NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260521_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 05/21 00Z 0.67 3118  69  30   9 0.00
Thu 05/21 01Z 0.73 3121  71  18   7 0.00
Thu 05/21 02Z 0.75 3222  72  11   6 0.00
Thu 05/21 03Z 0.67 3225  71  11   5 0.00
Thu 05/21 04Z 0.47 3325  69  10   4 0.00
Thu 05/21 05Z 0.31 3424  66  10   3 0.00
Thu 05/21 06Z 0.18 3421  65  12   3 0.00
Thu 05/21 07Z 0.15 3420  64  13   2 0.00
Thu 05/21 08Z 0.13 3420  65  11   1 0.00
Thu 05/21 09Z 0.13 3421  64   9   0 0.00
Thu 05/21 10Z 0.11 3420  63   6   0 0.00
Thu 05/21 11Z 0.10 3419  60   4   0 0.00
Thu 05/21 12Z 0.11 3416  55   3   0 0.00
Thu 05/21 13Z 0.12 3414  50   3   0 0.00
Thu 05/21 14Z 0.14 3313  47   3   0 0.00
Thu 05/21 15Z 0.17 3313  45   4   0 0.00
Thu 05/21 16Z 0.20 3313  45   4   0 0.00
Thu 05/21 17Z 0.32 3313  44   4   0 0.00
Thu 05/21 18Z 0.53 3314  43   5   0 0.00
Thu 05/21 19Z 0.55 3314  40   5   0 0.00
Thu 05/21 20Z 0.53 3314  39   5   0 0.00
Thu 05/21 21Z 0.46 3315  40   5   0 0.00
Thu 05/21 22Z 0.34 3315  41   4   1 0.00
Thu 05/21 23Z 0.28 3315  40   4   1 0.00
Fri 05/22 00Z 0.28 3317  41   4   1 0.00
Fri 05/22 01Z 0.21 3417  42   4   0 0.00
Fri 05/22 02Z 0.17 3417  43   3   0 0.00
Fri 05/22 03Z 0.17 3516  45   2   0 0.00
Fri 05/22 04Z 0.14 3516  47   2   0 0.00
Fri 05/22 05Z 0.05 0014  48   2   0 0.00
Fri 05/22 06Z 0.08 0013  46   3   0 0.00
Fri 05/22 07Z 0.09 0012  44   3   0 0.00
Fri 05/22 08Z 0.09 0112  40   3   0 0.00
Fri 05/22 09Z 0.12 0113  36   3   0 0.00
Fri 05/22 10Z 0.18 0213  33   3   1 0.00
Fri 05/22 11Z 0.20 0312  33   4   0 0.00
Fri 05/22 12Z 0.23 0411  33   5   0 0.00
Fri 05/22 13Z 0.21 0408  34   5   1 0.00
Fri 05/22 14Z 0.26 0407  36   6   1 0.00
Fri 05/22 15Z 0.39 0404  40   6   1 0.00
Fri 05/22 16Z 0.71 0303  43   8   1 0.00
Fri 05/22 17Z 0.59 0102  45   9   2 0.00
Fri 05/22 18Z 0.73 0101  46  12   2 0.00
Fri 05/22 19Z 0.61 3502  47  14   3 0.00
Fri 05/22 20Z 0.37 3402  47  15   3 0.00
Fri 05/22 21Z 0.21 3502  48  16   4 0.00
Fri 05/22 22Z 0.14 3302  50  16   4 0.00
Fri 05/22 23Z 0.05 0002  50  18   4 0.00
Sat 05/23 00Z 0.10 0203  49  19   4 0.00
Sat 05/23 01Z 0.12 0303  47  21   4 0.00
Sat 05/23 02Z 0.20 0504  46  21   4 0.00
Sat 05/23 03Z 0.27 0505  45  22   4 0.00
Sat 05/23 04Z 0.36 0607  44  21   4 0.00
Sat 05/23 05Z 0.43 0708  45  21   4 0.00
Sat 05/23 06Z 0.53 0709  46  19   4 0.00
Sat 05/23 07Z 0.58 0810  46  17   4 0.00
Sat 05/23 08Z 0.67 0911  45  15   3 0.00
Sat 05/23 09Z 0.69 0912  44  13   3 0.00
Sat 05/23 10Z 0.70 1013  44   9   3 0.00
Sat 05/23 11Z 0.69 1014  45   6   3 0.00

Run total areal avg QPF for the 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