Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261016_0600
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 10/16 06Z 0.13 1925  65  62   7 0.00
Fri 10/16 07Z 0.14 1929  70  84   7 0.00
Fri 10/16 08Z 0.12 1833  72  97   7 0.00
Fri 10/16 09Z 0.13 1937  90  98   6 0.03
Fri 10/16 10Z 0.18 1940  96  97   7 0.14
Fri 10/16 11Z 0.30 2043  98  98   8 0.16
Fri 10/16 12Z 0.45 2145  98  96   9 0.22
Fri 10/16 13Z 0.52 2142  98  95  11 0.08
Fri 10/16 14Z 0.54 2240  98  94  12 0.06
Fri 10/16 15Z 0.54 2236  98  91  13 0.05
Fri 10/16 16Z 0.54 2334  98  87  13 0.05
Fri 10/16 17Z 0.60 2334  98  96  13 0.17
Fri 10/16 18Z 0.66 2432  97  93  13 0.12
Fri 10/16 19Z 0.74 2432  97  92  12 0.06
Fri 10/16 20Z 0.85 2432  96  82  11 0.04
Fri 10/16 21Z 1.02 2532  96  77  10 0.04
Fri 10/16 22Z 1.04 2631  98  68   9 0.06
Fri 10/16 23Z 1.16 2732  98  66   7 0.07
Sat 10/17 00Z 0.95 2828  97  79   5 0.04
Sat 10/17 01Z 0.80 3027  96  69   2 0.03
Sat 10/17 02Z 0.83 3027  96  47   0 0.03
Sat 10/17 03Z 0.77 3128  97  48  -1 0.02
Sat 10/17 04Z 0.65 3227  97  49  -2 0.02
Sat 10/17 05Z 0.60 3226  97  53  -2 0.02
Sat 10/17 06Z 0.59 3227  97  50  -3 0.02
Sat 10/17 07Z 0.55 3327  96  46  -4 0.01
Sat 10/17 08Z 0.59 3328  96  44  -4 0.01
Sat 10/17 09Z 0.62 3327  96  44  -5 0.01
Sat 10/17 10Z 0.62 3326  96  33  -5 0.01
Sat 10/17 11Z 0.53 3326  94  11  -6 0.01
Sat 10/17 12Z 0.53 3326  93   2  -6 0.01
Sat 10/17 13Z 0.50 3326  92   1  -7 0.01
Sat 10/17 14Z 0.40 3324  91   2  -8 0.01
Sat 10/17 15Z 0.34 3323  81   4  -8 0.00
Sat 10/17 16Z 0.37 3322  72   2  -8 0.00
Sat 10/17 17Z 0.67 3320  70   3  -9 0.00
Sat 10/17 18Z 1.06 3318  69   4  -9 0.00
Sat 10/17 19Z 1.31 3219  67   4  -9 0.00
Sat 10/17 20Z 1.87 3220  64   5  -8 0.00
Sat 10/17 21Z 2.61 3221  66   7  -8 0.00
Sat 10/17 22Z 1.19 3122  65  24  -8 0.00
Sat 10/17 23Z 0.82 3124  58  29  -8 0.00
Sun 10/18 00Z 0.58 3224  50  23  -7 0.00
Sun 10/18 01Z 0.47 3224  43  23  -6 0.00
Sun 10/18 02Z 0.42 3223  39  29  -6 0.00
Sun 10/18 03Z 0.39 3223  38  14  -6 0.00
Sun 10/18 04Z 0.41 3222  44   5  -6 0.00
Sun 10/18 05Z 0.45 3222  51   7  -6 0.00
Sun 10/18 06Z 0.44 3220  58  16  -6 0.00
Sun 10/18 07Z 0.46 3220  61   8  -6 0.00
Sun 10/18 08Z 0.46 3219  61   4  -6 0.00
Sun 10/18 09Z 0.42 3218  57   2  -5 0.00
Sun 10/18 10Z 0.39 3117  53   5  -4 0.00
Sun 10/18 11Z 0.34 3116  47   9  -3 0.00
Sun 10/18 12Z 0.32 3015  41  32  -2 0.00
Sun 10/18 13Z 0.33 3015  36  48  -2 0.00
Sun 10/18 14Z 0.33 2915  38  52  -1 0.00
Sun 10/18 15Z 0.32 2914  47  52   0 0.00
Sun 10/18 16Z 0.29 2913  51  47   0 0.00
Sun 10/18 17Z 0.28 2912  48  42   1 0.00

Run total areal avg QPF for the greens is: 1.61 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