NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260203_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)
=== ===== === ==== ==== === === === ====
Tue 02/03 18Z 0.21 2504  83  56 -11 0.00
Tue 02/03 19Z 0.30 2505  81  71 -11 0.00
Tue 02/03 20Z 0.28 2506  81  77 -11 0.00
Tue 02/03 21Z 0.25 2606  80  70 -11 0.00
Tue 02/03 22Z 0.23 2607  83  68 -11 0.00
Tue 02/03 23Z 0.28 2708  86  83 -12 0.00
Wed 02/04 00Z 0.31 2709  90  82 -12 0.00
Wed 02/04 01Z 0.43 2711  93  77 -12 0.00
Wed 02/04 02Z 0.50 2712  91  86 -12 0.00
Wed 02/04 04Z 0.71 2716  82  51 -13 0.00
Wed 02/04 05Z 0.76 2617  86  49 -13 0.00
Wed 02/04 06Z 0.71 2717  91  46 -13 0.00
Wed 02/04 07Z 0.64 2716  92  47 -13 0.00
Wed 02/04 08Z 0.57 2715  91  53 -14 0.00
Wed 02/04 09Z 0.60 2814  92  54 -14 0.01
Wed 02/04 10Z 0.69 2715  90  48 -15 0.01
Wed 02/04 11Z 0.47 2713  84  60 -15 0.01
Wed 02/04 12Z 0.29 2811  78  62 -15 0.00
Wed 02/04 13Z 0.22 3013  74  58 -14 0.00
Wed 02/04 14Z 0.20 3115  73  56 -14 0.00
Wed 02/04 15Z 0.24 3117  79  54 -14 0.00
Wed 02/04 16Z 0.30 3118  86  43 -14 0.00
Wed 02/04 17Z 0.39 3117  89  47 -14 0.00
Wed 02/04 18Z 0.50 3016  85  43 -14 0.00
Wed 02/04 19Z 0.56 3015  86  35 -14 0.00
Wed 02/04 20Z 0.46 3015  87  31 -13 0.00
Wed 02/04 21Z 0.33 3114  87  28 -13 0.00
Wed 02/04 23Z 0.29 3114  89  30 -12 0.00
Thu 02/05 00Z 0.25 3115  87  31 -12 0.00
Thu 02/05 01Z 0.23 3115  85  31 -12 0.00
Thu 02/05 02Z 0.20 3114  82  32 -12 0.00
Thu 02/05 03Z 0.19 3113  80  32 -12 0.00
Thu 02/05 04Z 0.18 3011  79  31 -12 0.00
Thu 02/05 05Z 0.19 3011  79  31 -12 0.00
Thu 02/05 06Z 0.20 2910  79  31 -12 0.00
Thu 02/05 07Z 0.21 2811  81  32 -12 0.00
Thu 02/05 08Z 0.23 2812  82  32 -12 0.00
Thu 02/05 09Z 0.25 2913  83  31 -13 0.00
Thu 02/05 10Z 0.24 2914  82  31 -13 0.00
Thu 02/05 11Z 0.24 3015  82  62 -13 0.00
Thu 02/05 12Z 0.25 3017  83  70 -13 0.00
Thu 02/05 13Z 0.24 3118  81  52 -13 0.00
Thu 02/05 14Z 0.24 3118  80  10 -14 0.00
Thu 02/05 15Z 0.23 3117  79   4 -14 0.00
Thu 02/05 16Z 0.22 3117  78   3 -14 0.00
Thu 02/05 17Z 0.24 3116  77   4 -15 0.00
Thu 02/05 18Z 0.26 3115  75   4 -15 0.00
Thu 02/05 19Z 0.24 3215  70   4 -15 0.00
Thu 02/05 20Z 0.21 3215  66   2 -14 0.00
Thu 02/05 21Z 0.19 3215  63   3 -14 0.00
Thu 02/05 22Z 0.16 3215  60   5 -13 0.00
Thu 02/05 23Z 0.12 3316  55   5 -12 0.00
Fri 02/06 00Z 0.08 3315  51   6 -12 0.00
Fri 02/06 01Z 0.05 3313  47   6 -11 0.00
Fri 02/06 02Z 0.04 3412  42   6 -11 0.00
Fri 02/06 03Z 0.02 3409  38   6 -10 0.00
Fri 02/06 04Z 0.02 3407  36   7 -10 0.00
Fri 02/06 05Z 0.02 3307  33   8 -10 0.00

Run total areal avg QPF for the Central_Greens is: 0.03 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