GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20260201_0600
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)
=== ===== === ==== ==== === === === ====
Sun 02/01 06Z 0.08 0212  69  31 -12 0.00
Sun 02/01 09Z 0.08 0115  67  21 -11 0.00
Sun 02/01 12Z 0.07 0117  66  18 -10 0.00
Sun 02/01 15Z 0.08 0118  68  15 -10 0.00
Sun 02/01 18Z 0.07 0115  78  15 -11 0.00
Sun 02/01 21Z 0.03 0018  69  14 -10 0.00
Mon 02/02 00Z 0.02 0023  53  13 -10 0.00
Mon 02/02 03Z 0.04 3520  67  20 -11 0.00
Mon 02/02 06Z 0.10 3419  68  32 -10 0.00
Mon 02/02 09Z 0.11 3420  61  32 -10 0.00
Mon 02/02 12Z 0.11 3418  53  27 -10 0.00
Mon 02/02 15Z 0.12 3316  51  18 -10 0.00
Mon 02/02 18Z 0.17 3215  51  12 -10 0.00
Mon 02/02 21Z 0.22 3217  58  10 -10 0.00
Tue 02/03 00Z 0.19 3215  51  35 -10 0.00
Tue 02/03 03Z 0.13 3212  52  61  -9 0.00
Tue 02/03 06Z 0.18 3010  56  68  -9 0.00
Tue 02/03 09Z 0.16 2908  52  56  -9 0.00
Tue 02/03 12Z 0.13 2706  51  15  -9 0.00
Tue 02/03 15Z 0.14 2406  53  83  -9 0.00
Tue 02/03 18Z 0.18 2307  83  61 -10 0.00
Tue 02/03 21Z 0.25 2307  92  21 -11 0.00
Wed 02/04 00Z 0.38 2411  93  27 -11 0.00
Wed 02/04 03Z 0.54 2413  92  50 -12 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