NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260911_1800
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)
=== ===== === ==== ==== === === === ====
Fri 09/11 18Z 0.77 3012  83  11   6 0.00
Fri 09/11 19Z 0.61 3014  77  15   7 0.00
Fri 09/11 20Z 0.56 3015  74  19   8 0.00
Fri 09/11 21Z 0.51 3015  71  21   8 0.00
Fri 09/11 22Z 0.45 3016  64  21   8 0.00
Fri 09/11 23Z 0.43 3117  61  21   9 0.00
Sat 09/12 00Z 0.38 3116  59  21   9 0.00
Sat 09/12 01Z 0.34 3117  57  24   9 0.00
Sat 09/12 02Z 0.26 3215  55  29  10 0.00
Sat 09/12 03Z 0.20 3213  52  33  10 0.00
Sat 09/12 04Z 0.15 3211  49  34  11 0.00
Sat 09/12 05Z 0.12 3208  46  34  11 0.00
Sat 09/12 06Z 0.09 3206  43  35  11 0.00
Sat 09/12 07Z 0.08 3004  41  36  11 0.00
Sat 09/12 08Z 0.07 3003  38  36  12 0.00
Sat 09/12 09Z 0.08 2903  37  36  12 0.00
Sat 09/12 10Z 0.05 2802  37  35  12 0.00
Sat 09/12 11Z 0.02 2102  36  33  12 0.00
Sat 09/12 12Z 0.01 1804  36  31  12 0.00
Sat 09/12 13Z 0.02 1806  36  29  12 0.00
Sat 09/12 14Z 0.05 1909  38  27  12 0.00
Sat 09/12 15Z 0.11 2010  42  25  12 0.00
Sat 09/12 16Z 0.15 2011  49  23  12 0.00
Sat 09/12 17Z 0.14 2011  52  20  12 0.00
Sat 09/12 18Z 0.14 2011  56  18  12 0.00
Sat 09/12 19Z 0.15 1912  60  15  12 0.00
Sat 09/12 20Z 0.18 1914  63  11  12 0.00
Sat 09/12 21Z 0.23 2016  65   5  12 0.00
Sat 09/12 22Z 0.25 2018  61   5  12 0.00
Sat 09/12 23Z 0.27 2019  59   9  12 0.00
Sun 09/13 00Z 0.34 2120  63  17  13 0.00
Sun 09/13 01Z 0.35 2120  69  15  13 0.00
Sun 09/13 02Z 0.38 2221  76  20  13 0.00
Sun 09/13 03Z 0.37 2220  77  33  13 0.00
Sun 09/13 04Z 0.37 2221  81  45  13 0.00
Sun 09/13 05Z 0.40 2222  87  61  13 0.00
Sun 09/13 06Z 0.37 2223  93  81  13 0.03
Sun 09/13 07Z 0.39 2224  95  89  13 0.09
Sun 09/13 08Z 0.41 2223  95  88  14 0.02
Sun 09/13 09Z 0.40 2223  95  85  14 0.02
Sun 09/13 10Z 0.41 2323  97  90  14 0.03
Sun 09/13 11Z 0.43 2322  97  73  14 0.04
Sun 09/13 12Z 0.42 2320  96  76  14 0.04
Sun 09/13 13Z 0.40 2319  96  78  14 0.05
Sun 09/13 14Z 0.41 2320  97  73  14 0.07
Sun 09/13 15Z 0.44 2320  98  64  13 0.13
Sun 09/13 16Z 0.43 2220  96  49  13 0.04
Sun 09/13 17Z 0.42 2219  96  42  13 0.01
Sun 09/13 18Z 0.37 2217  95  44  14 0.01
Sun 09/13 19Z 0.36 2215  95  52  14 0.01
Sun 09/13 20Z 0.40 2314  92  54  14 0.00
Sun 09/13 21Z 0.44 2414  91  43  14 0.00
Sun 09/13 22Z 0.57 2516  93  26  13 0.00
Sun 09/13 23Z 0.71 2619  94  25  13 0.01
Mon 09/14 00Z 0.66 2720  86  30  13 0.02
Mon 09/14 01Z 0.78 2722  91  38  12 0.04
Mon 09/14 02Z 0.72 2822  82  45  12 0.03
Mon 09/14 03Z 0.84 2823  76  38  11 0.01
Mon 09/14 04Z 0.73 2922  78  47  10 0.00
Mon 09/14 05Z 0.74 2922  85  49   9 0.01

Run total areal avg QPF for the greens is: 0.71 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