NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260507_1800
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 18Z 8.89 2712  68  49   0 0.00
Thu 05/07 19Z 9.95 2714  66  36   0 0.00
Thu 05/07 20Z 10.60 2715  65  38   0 0.00
Thu 05/07 21Z 10.03 2716  64  38   0 0.00
Thu 05/07 22Z 9.97 2816  63  33   0 0.00
Thu 05/07 23Z 6.10 2816  62  35   0 0.00
Fri 05/08 00Z 2.47 2918  62  36  -1 0.00
Fri 05/08 01Z 1.52 2919  65  43  -1 0.00
Fri 05/08 02Z 1.20 2918  69  44  -1 0.00
Fri 05/08 03Z 1.02 3017  71  48  -2 0.00
Fri 05/08 04Z 1.05 2917  74  56  -2 0.00
Fri 05/08 05Z 0.92 2917  76  53  -2 0.00
Fri 05/08 06Z 0.85 3017  77  60  -2 0.00
Fri 05/08 07Z 0.78 3016  76  50  -2 0.00
Fri 05/08 08Z 0.86 3015  75  42  -3 0.00
Fri 05/08 09Z 0.72 2915  72  39  -2 0.00
Fri 05/08 10Z 0.69 2915  71  40  -3 0.00
Fri 05/08 11Z 0.66 2914  69  43  -3 0.00
Fri 05/08 12Z 0.96 2813  69  38  -3 0.00
Fri 05/08 13Z 5.66 2812  68  36  -3 0.00
Fri 05/08 14Z 8.25 2811  66  42  -3 0.00
Fri 05/08 15Z 8.18 2711  66  54  -2 0.00
Fri 05/08 16Z 7.61 2711  66  65  -2 0.00
Fri 05/08 17Z 7.50 2710  65  74  -1 0.00
Fri 05/08 18Z 7.18 2711  65  76  -1 0.00
Fri 05/08 19Z 6.59 2711  68  78  -1 0.00
Fri 05/08 20Z 6.62 2711  67  76  -1 0.00
Fri 05/08 21Z 6.13 2711  70  72  -1 0.00
Fri 05/08 22Z 3.96 2710  70  63   0 0.00
Fri 05/08 23Z 1.67 2710  70  56   0 0.00
Sat 05/09 00Z 0.97 2712  69  47   0 0.00
Sat 05/09 01Z 1.43 2714  70  44  -1 0.00
Sat 05/09 02Z 1.20 2714  70  35  -1 0.00
Sat 05/09 03Z 1.15 2814  69  28  -1 0.00
Sat 05/09 04Z 1.03 2714  69  37  -1 0.00
Sat 05/09 05Z 0.83 2713  67  41  -1 0.00
Sat 05/09 06Z 0.67 2612  68  42  -1 0.00
Sat 05/09 07Z 0.59 2512  65  55  -1 0.00
Sat 05/09 08Z 0.53 2512  59  44  -1 0.00
Sat 05/09 09Z 0.45 2510  57  26  -1 0.00
Sat 05/09 10Z 0.38 2409  54  15  -1 0.00
Sat 05/09 11Z 0.30 2208  50   8   0 0.00
Sat 05/09 12Z 0.25 2109  48   7   0 0.00
Sat 05/09 13Z 0.30 1910  51   6   0 0.00
Sat 05/09 14Z 0.55 1811  59  12   0 0.00
Sat 05/09 15Z 0.64 1812  67  27   0 0.00
Sat 05/09 16Z 0.41 1813  74  45   0 0.01
Sat 05/09 17Z 0.24 1713  78  61   0 0.02
Sat 05/09 18Z 0.42 1614  82  70   0 0.02
Sat 05/09 19Z 0.65 1617  88  76   0 0.04
Sat 05/09 20Z 0.42 1519  92  83   0 0.02
Sat 05/09 21Z 0.17 1619  94  78   1 0.01
Sat 05/09 22Z 0.12 1619  95  77   2 0.01
Sat 05/09 23Z 0.08 1719  96  78   2 0.01
Sun 05/10 00Z 0.08 1819  96  82   3 0.01
Sun 05/10 01Z 0.15 1920  96  68   3 0.01
Sun 05/10 02Z 0.26 2022  97  46   3 0.01
Sun 05/10 03Z 0.32 2021  98  41   3 0.01
Sun 05/10 04Z 0.41 2122  97  43   3 0.01
Sun 05/10 05Z 0.44 2123  94  49   3 0.01

Run total areal avg QPF for the greens is: 0.20 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