NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260508_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 05/08 00Z 0.67 2913  64  45   0 0.00
Fri 05/08 01Z 0.86 2915  62  49  -1 0.00
Fri 05/08 02Z 1.07 2916  59  47  -1 0.00
Fri 05/08 03Z 1.70 2917  61  48  -1 0.00
Fri 05/08 04Z 1.41 2918  68  58  -2 0.00
Fri 05/08 05Z 0.97 2818  72  65  -2 0.00
Fri 05/08 06Z 0.89 2919  73  60  -2 0.00
Fri 05/08 07Z 0.87 2920  72  54  -2 0.00
Fri 05/08 08Z 0.87 2920  73  56  -3 0.00
Fri 05/08 09Z 0.88 2920  72  56  -3 0.00
Fri 05/08 10Z 0.85 2919  70  55  -3 0.00
Fri 05/08 11Z 0.89 2917  69  57  -3 0.00
Fri 05/08 12Z 1.22 2916  69  59  -3 0.00
Fri 05/08 13Z 5.64 2813  68  64  -3 0.00
Fri 05/08 14Z 7.94 2811  66  63  -3 0.00
Fri 05/08 15Z 7.57 2710  65  62  -2 0.00
Fri 05/08 16Z 7.32 2610  65  62  -2 0.00
Fri 05/08 17Z 7.35 2610  64  71  -1 0.00
Fri 05/08 18Z 6.84 2610  68  82  -1 0.00
Fri 05/08 19Z 6.36 2612  72  88  -1 0.00
Fri 05/08 20Z 5.25 2612  75  84  -1 0.00
Fri 05/08 21Z 5.26 2712  72  76  -1 0.00
Fri 05/08 22Z 4.06 2711  71  69  -1 0.00
Fri 05/08 23Z 2.38 2811  70  60  -1 0.00
Sat 05/09 00Z 1.03 2812  71  47  -1 0.00
Sat 05/09 01Z 1.21 2813  72  43  -1 0.00
Sat 05/09 02Z 1.38 2814  71  39  -2 0.00
Sat 05/09 03Z 1.46 2815  69  32  -2 0.00
Sat 05/09 04Z 1.08 2815  68  31  -2 0.00
Sat 05/09 05Z 0.79 2814  67  34  -2 0.00
Sat 05/09 06Z 0.67 2813  66  32  -2 0.00
Sat 05/09 07Z 0.62 2812  65  25  -2 0.00
Sat 05/09 08Z 0.57 2710  62  16  -2 0.00
Sat 05/09 09Z 0.56 2609  62  12  -2 0.00
Sat 05/09 10Z 0.45 2508  62   8  -1 0.00
Sat 05/09 11Z 0.34 2307  62   7  -1 0.00
Sat 05/09 12Z 0.35 2108  59   9  -1 0.00
Sat 05/09 13Z 0.43 1910  58  12  -1 0.00
Sat 05/09 14Z 0.38 1812  56  25  -1 0.00
Sat 05/09 15Z 0.88 1713  57  40   0 0.00
Sat 05/09 16Z 0.81 1714  67  53   0 0.00
Sat 05/09 17Z 0.77 1716  78  71   0 0.02
Sat 05/09 18Z 0.55 1719  84  80   0 0.03
Sat 05/09 19Z 0.17 1721  89  84   0 0.02
Sat 05/09 20Z 0.04 1722  94  91   0 0.02
Sat 05/09 21Z 0.05 1822  96  88   1 0.01
Sat 05/09 22Z 0.06 1822  96  75   2 0.01
Sat 05/09 23Z 0.14 1923  97  68   2 0.01
Sun 05/10 00Z 0.20 2024  97  37   3 0.02
Sun 05/10 01Z 0.26 2023  98  40   3 0.02
Sun 05/10 02Z 0.31 2123  97  61   3 0.01
Sun 05/10 03Z 0.38 2124  95  76   4 0.01
Sun 05/10 04Z 0.44 2125  93  72   5 0.01
Sun 05/10 05Z 0.46 2127  88  76   5 0.01
Sun 05/10 06Z 0.68 2232  93  90   5 0.01
Sun 05/10 07Z 0.80 2330  91  90   4 0.04
Sun 05/10 08Z 0.89 2427  93  79   3 0.03
Sun 05/10 09Z 0.86 2526  88  68   3 0.02
Sun 05/10 10Z 0.80 2525  74  63   3 0.01
Sun 05/10 11Z 0.72 2623  62  38   3 0.01

Run total areal avg QPF for the greens is: 0.32 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