NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260911_0000
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 09/11 00Z 0.79 2921  74  31  11 0.00
Fri 09/11 01Z 0.89 2922  81  23  10 0.00
Fri 09/11 02Z 0.83 3022  87  26   9 0.01
Fri 09/11 03Z 0.66 3022  92  19   8 0.01
Fri 09/11 04Z 0.50 3121  93  10   8 0.01
Fri 09/11 05Z 0.43 3121  92   4   7 0.00
Fri 09/11 06Z 0.46 3122  87   2   7 0.00
Fri 09/11 07Z 0.53 3122  83   3   6 0.00
Fri 09/11 08Z 0.55 3023  81   3   6 0.00
Fri 09/11 09Z 0.53 3023  80   2   6 0.00
Fri 09/11 10Z 0.48 3023  79   2   6 0.00
Fri 09/11 11Z 0.43 3124  74   3   6 0.00
Fri 09/11 12Z 0.37 3123  69   4   6 0.00
Fri 09/11 13Z 0.36 3122  67   4   6 0.00
Fri 09/11 14Z 0.33 3121  63   6   6 0.00
Fri 09/11 15Z 0.34 3119  63   7   6 0.00
Fri 09/11 16Z 0.35 3118  64   8   6 0.00
Fri 09/11 17Z 0.39 3117  65   8   7 0.00
Fri 09/11 18Z 0.44 3017  66   9   7 0.00
Fri 09/11 19Z 0.48 3016  66  12   7 0.00
Fri 09/11 20Z 0.57 3015  68  14   7 0.00
Fri 09/11 21Z 0.61 3014  68  16   7 0.00
Fri 09/11 22Z 0.55 3015  65  17   7 0.00
Fri 09/11 23Z 0.45 3016  60  17   8 0.00
Sat 09/12 00Z 0.33 3116  57  18   8 0.00
Sat 09/12 01Z 0.24 3215  54  22   9 0.00
Sat 09/12 02Z 0.15 3314  51  26   9 0.00
Sat 09/12 03Z 0.11 3312  49  31  10 0.00
Sat 09/12 04Z 0.10 3210  48  36  10 0.00
Sat 09/12 05Z 0.08 3208  45  42  11 0.00
Sat 09/12 06Z 0.06 3307  42  46  11 0.00
Sat 09/12 07Z 0.05 3204  41  47  11 0.00
Sat 09/12 08Z 0.07 3004  40  46  11 0.00
Sat 09/12 09Z 0.05 2802  39  42  12 0.00
Sat 09/12 10Z 0.05 2402  38  39  12 0.00
Sat 09/12 11Z 0.07 2103  38  36  11 0.00
Sat 09/12 12Z 0.06 2004  36  37  11 0.00
Sat 09/12 13Z 0.06 1906  36  37  11 0.00
Sat 09/12 14Z 0.07 1808  39  35  11 0.00
Sat 09/12 15Z 0.09 1909  42  30  11 0.00
Sat 09/12 16Z 0.18 1910  48  30  11 0.00
Sat 09/12 17Z 0.25 1911  54  28  11 0.00
Sat 09/12 18Z 0.34 1911  60  23  10 0.00
Sat 09/12 19Z 0.34 1911  63  17  11 0.00
Sat 09/12 20Z 0.27 1912  62  10  11 0.00
Sat 09/12 21Z 0.28 1914  59   5  12 0.00
Sat 09/12 22Z 0.37 2016  63   4  12 0.00
Sat 09/12 23Z 0.43 2018  67   4  12 0.00
Sun 09/13 00Z 0.48 2119  74   5  12 0.00
Sun 09/13 01Z 0.51 2121  81  29  12 0.00
Sun 09/13 02Z 0.46 2121  84  61  13 0.00
Sun 09/13 03Z 0.51 2223  89  85  13 0.00
Sun 09/13 04Z 0.51 2223  89  80  13 0.00
Sun 09/13 05Z 0.46 2222  87  84  13 0.00
Sun 09/13 06Z 0.39 2121  89  89  13 0.00
Sun 09/13 07Z 0.37 2122  94  96  13 0.03
Sun 09/13 08Z 0.43 2125  96  90  13 0.16
Sun 09/13 09Z 0.50 2228  95  87  14 0.08
Sun 09/13 10Z 0.52 2327  97  69  14 0.02
Sun 09/13 11Z 0.55 2327  98  61  14 0.03

Run total areal avg QPF for the Central_Greens is: 0.35 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