NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260203_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 02/03 18Z 0.17 2504  83  57 -11 0.00
Tue 02/03 19Z 0.25 2505  82  66 -11 0.00
Tue 02/03 20Z 0.24 2505  81  70 -12 0.00
Tue 02/03 21Z 0.22 2606  81  67 -12 0.00
Tue 02/03 22Z 0.21 2606  83  67 -12 0.00
Tue 02/03 23Z 0.26 2607  85  80 -12 0.00
Wed 02/04 00Z 0.27 2707  89  83 -12 0.00
Wed 02/04 01Z 0.34 2709  91  81 -12 0.00
Wed 02/04 02Z 0.39 2709  91  88 -12 0.00
Wed 02/04 04Z 0.54 2712  85  64 -13 0.00
Wed 02/04 05Z 0.58 2612  87  59 -13 0.00
Wed 02/04 06Z 0.56 2713  91  57 -13 0.00
Wed 02/04 07Z 0.54 2713  93  58 -13 0.00
Wed 02/04 08Z 0.53 2713  92  63 -13 0.00
Wed 02/04 09Z 0.55 2713  92  66 -14 0.01
Wed 02/04 10Z 0.60 2714  90  62 -15 0.01
Wed 02/04 11Z 0.42 2712  85  68 -15 0.01
Wed 02/04 12Z 0.29 2811  80  69 -14 0.01
Wed 02/04 13Z 0.27 3013  78  65 -14 0.00
Wed 02/04 14Z 0.31 3115  80  62 -14 0.00
Wed 02/04 15Z 0.38 3118  85  58 -14 0.00
Wed 02/04 16Z 0.45 3018  89  49 -14 0.00
Wed 02/04 17Z 0.52 3018  90  53 -14 0.00
Wed 02/04 18Z 0.58 3017  87  47 -14 0.00
Wed 02/04 19Z 0.58 3016  89  41 -14 0.00
Wed 02/04 20Z 0.52 3016  90  37 -13 0.00
Wed 02/04 21Z 0.43 3016  90  34 -13 0.00
Wed 02/04 23Z 0.39 3016  89  35 -12 0.00
Thu 02/05 00Z 0.35 3016  87  36 -12 0.00
Thu 02/05 01Z 0.32 3116  84  36 -12 0.00
Thu 02/05 02Z 0.29 3115  82  36 -12 0.00
Thu 02/05 03Z 0.27 3014  81  37 -12 0.00
Thu 02/05 04Z 0.25 3013  79  37 -12 0.00
Thu 02/05 05Z 0.26 2913  79  37 -12 0.00
Thu 02/05 06Z 0.27 2913  81  37 -12 0.00
Thu 02/05 07Z 0.29 2813  82  36 -12 0.00
Thu 02/05 08Z 0.32 2814  84  36 -13 0.00
Thu 02/05 09Z 0.34 2916  86  37 -13 0.00
Thu 02/05 10Z 0.34 2916  85  44 -13 0.00
Thu 02/05 11Z 0.36 2917  85  66 -14 0.00
Thu 02/05 12Z 0.37 3019  85  71 -14 0.00
Thu 02/05 13Z 0.36 3019  85  45 -14 0.00
Thu 02/05 14Z 0.36 3119  84   7 -15 0.00
Thu 02/05 15Z 0.35 3118  84   4 -15 0.00
Thu 02/05 16Z 0.34 3117  83   3 -15 0.00
Thu 02/05 17Z 0.36 3116  82   4 -15 0.00
Thu 02/05 18Z 0.36 3116  80   4 -15 0.00
Thu 02/05 19Z 0.32 3115  74   4 -15 0.00
Thu 02/05 20Z 0.30 3115  69   3 -15 0.00
Thu 02/05 21Z 0.26 3115  65   3 -14 0.00
Thu 02/05 22Z 0.23 3215  61   5 -14 0.00
Thu 02/05 23Z 0.18 3215  54   5 -13 0.00
Fri 02/06 00Z 0.14 3314  49   6 -12 0.00
Fri 02/06 01Z 0.10 3312  46   6 -12 0.00
Fri 02/06 02Z 0.07 3311  41   6 -11 0.00
Fri 02/06 03Z 0.05 3409  37   7 -11 0.00
Fri 02/06 04Z 0.05 3307  35   7 -11 0.00
Fri 02/06 05Z 0.04 3306  33   8 -10 0.00

Run total areal avg QPF for the greens is: 0.04 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