Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260505_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)
=== ===== === ==== ==== === === === ====
Tue 05/05 06Z 0.73 2136  61  75   9 0.00
Tue 05/05 07Z 0.77 2238  60  83   9 0.00
Tue 05/05 08Z 0.77 2236  61  60   9 0.00
Tue 05/05 09Z 0.80 2236  68  46   9 0.00
Tue 05/05 10Z 0.73 2232  73  70   9 0.00
Tue 05/05 11Z 0.73 2332  76  77   9 0.00
Tue 05/05 12Z 0.81 2333  83  91   9 0.01
Tue 05/05 13Z 0.79 2333  79  75   9 0.01
Tue 05/05 14Z 0.87 2331  75  75  10 0.00
Tue 05/05 15Z 1.24 2232  75  85  10 0.00
Tue 05/05 16Z 4.07 2230  72  74  10 0.00
Tue 05/05 17Z 9.10 2228  72  65  10 0.00
Tue 05/05 18Z 9.07 2127  73  63  11 0.01
Tue 05/05 19Z 8.68 2127  70  72  11 0.00
Tue 05/05 20Z 4.55 2228  77  73  11 0.12
Tue 05/05 21Z 2.97 2228  79  74  11 0.05
Tue 05/05 22Z 2.47 2329  81  87  10 0.08
Tue 05/05 23Z 1.20 2232  81  89  10 0.04
Wed 05/06 00Z 0.88 2333  82  68  10 0.09
Wed 05/06 01Z 0.94 2334  81  81  10 0.00
Wed 05/06 02Z 0.94 2429  86  96   9 0.10
Wed 05/06 03Z 0.88 2624  95  96   7 0.12
Wed 05/06 04Z 0.66 2521  96  99   7 0.11
Wed 05/06 05Z 0.59 2520  89  97   6 0.06
Wed 05/06 06Z 0.49 2517  87  93   5 0.03
Wed 05/06 07Z 0.33 2513  94  85   5 0.04
Wed 05/06 08Z 0.22 2311  94  84   5 0.02
Wed 05/06 09Z 0.17 2113  95  83   6 0.01
Wed 05/06 10Z 0.10 1916  95  69   7 0.01
Wed 05/06 11Z 0.08 1919  97  73   7 0.01
Wed 05/06 12Z 0.11 1922  98  65   7 0.02
Wed 05/06 13Z 0.17 1923  99  72   7 0.04
Wed 05/06 14Z 0.19 1924  98  86   8 0.05
Wed 05/06 15Z 0.19 1922  99  84   8 0.06
Wed 05/06 16Z 0.18 1920  99  92   8 0.07
Wed 05/06 17Z 0.25 2020  99  97   7 0.14
Wed 05/06 18Z 0.21 2016  99  99   6 0.16
Wed 05/06 19Z 0.20 2410  99  99   5 0.16
Wed 05/06 20Z 0.19 2810  96  97   4 0.14
Wed 05/06 21Z 0.22 3013  96  94   3 0.03
Wed 05/06 22Z 0.23 3114  93  81   2 0.01
Wed 05/06 23Z 0.21 3215  86  42   1 0.00
Thu 05/07 00Z 0.22 3216  79  22   1 0.00
Thu 05/07 01Z 0.23 3216  64  12   1 0.00
Thu 05/07 02Z 0.27 3116  49   7   0 0.00
Thu 05/07 03Z 0.35 3117  54   5   0 0.00
Thu 05/07 04Z 0.37 3118  69   5   0 0.00
Thu 05/07 05Z 0.45 3118  79  16   0 0.00
Thu 05/07 06Z 0.48 3017  81  23   0 0.00
Thu 05/07 07Z 0.52 2919  79  19   0 0.00
Thu 05/07 08Z 0.50 2919  68  28   0 0.00
Thu 05/07 09Z 0.55 2920  57  29   0 0.00
Thu 05/07 10Z 0.63 2821  56  45   0 0.00
Thu 05/07 11Z 0.66 2823  53  45  -1 0.00
Thu 05/07 12Z 0.65 2822  49  32  -1 0.00
Thu 05/07 13Z 0.66 2821  51  25  -1 0.00
Thu 05/07 14Z 0.80 2820  55  21  -2 0.00
Thu 05/07 15Z 2.89 2717  61  22  -2 0.00
Thu 05/07 16Z 11.25 2716  68  19  -2 0.00
Thu 05/07 17Z 11.90 2716  64  21  -1 0.00

Run total areal avg QPF for the greens is: 1.80 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