NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260317_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 03/17 18Z 18.82 2527  72  24 -13 0.00
Tue 03/17 19Z 20.36 2529  70  27 -13 0.00
Tue 03/17 20Z 19.52 2630  72  36 -14 0.00
Tue 03/17 21Z 17.41 2729  73  35 -14 0.00
Tue 03/17 22Z 16.73 2728  77  39 -15 0.00
Tue 03/17 23Z 12.80 2827  82  41 -16 0.00
Wed 03/18 00Z 10.31 2827  84  41 -17 0.00
Wed 03/18 01Z 8.09 2827  86  43 -18 0.00
Wed 03/18 02Z 4.64 2824  85  42 -18 0.00
Wed 03/18 03Z 3.23 2822  86  44 -18 0.00
Wed 03/18 04Z 2.20 2821  86  45 -18 0.00
Wed 03/18 05Z 1.68 2820  86  49 -18 0.00
Wed 03/18 06Z 1.55 2720  85  42 -18 0.00
Wed 03/18 07Z 1.78 2721  82  29 -18 0.00
Wed 03/18 08Z 1.80 2822  77  15 -18 0.00
Wed 03/18 09Z 1.74 2821  73   8 -18 0.00
Wed 03/18 10Z 1.18 2919  73   4 -18 0.00
Wed 03/18 11Z 0.53 3015  75   4 -18 0.00
Wed 03/18 12Z 0.38 3014  75   5 -18 0.00
Wed 03/18 13Z 0.39 3011  75   5 -18 0.00
Wed 03/18 14Z 0.50 2908  71   6 -18 0.00
Wed 03/18 15Z 0.83 2707  63   7 -18 0.00
Wed 03/18 16Z 0.92 2605  54   8 -17 0.00
Wed 03/18 17Z 0.90 2604  44   7 -16 0.00
Wed 03/18 18Z 0.56 2903  37   8 -15 0.00
Wed 03/18 19Z 0.58 2903  33   8 -14 0.00
Wed 03/18 20Z 0.56 2103  32   7 -13 0.00
Wed 03/18 21Z 0.47 1905  31   8 -13 0.00
Wed 03/18 22Z 0.28 1807  30  10 -13 0.00
Wed 03/18 23Z 0.25 1910  30   9 -12 0.00
Thu 03/19 00Z 0.27 1912  29   7 -12 0.00
Thu 03/19 01Z 0.30 1913  30   6 -12 0.00
Thu 03/19 02Z 0.38 2013  37   6 -12 0.00
Thu 03/19 03Z 0.48 2014  44   8 -12 0.00
Thu 03/19 04Z 0.51 2015  49  10 -12 0.00
Thu 03/19 05Z 0.55 2115  54   8 -11 0.00
Thu 03/19 06Z 0.56 2116  56  11 -11 0.00
Thu 03/19 07Z 0.55 2117  53  30 -11 0.00
Thu 03/19 08Z 0.56 2118  54  42 -11 0.00
Thu 03/19 09Z 0.55 2117  58  78 -11 0.00
Thu 03/19 10Z 0.52 2117  60  90 -11 0.00
Thu 03/19 11Z 0.43 2116  63  89 -11 0.00
Thu 03/19 12Z 0.39 2016  65  88 -10 0.00
Thu 03/19 13Z 0.35 2016  65  86 -10 0.00
Thu 03/19 14Z 0.30 1916  63  87 -10 0.00
Thu 03/19 15Z 0.50 1915  63  90 -10 0.00
Thu 03/19 16Z 1.53 1915  63  94  -9 0.00
Thu 03/19 17Z 2.34 1915  63  92  -9 0.00
Thu 03/19 18Z 3.02 1915  61  91  -8 0.00
Thu 03/19 19Z 3.10 1915  61  93  -7 0.00
Thu 03/19 20Z 2.19 1916  65  95  -7 0.00
Thu 03/19 21Z 0.95 1916  69  92  -7 0.00
Thu 03/19 22Z 0.50 1916  71  88  -6 0.00
Thu 03/19 23Z 0.52 1918  73  81  -6 0.00
Fri 03/20 00Z 0.56 2019  75  79  -7 0.00
Fri 03/20 01Z 0.56 2020  76  55  -6 0.00
Fri 03/20 02Z 0.57 2121  80  61  -6 0.00
Fri 03/20 03Z 0.57 2123  85  79  -6 0.00
Fri 03/20 04Z 0.56 2224  88  85  -5 0.00
Fri 03/20 05Z 0.54 2225  93  90  -5 0.01

Run total areal avg QPF for the Central_Greens is: 0.01 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