NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260520_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 05/20 12Z 0.90 2722  92  68  13 0.00
Wed 05/20 13Z 0.97 2724  88  68  13 0.00
Wed 05/20 14Z 1.13 2724  92  80  13 0.00
Wed 05/20 15Z 1.40 2624  96  80  13 0.02
Wed 05/20 16Z 1.18 2626  96  81  14 0.04
Wed 05/20 17Z 1.59 2725  94  71  13 0.04
Wed 05/20 18Z 1.19 2723  94  66  12 0.02
Wed 05/20 19Z 1.57 2821  91  59  11 0.01
Wed 05/20 20Z 2.42 2920  92  59  11 0.01
Wed 05/20 21Z 1.99 3020  89  57  10 0.01
Wed 05/20 22Z 0.52 3121  78  58   9 0.00
Wed 05/20 23Z 0.48 3122  77  55   8 0.00
Thu 05/21 00Z 0.45 3123  73  47   7 0.00
Thu 05/21 01Z 0.34 3223  69  32   6 0.00
Thu 05/21 02Z 0.29 3223  69  19   5 0.00
Thu 05/21 03Z 0.28 3223  66  11   5 0.00
Thu 05/21 04Z 0.23 3223  63   8   4 0.00
Thu 05/21 05Z 0.19 3323  57   8   4 0.00
Thu 05/21 06Z 0.17 3324  56   5   3 0.00
Thu 05/21 07Z 0.17 3327  58   2   2 0.00
Thu 05/21 08Z 0.14 3326  61   1   2 0.00
Thu 05/21 09Z 0.11 3325  61   1   2 0.00
Thu 05/21 10Z 0.10 3324  55   2   2 0.00
Thu 05/21 11Z 0.09 3323  48   3   2 0.00
Thu 05/21 12Z 0.08 3321  45   3   2 0.00
Thu 05/21 13Z 0.06 3419  44   4   1 0.00
Thu 05/21 14Z 0.07 3317  43   4   1 0.00
Thu 05/21 15Z 0.07 3416  42   4   1 0.00
Thu 05/21 16Z 0.07 3414  43   4   0 0.00
Thu 05/21 17Z 0.09 3313  42   4   0 0.00
Thu 05/21 18Z 0.20 3314  41   4   0 0.00
Thu 05/21 19Z 0.22 3313  38   4   1 0.00
Thu 05/21 20Z 0.16 3414  35   4   1 0.00
Thu 05/21 21Z 0.11 3314  34   4   1 0.00
Thu 05/21 22Z 0.08 3414  33   4   1 0.00
Thu 05/21 23Z 0.07 3415  33   3   1 0.00
Fri 05/22 00Z 0.03 3417  32   3   1 0.00
Fri 05/22 01Z 0.05 3518  32   3   1 0.00
Fri 05/22 02Z 0.11 0018  34   4   1 0.00
Fri 05/22 03Z 0.12 0016  35   4   1 0.00
Fri 05/22 04Z 0.15 0115  34   3   1 0.00
Fri 05/22 05Z 0.17 0114  34   3   1 0.00
Fri 05/22 06Z 0.20 0113  36   2   0 0.00
Fri 05/22 07Z 0.21 0113  39   2   0 0.00
Fri 05/22 08Z 0.28 0214  40   3   0 0.00
Fri 05/22 09Z 0.29 0312  35   3   1 0.00
Fri 05/22 10Z 0.22 0310  32   4   1 0.00
Fri 05/22 11Z 0.25 0411  29   4   1 0.00
Fri 05/22 12Z 0.26 0411  31   6   1 0.00
Fri 05/22 13Z 0.26 0409  36   7   1 0.00
Fri 05/22 14Z 0.28 0407  39   7   1 0.00
Fri 05/22 15Z 0.47 0305  42   7   1 0.00
Fri 05/22 16Z 0.62 0203  45   9   1 0.00
Fri 05/22 17Z 0.38 0002  48  11   2 0.00
Fri 05/22 18Z 0.37 3202  50  12   3 0.00
Fri 05/22 19Z 0.41 3203  52  14   3 0.00
Fri 05/22 20Z 0.82 3103  53  15   4 0.00
Fri 05/22 21Z 0.65 3104  50  17   4 0.00
Fri 05/22 22Z 0.27 3305  47  19   4 0.00
Fri 05/22 23Z 0.09 3406  44  21   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.15 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