NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260910_1200
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)
=== ===== === ==== ==== === === === ====
Thu 09/10 12Z 1.18 2828  93  45  12 0.00
Thu 09/10 13Z 1.17 2829  91  38  12 0.00
Thu 09/10 14Z 1.17 2728  89  27  12 0.00
Thu 09/10 15Z 1.36 2727  88  16  12 0.00
Thu 09/10 16Z 3.94 2725  88  12  11 0.00
Thu 09/10 17Z 13.15 2725  86   7  11 0.00
Thu 09/10 18Z 16.01 2726  79   7  11 0.00
Thu 09/10 19Z 18.30 2727  72   8  11 0.00
Thu 09/10 20Z 16.53 2827  67   8  11 0.00
Thu 09/10 21Z 11.13 2826  69  10  10 0.00
Thu 09/10 22Z 3.59 2926  72   9  10 0.00
Thu 09/10 23Z 2.29 2925  80  14   9 0.01
Fri 09/11 00Z 1.73 2926  87  11   8 0.01
Fri 09/11 01Z 1.13 3025  90   7   7 0.01
Fri 09/11 02Z 0.82 3024  91   6   7 0.01
Fri 09/11 03Z 0.77 3024  91   6   6 0.00
Fri 09/11 04Z 0.67 3024  91   5   5 0.00
Fri 09/11 05Z 0.66 3025  89   4   5 0.00
Fri 09/11 06Z 0.61 3025  86   4   5 0.00
Fri 09/11 07Z 0.54 3024  82   4   5 0.00
Fri 09/11 08Z 0.51 3024  81   4   5 0.00
Fri 09/11 09Z 0.43 3022  77   4   5 0.00
Fri 09/11 10Z 0.41 3122  74   3   5 0.00
Fri 09/11 11Z 0.39 3122  72   3   6 0.00
Fri 09/11 12Z 0.37 3122  69   3   6 0.00
Fri 09/11 13Z 0.34 3121  63   3   6 0.00
Fri 09/11 14Z 0.35 3121  58   4   7 0.00
Fri 09/11 15Z 0.35 3119  53   5   7 0.00
Fri 09/11 16Z 0.36 3118  51   6   7 0.00
Fri 09/11 17Z 0.40 3117  51   7   6 0.00
Fri 09/11 18Z 0.47 3017  53   8   6 0.00
Fri 09/11 19Z 0.53 3017  56  10   6 0.00
Fri 09/11 20Z 0.54 3016  59  12   7 0.00
Fri 09/11 21Z 0.53 3015  59  14   7 0.00
Fri 09/11 22Z 0.48 3016  56  18   7 0.00
Fri 09/11 23Z 0.42 3116  51  24   8 0.00
Sat 09/12 00Z 0.36 3116  46  27   8 0.00
Sat 09/12 01Z 0.29 3216  44  31   9 0.00
Sat 09/12 02Z 0.23 3215  41  30   9 0.00
Sat 09/12 03Z 0.18 3213  40  29  10 0.00
Sat 09/12 04Z 0.13 3311  38  30  10 0.00
Sat 09/12 05Z 0.10 3309  36  30  11 0.00
Sat 09/12 06Z 0.09 3207  34  31  11 0.00
Sat 09/12 07Z 0.08 3205  33  33  11 0.00
Sat 09/12 08Z 0.07 3104  31  35  11 0.00
Sat 09/12 09Z 0.04 3102  30  34  11 0.00
Sat 09/12 10Z 0.02 2500  30  36  12 0.00
Sat 09/12 11Z 0.04 2102  29  37  11 0.00
Sat 09/12 12Z 0.03 2003  29  36  11 0.00
Sat 09/12 13Z 0.03 1905  29  36  11 0.00
Sat 09/12 14Z 0.04 1908  32  33  11 0.00
Sat 09/12 15Z 0.08 1909  36  28  11 0.00
Sat 09/12 16Z 0.11 2010  41  24  11 0.00
Sat 09/12 17Z 0.13 2011  46  19  11 0.00
Sat 09/12 18Z 0.15 2011  49  15  11 0.00
Sat 09/12 19Z 0.17 1912  52   9  12 0.00
Sat 09/12 20Z 0.18 1913  54   7  12 0.00
Sat 09/12 21Z 0.20 2015  54   9  12 0.00
Sat 09/12 22Z 0.27 2017  53  11  12 0.00
Sat 09/12 23Z 0.33 2119  51  14  12 0.00

Run total areal avg QPF for the greens is: 0.04 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