NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260507_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)
=== ===== === ==== ==== === === === ====
Thu 05/07 00Z 0.21 3112  95  98   3 0.00
Thu 05/07 01Z 0.28 3014  90  95   2 0.01
Thu 05/07 02Z 0.27 3114  82  90   2 0.01
Thu 05/07 03Z 0.33 3117  78  92   1 0.00
Thu 05/07 04Z 0.44 3017  85  92   0 0.01
Thu 05/07 05Z 0.52 3017  86  91   0 0.00
Thu 05/07 06Z 0.46 2915  84  83   0 0.00
Thu 05/07 07Z 0.53 2916  87  70   0 0.00
Thu 05/07 08Z 0.61 2817  91  55   0 0.00
Thu 05/07 09Z 0.66 2819  93  48  -1 0.01
Thu 05/07 10Z 0.57 2718  86  52  -1 0.01
Thu 05/07 11Z 0.68 2721  74  38  -2 0.00
Thu 05/07 12Z 0.57 2819  64  21  -2 0.00
Thu 05/07 13Z 0.70 2820  70  22  -3 0.00
Thu 05/07 14Z 0.93 2919  75  25  -3 0.00
Thu 05/07 15Z 5.71 2817  79  35  -3 0.00
Thu 05/07 16Z 10.26 2815  78  43  -2 0.00
Thu 05/07 17Z 10.46 2714  72  49  -1 0.00
Thu 05/07 18Z 10.81 2715  65  39  -1 0.00
Thu 05/07 19Z 11.83 2716  58  32   0 0.00
Thu 05/07 20Z 12.26 2717  54  28   0 0.00
Thu 05/07 21Z 11.83 2817  53  29   0 0.00
Thu 05/07 22Z 10.77 2817  55  28   0 0.00
Thu 05/07 23Z 7.33 2917  56  28   0 0.00
Fri 05/08 00Z 2.19 2919  58  25  -1 0.00
Fri 05/08 01Z 2.00 2919  63  27  -1 0.00
Fri 05/08 02Z 1.95 2919  65  27  -2 0.00
Fri 05/08 03Z 1.72 2919  69  27  -2 0.00
Fri 05/08 04Z 1.36 2919  72  30  -2 0.00
Fri 05/08 05Z 1.08 2919  72  37  -2 0.00
Fri 05/08 06Z 0.89 2918  72  45  -2 0.00
Fri 05/08 07Z 0.81 2918  71  42  -2 0.00
Fri 05/08 08Z 0.79 2918  70  57  -2 0.00
Fri 05/08 09Z 0.76 2917  69  56  -3 0.00
Fri 05/08 10Z 0.74 2916  68  55  -3 0.00
Fri 05/08 11Z 0.74 2915  71  58  -3 0.00
Fri 05/08 12Z 1.05 2814  76  60  -3 0.00
Fri 05/08 13Z 2.72 2813  78  56  -3 0.00
Fri 05/08 14Z 6.32 2711  73  54  -3 0.00
Fri 05/08 15Z 8.18 2711  72  56  -3 0.00
Fri 05/08 16Z 8.33 2712  73  52  -2 0.00
Fri 05/08 17Z 8.20 2812  68  53  -2 0.00
Fri 05/08 18Z 8.19 2812  68  57  -2 0.00
Fri 05/08 19Z 8.06 2812  70  52  -2 0.00
Fri 05/08 20Z 8.32 2812  68  54  -2 0.00
Fri 05/08 21Z 6.51 2711  69  34  -2 0.00
Fri 05/08 22Z 6.98 2711  67  27  -1 0.00
Fri 05/08 23Z 4.85 2712  66  23  -1 0.00
Sat 05/09 00Z 2.52 2714  66  19  -2 0.00
Sat 05/09 01Z 1.90 2714  66  13  -2 0.00
Sat 05/09 02Z 1.68 2715  65  12  -2 0.00
Sat 05/09 03Z 1.28 2714  64  15  -2 0.00
Sat 05/09 04Z 1.04 2713  60  19  -2 0.00
Sat 05/09 05Z 0.75 2712  57  19  -2 0.00
Sat 05/09 06Z 0.62 2611  56  19  -2 0.00
Sat 05/09 07Z 0.52 2610  55  23  -2 0.00
Sat 05/09 08Z 0.43 2609  54  21  -1 0.00
Sat 05/09 09Z 0.35 2507  54  18  -1 0.00
Sat 05/09 10Z 0.29 2406  54  19  -1 0.00
Sat 05/09 11Z 0.19 2106  53  17  -1 0.00

Run total areal avg QPF for the greens is: 0.05 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