Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20250701_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)
=== ===== === ==== ==== === === === ====
Tue 07/01 06Z 0.49 2220  75  74  17 0.00
Tue 07/01 09Z 0.46 2221  80  88  17 0.06
Tue 07/01 12Z 0.55 2223  96  93  15 0.06
Tue 07/01 15Z 0.62 2519  99  84  15 0.10
Tue 07/01 18Z 0.80 2518  92  51  15 0.03
Tue 07/01 21Z 1.23 2620  73  70  17 0.03
Wed 07/02 00Z 1.03 2823  61  83  15 0.04
Wed 07/02 03Z 0.72 2718  61  71  15 0.00
Wed 07/02 06Z 0.62 2817  71  54  14 0.00
Wed 07/02 09Z 0.50 2814  75  48  13 0.00
Wed 07/02 12Z 0.40 2711  80  24  13 0.00
Wed 07/02 15Z 0.86 2709  75  21  12 0.00
Wed 07/02 18Z 3.29 2709  58  28  14 0.00
Wed 07/02 21Z 1.13 2807  58  65  15 0.00
Thu 07/03 00Z 0.41 2809  59  82  15 0.00
Thu 07/03 03Z 0.31 2907  62  82  15 0.00
Thu 07/03 06Z 0.41 2709  62  87  15 0.01
Thu 07/03 09Z 0.40 2710  63  75  14 0.00
Thu 07/03 12Z 0.42 2512  63  82  14 0.00
Thu 07/03 15Z 0.55 2613  70  75  12 0.04
Thu 07/03 18Z 1.10 2616  73  80  12 0.04
Thu 07/03 21Z 1.47 2817  58  69  13 0.01
Fri 07/04 00Z 0.79 3019  63  76  12 0.02
Fri 07/04 03Z 0.46 3013  63  77  11 0.01

Run total areal avg QPF for the greens is: 0.45 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