GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20260706_0000
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)
=== ===== === ==== ==== === === === ====
Mon 07/06 00Z 0.09 0002  52  31  14 0.00
Mon 07/06 03Z 0.22 0704  54  21  14 0.00
Mon 07/06 06Z 0.21 1205  59  16  13 0.00
Mon 07/06 09Z 0.16 1408  66  18  13 0.00
Mon 07/06 12Z 0.15 1509  72  16  13 0.00
Mon 07/06 15Z 0.28 1509  78  15  12 0.00
Mon 07/06 18Z 0.71 1409  68  30  12 0.00
Mon 07/06 21Z 0.80 1311  67  30  13 0.01
Tue 07/07 00Z 0.38 1313  67  43  12 0.00
Tue 07/07 03Z 0.30 1315  65  51  12 0.00
Tue 07/07 06Z 0.27 1314  68  63  12 0.00
Tue 07/07 09Z 0.31 1213  69  64  12 0.00
Tue 07/07 12Z 0.30 1214  78  74  12 0.04
Tue 07/07 15Z 0.28 1212  81  76  12 0.04
Tue 07/07 18Z 0.41 1210  81  74  11 0.03
Tue 07/07 21Z 0.47 1107  79  63  11 0.00
Wed 07/08 00Z 0.22 1107  78  53  12 0.00
Wed 07/08 03Z 0.15 1004  74  26  12 0.00
Wed 07/08 06Z 0.06 0101  70  16  12 0.00
Wed 07/08 09Z 0.08 3406  69  16  12 0.00
Wed 07/08 12Z 0.07 3504  75   9  12 0.00
Wed 07/08 15Z 0.22 3004  77  10  12 0.00
Wed 07/08 18Z 1.06 2905  59  13  14 0.00
Wed 07/08 21Z 1.10 2806  61  22  15 0.00

Run total areal avg QPF for the greens is: 0.12 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