NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260519_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 05/19 18Z 1.87 2420  79  81  16 0.00
Tue 05/19 19Z 4.41 2520  84  86  16 0.01
Tue 05/19 20Z 3.82 2520  84  95  16 0.01
Tue 05/19 21Z 3.37 2626  77  71  16 0.04
Tue 05/19 22Z 2.86 2722  83  56  15 0.00
Tue 05/19 23Z 1.96 2722  85  40  15 0.00
Wed 05/20 00Z 1.41 2624  83  41  15 0.00
Wed 05/20 01Z 1.00 2625  78  41  16 0.00
Wed 05/20 02Z 1.04 2529  78  56  16 0.00
Wed 05/20 03Z 1.13 2531  81  63  16 0.00
Wed 05/20 04Z 1.17 2533  79  63  17 0.00
Wed 05/20 05Z 1.45 2438  78  63  17 0.00
Wed 05/20 06Z 1.36 2538  76  55  17 0.00
Wed 05/20 07Z 1.18 2535  83  52  17 0.00
Wed 05/20 08Z 1.22 2634  90  54  15 0.01
Wed 05/20 09Z 1.08 2631  90  50  14 0.01
Wed 05/20 10Z 0.93 2628  92  49  14 0.00
Wed 05/20 11Z 0.83 2729  90  58  14 0.00
Wed 05/20 12Z 0.83 2728  92  62  14 0.00
Wed 05/20 13Z 0.88 2726  94  66  13 0.00
Wed 05/20 14Z 0.96 2724  95  53  13 0.01
Wed 05/20 15Z 1.08 2624  96  60  12 0.02
Wed 05/20 16Z 1.23 2725  95  59  12 0.04
Wed 05/20 17Z 2.73 2724  92  49  11 0.02
Wed 05/20 18Z 7.55 2721  82  38  10 0.00
Wed 05/20 19Z 11.78 2820  74  36  10 0.00
Wed 05/20 20Z 9.74 2920  71  31  10 0.00
Wed 05/20 21Z 7.32 2920  71  29   9 0.00
Wed 05/20 22Z 3.20 3020  73  27   8 0.00
Wed 05/20 23Z 0.85 3022  78  24   7 0.00
Thu 05/21 00Z 0.67 3124  77  18   6 0.00
Thu 05/21 01Z 0.55 3124  80  16   5 0.00
Thu 05/21 02Z 0.40 3124  76  13   5 0.00
Thu 05/21 03Z 0.33 3225  70   9   4 0.00
Thu 05/21 04Z 0.28 3225  65   5   3 0.00
Thu 05/21 05Z 0.23 3225  63   4   3 0.00
Thu 05/21 06Z 0.21 3326  63   3   2 0.00
Thu 05/21 07Z 0.19 3328  64   2   1 0.00
Thu 05/21 08Z 0.14 3328  63   2   1 0.00
Thu 05/21 09Z 0.11 3327  58   2   1 0.00
Thu 05/21 10Z 0.08 3427  50   3   1 0.00
Thu 05/21 11Z 0.06 3425  46   3   1 0.00
Thu 05/21 12Z 0.05 3423  45   3   1 0.00
Thu 05/21 13Z 0.05 3421  44   2   1 0.00
Thu 05/21 14Z 0.04 3420  44   2   1 0.00
Thu 05/21 15Z 0.05 3418  45   2   0 0.00
Thu 05/21 16Z 0.08 3416  46   2   0 0.00
Thu 05/21 17Z 0.15 3415  47   3   0 0.00
Thu 05/21 18Z 0.16 3415  44   4   0 0.00
Thu 05/21 19Z 0.21 3415  40   5   1 0.00
Thu 05/21 20Z 0.28 3316  36   6   1 0.00
Thu 05/21 21Z 0.19 3317  32   8   1 0.00
Thu 05/21 22Z 0.17 3319  30  10   1 0.00
Thu 05/21 23Z 0.15 3320  29   7   2 0.00
Fri 05/22 00Z 0.11 3420  32   4   2 0.00
Fri 05/22 01Z 0.08 3419  36   3   2 0.00
Fri 05/22 02Z 0.02 3418  35   4   2 0.00
Fri 05/22 03Z 0.03 3516  35   5   2 0.00
Fri 05/22 04Z 0.08 3515  35   4   2 0.00
Fri 05/22 05Z 0.06 3513  34   5   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.17 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