Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20261106_1200
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 11/06 12Z 0.25 2406  75  20   7 0.00
Fri 11/06 15Z 0.12 2007  72  43   7 0.00
Fri 11/06 18Z 0.15 2204  79  60   7 0.00
Fri 11/06 21Z 0.08 1900  80  60   7 0.00
Sat 11/07 00Z 0.15 0604  83  58   7 0.00
Sat 11/07 03Z 0.17 0506  84  57   7 0.00
Sat 11/07 06Z 0.14 0605  85  70   7 0.00
Sat 11/07 09Z 0.14 0804  90  74   6 0.00
Sat 11/07 12Z 0.17 1006  94  90   6 0.01
Sat 11/07 15Z 0.19 1207  97  95   6 0.04
Sat 11/07 18Z 0.11 1204  99  96   5 0.04
Sat 11/07 21Z 0.05 1000 100  97   4 0.08
Sun 11/08 00Z 0.08 3204 100  96   4 0.09
Sun 11/08 03Z 0.12 3310  99  97   3 0.06
Sun 11/08 06Z 0.17 3316  99  94   2 0.06
Sun 11/08 09Z 0.21 3320  99  94   1 0.04
Sun 11/08 12Z 0.28 3222  99  95   0 0.01
Sun 11/08 15Z 0.34 3220  99  82   0 0.00
Sun 11/08 18Z 0.52 2918  98   9   0 0.00
Sun 11/08 21Z 0.62 2717  85  19   0 0.00
Mon 11/09 00Z 0.74 2621  68  34   1 0.00
Mon 11/09 03Z 0.99 2625  78  70   0 0.00
Mon 11/09 06Z 1.00 2626  88  28   0 0.00
Mon 11/09 09Z 1.01 2523  88  85   0 0.00

Run total areal avg QPF for the greens is: 0.43 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