NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260127_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)
=== ===== === ==== ==== === === === ====
Tue 01/27 06Z 0.51 3022  85  68 -21 0.00
Tue 01/27 07Z 0.55 3025  89  60 -21 0.00
Tue 01/27 08Z 0.59 3027  84  52 -21 0.00
Tue 01/27 09Z 0.57 3028  81  43 -20 0.00
Tue 01/27 10Z 0.49 3027  76  29 -20 0.00
Tue 01/27 11Z 0.47 3028  77  30 -20 0.00
Tue 01/27 12Z 0.44 3028  72  41 -19 0.00
Tue 01/27 13Z 0.43 3025  71  42 -19 0.00
Tue 01/27 14Z 0.43 2820  71  52 -19 0.00
Tue 01/27 15Z 0.51 2718  81  72 -19 0.00
Tue 01/27 16Z 0.57 2616  84  78 -19 0.00
Tue 01/27 17Z 0.53 2515  83  80 -18 0.01
Tue 01/27 18Z 0.49 2413  80  81 -18 0.01
Tue 01/27 19Z 0.50 2312  84  82 -18 0.01
Tue 01/27 20Z 2.20 2313  85  81 -19 0.00
Tue 01/27 21Z 1.29 2216  86  81 -19 0.01
Tue 01/27 22Z 1.68 2318  89  79 -19 0.01
Tue 01/27 23Z 2.28 2522  91  75 -20 0.01
Wed 01/28 00Z 1.56 2623  82  71 -20 0.00
Wed 01/28 01Z 1.28 2722  77  69 -20 0.00
Wed 01/28 02Z 0.84 2721  76  70 -20 0.00
Wed 01/28 03Z 0.79 2721  83  71 -19 0.00
Wed 01/28 04Z 0.78 2721  86  70 -19 0.00
Wed 01/28 05Z 0.77 2821  87  71 -20 0.01
Wed 01/28 06Z 0.74 2820  87  68 -20 0.01
Wed 01/28 07Z 0.71 2921  88  64 -20 0.00
Wed 01/28 08Z 0.68 2921  89  61 -20 0.00
Wed 01/28 09Z 0.62 2921  89  56 -20 0.00
Wed 01/28 10Z 0.52 3020  88  53 -20 0.00
Wed 01/28 11Z 0.42 3019  88  44 -20 0.00
Wed 01/28 12Z 0.43 3019  90  37 -20 0.00
Wed 01/28 13Z 0.39 3018  87  29 -20 0.00
Wed 01/28 14Z 0.34 3015  83  29 -20 0.00
Wed 01/28 15Z 0.37 2912  81  32 -20 0.00
Wed 01/28 16Z 0.44 2810  80  32 -19 0.00
Wed 01/28 17Z 0.87 2707  77  33 -19 0.00
Wed 01/28 18Z 2.32 2707  76  36 -19 0.00
Wed 01/28 19Z 4.20 2708  77  38 -19 0.00
Wed 01/28 20Z 2.78 2808  77  41 -19 0.00
Wed 01/28 21Z 0.83 2807  80  41 -19 0.00
Wed 01/28 22Z 0.54 2708  86  43 -19 0.00
Wed 01/28 23Z 0.56 2609  91  43 -19 0.00
Thu 01/29 00Z 0.56 2710  92  48 -19 0.00
Thu 01/29 01Z 0.51 2910  90  62 -19 0.00
Thu 01/29 02Z 0.41 3011  86  75 -19 0.00
Thu 01/29 03Z 0.35 3111  85  79 -19 0.00
Thu 01/29 04Z 0.34 3112  84  79 -19 0.00
Thu 01/29 05Z 0.37 3113  85  79 -19 0.01
Thu 01/29 06Z 0.43 3113  87  78 -20 0.01
Thu 01/29 07Z 0.42 3114  89  77 -20 0.00
Thu 01/29 08Z 0.38 3115  90  75 -20 0.00
Thu 01/29 09Z 0.37 3217  92  74 -20 0.00
Thu 01/29 10Z 0.41 3117  93  70 -20 0.00
Thu 01/29 11Z 0.41 3117  92  68 -20 0.00
Thu 01/29 12Z 0.38 3116  91  67 -19 0.00
Thu 01/29 13Z 0.36 3115  92  70 -19 0.00
Thu 01/29 14Z 0.38 3014  91  70 -19 0.00
Thu 01/29 15Z 0.41 3013  91  68 -19 0.00
Thu 01/29 16Z 0.53 3013  89  64 -19 0.00
Thu 01/29 17Z 1.51 3014  88  61 -19 0.00

Run total areal avg QPF for the Central_Greens is: 0.10 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