Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20260207_1800
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)
=== ===== === ==== ==== === === === ====
Sat 02/07 18Z 0.24 3217  98 100 -21 0.00
Sat 02/07 21Z 0.24 3319  98  99 -23 0.01
Sun 02/08 00Z 0.21 3321  97  98 -23 0.01
Sun 02/08 03Z 0.19 3320  96  98 -23 0.01
Sun 02/08 06Z 0.14 3317  97  98 -22 0.01
Sun 02/08 09Z 0.13 3318  96  96 -20 0.00
Sun 02/08 12Z 0.12 3320  97  91 -20 0.00
Sun 02/08 15Z 0.10 3419  95  89 -19 0.00
Sun 02/08 18Z 0.11 3419  88  59 -17 0.00
Sun 02/08 21Z 0.13 3321  84  54 -16 0.00
Mon 02/09 00Z 0.16 3324  83  53 -15 0.00
Mon 02/09 03Z 0.16 3323  79  48 -14 0.00
Mon 02/09 06Z 0.18 3323  81  41 -13 0.00
Mon 02/09 09Z 0.20 3325  82  34 -14 0.00
Mon 02/09 12Z 0.18 3326  72  15 -14 0.00
Mon 02/09 15Z 0.15 3324  64  59 -13 0.00
Mon 02/09 18Z 0.18 3321  61  69 -12 0.00
Mon 02/09 21Z 0.19 3219  54  66 -11 0.00
Tue 02/10 00Z 0.19 3218  52  48 -10 0.00
Tue 02/10 03Z 0.10 3316  48  18  -9 0.00
Tue 02/10 06Z 0.12 3313  44  24  -8 0.00
Tue 02/10 09Z 0.09 3209  37  31  -7 0.00
Tue 02/10 12Z 0.07 3105  34  50  -6 0.00
Tue 02/10 15Z 0.04 2004  39  60  -4 0.00

Run total areal avg QPF for the greens is: 0.04 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