GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20260204_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)
=== ===== === ==== ==== === === === ====
Wed 02/04 06Z 0.41 2610  90  73 -13 0.00
Wed 02/04 09Z 0.42 2610  91  90 -13 0.00
Wed 02/04 12Z 0.36 3013  94  94 -15 0.03
Wed 02/04 15Z 0.31 3013  94  79 -15 0.01
Wed 02/04 18Z 0.39 3013  95  49 -14 0.00
Wed 02/04 21Z 0.47 3014  93  46 -14 0.00
Thu 02/05 00Z 0.34 3013  93  41 -13 0.01
Thu 02/05 03Z 0.31 3011  93  40 -13 0.01
Thu 02/05 06Z 0.30 2810  92  45 -13 0.00
Thu 02/05 09Z 0.34 2811  95  68 -14 0.00
Thu 02/05 12Z 0.39 2913  96  97 -15 0.01
Thu 02/05 15Z 0.34 3012  96   4 -17 0.01
Thu 02/05 18Z 0.63 3012  95   3 -18 0.00
Thu 02/05 21Z 0.39 3012  92   3 -17 0.00
Fri 02/06 00Z 0.16 3210  74  10 -15 0.00
Fri 02/06 03Z 0.06 3307  54  12 -12 0.00
Fri 02/06 06Z 0.05 3204  42   8 -11 0.00
Fri 02/06 09Z 0.06 2603  36  20 -11 0.00
Fri 02/06 12Z 0.05 2104  27  53 -10 0.00
Fri 02/06 15Z 0.07 2007  36  37 -11 0.00
Fri 02/06 18Z 0.07 1908  52  16 -11 0.00
Fri 02/06 21Z 0.09 1910  68  72 -11 0.00
Sat 02/07 00Z 0.10 1911  76  97 -12 0.00
Sat 02/07 03Z 0.11 2011  95  98 -11 0.01

Run total areal avg QPF for the greens is: 0.09 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