NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260507_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 05/07 18Z 7.76 2811  67  45   0 0.00
Thu 05/07 19Z 8.82 2713  65  32   0 0.00
Thu 05/07 20Z 9.22 2714  65  33   0 0.00
Thu 05/07 21Z 9.93 2715  63  34   0 0.00
Thu 05/07 22Z 8.83 2815  63  29   0 0.00
Thu 05/07 23Z 5.61 2815  62  25   0 0.00
Fri 05/08 00Z 2.31 2917  60  25   0 0.00
Fri 05/08 01Z 1.45 2917  60  28  -1 0.00
Fri 05/08 02Z 1.12 3017  63  31  -1 0.00
Fri 05/08 03Z 0.93 3016  65  34  -1 0.00
Fri 05/08 04Z 0.97 3016  69  50  -2 0.00
Fri 05/08 05Z 0.82 2916  72  47  -2 0.00
Fri 05/08 06Z 0.70 3017  73  53  -2 0.00
Fri 05/08 07Z 0.63 3016  74  40  -2 0.00
Fri 05/08 08Z 0.64 3015  75  33  -2 0.00
Fri 05/08 09Z 0.58 3015  71  34  -2 0.00
Fri 05/08 10Z 0.56 2915  70  37  -2 0.00
Fri 05/08 11Z 0.55 2914  69  43  -2 0.00
Fri 05/08 12Z 0.94 2813  67  36  -3 0.00
Fri 05/08 13Z 5.81 2813  66  32  -3 0.00
Fri 05/08 14Z 8.12 2712  63  39  -2 0.00
Fri 05/08 15Z 8.03 2711  63  55  -2 0.00
Fri 05/08 16Z 7.66 2711  63  70  -1 0.00
Fri 05/08 17Z 7.74 2711  61  81  -1 0.00
Fri 05/08 18Z 7.97 2711  61  85   0 0.00
Fri 05/08 19Z 6.14 2711  65  87   0 0.00
Fri 05/08 20Z 6.79 2711  63  84   0 0.00
Fri 05/08 21Z 5.86 2711  68  79   0 0.00
Fri 05/08 22Z 3.61 2710  69  64   0 0.00
Fri 05/08 23Z 1.67 2711  70  56   0 0.00
Sat 05/09 00Z 0.89 2713  69  47   0 0.00
Sat 05/09 01Z 1.36 2714  69  30   0 0.00
Sat 05/09 02Z 1.30 2814  67  21  -1 0.00
Sat 05/09 03Z 1.12 2813  68  28  -1 0.00
Sat 05/09 04Z 0.96 2713  68  37  -1 0.00
Sat 05/09 05Z 0.80 2712  68  36  -1 0.00
Sat 05/09 06Z 0.61 2611  65  34  -1 0.00
Sat 05/09 07Z 0.50 2511  61  44  -1 0.00
Sat 05/09 08Z 0.42 2510  55  34  -1 0.00
Sat 05/09 09Z 0.36 2508  51  18   0 0.00
Sat 05/09 10Z 0.33 2408  47  11   0 0.00
Sat 05/09 11Z 0.31 2209  44   7   0 0.00
Sat 05/09 12Z 0.30 2010  41   6   0 0.00
Sat 05/09 13Z 0.35 1911  46   6   0 0.00
Sat 05/09 14Z 1.38 1812  58  15   0 0.00
Sat 05/09 15Z 1.48 1813  75  38   0 0.00
Sat 05/09 16Z 0.58 1814  89  65   0 0.01
Sat 05/09 17Z 0.23 1714  92  90   0 0.02
Sat 05/09 18Z 0.05 1614  95  97   0 0.04
Sat 05/09 19Z 0.12 1517  96  93   0 0.05
Sat 05/09 20Z 0.17 1519  96  89   0 0.03
Sat 05/09 21Z 0.11 1518  96  82   1 0.02
Sat 05/09 22Z 0.06 1717  97  86   2 0.02
Sat 05/09 23Z 0.10 1817  98  80   3 0.01
Sun 05/10 00Z 0.18 1917  98  81   3 0.01
Sun 05/10 01Z 0.28 2018  98  62   3 0.01
Sun 05/10 02Z 0.39 2021  98  40   3 0.02
Sun 05/10 03Z 0.45 2119  98  42   3 0.01
Sun 05/10 04Z 0.55 2220  98  41   3 0.01
Sun 05/10 05Z 0.57 2221  96  44   3 0.01

Run total areal avg QPF for the Central_Greens is: 0.27 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