Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260123_0600
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)
=== ===== === ==== ==== === === === ====
Fri 01/23 06Z 1.13 2625  83  36 -15 0.00
Fri 01/23 07Z 2.53 2625  88  27 -16 0.00
Fri 01/23 08Z 3.73 2625  86  27 -16 0.00
Fri 01/23 09Z 1.83 2624  85  33 -17 0.00
Fri 01/23 10Z 1.42 2623  86  35 -17 0.01
Fri 01/23 11Z 1.44 2623  88  44 -17 0.00
Fri 01/23 12Z 1.25 2624  87  55 -17 0.01
Fri 01/23 13Z 1.26 2624  86  66 -17 0.01
Fri 01/23 14Z 3.93 2620  88  64 -18 0.00
Fri 01/23 15Z 4.70 2519  88  67 -17 0.01
Fri 01/23 16Z 7.28 2518  86  62 -17 0.01
Fri 01/23 17Z 10.44 2620  81  60 -17 0.01
Fri 01/23 18Z 10.45 2621  79  57 -18 0.01
Fri 01/23 19Z 10.26 2622  80  55 -18 0.01
Fri 01/23 20Z 12.22 2623  75  59 -18 0.01
Fri 01/23 21Z 10.85 2724  78  61 -19 0.01
Fri 01/23 22Z 5.00 2825  82  71 -20 0.01
Fri 01/23 23Z 5.49 2926  76  69 -21 0.01
Sat 01/24 00Z 8.86 2828  67  45 -22 0.00
Sat 01/24 01Z 8.31 2830  73  55 -23 0.00
Sat 01/24 02Z 14.03 2833  71  28 -25 0.00
Sat 01/24 03Z 10.45 2930  74  28 -26 0.00
Sat 01/24 04Z 2.79 3028  72  25 -26 0.00
Sat 01/24 05Z 4.35 3029  75  20 -27 0.00
Sat 01/24 06Z 4.26 3028  71  22 -28 0.00
Sat 01/24 07Z 1.54 3029  60  19 -29 0.00
Sat 01/24 08Z 0.79 3028  59  17 -28 0.00
Sat 01/24 09Z 0.51 3127  59  19 -28 0.00
Sat 01/24 10Z 0.43 3127  62  19 -27 0.00
Sat 01/24 11Z 0.37 3127  61  19 -26 0.00
Sat 01/24 12Z 0.33 3128  58  19 -25 0.00
Sat 01/24 13Z 0.32 3128  55  19 -25 0.00
Sat 01/24 14Z 0.30 3127  51  19 -24 0.00
Sat 01/24 15Z 0.31 3126  48  19 -24 0.00
Sat 01/24 16Z 0.32 3125  46  21 -24 0.00
Sat 01/24 17Z 0.33 3124  47  21 -24 0.00
Sat 01/24 18Z 0.34 3123  49  19 -24 0.00
Sat 01/24 19Z 0.35 3022  53  16 -24 0.00
Sat 01/24 20Z 0.37 3021  56  13 -24 0.00
Sat 01/24 21Z 0.40 3020  57  13 -24 0.00
Sat 01/24 22Z 0.40 3020  55  12 -24 0.00
Sat 01/24 23Z 0.39 3020  53  11 -23 0.00
Sun 01/25 00Z 0.33 3020  50  11 -22 0.00
Sun 01/25 01Z 0.27 3120  48  13 -21 0.00
Sun 01/25 02Z 0.25 3120  46  14 -21 0.00
Sun 01/25 03Z 0.23 3120  42  14 -20 0.00
Sun 01/25 04Z 0.20 3119  37  13 -20 0.00
Sun 01/25 05Z 0.18 3118  33  10 -19 0.00
Sun 01/25 06Z 0.18 3117  31   9 -19 0.00
Sun 01/25 07Z 0.16 3116  29   9 -18 0.00
Sun 01/25 08Z 0.16 3115  29   9 -18 0.00
Sun 01/25 09Z 0.16 3114  28   9 -18 0.00
Sun 01/25 10Z 0.13 3111  26  10 -17 0.00
Sun 01/25 11Z 0.15 3011  25  12 -17 0.00
Sun 01/25 12Z 0.13 2908  25  15 -17 0.00
Sun 01/25 13Z 0.09 2906  23  19 -16 0.00
Sun 01/25 14Z 0.07 2905  22  27 -16 0.00
Sun 01/25 15Z 0.05 2502  22  45 -15 0.00
Sun 01/25 16Z 0.03 2002  24  65 -15 0.00
Sun 01/25 17Z 0.04 1904  27  81 -15 0.00

Run total areal avg QPF for the Central_Greens is: 0.12 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