Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261021_0000
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 00Z 0.22 0217  51   7   6 0.00
Wed 10/21 01Z 0.24 0219  46   7   6 0.00
Wed 10/21 02Z 0.26 0319  43   8   7 0.00
Wed 10/21 03Z 0.30 0320  41   8   7 0.00
Wed 10/21 04Z 0.31 0418  41   8   7 0.00
Wed 10/21 05Z 0.30 0516  44   8   6 0.00
Wed 10/21 06Z 0.30 0714  47   8   6 0.00
Wed 10/21 07Z 0.26 0712  49   7   6 0.00
Wed 10/21 08Z 0.22 0810  50   6   5 0.00
Wed 10/21 09Z 0.17 0708  48   5   6 0.00
Wed 10/21 10Z 0.15 0608  43   4   6 0.00
Wed 10/21 11Z 0.15 0409  38   3   7 0.00
Wed 10/21 12Z 0.15 0409  37   2   7 0.00
Wed 10/21 13Z 0.16 0508  39   2   7 0.00
Wed 10/21 14Z 0.15 0508  40   2   7 0.00
Wed 10/21 15Z 0.12 0407  39   2   7 0.00
Wed 10/21 16Z 0.11 0307  38   2   8 0.00
Wed 10/21 17Z 0.12 0407  40   2   7 0.00
Wed 10/21 18Z 0.13 0606  42   2   7 0.00
Wed 10/21 19Z 0.10 0604  42   2   7 0.00
Wed 10/21 20Z 0.09 0404  41   2   7 0.00
Wed 10/21 21Z 0.08 0404  38   2   8 0.00
Wed 10/21 22Z 0.08 0504  36   3   8 0.00
Wed 10/21 23Z 0.07 0403  36   3   7 0.00
Thu 10/22 00Z 0.06 0204  33   3   8 0.00
Thu 10/22 01Z 0.05 0105  32   3   8 0.00
Thu 10/22 02Z 0.06 0106  31   4   8 0.00
Thu 10/22 03Z 0.05 0108  30   4   8 0.00
Thu 10/22 04Z 0.05 0010  29   5   8 0.00
Thu 10/22 05Z 0.08 0012  26   7   8 0.00
Thu 10/22 06Z 0.10 0113  23  10   8 0.00
Thu 10/22 07Z 0.10 0015  21  12   8 0.00
Thu 10/22 08Z 0.11 0017  19  14   8 0.00
Thu 10/22 09Z 0.11 0019  18  16   7 0.00
Thu 10/22 10Z 0.11 0021  16  17   7 0.00
Thu 10/22 11Z 0.12 0022  18  18   8 0.00
Thu 10/22 12Z 0.12 0022  29  17   7 0.00
Thu 10/22 13Z 0.11 0023  44  19   7 0.00
Thu 10/22 14Z 0.10 0022  61  25   6 0.00
Thu 10/22 15Z 0.09 0022  72  40   5 0.00
Thu 10/22 16Z 0.09 3522  82  51   4 0.00
Thu 10/22 17Z 0.11 3523  88  32   4 0.00
Thu 10/22 18Z 0.13 3524  90  12   2 0.00
Thu 10/22 19Z 0.14 3523  89  15   2 0.00
Thu 10/22 20Z 0.17 0026  73  24   2 0.00
Thu 10/22 21Z 0.16 0028  61  25   2 0.00
Thu 10/22 22Z 0.16 0030  55  17   2 0.00
Thu 10/22 23Z 0.19 0032  47  20   1 0.00
Fri 10/23 00Z 0.23 0033  47  28   1 0.00
Fri 10/23 01Z 0.29 0134  50  15   0 0.00
Fri 10/23 02Z 0.35 0134  53   4   0 0.00
Fri 10/23 03Z 0.42 0133  49   1  -1 0.00
Fri 10/23 04Z 0.43 0131  51   1  -2 0.00
Fri 10/23 05Z 0.35 0129  52   3  -2 0.00
Fri 10/23 06Z 0.31 0128  56   3  -2 0.00
Fri 10/23 07Z 0.31 0129  52   3  -1 0.00
Fri 10/23 08Z 0.30 0130  46   1   0 0.00
Fri 10/23 09Z 0.31 0230  38   2   0 0.00
Fri 10/23 10Z 0.30 0229  38   2   0 0.00
Fri 10/23 11Z 0.28 0128  43   2   0 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