Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260614_1200
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)
=== ===== === ==== ==== === === === ====
Sun 06/14 12Z 0.49 2417  73  46  14 0.00
Sun 06/14 15Z 0.78 2217  83  46  14 0.00
Sun 06/14 18Z 1.02 2023  80  65  15 0.05
Sun 06/14 21Z 2.79 2321  86  91  14 0.35
Mon 06/15 00Z 0.57 2125  81  91  15 0.16
Mon 06/15 03Z 0.73 2420  94  96  13 0.39
Mon 06/15 06Z 0.42 2916  92  82  11 0.36
Mon 06/15 09Z 0.39 3014  96  89   9 0.02
Mon 06/15 12Z 0.41 2915  87  54   7 0.00
Mon 06/15 15Z 0.68 2913  89  13   6 0.00
Mon 06/15 18Z 4.29 2912  87  21   6 0.00
Mon 06/15 21Z 4.71 3013  85  22   6 0.00
Tue 06/16 00Z 1.14 3014  85  23   6 0.00
Tue 06/16 03Z 0.96 3019  89  12   5 0.00
Tue 06/16 06Z 0.86 3119  92   3   4 0.00
Tue 06/16 09Z 0.47 3217  87   6   3 0.00
Tue 06/16 12Z 0.29 3212  81  35   4 0.00
Tue 06/16 15Z 0.70 2908  77  58   5 0.00
Tue 06/16 18Z 3.06 2707  71  46   7 0.00
Tue 06/16 21Z 2.63 2507  68  40   8 0.00
Wed 06/17 00Z 0.72 2409  73  32   9 0.00
Wed 06/17 03Z 0.78 2411  72  28   8 0.00
Wed 06/17 06Z 0.73 2410  71  24   8 0.00
Wed 06/17 09Z 0.70 2410  72  28   8 0.00
Wed 06/17 12Z 0.23 2009  71  20   8 0.00
Wed 06/17 15Z 0.31 1712  73  16   9 0.00
Wed 06/17 18Z 0.54 1814  68  22  10 0.00
Wed 06/17 21Z 1.06 1715  64  39  11 0.00
Thu 06/18 00Z 0.24 1822  73  75  11 0.01

Run total areal avg QPF for the greens is: 1.34 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