NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250418_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)
=== ===== === ==== ==== === === === ====
Fri 04/18 18Z 2.66 2015  35  88   5 0.00
Fri 04/18 19Z 2.53 1919  35  93   6 0.00
Fri 04/18 20Z 2.09 1923  38  88   7 0.00
Fri 04/18 21Z 0.82 1927  43  91   7 0.00
Fri 04/18 22Z 0.76 2030  48  86   8 0.00
Fri 04/18 23Z 1.06 2134  55  95   7 0.00
Sat 04/19 00Z 1.10 2237  60  92   7 0.00
Sat 04/19 01Z 1.22 2339  69  92   7 0.00
Sat 04/19 02Z 1.04 2338  67  93   8 0.00
Sat 04/19 03Z 1.04 2339  71  91   8 0.00
Sat 04/19 04Z 0.90 2338  69  90  10 0.00
Sat 04/19 05Z 0.82 2338  67  77  11 0.00
Sat 04/19 06Z 0.77 2437  65  90  12 0.00
Sat 04/19 07Z 0.72 2435  65  83  13 0.00
Sat 04/19 08Z 0.66 2432  64  64  13 0.00
Sat 04/19 09Z 0.69 2433  68  71  13 0.00
Sat 04/19 10Z 0.67 2430  72  63  12 0.00
Sat 04/19 11Z 0.66 2528  78  49  12 0.00
Sat 04/19 12Z 0.60 2427  86  45  12 0.00
Sat 04/19 13Z 0.72 2432  92  56  12 0.00
Sat 04/19 14Z 0.78 2435  93  68  12 0.02
Sat 04/19 15Z 0.82 2435  94  77  12 0.01
Sat 04/19 16Z 0.77 2535  91  78  13 0.02
Sat 04/19 17Z 0.83 2435  90  85  13 0.02
Sat 04/19 18Z 1.06 2438  91  81  13 0.01
Sat 04/19 19Z 1.34 2441  92  85  12 0.03
Sat 04/19 20Z 1.31 2539  93  90  11 0.04
Sat 04/19 21Z 1.43 2535  94  39  11 0.01
Sat 04/19 22Z 1.63 2636  96  36  10 0.03
Sat 04/19 23Z 1.49 2634  93  29  10 0.02
Sun 04/20 00Z 1.33 2735  87  47   9 0.01
Sun 04/20 01Z 1.32 2736  82  30   8 0.00
Sun 04/20 02Z 1.35 2739  83  21   7 0.00
Sun 04/20 03Z 1.41 2739  81  23   5 0.00
Sun 04/20 04Z 1.42 2839  80  35   3 0.00
Sun 04/20 05Z 0.96 2936  83  34   1 0.01
Sun 04/20 06Z 0.80 3035  89  25   0 0.01
Sun 04/20 07Z 0.89 3035  88  12  -3 0.01
Sun 04/20 08Z 0.76 3034  81  10  -4 0.01
Sun 04/20 09Z 0.69 3034  80   8  -4 0.00
Sun 04/20 10Z 0.69 3034  81   8  -6 0.00
Sun 04/20 11Z 0.66 3135  81   9  -6 0.00
Sun 04/20 12Z 0.55 3135  77   8  -7 0.00
Sun 04/20 13Z 0.49 3133  73   7  -7 0.00
Sun 04/20 14Z 0.47 3130  69   8  -7 0.00
Sun 04/20 15Z 0.56 3127  66  14  -7 0.00
Sun 04/20 16Z 0.89 3026  63  15  -7 0.00
Sun 04/20 17Z 2.49 3025  61  14  -6 0.00
Sun 04/20 18Z 3.37 3025  59  11  -6 0.00
Sun 04/20 19Z 7.71 3026  58   9  -5 0.00
Sun 04/20 20Z 10.81 3026  55   7  -4 0.00
Sun 04/20 21Z 7.90 3026  51   4  -4 0.00
Sun 04/20 22Z 3.39 3127  48   3  -3 0.00
Sun 04/20 23Z 0.94 3128  46   3  -3 0.00
Mon 04/21 00Z 0.48 3230  42   2  -2 0.00
Mon 04/21 01Z 0.29 3332  40   2  -1 0.00
Mon 04/21 02Z 0.22 3331  41   2   0 0.00
Mon 04/21 03Z 0.10 3429  37   2   0 0.00
Mon 04/21 04Z 0.05 3425  35   2   0 0.00
Mon 04/21 05Z 0.02 3423  35   6   0 0.00

Run total areal avg QPF for the Central_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