NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260128_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)
=== ===== === ==== ==== === === === ====
Wed 01/28 06Z 0.68 2819  85  70 -20 0.00
Wed 01/28 07Z 0.57 2919  89  66 -20 0.00
Wed 01/28 08Z 0.59 2920  89  65 -20 0.00
Wed 01/28 09Z 0.57 2921  86  58 -20 0.00
Wed 01/28 10Z 0.53 2921  81  48 -19 0.00
Wed 01/28 11Z 0.48 2921  79  43 -19 0.00
Wed 01/28 12Z 0.42 3020  80  37 -19 0.00
Wed 01/28 13Z 0.36 3018  79  31 -19 0.00
Wed 01/28 14Z 0.32 3017  77  31 -19 0.00
Wed 01/28 15Z 0.35 2914  77  35 -19 0.00
Wed 01/28 16Z 0.37 2812  74  40 -19 0.00
Wed 01/28 17Z 0.46 2711  70  47 -18 0.00
Wed 01/28 18Z 0.64 2811  69  52 -18 0.00
Wed 01/28 19Z 0.82 2809  71  55 -18 0.00
Wed 01/28 20Z 0.90 2810  76  56 -18 0.00
Wed 01/28 21Z 0.86 2711  85  64 -18 0.00
Wed 01/28 22Z 0.81 2712  89  70 -18 0.00
Wed 01/28 23Z 0.80 2812  89  72 -18 0.00
Thu 01/29 00Z 0.70 2912  85  73 -18 0.00
Thu 01/29 01Z 0.63 2914  81  74 -18 0.00
Thu 01/29 02Z 0.49 3013  77  73 -18 0.00
Thu 01/29 03Z 0.43 3012  81  80 -19 0.00
Thu 01/29 04Z 0.42 3011  85  81 -19 0.00
Thu 01/29 05Z 0.44 3012  87  80 -19 0.00
Thu 01/29 06Z 0.45 2912  89  79 -19 0.00
Thu 01/29 07Z 0.39 3013  89  78 -19 0.00
Thu 01/29 08Z 0.34 3113  88  76 -19 0.00
Thu 01/29 09Z 0.35 3013  86  71 -19 0.00
Thu 01/29 10Z 0.37 2913  85  65 -19 0.00
Thu 01/29 11Z 0.37 2912  84  63 -19 0.00
Thu 01/29 12Z 0.37 2813  83  61 -19 0.00
Thu 01/29 13Z 0.37 2913  85  59 -20 0.00
Thu 01/29 14Z 0.37 2914  87  57 -20 0.00
Thu 01/29 15Z 0.41 2914  88  56 -20 0.00
Thu 01/29 16Z 0.50 3014  88  58 -20 0.00
Thu 01/29 17Z 1.05 3014  88  59 -20 0.00
Thu 01/29 18Z 2.41 3114  87  65 -20 0.00
Thu 01/29 19Z 3.23 3114  88  66 -19 0.00
Thu 01/29 20Z 2.16 3014  89  64 -19 0.00
Thu 01/29 21Z 1.11 2915  91  61 -19 0.00
Thu 01/29 22Z 1.35 2918  92  58 -19 0.01
Thu 01/29 23Z 1.71 2921  89  56 -19 0.01
Fri 01/30 00Z 1.94 2924  86  53 -20 0.00
Fri 01/30 01Z 1.85 2924  85  52 -21 0.00
Fri 01/30 02Z 1.53 3024  86  50 -21 0.00
Fri 01/30 03Z 1.10 3024  89  48 -22 0.00
Fri 01/30 04Z 0.77 3024  89  46 -22 0.00
Fri 01/30 05Z 0.63 3025  80  43 -22 0.00
Fri 01/30 06Z 0.54 3027  75  39 -22 0.00
Fri 01/30 07Z 0.53 3028  74  37 -22 0.00
Fri 01/30 08Z 0.51 3028  74  38 -22 0.00
Fri 01/30 09Z 0.47 3028  73  40 -22 0.00
Fri 01/30 10Z 0.44 3028  73  48 -22 0.00
Fri 01/30 11Z 0.40 3028  73  61 -22 0.00
Fri 01/30 12Z 0.35 3027  74  72 -21 0.00
Fri 01/30 13Z 0.32 3126  77  81 -21 0.00
Fri 01/30 14Z 0.29 3126  80  83 -21 0.00
Fri 01/30 15Z 0.28 3125  81  84 -21 0.00
Fri 01/30 16Z 0.27 3123  81  84 -20 0.00
Fri 01/30 17Z 0.27 3122  81  83 -20 0.00

Run total areal avg QPF for the Central_Greens is: 0.02 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