Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261019_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 10/19 06Z 0.19 2709  48  19   9 0.00
Mon 10/19 07Z 0.19 2810  50  19   9 0.00
Mon 10/19 08Z 0.17 2909  47  18   9 0.00
Mon 10/19 10Z 0.12 3007  37  16   9 0.00
Mon 10/19 12Z 0.11 2905  34  17   8 0.00
Mon 10/19 14Z 0.11 2604  34  18   8 0.00
Mon 10/19 15Z 0.13 2505  33  17   9 0.00
Mon 10/19 16Z 0.15 2606  31  15   9 0.00
Mon 10/19 17Z 0.17 2707  29  13  10 0.00
Mon 10/19 18Z 0.17 2808  28  13  10 0.00
Mon 10/19 19Z 0.18 2909  24  14  11 0.00
Mon 10/19 20Z 0.17 2909  23  15  11 0.00
Mon 10/19 21Z 0.16 3010  22  16  11 0.00
Mon 10/19 22Z 0.16 3111  25  15  11 0.00
Mon 10/19 23Z 0.15 3213  31  14  10 0.00
Tue 10/20 00Z 0.14 3214  37  15   9 0.00
Tue 10/20 01Z 0.08 3316  40  16   9 0.00
Tue 10/20 02Z 0.03 3516  39  14   9 0.00
Tue 10/20 03Z 0.05 3516  40  11   9 0.00
Tue 10/20 04Z 0.07 3517  45  10   9 0.00
Tue 10/20 05Z 0.09 0019  51   9   9 0.00
Tue 10/20 06Z 0.12 0019  54  12   9 0.00
Tue 10/20 07Z 0.14 0119  50  17   9 0.00
Tue 10/20 08Z 0.16 0121  40  18   9 0.00
Tue 10/20 09Z 0.19 0122  33  14   9 0.00
Tue 10/20 10Z 0.22 0123  30  10   9 0.00
Tue 10/20 11Z 0.22 0124  28   5   9 0.00
Tue 10/20 12Z 0.23 0124  27   2   9 0.00
Tue 10/20 13Z 0.24 0224  27   3   8 0.00
Tue 10/20 14Z 0.24 0223  29   4   8 0.00
Tue 10/20 15Z 0.22 0222  31   5   8 0.00
Tue 10/20 16Z 0.19 0120  34   6   7 0.00
Tue 10/20 17Z 0.18 0119  41   6   7 0.00
Tue 10/20 18Z 0.19 0119  48   6   7 0.00
Tue 10/20 19Z 0.21 0119  51   6   6 0.00
Tue 10/20 20Z 0.22 0119  51   7   6 0.00
Tue 10/20 21Z 0.22 0120  49   8   6 0.00
Tue 10/20 22Z 0.25 0222  47   8   6 0.00
Tue 10/20 23Z 0.27 0223  42   8   7 0.00
Wed 10/21 00Z 0.29 0323  38   8   7 0.00
Wed 10/21 01Z 0.29 0322  36   9   7 0.00
Wed 10/21 02Z 0.29 0321  35   9   7 0.00
Wed 10/21 03Z 0.27 0419  34   9   7 0.00
Wed 10/21 04Z 0.26 0416  34   9   7 0.00
Wed 10/21 05Z 0.23 0514  34  10   7 0.00
Wed 10/21 06Z 0.19 0511  32   9   7 0.00
Wed 10/21 07Z 0.16 0410  28   9   7 0.00
Wed 10/21 08Z 0.17 0410  28   9   7 0.00
Wed 10/21 09Z 0.17 0410  29   9   7 0.00
Wed 10/21 10Z 0.17 0411  28   8   8 0.00
Wed 10/21 11Z 0.17 0511  28   8   8 0.00
Wed 10/21 12Z 0.17 0511  27   8   8 0.00
Wed 10/21 13Z 0.17 0510  28   8   8 0.00
Wed 10/21 14Z 0.17 0510  29   8   8 0.00
Wed 10/21 15Z 0.16 0609  31   8   8 0.00
Wed 10/21 16Z 0.16 0608  32   8   8 0.00
Wed 10/21 17Z 0.15 0708  33   8   8 0.00

Run total areal avg QPF for the Central_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