GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20250313_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)
=== ===== === ==== ==== === === === ====
Thu 03/13 18Z 0.09 1816  84  35  -4 0.00
Thu 03/13 21Z 0.16 1917  82  11  -4 0.00
Fri 03/14 00Z 0.23 2016  76   7  -2 0.00
Fri 03/14 03Z 0.25 2114  73  10  -1 0.00
Fri 03/14 06Z 0.26 2212  71  17   0 0.00
Fri 03/14 09Z 0.26 2509  69  20   0 0.00
Fri 03/14 12Z 0.24 2508  68  28   0 0.00
Fri 03/14 15Z 0.15 2307  65  35   1 0.00
Fri 03/14 18Z 0.11 2009  63  32   2 0.00
Fri 03/14 21Z 0.17 2012  63  42   3 0.00
Sat 03/15 00Z 0.25 2115  53  34   5 0.00
Sat 03/15 03Z 0.24 2115  53  31   6 0.00
Sat 03/15 06Z 0.20 2116  49  27   7 0.00
Sat 03/15 09Z 0.20 2019  54  23   7 0.00
Sat 03/15 12Z 0.23 2023  54  38   7 0.00
Sat 03/15 15Z 0.23 2026  57  45   8 0.00
Sat 03/15 18Z 0.18 1925  64  36   8 0.00
Sat 03/15 21Z 0.23 2024  74  34   7 0.00
Sun 03/16 00Z 0.24 2027  68  59   9 0.00
Sun 03/16 03Z 0.33 2033  67  55   9 0.00
Sun 03/16 06Z 0.32 2037  78  22   8 0.00
Sun 03/16 09Z 0.35 2037  94  19   8 0.00
Sun 03/16 12Z 0.30 1936  92  32   7 0.00
Sun 03/16 15Z 0.46 1941  93  68   8 0.00

Run total areal avg QPF for the 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