Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20261018_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 10/18 12Z 0.58 2917  79  60  -2 0.00
Sun 10/18 15Z 0.54 2914  80  43  -1 0.00
Sun 10/18 18Z 0.40 2611  62  37   1 0.00
Sun 10/18 21Z 0.33 2413  49  20   3 0.00
Mon 10/19 00Z 0.35 2716  36  17   7 0.00
Mon 10/19 03Z 0.30 2714  20  23   9 0.00
Mon 10/19 06Z 0.27 2512  20  24   9 0.00
Mon 10/19 09Z 0.30 2514  20  24   9 0.00
Mon 10/19 12Z 0.34 2614  14  24   9 0.00
Mon 10/19 15Z 0.36 2715   9  27   9 0.00
Mon 10/19 18Z 0.32 2713  10  31  10 0.00
Mon 10/19 21Z 0.33 2914  14  30  10 0.00
Tue 10/20 00Z 0.26 3012  25  23  10 0.00
Tue 10/20 03Z 0.16 3211  34  17  10 0.00
Tue 10/20 06Z 0.08 3414  47  13   9 0.00
Tue 10/20 09Z 0.03 0015  44  14   9 0.00
Tue 10/20 12Z 0.09 0120  31  14   8 0.00
Tue 10/20 15Z 0.17 0221  28   8   7 0.00
Tue 10/20 18Z 0.13 0216  34   3   6 0.00
Tue 10/20 21Z 0.12 0217  40   4   6 0.00
Wed 10/21 00Z 0.20 0319  42   4   7 0.00
Wed 10/21 03Z 0.22 0515  46   5   6 0.00
Wed 10/21 06Z 0.19 0710  52   5   6 0.00
Wed 10/21 09Z 0.20 0514  47   5   6 0.00
Wed 10/21 12Z 0.19 0811  43   5   7 0.00
Wed 10/21 15Z 0.20 1012  42   6   8 0.00
Wed 10/21 18Z 0.17 1111  46   6   8 0.00
Wed 10/21 21Z 0.14 1310  48   6   9 0.00
Thu 10/22 00Z 0.10 1409  45   6   9 0.00

Run total areal avg QPF for the greens is: 0.00 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