Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260122_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 01/22 18Z 2.22 2421  91  79  -9 0.00
Thu 01/22 19Z 4.57 2527  94  71  -9 0.00
Thu 01/22 20Z 15.42 2531  86  62 -10 0.00
Thu 01/22 21Z 13.48 2634  74  66 -11 0.01
Thu 01/22 22Z 4.33 2729  73  46 -12 0.00
Thu 01/22 23Z 3.45 2627  76  55 -13 0.00
Fri 01/23 00Z 2.03 2623  79  70 -13 0.00
Fri 01/23 01Z 1.71 2622  88  71 -13 0.01
Fri 01/23 02Z 1.26 2623  89  44 -13 0.01
Fri 01/23 03Z 1.74 2525  92  37 -14 0.01
Fri 01/23 04Z 1.97 2527  91  26 -14 0.01
Fri 01/23 05Z 2.51 2627  88  24 -15 0.01
Fri 01/23 06Z 3.05 2726  86  20 -16 0.00
Fri 01/23 07Z 2.00 2725  82  21 -17 0.01
Fri 01/23 08Z 1.51 2624  84  22 -18 0.01
Fri 01/23 09Z 1.68 2624  87  19 -18 0.01
Fri 01/23 10Z 1.50 2622  87  22 -18 0.01
Fri 01/23 11Z 1.36 2621  87  26 -18 0.00
Fri 01/23 12Z 1.20 2522  86  24 -18 0.00
Fri 01/23 13Z 1.14 2524  89  40 -18 0.00
Fri 01/23 14Z 1.47 2426  92  33 -18 0.00
Fri 01/23 15Z 6.38 2525  93  46 -18 0.01
Fri 01/23 16Z 12.69 2625  85  55 -19 0.01
Fri 01/23 17Z 13.09 2724  75  58 -19 0.01
Fri 01/23 18Z 12.05 2721  73  59 -19 0.01
Fri 01/23 19Z 10.34 2721  73  64 -19 0.01
Fri 01/23 20Z 10.23 2721  74  69 -20 0.01
Fri 01/23 21Z 9.56 2723  74  68 -20 0.01
Fri 01/23 22Z 6.80 2823  76  71 -21 0.01
Fri 01/23 23Z 4.37 2823  76  68 -21 0.01
Sat 01/24 00Z 5.88 2827  70  59 -22 0.01
Sat 01/24 01Z 8.87 2834  68  54 -24 0.00
Sat 01/24 02Z 9.52 2834  59  35 -25 0.00
Sat 01/24 03Z 7.72 2832  56  31 -26 0.00
Sat 01/24 04Z 3.99 2930  71  29 -26 0.00
Sat 01/24 05Z 2.00 3028  75  28 -27 0.00
Sat 01/24 06Z 2.45 3029  74  26 -27 0.00
Sat 01/24 07Z 1.22 3029  67  25 -28 0.00
Sat 01/24 08Z 0.94 3030  65  28 -28 0.00
Sat 01/24 09Z 0.56 3130  64  28 -27 0.00
Sat 01/24 10Z 0.42 3130  65  27 -26 0.00
Sat 01/24 11Z 0.36 3130  62  24 -25 0.00
Sat 01/24 12Z 0.32 3130  60  20 -25 0.00
Sat 01/24 13Z 0.30 3130  57  17 -24 0.00
Sat 01/24 14Z 0.28 3128  53  15 -23 0.00
Sat 01/24 15Z 0.28 3126  51  13 -23 0.00
Sat 01/24 16Z 0.29 3124  50  12 -23 0.00
Sat 01/24 17Z 0.31 3123  50  14 -24 0.00
Sat 01/24 18Z 0.34 3021  51  16 -24 0.00
Sat 01/24 19Z 0.39 3021  55  14 -24 0.00
Sat 01/24 20Z 0.45 2920  59  10 -24 0.00
Sat 01/24 21Z 0.46 2919  58  11 -24 0.00
Sat 01/24 22Z 0.44 3020  54  11 -23 0.00
Sat 01/24 23Z 0.37 3021  50   9 -22 0.00
Sun 01/25 00Z 0.29 3121  47   9 -21 0.00
Sun 01/25 01Z 0.23 3121  44   9 -20 0.00
Sun 01/25 02Z 0.21 3120  42   9 -20 0.00
Sun 01/25 04Z 0.20 3119  35  10 -19 0.00
Sun 01/25 05Z 0.18 3118  32  10 -18 0.00

Run total areal avg QPF for the Central_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