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_1200
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 12Z 0.76 2624  76  34  16 0.00
Tue 05/19 13Z 0.84 2623  75  46  16 0.00
Tue 05/19 14Z 1.12 2623  77  59  16 0.00
Tue 05/19 15Z 1.49 2522  83  83  15 0.00
Tue 05/19 16Z 3.47 2421  85  75  15 0.00
Tue 05/19 17Z 4.80 2419  86  72  16 0.00
Tue 05/19 18Z 6.29 2419  86  80  16 0.00
Tue 05/19 19Z 7.53 2522  84  80  16 0.03
Tue 05/19 20Z 5.54 2623  82  79  16 0.07
Tue 05/19 21Z 2.87 2626  79  78  16 0.12
Tue 05/19 22Z 1.14 2730  80  69  15 0.05
Tue 05/19 23Z 0.99 2731  78  48  16 0.00
Wed 05/20 00Z 1.01 2628  81  43  16 0.00
Wed 05/20 01Z 0.97 2628  76  64  17 0.00
Wed 05/20 02Z 1.09 2630  76  81  17 0.00
Wed 05/20 03Z 1.07 2530  73  71  17 0.00
Wed 05/20 04Z 1.28 2433  77  56  17 0.00
Wed 05/20 05Z 1.57 2438  82  58  16 0.00
Wed 05/20 06Z 1.31 2537  82  56  16 0.00
Wed 05/20 07Z 1.16 2535  88  52  16 0.00
Wed 05/20 08Z 1.03 2533  88  57  16 0.00
Wed 05/20 09Z 1.08 2632  91  50  15 0.00
Wed 05/20 10Z 1.01 2631  94  55  14 0.01
Wed 05/20 11Z 1.01 2630  94  50  13 0.01
Wed 05/20 12Z 0.96 2730  93  50  13 0.01
Wed 05/20 13Z 1.04 2729  96  48  12 0.01
Wed 05/20 14Z 1.17 2727  97  44  11 0.02
Wed 05/20 15Z 1.27 2727  93  35  11 0.03
Wed 05/20 16Z 3.88 2725  80  30  10 0.01
Wed 05/20 17Z 10.63 2823  71  37  10 0.00
Wed 05/20 18Z 12.72 2822  66  21  10 0.00
Wed 05/20 19Z 10.55 2921  66  18   9 0.00
Wed 05/20 20Z 7.76 2921  69  17   9 0.00
Wed 05/20 21Z 5.22 3023  67  16   8 0.00
Wed 05/20 22Z 1.44 3023  76  14   7 0.00
Wed 05/20 23Z 0.63 3024  81  14   6 0.00
Thu 05/21 00Z 0.58 3125  79  11   4 0.00
Thu 05/21 01Z 0.50 3124  77  10   4 0.00
Thu 05/21 02Z 0.43 3124  73   9   3 0.00
Thu 05/21 03Z 0.43 3225  73   8   2 0.00
Thu 05/21 04Z 0.42 3226  74   7   1 0.00
Thu 05/21 05Z 0.32 3225  72   5   0 0.00
Thu 05/21 06Z 0.25 3226  68   4   0 0.00
Thu 05/21 07Z 0.22 3228  65   4   0 0.00
Thu 05/21 08Z 0.19 3328  61   4   0 0.00
Thu 05/21 09Z 0.16 3327  56   4   1 0.00
Thu 05/21 10Z 0.11 3326  52   4   1 0.00
Thu 05/21 11Z 0.08 3324  50   4   1 0.00
Thu 05/21 12Z 0.07 3422  47   4   1 0.00
Thu 05/21 13Z 0.06 3419  46   5   1 0.00
Thu 05/21 14Z 0.06 3416  47   5   0 0.00
Thu 05/21 15Z 0.07 3415  47   5   0 0.00
Thu 05/21 16Z 0.07 3415  46   4   0 0.00
Thu 05/21 17Z 0.17 3314  44   4   0 0.00
Thu 05/21 18Z 0.26 3314  41   4   0 0.00
Thu 05/21 19Z 0.30 3315  37   4   0 0.00
Thu 05/21 20Z 0.27 3316  34   5   1 0.00
Thu 05/21 21Z 0.26 3317  33   7   1 0.00
Thu 05/21 22Z 0.25 3318  35   6   1 0.00
Thu 05/21 23Z 0.19 3318  37   6   1 0.00

Run total areal avg QPF for the Central_Greens is: 0.37 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