NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260828_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 08/28 06Z 0.51 2416  90  75  13 0.00
Fri 08/28 07Z 0.53 2516  90  75  13 0.00
Fri 08/28 08Z 0.57 2517  92  75  13 0.00
Fri 08/28 09Z 0.59 2617  94  67  12 0.00
Fri 08/28 10Z 0.57 2715  93  52  12 0.01
Fri 08/28 11Z 0.54 2814  92  46  12 0.01
Fri 08/28 12Z 0.47 2812  93  40  12 0.01
Fri 08/28 13Z 0.43 2811  91  39  11 0.00
Fri 08/28 14Z 0.41 2710  90  36  11 0.00
Fri 08/28 15Z 0.46 2709  90  46  11 0.00
Fri 08/28 16Z 0.49 2709  91  47  11 0.01
Fri 08/28 17Z 0.53 2811  92  60  11 0.02
Fri 08/28 18Z 0.63 2914  91  55  11 0.03
Fri 08/28 19Z 0.47 2914  90  34  11 0.02
Fri 08/28 20Z 0.41 2914  86  26  10 0.02
Fri 08/28 21Z 0.42 2914  82  20  10 0.00
Fri 08/28 22Z 0.40 3014  81  24   9 0.00
Fri 08/28 23Z 0.37 3014  79  27   9 0.00
Sat 08/29 00Z 0.37 3015  78  21   9 0.00
Sat 08/29 01Z 0.37 3017  76  14   9 0.00
Sat 08/29 02Z 0.36 3118  76   9   8 0.00
Sat 08/29 03Z 0.32 3117  77   7   8 0.00
Sat 08/29 04Z 0.32 3117  77   6   8 0.00
Sat 08/29 05Z 0.29 3217  75   7   7 0.00
Sat 08/29 06Z 0.26 3216  74   7   7 0.00
Sat 08/29 07Z 0.24 3216  70   7   7 0.00
Sat 08/29 08Z 0.23 3216  65   7   7 0.00
Sat 08/29 09Z 0.21 3315  65   6   7 0.00
Sat 08/29 10Z 0.23 3315  66   5   6 0.00
Sat 08/29 11Z 0.24 3214  66   5   7 0.00
Sat 08/29 12Z 0.26 3212  66   6   7 0.00
Sat 08/29 13Z 0.29 3112  67   7   7 0.00
Sat 08/29 14Z 0.30 3010  68   6   7 0.00
Sat 08/29 15Z 0.32 2909  68   7   7 0.00
Sat 08/29 16Z 0.31 2808  65   9   8 0.00
Sat 08/29 17Z 0.46 2708  66  10   8 0.00
Sat 08/29 18Z 0.69 2710  69  12   8 0.00
Sat 08/29 19Z 0.69 2709  71  13   8 0.00
Sat 08/29 20Z 0.63 2608  73  10   8 0.00
Sat 08/29 21Z 0.62 2609  75  11   9 0.00
Sat 08/29 22Z 0.59 2511  77  19   9 0.00
Sat 08/29 23Z 0.67 2514  79  24   9 0.00
Sun 08/30 00Z 0.77 2517  78  16   9 0.00
Sun 08/30 01Z 0.79 2618  76  11   9 0.00
Sun 08/30 02Z 0.76 2718  75  12  10 0.00
Sun 08/30 03Z 0.86 2720  76  13  10 0.00
Sun 08/30 04Z 0.98 2721  75  18  10 0.00
Sun 08/30 05Z 1.09 2822  77  24   9 0.00
Sun 08/30 06Z 1.10 2723  78  27   9 0.00
Sun 08/30 07Z 1.12 2723  80  29   9 0.01
Sun 08/30 08Z 1.03 2724  81  34  10 0.01
Sun 08/30 09Z 1.00 2723  82  35  10 0.00
Sun 08/30 10Z 0.94 2722  81  41  10 0.00
Sun 08/30 11Z 0.85 2721  80  44  10 0.00
Sun 08/30 12Z 0.85 2721  82  51  10 0.00
Sun 08/30 13Z 0.82 2720  83  54  10 0.01
Sun 08/30 14Z 0.82 2719  82  52  10 0.00
Sun 08/30 15Z 0.83 2617  79  62  10 0.00
Sun 08/30 16Z 0.83 2617  76  68  10 0.00
Sun 08/30 17Z 1.09 2516  76  85  10 0.00

Run total areal avg QPF for the greens is: 0.16 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