NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260828_0000
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 00Z 0.42 2121  92  79  13 0.00
Fri 08/28 01Z 0.49 2123  92  74  14 0.00
Fri 08/28 02Z 0.56 2224  92  74  13 0.01
Fri 08/28 03Z 0.62 2224  88  72  14 0.01
Fri 08/28 04Z 0.67 2422  90  63  13 0.01
Fri 08/28 05Z 0.66 2521  91  64  13 0.01
Fri 08/28 06Z 0.63 2520  89  56  13 0.01
Fri 08/28 07Z 0.56 2617  88  47  13 0.01
Fri 08/28 08Z 0.47 2614  88  47  13 0.00
Fri 08/28 09Z 0.40 2712  88  48  12 0.00
Fri 08/28 10Z 0.37 2811  89  52  12 0.00
Fri 08/28 11Z 0.34 2810  90  54  12 0.00
Fri 08/28 12Z 0.30 2809  89  51  12 0.01
Fri 08/28 13Z 0.28 2708  89  48  11 0.01
Fri 08/28 14Z 0.27 2707  90  38  11 0.01
Fri 08/28 15Z 0.30 2708  90  32  11 0.01
Fri 08/28 16Z 0.33 2709  90  32  11 0.01
Fri 08/28 17Z 0.35 2809  89  26  11 0.00
Fri 08/28 18Z 0.38 2809  90  27  11 0.00
Fri 08/28 19Z 0.42 2910  91  19  11 0.01
Fri 08/28 20Z 0.43 2910  89  29  11 0.01
Fri 08/28 21Z 0.32 2911  84  20  11 0.01
Fri 08/28 22Z 0.30 3011  80  22  11 0.00
Fri 08/28 23Z 0.30 3012  74  17  10 0.00
Sat 08/29 00Z 0.28 3013  70  15  10 0.00
Sat 08/29 01Z 0.26 3113  67  11  10 0.00
Sat 08/29 02Z 0.25 3114  65   7   9 0.00
Sat 08/29 03Z 0.25 3114  66   6   9 0.00
Sat 08/29 04Z 0.24 3215  65   7   9 0.00
Sat 08/29 05Z 0.24 3215  64   7   8 0.00
Sat 08/29 06Z 0.23 3215  63   8   8 0.00
Sat 08/29 07Z 0.22 3214  63   7   8 0.00
Sat 08/29 08Z 0.19 3212  61   9   9 0.00
Sat 08/29 09Z 0.20 3212  59  12   9 0.00
Sat 08/29 10Z 0.20 3213  55  12   9 0.00
Sat 08/29 11Z 0.20 3213  53  11   9 0.00
Sat 08/29 12Z 0.20 3112  53  11   9 0.00
Sat 08/29 13Z 0.19 3111  55  11   8 0.00
Sat 08/29 14Z 0.19 3109  59  18   8 0.00
Sat 08/29 15Z 0.21 2907  62  24   8 0.00
Sat 08/29 16Z 0.23 2806  62  26   8 0.00
Sat 08/29 17Z 0.35 2807  61  25   8 0.00
Sat 08/29 18Z 0.45 2807  61  14   8 0.00
Sat 08/29 19Z 0.46 2808  66  13   9 0.00
Sat 08/29 20Z 0.53 2708  72  14   9 0.00
Sat 08/29 21Z 0.66 2709  79  12   9 0.00
Sat 08/29 22Z 0.71 2611  83  13   9 0.00
Sat 08/29 23Z 0.71 2613  85   7   9 0.00
Sun 08/30 00Z 0.81 2515  87   5   9 0.00
Sun 08/30 01Z 1.03 2618  89   7   9 0.00
Sun 08/30 02Z 1.16 2619  89  11   8 0.00
Sun 08/30 03Z 1.06 2720  85  16   9 0.00
Sun 08/30 04Z 1.03 2721  81  18   9 0.00
Sun 08/30 05Z 1.01 2822  87  26   9 0.00
Sun 08/30 06Z 0.92 2722  88  29   9 0.00
Sun 08/30 07Z 0.98 2723  89  28   9 0.01
Sun 08/30 08Z 0.96 2623  90  28   9 0.01
Sun 08/30 09Z 0.97 2623  89  27   9 0.01
Sun 08/30 10Z 1.00 2624  88  27   9 0.01
Sun 08/30 11Z 0.94 2624  87  23   9 0.01

Run total areal avg QPF for the greens is: 0.19 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