Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261021_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 10/21 00Z 0.15 0217  49   7   6 0.00
Wed 10/21 01Z 0.17 0218  45   8   6 0.00
Wed 10/21 02Z 0.19 0219  42   8   6 0.00
Wed 10/21 03Z 0.22 0318  40   8   7 0.00
Wed 10/21 04Z 0.24 0417  40   7   7 0.00
Wed 10/21 05Z 0.25 0515  41   7   6 0.00
Wed 10/21 06Z 0.25 0613  44   6   6 0.00
Wed 10/21 07Z 0.23 0711  46   6   6 0.00
Wed 10/21 08Z 0.20 0709  46   5   5 0.00
Wed 10/21 09Z 0.15 0708  44   4   6 0.00
Wed 10/21 10Z 0.12 0507  40   3   6 0.00
Wed 10/21 11Z 0.11 0408  36   3   7 0.00
Wed 10/21 12Z 0.12 0408  34   2   7 0.00
Wed 10/21 13Z 0.12 0508  35   2   7 0.00
Wed 10/21 14Z 0.12 0507  36   2   7 0.00
Wed 10/21 15Z 0.11 0506  37   2   7 0.00
Wed 10/21 16Z 0.09 0406  37   2   7 0.00
Wed 10/21 17Z 0.09 0406  38   2   7 0.00
Wed 10/21 18Z 0.10 0505  40   2   7 0.00
Wed 10/21 19Z 0.08 0504  42   2   7 0.00
Wed 10/21 20Z 0.06 0503  42   3   7 0.00
Wed 10/21 21Z 0.05 0403  40   3   7 0.00
Wed 10/21 22Z 0.05 0403  38   3   7 0.00
Wed 10/21 23Z 0.05 0303  37   3   7 0.00
Thu 10/22 00Z 0.04 0203  34   4   7 0.00
Thu 10/22 01Z 0.03 0004  32   4   8 0.00
Thu 10/22 02Z 0.04 0006  29   6   8 0.00
Thu 10/22 03Z 0.03 0008  27  10   8 0.00
Thu 10/22 04Z 0.03 3510  25  12   8 0.00
Thu 10/22 05Z 0.04 0011  21  13   8 0.00
Thu 10/22 06Z 0.06 0012  19  14   8 0.00
Thu 10/22 07Z 0.05 0014  19  15   7 0.00
Thu 10/22 08Z 0.05 0016  18  16   7 0.00
Thu 10/22 09Z 0.05 0018  19  18   7 0.00
Thu 10/22 10Z 0.04 0020  24  18   7 0.00
Thu 10/22 11Z 0.04 0020  34  18   7 0.00
Thu 10/22 12Z 0.05 0020  43  24   7 0.00
Thu 10/22 13Z 0.05 0021  56  33   6 0.00
Thu 10/22 14Z 0.04 0021  71  37   5 0.00
Thu 10/22 15Z 0.02 3521  80  44   4 0.00
Thu 10/22 16Z 0.02 3522  86  40   4 0.00
Thu 10/22 17Z 0.04 3522  90  27   3 0.00
Thu 10/22 18Z 0.04 3524  87  17   2 0.00
Thu 10/22 19Z 0.05 0024  79  20   2 0.00
Thu 10/22 20Z 0.04 0025  69  23   2 0.00
Thu 10/22 21Z 0.03 0027  59  23   2 0.00
Thu 10/22 22Z 0.04 0030  53  17   2 0.00
Thu 10/22 23Z 0.08 0031  49  22   1 0.00
Fri 10/23 00Z 0.13 0032  49  27   0 0.00
Fri 10/23 01Z 0.21 0133  50  13   0 0.00
Fri 10/23 02Z 0.28 0133  51   4   0 0.00
Fri 10/23 03Z 0.30 0133  50   2  -1 0.00
Fri 10/23 04Z 0.29 0131  52   2  -2 0.00
Fri 10/23 05Z 0.25 0129  54   4  -2 0.00
Fri 10/23 06Z 0.23 0128  56   3  -2 0.00
Fri 10/23 07Z 0.22 0129  53   3  -1 0.00
Fri 10/23 08Z 0.20 0228  47   1   0 0.00
Fri 10/23 09Z 0.22 0228  42   2   0 0.00
Fri 10/23 10Z 0.20 0227  42   2   0 0.00
Fri 10/23 11Z 0.19 0227  45   3   0 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