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_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 05/20 00Z 1.08 2617  73  41  16 0.00
Wed 05/20 01Z 1.20 2520  70  44  16 0.00
Wed 05/20 02Z 1.26 2525  68  50  16 0.00
Wed 05/20 03Z 1.36 2530  66  58  17 0.00
Wed 05/20 04Z 1.49 2533  71  77  17 0.00
Wed 05/20 05Z 1.59 2435  73  66  17 0.00
Wed 05/20 06Z 1.78 2540  78  63  16 0.00
Wed 05/20 07Z 1.59 2636  81  63  16 0.01
Wed 05/20 08Z 1.41 2636  81  72  15 0.00
Wed 05/20 09Z 1.31 2634  81  70  15 0.00
Wed 05/20 10Z 1.29 2631  86  63  15 0.00
Wed 05/20 11Z 1.13 2629  90  60  15 0.00
Wed 05/20 12Z 0.97 2627  91  62  15 0.00
Wed 05/20 13Z 0.98 2626  92  70  14 0.01
Wed 05/20 14Z 1.15 2627  95  76  14 0.02
Wed 05/20 15Z 1.40 2727  93  87  13 0.03
Wed 05/20 16Z 2.42 2724  90  76  12 0.01
Wed 05/20 17Z 9.54 2722  85  66  11 0.00
Wed 05/20 18Z 11.87 2722  78  56  11 0.00
Wed 05/20 19Z 12.27 2820  72  46  11 0.00
Wed 05/20 20Z 9.89 2820  72  42  11 0.00
Wed 05/20 21Z 7.60 2921  72  44  10 0.00
Wed 05/20 22Z 3.17 3021  77  42   9 0.00
Wed 05/20 23Z 0.93 3121  82  40   8 0.00
Thu 05/21 00Z 0.62 3123  81  36   7 0.00
Thu 05/21 01Z 0.55 3124  80  28   6 0.00
Thu 05/21 02Z 0.46 3123  77  18   5 0.00
Thu 05/21 03Z 0.34 3223  74  13   5 0.00
Thu 05/21 04Z 0.28 3224  63   9   4 0.00
Thu 05/21 05Z 0.24 3225  62   6   3 0.00
Thu 05/21 06Z 0.19 3325  58   5   3 0.00
Thu 05/21 07Z 0.16 3325  59   2   2 0.00
Thu 05/21 08Z 0.12 3326  60   2   1 0.00
Thu 05/21 09Z 0.07 3425  54   2   1 0.00
Thu 05/21 10Z 0.06 3426  48   3   0 0.00
Thu 05/21 11Z 0.05 3425  45   3   0 0.00
Thu 05/21 12Z 0.07 3423  45   3   0 0.00
Thu 05/21 13Z 0.07 3420  44   3   0 0.00
Thu 05/21 14Z 0.09 3318  43   3   0 0.00
Thu 05/21 15Z 0.10 3317  43   2   0 0.00
Thu 05/21 16Z 0.14 3417  42   2   0 0.00
Thu 05/21 17Z 0.23 3317  41   3   0 0.00
Thu 05/21 18Z 0.22 3417  39   3   0 0.00
Thu 05/21 19Z 0.20 3417  37   3   0 0.00
Thu 05/21 20Z 0.13 3417  34   5   1 0.00
Thu 05/21 21Z 0.13 3417  32   5   1 0.00
Thu 05/21 22Z 0.05 3417  29   5   2 0.00
Thu 05/21 23Z 0.03 3418  26   7   2 0.00
Fri 05/22 00Z 0.02 3520  22   7   3 0.00
Fri 05/22 01Z 0.06 3520  22   8   3 0.00
Fri 05/22 02Z 0.07 3519  26   8   3 0.00
Fri 05/22 03Z 0.06 3518  31   9   3 0.00
Fri 05/22 04Z 0.07 3517  35   8   3 0.00
Fri 05/22 05Z 0.09 0018  37   6   2 0.00
Fri 05/22 06Z 0.13 0017  37   6   2 0.00
Fri 05/22 07Z 0.18 0117  37   6   2 0.00
Fri 05/22 08Z 0.23 0115  36   6   2 0.00
Fri 05/22 09Z 0.20 0112  36   5   2 0.00
Fri 05/22 10Z 0.15 0110  38   6   1 0.00
Fri 05/22 11Z 0.16 0110  41   6   1 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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