 11Z 1.08 2629  92  67  14 0.01
Wed 05/20 12Z 1.00 2628  93  64  14 0.01
Wed 05/20 13Z 1.02 2627  94  73  14 0.02
Wed 05/20 14Z 1.15 2627  96  77  13 0.04
Wed 05/20 15Z 1.35 2727  92  77  12 0.04
Wed 05/20 16Z 2.59 2724  88  63  11 0.01
Wed 05/20 17Z 7.17 2723  85  56  11 0.01
Wed 05/20 18Z 8.57 2823  82  48  11 0.01
Wed 05/20 19Z 8.54 2822  75  39  10 0.01
Wed 05/20 20Z 7.08 2922  74  34  10 0.01
Wed 05/20 21Z 6.08 2922  72  33   9 0.00
Wed 05/20 22Z 2.76 3023  76  31   8 0.00
Wed 05/20 23Z 1.12 3022  80  28   7 0.00
Thu 05/21 00Z 0.86 3024  80  25   6 0.00
Thu 05/21 01Z 0.76 3125  79  19   5 0.00
Thu 05/21 02Z 0.60 3124  75  13   4 0.00
Thu 05/21 03Z 0.50 3224  72   9   3 0.00
Thu 05/21 04Z 0.43 3225  65   7   3 0.00
Thu 05/21 05Z 0.37 3225  65   4   2 0.00
Thu 05/21 06Z 0.31 3325  61   4   1 0.00
Thu 05/21 07Z 0.28 3325  59   3   0 0.00
Thu 05/21 08Z 0.23 3325  58   3   0 0.00
Thu 05/21 09Z 0.18 3425  53   3   0 0.00
Thu 05/21 10Z 0.17 3426  49   3   0 0.00
Thu 05/21 11Z 0.17 3425  48   3   0 0.00
Thu 05/21 12Z 0.16 3422  48   3   0 0.00
Thu 05/21 13Z 0.16 3420  47   3   0 0.00
Thu 05/21 14Z 0.19 3318  47   3  -1 0.00
Thu 05/21 15Z 0.20 3317  47   3  -1 0.00
Thu 05/21 16Z 0.26 3316  46   3   0 0.00
Thu 05/21 17Z 0.36 3316  45   3   0 0.00
Thu 05/21 18Z 0.39 3316  45   3   0 0.00
Thu 05/21 19Z 0.36 3316  43   5   0 0.00
Thu 05/21 20Z 0.28 3416  40   6   0 0.00
Thu 05/21 21Z 0.24 3416  37   8   1 0.00
Thu 05/21 22Z 0.16 3416  35   8   1 0.00
Thu 05/21 23Z 0.15 3417  32  11   2 0.00
Fri 05/22 00Z 0.16 3418  30  11   2 0.00
Fri 05/22 01Z 0.15 3419  31  12   2 0.00
Fri 05/22 02Z 0.15 3418  33  11   2 0.00
Fri 05/22 03Z 0.16 3417  37  12   2 0.00
Fri 05/22 04Z 0.13 3417  39  11   2 0.00
Fri 05/22 05Z 0.13 3517  40  10   2 0.00
Fri 05/22 06Z 0.10 3516  40   9   2 0.00
Fri 05/22 07Z 0.13 0016  40   9   1 0.00
Fri 05/22 08Z 0.17 0015  40   7   1 0.00
Fri 05/22 09Z 0.21 3513  41   8   1 0.00
Fri 05/22 10Z 0.28 3412  44   9   1 0.00
Fri 05/22 11Z 0.30 3412  47   8   1 0.00

Run total areal avg QPF for the greens is: 0.26 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