NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260910_1200
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)
=== ===== === ==== ==== === === === ====
Thu 09/10 12Z 1.05 2826  94  37  12 0.00
Thu 09/10 13Z 1.08 2828  92  35  12 0.00
Thu 09/10 14Z 1.09 2727  89  24  12 0.00
Thu 09/10 15Z 1.32 2726  90  11  12 0.00
Thu 09/10 16Z 3.79 2725  88   9  12 0.00
Thu 09/10 17Z 14.55 2724  85   5  12 0.00
Thu 09/10 18Z 19.06 2727  75   6  12 0.00
Thu 09/10 19Z 19.16 2727  67   6  12 0.00
Thu 09/10 20Z 17.36 2827  62   6  12 0.00
Thu 09/10 21Z 12.37 2826  61   6  11 0.00
Thu 09/10 22Z 4.08 2825  64   7  11 0.00
Thu 09/10 23Z 2.75 2924  71   7  10 0.00
Fri 09/11 00Z 1.90 2923  85   8   9 0.01
Fri 09/11 01Z 1.05 3023  92   6   8 0.01
Fri 09/11 02Z 0.66 3022  96   4   7 0.01
Fri 09/11 03Z 0.58 3022  95   4   7 0.01
Fri 09/11 04Z 0.50 3122  95   4   6 0.01
Fri 09/11 05Z 0.52 3024  93   4   6 0.00
Fri 09/11 06Z 0.49 3025  88   3   6 0.00
Fri 09/11 07Z 0.44 3024  84   3   6 0.00
Fri 09/11 08Z 0.40 3023  81   3   6 0.00
Fri 09/11 09Z 0.35 3122  77   3   6 0.00
Fri 09/11 10Z 0.33 3122  74   3   6 0.00
Fri 09/11 11Z 0.30 3122  71   3   6 0.00
Fri 09/11 12Z 0.27 3121  69   3   6 0.00
Fri 09/11 13Z 0.25 3120  63   3   7 0.00
Fri 09/11 14Z 0.26 3120  58   3   7 0.00
Fri 09/11 15Z 0.26 3119  52   4   7 0.00
Fri 09/11 16Z 0.27 3117  49   5   7 0.00
Fri 09/11 17Z 0.30 3116  49   6   7 0.00
Fri 09/11 18Z 0.36 3116  52   8   7 0.00
Fri 09/11 19Z 0.43 3116  59   9   7 0.00
Fri 09/11 20Z 0.45 3015  65  12   7 0.00
Fri 09/11 21Z 0.44 3014  65  14   7 0.00
Fri 09/11 22Z 0.40 3015  62  17   7 0.00
Fri 09/11 23Z 0.33 3115  55  19   8 0.00
Sat 09/12 00Z 0.27 3115  49  21   9 0.00
Sat 09/12 01Z 0.20 3216  45  24   9 0.00
Sat 09/12 02Z 0.15 3215  42  26  10 0.00
Sat 09/12 03Z 0.11 3313  40  27  10 0.00
Sat 09/12 04Z 0.06 3311  37  29  11 0.00
Sat 09/12 05Z 0.04 3309  36  29  11 0.00
Sat 09/12 06Z 0.05 3307  34  30  11 0.00
Sat 09/12 07Z 0.04 3205  32  34  11 0.00
Sat 09/12 08Z 0.04 3203  30  35  11 0.00
Sat 09/12 09Z 0.02 3302  28  34  12 0.00
Sat 09/12 10Z 0.02 2100  28  36  12 0.00
Sat 09/12 11Z 0.05 2003  28  36  12 0.00
Sat 09/12 12Z 0.04 1904  27  36  11 0.00
Sat 09/12 13Z 0.05 1805  28  35  11 0.00
Sat 09/12 14Z 0.08 1908  33  32  11 0.00
Sat 09/12 15Z 0.13 1909  37  27  11 0.00
Sat 09/12 16Z 0.16 2009  43  22  11 0.00
Sat 09/12 17Z 0.19 1910  48  17  11 0.00
Sat 09/12 18Z 0.21 1910  51  13  11 0.00
Sat 09/12 19Z 0.24 1911  54   8  11 0.00
Sat 09/12 20Z 0.27 1912  56   7  11 0.00
Sat 09/12 21Z 0.27 2014  56   9  12 0.00
Sat 09/12 22Z 0.34 2015  56  10  12 0.00
Sat 09/12 23Z 0.40 2117  57  14  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.05 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