NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260824_1200
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)
=== ===== === ==== ==== === === === ====
Mon 08/24 12Z 0.19 1914  81  41   9 0.00
Mon 08/24 13Z 0.29 2016  83  51   9 0.00
Mon 08/24 14Z 0.50 2116  89  63   9 0.00
Mon 08/24 15Z 1.38 2116  90  64   9 0.00
Mon 08/24 16Z 1.25 2117  91  63   9 0.00
Mon 08/24 17Z 0.96 2119  85  57   9 0.04
Mon 08/24 18Z 1.87 2218  82  52   9 0.01
Mon 08/24 19Z 3.53 2217  85  51   9 0.00
Mon 08/24 20Z 1.41 2316  84  57   9 0.01
Mon 08/24 21Z 1.27 2316  84  62   9 0.00
Mon 08/24 22Z 0.90 2315  84  63   9 0.00
Mon 08/24 23Z 0.94 2317  83  66   9 0.00
Tue 08/25 00Z 1.02 2318  81  69   9 0.00
Tue 08/25 01Z 1.05 2319  81  70   9 0.00
Tue 08/25 02Z 0.92 2318  82  70   9 0.00
Tue 08/25 03Z 0.73 2318  82  76   9 0.00
Tue 08/25 04Z 0.59 2316  83  72   9 0.00
Tue 08/25 05Z 0.41 2312  83  69   9 0.00
Tue 08/25 06Z 0.32 2311  83  71   9 0.00
Tue 08/25 07Z 0.31 2311  83  72   9 0.00
Tue 08/25 08Z 0.32 2411  85  74   9 0.00
Tue 08/25 09Z 0.30 2312  87  80   9 0.00
Tue 08/25 10Z 0.32 2312  89  75   9 0.00
Tue 08/25 11Z 0.34 2412  91  79   9 0.01
Tue 08/25 12Z 0.35 2413  93  74   9 0.00
Tue 08/25 13Z 0.32 2411  95  73   9 0.00
Tue 08/25 14Z 0.31 2509  96  68   9 0.00
Tue 08/25 15Z 0.33 2608  96  66   9 0.00
Tue 08/25 16Z 0.36 2707  96  77   8 0.00
Tue 08/25 17Z 0.42 2808  97  74   9 0.00
Tue 08/25 18Z 0.46 2810  97  71   9 0.01
Tue 08/25 19Z 0.43 2910  94  66   9 0.01
Tue 08/25 20Z 0.39 3010  95  68   9 0.02
Tue 08/25 21Z 0.37 3112  93  69   9 0.03
Tue 08/25 22Z 0.38 3113  94  62   9 0.01
Tue 08/25 23Z 0.32 3112  91  58  10 0.01
Wed 08/26 00Z 0.31 3112  90  53   9 0.01
Wed 08/26 01Z 0.33 3112  91  48   9 0.00
Wed 08/26 02Z 0.36 3013  94  49   9 0.01
Wed 08/26 03Z 0.37 3013  96  51   9 0.02
Wed 08/26 04Z 0.34 3013  95  50   9 0.02
Wed 08/26 05Z 0.32 3113  95  51   9 0.01
Wed 08/26 06Z 0.31 3012  95  52   9 0.01
Wed 08/26 07Z 0.28 3011  94  48   9 0.01
Wed 08/26 08Z 0.27 3011  92  43   9 0.01
Wed 08/26 09Z 0.25 3011  93  42   9 0.00
Wed 08/26 10Z 0.25 3010  93  39   9 0.01
Wed 08/26 11Z 0.21 3109  92  36   9 0.01
Wed 08/26 12Z 0.17 3107  91  35   9 0.00
Wed 08/26 13Z 0.14 3006  91  34   9 0.00
Wed 08/26 14Z 0.14 2905  90  28   9 0.00
Wed 08/26 15Z 0.13 2804  90  24   9 0.00
Wed 08/26 16Z 0.14 2704  90  22   9 0.00
Wed 08/26 17Z 0.14 2604  89  19   9 0.00
Wed 08/26 18Z 0.15 2504  89  18   9 0.00
Wed 08/26 19Z 0.14 2503  88  17   9 0.00
Wed 08/26 20Z 0.14 2403  88  15  10 0.00
Wed 08/26 21Z 0.15 2504  87  14  10 0.00
Wed 08/26 22Z 0.13 2403  85  13  10 0.00
Wed 08/26 23Z 0.10 2303  84  13  11 0.00

Run total areal avg QPF for the greens is: 0.28 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