GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20251119_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)
=== ===== === ==== ==== === === === ====
Wed 11/19 00Z 0.49 2916  84  33  -7 0.00
Wed 11/19 03Z 0.37 2812  80  28  -6 0.00
Wed 11/19 06Z 0.33 2811  76  19  -7 0.00
Wed 11/19 09Z 0.29 2809  75   5  -7 0.00
Wed 11/19 12Z 0.23 3009  71   3  -7 0.00
Wed 11/19 15Z 0.16 3007  68   5  -7 0.00
Wed 11/19 18Z 0.15 3106  61   8  -6 0.00
Wed 11/19 21Z 0.15 3107  52   9  -5 0.00
Thu 11/20 00Z 0.08 3306  50  14  -4 0.00
Thu 11/20 03Z 0.04 3303  47  22  -3 0.00
Thu 11/20 06Z 0.06 2902  43  26  -2 0.00
Thu 11/20 09Z 0.09 2704  43  51  -3 0.00
Thu 11/20 12Z 0.06 2702  39  60  -2 0.00
Thu 11/20 15Z 0.07 2503  38  67  -1 0.00
Thu 11/20 18Z 0.08 2403  41  62  -1 0.00
Thu 11/20 21Z 0.06 2204  39  59   0 0.00
Fri 11/21 00Z 0.09 2206  36  59   0 0.00
Fri 11/21 03Z 0.14 2208  32  47   0 0.00
Fri 11/21 06Z 0.14 2210  33  32   1 0.00
Fri 11/21 09Z 0.27 2413  43  36   0 0.00
Fri 11/21 12Z 0.29 2314  60  61   0 0.00
Fri 11/21 15Z 0.39 2416  83  76   0 0.00
Fri 11/21 18Z 0.37 2219  85  97   2 0.00
Fri 11/21 21Z 0.50 2323  89  93   2 0.02

Run total areal avg QPF for the greens is: 0.02 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