GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20260227_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 02/27 00Z 0.50 2814  86  47 -13 0.00
Fri 02/27 03Z 0.31 2910  79  42 -13 0.00
Fri 02/27 06Z 0.24 2809  74  66 -12 0.00
Fri 02/27 09Z 0.25 2710  67  71 -10 0.00
Fri 02/27 12Z 0.29 2613  66  75  -9 0.00
Fri 02/27 15Z 0.30 2414  68  82  -8 0.00
Fri 02/27 18Z 0.36 2315  76  91  -7 0.00
Fri 02/27 21Z 0.50 2419  82  87  -6 0.00
Sat 02/28 00Z 0.65 2422  90  53  -5 0.00
Sat 02/28 03Z 0.61 2323  84  66  -4 0.00
Sat 02/28 06Z 0.53 2228  72  60  -2 0.00
Sat 02/28 09Z 0.58 2135  68  42  -1 0.00
Sat 02/28 12Z 0.54 2140  76  79   0 0.00
Sat 02/28 15Z 0.67 2238  93  94  -1 0.00
Sat 02/28 18Z 0.83 2431  99  39  -2 0.01
Sat 02/28 21Z 0.88 2524  96  21  -4 0.01
Sun 03/01 00Z 0.47 2817  73  22  -6 0.00
Sun 03/01 03Z 0.25 2910  77  34  -8 0.00
Sun 03/01 06Z 0.20 2909  83  77  -9 0.00
Sun 03/01 09Z 0.19 2909  82  95 -10 0.00
Sun 03/01 12Z 0.19 3010  94  96 -12 0.00
Sun 03/01 15Z 0.19 3110  97  98 -14 0.02
Sun 03/01 18Z 0.50 3113  96  82 -17 0.01
Sun 03/01 21Z 0.55 3116  95  28 -18 0.00

Run total areal avg QPF for the greens is: 0.05 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