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_1200
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 12Z 0.42 3017  80  32 -19 0.00
Wed 01/28 13Z 0.46 2918  80  28 -19 0.00
Wed 01/28 14Z 0.44 2916  80  28 -19 0.00
Wed 01/28 15Z 0.45 2815  78  35 -19 0.00
Wed 01/28 16Z 0.45 2813  72  43 -19 0.00
Wed 01/28 17Z 0.50 2812  69  52 -18 0.00
Wed 01/28 18Z 0.56 2912  69  61 -18 0.00
Wed 01/28 19Z 0.61 2811  70  63 -18 0.00
Wed 01/28 20Z 0.63 2810  75  56 -18 0.00
Wed 01/28 21Z 0.73 2711  83  52 -18 0.00
Wed 01/28 22Z 0.67 2811  83  49 -18 0.00
Wed 01/28 23Z 0.71 2912  79  48 -18 0.00
Thu 01/29 00Z 0.59 2912  77  48 -18 0.00
Thu 01/29 01Z 0.45 2910  80  52 -18 0.00
Thu 01/29 02Z 0.41 2909  84  55 -18 0.00
Thu 01/29 03Z 0.42 2809  87  57 -18 0.00
Thu 01/29 04Z 0.39 2809  91  62 -18 0.00
Thu 01/29 05Z 0.35 2909  90  65 -18 0.00
Thu 01/29 06Z 0.33 2910  87  65 -18 0.00
Thu 01/29 07Z 0.34 2911  83  64 -18 0.00
Thu 01/29 08Z 0.34 2911  83  62 -19 0.00
Thu 01/29 09Z 0.35 2911  84  56 -19 0.00
Thu 01/29 10Z 0.40 2812  85  52 -19 0.00
Thu 01/29 11Z 0.43 2814  85  50 -19 0.00
Thu 01/29 12Z 0.41 2814  82  51 -19 0.00
Thu 01/29 13Z 0.37 2914  83  59 -19 0.00
Thu 01/29 14Z 0.31 3012  83  64 -19 0.00
Thu 01/29 15Z 0.32 3011  85  68 -19 0.00
Thu 01/29 16Z 0.37 3011  87  68 -19 0.00
Thu 01/29 17Z 0.57 3011  87  66 -19 0.00
Thu 01/29 18Z 1.37 3014  88  62 -19 0.00
Thu 01/29 19Z 2.26 3015  90  59 -19 0.00
Thu 01/29 20Z 1.73 3014  92  60 -19 0.00
Thu 01/29 21Z 1.45 3015  92  59 -19 0.01
Thu 01/29 22Z 1.43 3018  93  54 -19 0.01
Thu 01/29 23Z 0.92 3121  92  48 -20 0.01
Fri 01/30 00Z 0.75 3121  92  44 -20 0.00
Fri 01/30 01Z 0.69 3123  89  39 -21 0.00
Fri 01/30 02Z 0.75 3024  86  38 -22 0.00
Fri 01/30 03Z 0.78 3025  86  37 -23 0.00
Fri 01/30 04Z 0.74 3025  86  35 -23 0.00
Fri 01/30 05Z 0.73 3025  86  34 -24 0.00
Fri 01/30 06Z 0.71 2926  83  32 -24 0.00
Fri 01/30 07Z 0.63 2928  75  28 -23 0.00
Fri 01/30 08Z 0.56 3030  67  27 -23 0.00
Fri 01/30 09Z 0.49 3029  65  28 -23 0.00
Fri 01/30 10Z 0.41 3028  63  30 -22 0.00
Fri 01/30 11Z 0.35 3028  62  37 -22 0.00
Fri 01/30 12Z 0.32 3127  62  49 -22 0.00
Fri 01/30 13Z 0.31 3026  65  61 -21 0.00
Fri 01/30 14Z 0.29 3025  69  72 -20 0.00
Fri 01/30 15Z 0.28 3024  72  79 -20 0.00
Fri 01/30 16Z 0.28 3022  75  83 -20 0.00
Fri 01/30 17Z 0.29 3021  77  81 -20 0.00
Fri 01/30 18Z 0.30 3020  76  80 -19 0.00
Fri 01/30 19Z 0.31 3019  77  77 -19 0.00
Fri 01/30 20Z 0.35 2919  79  74 -19 0.00
Fri 01/30 21Z 0.38 2919  80  67 -19 0.00
Fri 01/30 22Z 0.37 2920  81  63 -19 0.00
Fri 01/30 23Z 0.32 3021  83  60 -18 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