NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261030_0600
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 10/30 06Z 0.90 2629  89  94   8 0.00
Fri 10/30 07Z 0.90 2729  93  78   7 0.02
Fri 10/30 08Z 0.80 2825  90  58   7 0.01
Fri 10/30 09Z 0.81 2825  91  25   6 0.01
Fri 10/30 10Z 0.92 2828  88   3   6 0.01
Fri 10/30 11Z 1.02 2830  74   2   5 0.01
Fri 10/30 12Z 1.02 2830  72   5   4 0.00
Fri 10/30 13Z 0.81 2927  79   4   3 0.01
Fri 10/30 14Z 0.67 2925  89   5   2 0.01
Fri 10/30 15Z 0.72 3025  95   8   1 0.01
Fri 10/30 16Z 0.87 2924  97  11   0 0.01
Fri 10/30 17Z 1.23 2925  96  14   0 0.01
Fri 10/30 18Z 1.27 2926  93  15  -1 0.01
Fri 10/30 19Z 1.67 3026  92  15  -1 0.00
Fri 10/30 20Z 1.76 3028  91  11  -2 0.00
Fri 10/30 21Z 1.46 3029  92  10  -2 0.00
Fri 10/30 22Z 1.23 3030  94  13  -3 0.00
Fri 10/30 23Z 1.03 3029  96  17  -3 0.00
Sat 10/31 00Z 0.94 3129  97  22  -3 0.01
Sat 10/31 01Z 0.81 3130  97  28  -3 0.00
Sat 10/31 02Z 0.79 3129  98  25  -4 0.00
Sat 10/31 03Z 0.72 3130  97  26  -4 0.01
Sat 10/31 04Z 0.62 3229  95  28  -4 0.01
Sat 10/31 05Z 0.51 3229  93  26  -5 0.01
Sat 10/31 06Z 0.40 3228  92  14  -5 0.00
Sat 10/31 07Z 0.34 3227  91   9  -5 0.00
Sat 10/31 08Z 0.32 3226  91   9  -5 0.00
Sat 10/31 09Z 0.27 3225  90  14  -5 0.00
Sat 10/31 10Z 0.25 3224  88  16  -6 0.00
Sat 10/31 11Z 0.21 3323  86  22  -5 0.00
Sat 10/31 12Z 0.18 3321  81  25  -5 0.00
Sat 10/31 13Z 0.20 3220  79  27  -5 0.00
Sat 10/31 14Z 0.21 3219  76  29  -5 0.00
Sat 10/31 15Z 0.20 3219  68  23  -4 0.00
Sat 10/31 16Z 0.17 3218  60  18  -3 0.00
Sat 10/31 17Z 0.24 3218  61  25  -4 0.00
Sat 10/31 18Z 0.25 3117  60  29  -3 0.00
Sat 10/31 19Z 0.30 3116  59  26  -3 0.00
Sat 10/31 20Z 0.32 3116  62  15  -3 0.00
Sat 10/31 21Z 0.33 3016  65  34  -3 0.00
Sat 10/31 22Z 0.42 2919  67  30  -2 0.00
Sat 10/31 23Z 0.46 3020  66  23  -2 0.00
Sun 11/01 00Z 0.45 3021  64  22  -2 0.00
Sun 11/01 01Z 0.41 3021  62  18  -2 0.00
Sun 11/01 02Z 0.35 3020  58  10  -1 0.00
Sun 11/01 03Z 0.31 3119  55   5  -1 0.00
Sun 11/01 04Z 0.26 3118  53   5   0 0.00
Sun 11/01 05Z 0.25 3117  50   8   0 0.00
Sun 11/01 06Z 0.25 3016  47  11   0 0.00
Sun 11/01 07Z 0.27 3016  46  14   0 0.00
Sun 11/01 08Z 0.27 3016  45  13   0 0.00
Sun 11/01 09Z 0.29 3017  42  13   0 0.00
Sun 11/01 10Z 0.31 3018  37  12   1 0.00
Sun 11/01 11Z 0.33 3020  33   7   1 0.00
Sun 11/01 12Z 0.35 3021  31   6   1 0.00
Sun 11/01 13Z 0.35 3022  29   8   2 0.00
Sun 11/01 14Z 0.36 3123  28   6   2 0.00
Sun 11/01 15Z 0.33 3124  33   5   2 0.00
Sun 11/01 16Z 0.30 3123  42  22   3 0.00
Sun 11/01 17Z 0.30 3123  55  33   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.16 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