Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260129_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)
=== ===== === ==== ==== === === === ====
Thu 01/29 06Z 0.31 3012  83  75 -18 0.00
Thu 01/29 07Z 0.37 3115  84  75 -18 0.00
Thu 01/29 08Z 0.33 3115  83  72 -19 0.00
Thu 01/29 09Z 0.33 3115  79  68 -19 0.00
Thu 01/29 10Z 0.32 3015  76  63 -19 0.00
Thu 01/29 11Z 0.32 3015  75  60 -19 0.00
Thu 01/29 12Z 0.34 3015  75  58 -19 0.00
Thu 01/29 13Z 0.37 3016  79  55 -19 0.00
Thu 01/29 14Z 0.35 3016  79  54 -19 0.00
Thu 01/29 15Z 0.32 3015  79  54 -19 0.00
Thu 01/29 16Z 0.32 3115  81  54 -19 0.00
Thu 01/29 17Z 0.43 3115  82  54 -19 0.00
Thu 01/29 18Z 0.75 3016  81  56 -19 0.00
Thu 01/29 19Z 1.31 3017  85  58 -19 0.00
Thu 01/29 20Z 2.23 2916  91  56 -19 0.00
Thu 01/29 21Z 1.51 2918  93  53 -19 0.00
Thu 01/29 22Z 1.29 2919  92  48 -19 0.00
Thu 01/29 23Z 1.25 2922  91  44 -20 0.00
Fri 01/30 00Z 1.00 3023  90  43 -20 0.00
Fri 01/30 01Z 0.85 3025  88  41 -21 0.00
Fri 01/30 02Z 1.16 3027  85  38 -22 0.00
Fri 01/30 03Z 0.85 3028  82  35 -23 0.00
Fri 01/30 04Z 0.71 3029  82  30 -23 0.00
Fri 01/30 05Z 0.59 3029  78  28 -23 0.00
Fri 01/30 06Z 0.54 3029  72  28 -22 0.00
Fri 01/30 07Z 0.51 3029  69  28 -22 0.00
Fri 01/30 08Z 0.48 3029  66  27 -22 0.00
Fri 01/30 09Z 0.42 3028  63  30 -22 0.00
Fri 01/30 10Z 0.38 3028  61  37 -22 0.00
Fri 01/30 11Z 0.36 3028  62  47 -21 0.00
Fri 01/30 12Z 0.33 3028  64  58 -21 0.00
Fri 01/30 13Z 0.30 3028  68  69 -20 0.00
Fri 01/30 14Z 0.28 3126  73  76 -20 0.00
Fri 01/30 15Z 0.27 3124  76  78 -20 0.00
Fri 01/30 16Z 0.27 3022  78  79 -19 0.00
Fri 01/30 17Z 0.28 3020  78  78 -19 0.00
Fri 01/30 18Z 0.30 3020  78  74 -18 0.00
Fri 01/30 19Z 0.32 2920  78  68 -18 0.00
Fri 01/30 20Z 0.35 2920  79  61 -18 0.00
Fri 01/30 21Z 0.37 2921  81  53 -18 0.00
Fri 01/30 22Z 0.35 3021  82  49 -18 0.00
Fri 01/30 23Z 0.30 3021  83  47 -17 0.00
Sat 01/31 00Z 0.24 3120  84  46 -17 0.00
Sat 01/31 01Z 0.18 3120  83  46 -16 0.00
Sat 01/31 02Z 0.13 3219  83  45 -15 0.00
Sat 01/31 03Z 0.11 3219  83  46 -15 0.00
Sat 01/31 04Z 0.10 3219  83  46 -15 0.00
Sat 01/31 05Z 0.10 3218  82  47 -14 0.00
Sat 01/31 06Z 0.10 3217  81  48 -14 0.00
Sat 01/31 07Z 0.12 3216  81  51 -14 0.00
Sat 01/31 08Z 0.12 3216  81  52 -14 0.00
Sat 01/31 09Z 0.12 3216  81  52 -14 0.00
Sat 01/31 10Z 0.12 3216  80  51 -14 0.00
Sat 01/31 11Z 0.11 3216  80  50 -14 0.00
Sat 01/31 12Z 0.10 3216  80  49 -13 0.00
Sat 01/31 13Z 0.08 3215  79  46 -13 0.00
Sat 01/31 14Z 0.07 3314  78  42 -13 0.00
Sat 01/31 15Z 0.06 3312  78  40 -13 0.00
Sat 01/31 16Z 0.07 3211  78  40 -13 0.00
Sat 01/31 17Z 0.08 3211  77  37 -12 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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