Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261021_1200
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)
=== ===== === ==== ==== === === === ====
Wed 10/21 12Z 0.06 0603  51   2   5 0.00
Wed 10/21 13Z 0.07 0404  48   2   6 0.00
Wed 10/21 14Z 0.07 0305  46   2   6 0.00
Wed 10/21 15Z 0.09 0306  46   2   7 0.00
Wed 10/21 16Z 0.12 0406  48   2   6 0.00
Wed 10/21 17Z 0.14 0506  48   2   6 0.00
Wed 10/21 18Z 0.16 0806  49   2   6 0.00
Wed 10/21 19Z 0.14 0805  46   2   7 0.00
Wed 10/21 20Z 0.11 0704  45   2   7 0.00
Wed 10/21 21Z 0.10 0604  43   2   7 0.00
Wed 10/21 22Z 0.10 0604  38   2   7 0.00
Wed 10/21 23Z 0.10 0704  35   2   7 0.00
Thu 10/22 00Z 0.09 0604  35   2   7 0.00
Thu 10/22 01Z 0.06 0303  35   2   7 0.00
Thu 10/22 02Z 0.04 0006  34   2   8 0.00
Thu 10/22 03Z 0.03 3509  34   2   8 0.00
Thu 10/22 04Z 0.07 0011  33   2   8 0.00
Thu 10/22 05Z 0.10 0112  31   2   8 0.00
Thu 10/22 06Z 0.13 0213  30   3   8 0.00
Thu 10/22 07Z 0.15 0214  28   3   7 0.00
Thu 10/22 08Z 0.14 0115  26   5   7 0.00
Thu 10/22 09Z 0.14 0117  23  10   7 0.00
Thu 10/22 10Z 0.14 0020  23  14   7 0.00
Thu 10/22 11Z 0.16 0122  22  17   7 0.00
Thu 10/22 12Z 0.16 0123  19  19   7 0.00
Thu 10/22 13Z 0.16 0023  21  21   7 0.00
Thu 10/22 14Z 0.14 0022  30  19   7 0.00
Thu 10/22 15Z 0.12 0021  44  17   6 0.00
Thu 10/22 16Z 0.10 0022  60  16   5 0.00
Thu 10/22 17Z 0.09 3522  73  15   4 0.00
Thu 10/22 18Z 0.11 3523  81  23   4 0.00
Thu 10/22 19Z 0.11 3524  86  34   3 0.00
Thu 10/22 20Z 0.08 3526  89  34   2 0.00
Thu 10/22 21Z 0.07 3527  85  26   2 0.00
Thu 10/22 22Z 0.11 3528  71  20   2 0.00
Thu 10/22 23Z 0.14 0030  60  26   2 0.00
Fri 10/23 00Z 0.16 0029  56  34   2 0.00
Fri 10/23 01Z 0.20 0028  55  38   1 0.00
Fri 10/23 02Z 0.27 0127  58  23   0 0.00
Fri 10/23 03Z 0.33 0128  48  14   0 0.00
Fri 10/23 04Z 0.39 0228  45   7   0 0.00
Fri 10/23 05Z 0.37 0227  44   3   0 0.00
Fri 10/23 06Z 0.33 0126  46   1  -1 0.00
Fri 10/23 07Z 0.30 0125  48   3  -1 0.00
Fri 10/23 08Z 0.26 0125  48   2  -1 0.00
Fri 10/23 09Z 0.26 0126  41   2   0 0.00
Fri 10/23 10Z 0.29 0226  37   2   0 0.00
Fri 10/23 11Z 0.30 0226  42   1   0 0.00
Fri 10/23 12Z 0.31 0225  39   2   0 0.00
Fri 10/23 13Z 0.32 0224  37   4   0 0.00
Fri 10/23 14Z 0.30 0322  36   4   0 0.00
Fri 10/23 15Z 0.28 0320  35   3   0 0.00
Fri 10/23 16Z 0.26 0318  34   2   0 0.00
Fri 10/23 17Z 0.24 0316  33   2   0 0.00
Fri 10/23 18Z 0.21 0214  31   1   1 0.00
Fri 10/23 19Z 0.18 0213  26   2   2 0.00
Fri 10/23 20Z 0.17 0213  22   2   3 0.00
Fri 10/23 21Z 0.16 0213  18   2   4 0.00
Fri 10/23 22Z 0.15 0212  16   2   4 0.00
Fri 10/23 23Z 0.14 0311  15   2   4 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