Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261016_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 10/16 06Z 0.23 1925  67  75   7 0.00
Fri 10/16 07Z 0.25 1928  70  96   7 0.00
Fri 10/16 08Z 0.25 1932  71  99   7 0.00
Fri 10/16 09Z 0.27 1936  89  97   7 0.02
Fri 10/16 10Z 0.37 1940  95  96   8 0.05
Fri 10/16 11Z 0.49 2043  98  98   9 0.08
Fri 10/16 12Z 0.61 2144  98  94  10 0.19
Fri 10/16 13Z 0.66 2142  98  93  11 0.08
Fri 10/16 14Z 0.66 2239  98  91  12 0.03
Fri 10/16 15Z 0.62 2235  98  90  13 0.04
Fri 10/16 16Z 0.60 2233  98  94  13 0.06
Fri 10/16 17Z 0.68 2334  98  97  13 0.21
Fri 10/16 18Z 0.73 2432  97  95  13 0.13
Fri 10/16 19Z 0.81 2432  97  97  12 0.08
Fri 10/16 20Z 0.91 2432  96  91  12 0.05
Fri 10/16 21Z 1.08 2433  95  83  11 0.05
Fri 10/16 22Z 1.26 2532  98  76  10 0.04
Fri 10/16 23Z 1.37 2731  98  74   9 0.07
Sat 10/17 00Z 0.97 2827  97  81   7 0.04
Sat 10/17 01Z 0.57 3026  96  81   4 0.03
Sat 10/17 02Z 0.60 3027  95  45   1 0.01
Sat 10/17 03Z 0.62 3128  95  39   0 0.01
Sat 10/17 04Z 0.52 3227  97  36  -1 0.01
Sat 10/17 05Z 0.43 3226  96  48  -2 0.01
Sat 10/17 06Z 0.38 3227  97  47  -2 0.01
Sat 10/17 07Z 0.32 3327  96  41  -3 0.01
Sat 10/17 08Z 0.30 3327  95  35  -3 0.01
Sat 10/17 09Z 0.32 3327  96  36  -4 0.01
Sat 10/17 10Z 0.31 3326  95  26  -5 0.01
Sat 10/17 11Z 0.25 3326  93   8  -5 0.01
Sat 10/17 12Z 0.24 3326  91   1  -6 0.00
Sat 10/17 13Z 0.23 3326  90   1  -6 0.00
Sat 10/17 14Z 0.22 3324  90   2  -7 0.00
Sat 10/17 15Z 0.22 3324  84   3  -7 0.00
Sat 10/17 16Z 0.19 3322  73   2  -8 0.00
Sat 10/17 17Z 0.27 3320  67   3  -8 0.00
Sat 10/17 18Z 0.48 3319  63   4  -8 0.00
Sat 10/17 19Z 0.68 3320  60   3  -8 0.00
Sat 10/17 20Z 0.86 3222  55   5  -8 0.00
Sat 10/17 21Z 0.82 3222  61   7  -8 0.00
Sat 10/17 22Z 0.70 3222  62  24  -8 0.00
Sat 10/17 23Z 0.58 3224  56  23  -7 0.00
Sun 10/18 00Z 0.37 3225  48  17  -7 0.00
Sun 10/18 01Z 0.25 3324  38  22  -6 0.00
Sun 10/18 02Z 0.21 3324  33  25  -6 0.00
Sun 10/18 03Z 0.19 3323  33  14  -5 0.00
Sun 10/18 04Z 0.17 3322  37   3  -6 0.00
Sun 10/18 05Z 0.20 3321  45   3  -6 0.00
Sun 10/18 06Z 0.21 3320  53  16  -6 0.00
Sun 10/18 07Z 0.24 3320  57   8  -6 0.00
Sun 10/18 08Z 0.26 3219  60   4  -5 0.00
Sun 10/18 09Z 0.27 3218  58   2  -5 0.00
Sun 10/18 10Z 0.27 3217  54   7  -4 0.00
Sun 10/18 11Z 0.25 3116  48   9  -3 0.00
Sun 10/18 12Z 0.24 3115  41  29  -2 0.00
Sun 10/18 13Z 0.26 3015  36  41  -1 0.00
Sun 10/18 14Z 0.26 3015  35  49  -1 0.00
Sun 10/18 15Z 0.24 3014  42  53   0 0.00
Sun 10/18 16Z 0.22 3012  47  48   0 0.00
Sun 10/18 17Z 0.20 3011  46  42   1 0.00

Run total areal avg QPF for the Central_Greens is: 1.35 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