GFS EXPERIMENTAL Froude Number for the Green Mountains

Subject: GFS EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_GFS_20260608_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)
=== ===== === ==== ==== === === === ====
Mon 06/08 00Z 0.34 0222  85   3   7 0.00
Mon 06/08 03Z 0.61 0525  55   2   8 0.00
Mon 06/08 06Z 0.54 0618  43   4   8 0.00
Mon 06/08 09Z 0.37 0611  44   6   8 0.00
Mon 06/08 12Z 0.21 0407  47  10   7 0.00
Mon 06/08 15Z 0.15 0104  56  13   7 0.00
Mon 06/08 18Z 0.51 3203  53   9  10 0.00
Mon 06/08 21Z 0.42 2804  53   6  11 0.00
Tue 06/09 00Z 0.26 2805  43   4  12 0.00
Tue 06/09 03Z 0.29 2706  44   3  12 0.00
Tue 06/09 06Z 0.44 2611  49   3  12 0.00
Tue 06/09 09Z 0.41 2612  57   3  11 0.00
Tue 06/09 12Z 0.39 2712  69   2  11 0.00
Tue 06/09 15Z 0.38 2707  72   2  11 0.00
Tue 06/09 18Z 0.79 2609  68   2  13 0.00
Tue 06/09 21Z 0.99 2310  66   4  15 0.00
Wed 06/10 00Z 0.62 2513  61   3  16 0.00
Wed 06/10 03Z 0.52 2613  64   4  16 0.00
Wed 06/10 06Z 0.37 2510  71  19  15 0.00
Wed 06/10 09Z 0.28 2311  77  57  15 0.00
Wed 06/10 12Z 0.23 2113  77  62  15 0.00
Wed 06/10 15Z 0.22 2015  89  87  14 0.01
Wed 06/10 18Z 0.21 2016  98  97  13 0.17
Wed 06/10 21Z 0.29 2216  98  91  14 0.06

Run total areal avg QPF for the greens is: 0.24 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