NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260224_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)
=== ===== === ==== ==== === === === ====
Tue 02/24 00Z 0.14 3528  77  51 -11 0.00
Tue 02/24 01Z 0.22 3433  83  42 -12 0.00
Tue 02/24 02Z 0.35 3433  89  36 -12 0.00
Tue 02/24 03Z 0.37 3431  91  33 -13 0.00
Tue 02/24 04Z 0.37 3429  87  31 -13 0.00
Tue 02/24 05Z 0.33 3428  86  30 -13 0.00
Tue 02/24 06Z 0.29 3429  86  26 -14 0.00
Tue 02/24 07Z 0.36 3329  88  25 -14 0.00
Tue 02/24 08Z 0.43 3327  92  25 -15 0.00
Tue 02/24 09Z 0.45 3225  92  27 -15 0.00
Tue 02/24 10Z 0.41 3224  93  34 -15 0.01
Tue 02/24 11Z 0.36 3124  91  42 -15 0.00
Tue 02/24 12Z 0.35 3124  92  50 -15 0.00
Tue 02/24 13Z 0.33 3123  92  53 -15 0.00
Tue 02/24 14Z 0.32 3121  91  52 -16 0.00
Tue 02/24 15Z 0.32 3119  90  52 -16 0.00
Tue 02/24 16Z 0.32 3118  89  52 -16 0.00
Tue 02/24 17Z 0.32 3117  87  53 -15 0.00
Tue 02/24 18Z 0.34 3016  86  54 -15 0.00
Tue 02/24 19Z 0.38 3015  86  55 -15 0.00
Tue 02/24 20Z 0.42 3015  86  53 -15 0.00
Tue 02/24 21Z 0.43 2914  85  45 -15 0.00
Tue 02/24 22Z 0.49 2816  85  33 -15 0.00
Tue 02/24 23Z 0.51 2816  85  15 -15 0.00
Wed 02/25 00Z 0.51 2817  87   4 -15 0.00
Wed 02/25 01Z 0.42 2716  85   1 -14 0.00
Wed 02/25 02Z 0.31 2613  78   3 -13 0.00
Wed 02/25 03Z 0.27 2513  72   7 -13 0.00
Wed 02/25 04Z 0.18 2410  61  25 -12 0.00
Wed 02/25 05Z 0.18 2211  51  59 -11 0.00
Wed 02/25 06Z 0.20 2214  43  76 -11 0.00
Wed 02/25 07Z 0.23 2217  36  92 -11 0.00
Wed 02/25 08Z 0.21 2118  39  81 -10 0.00
Wed 02/25 09Z 0.19 2021  46  62 -10 0.00
Wed 02/25 10Z 0.20 2024  59  72 -10 0.00
Wed 02/25 11Z 0.17 1927  79  86  -9 0.00
Wed 02/25 12Z 0.17 1929  88  86  -9 0.02
Wed 02/25 13Z 0.24 2028  93  90  -9 0.02
Wed 02/25 14Z 0.31 2025  94  87  -9 0.01
Wed 02/25 15Z 0.36 2121  95  82  -9 0.01
Wed 02/25 16Z 0.41 2119  95  65  -9 0.01
Wed 02/25 17Z 0.44 2116  94  55  -9 0.00
Wed 02/25 18Z 0.58 2115  91  62  -8 0.00
Wed 02/25 19Z 1.34 2115  89  77  -8 0.00
Wed 02/25 20Z 1.58 2116  89  88  -8 0.00
Wed 02/25 21Z 0.89 2117  91  85  -7 0.00
Wed 02/25 22Z 0.59 2121  93  77  -7 0.00
Wed 02/25 23Z 0.73 2223  96  71  -7 0.02
Thu 02/26 00Z 1.20 2324  97  53  -7 0.03
Thu 02/26 01Z 1.91 2524  92  47  -9 0.02
Thu 02/26 02Z 1.67 2525  83  51 -10 0.00
Thu 02/26 03Z 1.52 2626  83  51 -10 0.00
Thu 02/26 04Z 1.24 2625  84  52 -11 0.00
Thu 02/26 06Z 1.20 2624  84  47 -12 0.00
Thu 02/26 07Z 1.40 2624  86  38 -12 0.00
Thu 02/26 08Z 1.52 2624  85  27 -13 0.00
Thu 02/26 09Z 1.41 2725  82  19 -14 0.00
Thu 02/26 10Z 1.61 2726  79  12 -14 0.00
Thu 02/26 11Z 1.25 2727  76  10 -14 0.00

Run total areal avg QPF for the greens is: 0.15 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