Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261020_1800
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)
=== ===== === ==== ==== === === === ====
Tue 10/20 18Z 0.17 0013  54   5   5 0.00
Tue 10/20 19Z 0.16 0015  55   5   5 0.00
Tue 10/20 20Z 0.17 0117  53   6   6 0.00
Tue 10/20 21Z 0.19 0119  49   6   6 0.00
Tue 10/20 22Z 0.24 0121  45   6   6 0.00
Tue 10/20 23Z 0.29 0221  41   6   6 0.00
Wed 10/21 00Z 0.30 0321  37   7   7 0.00
Wed 10/21 01Z 0.29 0319  34   7   7 0.00
Wed 10/21 02Z 0.29 0418  33   8   6 0.00
Wed 10/21 03Z 0.27 0415  34   8   6 0.00
Wed 10/21 04Z 0.24 0513  36   8   6 0.00
Wed 10/21 05Z 0.22 0611  37   8   6 0.00
Wed 10/21 06Z 0.20 0609  39   8   6 0.00
Wed 10/21 07Z 0.18 0608  40   8   6 0.00
Wed 10/21 08Z 0.16 0608  38   7   6 0.00
Wed 10/21 09Z 0.15 0608  38   7   6 0.00
Wed 10/21 10Z 0.14 0607  37   6   6 0.00
Wed 10/21 11Z 0.15 0608  35   5   6 0.00
Wed 10/21 12Z 0.14 0608  33   4   7 0.00
Wed 10/21 13Z 0.15 0508  32   4   7 0.00
Wed 10/21 14Z 0.14 0508  33   4   7 0.00
Wed 10/21 15Z 0.14 0608  34   4   7 0.00
Wed 10/21 16Z 0.12 0606  35   4   7 0.00
Wed 10/21 17Z 0.12 0506  33   3   8 0.00
Wed 10/21 18Z 0.11 0505  34   4   8 0.00
Wed 10/21 19Z 0.11 0505  33   3   8 0.00
Wed 10/21 20Z 0.12 0605  34   3   8 0.00
Wed 10/21 21Z 0.11 0605  33   3   8 0.00
Wed 10/21 22Z 0.10 0505  32   3   8 0.00
Wed 10/21 23Z 0.10 0406  32   3   8 0.00
Thu 10/22 00Z 0.10 0306  34   3   8 0.00
Thu 10/22 01Z 0.09 0208  33   3   8 0.00
Thu 10/22 02Z 0.10 0110  31   3   8 0.00
Thu 10/22 03Z 0.12 0212  29   3   8 0.00
Thu 10/22 04Z 0.13 0212  27   4   8 0.00
Thu 10/22 05Z 0.14 0115  24   6   8 0.00
Thu 10/22 06Z 0.15 0117  21   9   8 0.00
Thu 10/22 07Z 0.17 0119  19  11   8 0.00
Thu 10/22 08Z 0.19 0121  18  13   8 0.00
Thu 10/22 09Z 0.20 0122  17  15   7 0.00
Thu 10/22 10Z 0.20 0123  16  16   7 0.00
Thu 10/22 11Z 0.19 0124  20  17   7 0.00
Thu 10/22 12Z 0.20 0124  30  16   7 0.00
Thu 10/22 13Z 0.21 0124  49  17   6 0.00
Thu 10/22 14Z 0.20 0124  69  29   6 0.00
Thu 10/22 15Z 0.18 0024  78  44   5 0.00
Thu 10/22 16Z 0.13 0024  86  47   4 0.00
Thu 10/22 17Z 0.05 3524  90  33   3 0.00
Thu 10/22 18Z 0.04 3426  90  13   3 0.00
Thu 10/22 19Z 0.06 3527  77  15   3 0.00
Thu 10/22 20Z 0.07 3528  68  22   3 0.00
Thu 10/22 21Z 0.10 3530  70  20   2 0.00
Thu 10/22 22Z 0.14 3532  63  24   1 0.00
Thu 10/22 23Z 0.20 0033  54  33   0 0.00
Fri 10/23 00Z 0.23 0034  57  24   0 0.00
Fri 10/23 01Z 0.29 0035  58   6  -1 0.00
Fri 10/23 02Z 0.37 0135  54   2  -1 0.00
Fri 10/23 03Z 0.35 0034  53   4  -2 0.00
Fri 10/23 04Z 0.30 0033  58   5  -3 0.00
Fri 10/23 05Z 0.28 0032  62   7  -3 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