NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260511_1200
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)
=== ===== === ==== ==== === === === ====
Mon 05/11 12Z 0.57 2911  79  50  -2 0.00
Mon 05/11 13Z 0.87 2909  77  53  -2 0.00
Mon 05/11 14Z 2.31 2809  73  64  -2 0.00
Mon 05/11 15Z 4.91 2810  69  63  -1 0.00
Mon 05/11 16Z 7.11 2811  70  68  -1 0.00
Mon 05/11 17Z 6.71 2713  75  66  -1 0.00
Mon 05/11 18Z 7.33 2813  73  75  -1 0.00
Mon 05/11 19Z 4.58 2813  75  70  -1 0.00
Mon 05/11 20Z 5.55 2813  74  62   0 0.00
Mon 05/11 21Z 4.24 2913  77  71  -1 0.01
Mon 05/11 22Z 2.74 3014  77  74  -1 0.01
Mon 05/11 23Z 0.81 3115  80  70  -1 0.01
Tue 05/12 00Z 0.55 3216  78  51  -2 0.00
Tue 05/12 01Z 0.47 3317  77  60  -2 0.00
Tue 05/12 02Z 0.40 3317  76  70  -2 0.00
Tue 05/12 03Z 0.39 3318  79  64  -3 0.00
Tue 05/12 04Z 0.37 3319  83  54  -3 0.00
Tue 05/12 05Z 0.41 3419  78  47  -3 0.00
Tue 05/12 06Z 0.33 3419  76  39  -3 0.00
Tue 05/12 07Z 0.27 3419  74  34  -3 0.00
Tue 05/12 08Z 0.23 3417  72  26  -4 0.00
Tue 05/12 09Z 0.21 3416  71  25  -4 0.00
Tue 05/12 10Z 0.22 3415  70  29  -4 0.00
Tue 05/12 11Z 0.29 3414  71  35  -5 0.00
Tue 05/12 12Z 0.76 3313  73  37  -5 0.00
Tue 05/12 13Z 2.72 3213  77  33  -5 0.00
Tue 05/12 14Z 3.75 3212  78  26  -5 0.00
Tue 05/12 15Z 4.05 3211  74  25  -4 0.00
Tue 05/12 16Z 5.29 3112  72  25  -4 0.00
Tue 05/12 17Z 6.52 3013  72  31  -3 0.00
Tue 05/12 18Z 6.56 3013  72  34  -3 0.00
Tue 05/12 19Z 6.24 3012  71  34  -2 0.00
Tue 05/12 20Z 5.45 3011  68  28  -1 0.00
Tue 05/12 21Z 4.03 3109  66  23  -1 0.00
Tue 05/12 22Z 2.52 3108  64  21  -1 0.00
Tue 05/12 23Z 0.83 3107  63  21   0 0.00
Wed 05/13 00Z 0.42 3007  63  21   0 0.00
Wed 05/13 01Z 0.43 2807  63  24   0 0.00
Wed 05/13 02Z 0.35 2706  63  25   0 0.00
Wed 05/13 03Z 0.26 2605  63  26   0 0.00
Wed 05/13 04Z 0.24 2405  63  27   0 0.00
Wed 05/13 05Z 0.29 2307  63  23   0 0.00
Wed 05/13 06Z 0.29 2208  63  19   0 0.00
Wed 05/13 07Z 0.32 2110  61  18   0 0.00
Wed 05/13 08Z 0.36 2211  61  38   0 0.00
Wed 05/13 09Z 0.35 2112  62  72   0 0.00
Wed 05/13 10Z 0.36 2113  66  89   0 0.00
Wed 05/13 11Z 0.23 2013  66  95   0 0.00
Wed 05/13 12Z 0.16 1914  66  97   0 0.00
Wed 05/13 13Z 0.05 1816  71  98   1 0.00
Wed 05/13 14Z 0.08 1719  77  98   1 0.00
Wed 05/13 15Z 0.32 1622  83  97   1 0.01
Wed 05/13 16Z 0.19 1625  88  97   2 0.02
Wed 05/13 17Z 0.18 1627  93  97   3 0.03
Wed 05/13 18Z 0.13 1728  95  97   3 0.05
Wed 05/13 19Z 0.16 1730  96  96   3 0.06
Wed 05/13 20Z 0.15 1731  96  97   4 0.06
Wed 05/13 21Z 0.15 1830  96  97   4 0.06
Wed 05/13 22Z 0.15 1929  97  95   4 0.05
Wed 05/13 23Z 0.19 1930  97  95   4 0.07

Run total areal avg QPF for the greens is: 0.44 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