GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20251017_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)
=== ===== === ==== ==== === === === ====
Fri 10/17 00Z 0.08 3528  56  68  -1 0.00
Fri 10/17 03Z 0.12 0022  64  62  -1 0.00
Fri 10/17 06Z 0.14 0116  75  49   0 0.00
Fri 10/17 09Z 0.05 0015  75  45   0 0.00
Fri 10/17 12Z 0.03 3514  74  35   0 0.00
Fri 10/17 15Z 0.06 3512  74  18   0 0.00
Fri 10/17 18Z 0.22 3410  70  11   0 0.00
Fri 10/17 21Z 0.11 3411  62   8   1 0.00
Sat 10/18 00Z 0.07 3410  47  11   2 0.00
Sat 10/18 03Z 0.03 3508  42  20   2 0.00
Sat 10/18 06Z 0.05 3406  38  29   3 0.00
Sat 10/18 09Z 0.04 3406  35  45   3 0.00
Sat 10/18 12Z 0.03 3404  32  68   5 0.00
Sat 10/18 15Z 0.05 2902  32  85   5 0.00
Sat 10/18 18Z 0.05 2402  37  80   7 0.00
Sat 10/18 21Z 0.08 2104  45  74   8 0.00
Sun 10/19 00Z 0.08 2006  51  84  10 0.00
Sun 10/19 03Z 0.13 2109  57  95  10 0.00
Sun 10/19 06Z 0.16 2113  65  68  10 0.00
Sun 10/19 09Z 0.19 2115  58  56  11 0.00
Sun 10/19 12Z 0.14 2013  55  48  11 0.00
Sun 10/19 15Z 0.08 1917  56  49  12 0.00
Sun 10/19 18Z 0.04 1818  59  43  11 0.00
Sun 10/19 21Z 0.04 1724  65  44  10 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