NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260521_1800
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 18Z 1.75 3210  69   6   0 0.00
Thu 05/21 19Z 1.53 3212  64   6   1 0.00
Thu 05/21 20Z 1.05 3212  62   5   1 0.00
Thu 05/21 21Z 0.84 3312  61   5   1 0.00
Thu 05/21 22Z 0.63 3313  63   4   1 0.00
Thu 05/21 23Z 0.28 3312  63   3   1 0.00
Fri 05/22 00Z 0.21 3413  63   3   1 0.00
Fri 05/22 01Z 0.19 3414  64   2   0 0.00
Fri 05/22 02Z 0.19 3414  65   2   0 0.00
Fri 05/22 03Z 0.24 3414  65   2   0 0.00
Fri 05/22 04Z 0.25 3514  64   2   0 0.00
Fri 05/22 05Z 0.12 3513  64   2   0 0.00
Fri 05/22 06Z 0.05 0011  61   2   0 0.00
Fri 05/22 07Z 0.07 0011  59   2   0 0.00
Fri 05/22 08Z 0.10 0111  59   2   0 0.00
Fri 05/22 09Z 0.14 0111  58   3   0 0.00
Fri 05/22 10Z 0.18 0212  53   4   0 0.00
Fri 05/22 11Z 0.19 0212  48   5   0 0.00
Fri 05/22 12Z 0.22 0312  46   6   0 0.00
Fri 05/22 13Z 0.22 0310  45   6   0 0.00
Fri 05/22 14Z 0.30 0308  45   8   0 0.00
Fri 05/22 15Z 0.37 0205  46  11   0 0.00
Fri 05/22 16Z 0.56 0203  47  15   0 0.00
Fri 05/22 17Z 0.42 0102  47  16   1 0.00
Fri 05/22 18Z 0.36 3502  47  20   2 0.00
Fri 05/22 19Z 0.37 0002  47  19   3 0.00
Fri 05/22 20Z 0.32 3503  48  19   3 0.00
Fri 05/22 21Z 0.24 0003  50  17   3 0.00
Fri 05/22 22Z 0.16 0103  50  18   3 0.00
Fri 05/22 23Z 0.10 0202  49  19   4 0.00
Sat 05/23 00Z 0.12 0303  45  20   4 0.00
Sat 05/23 01Z 0.13 0304  42  20   4 0.00
Sat 05/23 02Z 0.22 0505  42  19   4 0.00
Sat 05/23 03Z 0.23 0505  43  18   4 0.00
Sat 05/23 04Z 0.29 0506  45  14   4 0.00
Sat 05/23 05Z 0.34 0607  46  11   3 0.00
Sat 05/23 06Z 0.42 0608  46   8   3 0.00
Sat 05/23 07Z 0.42 0609  46   6   3 0.00
Sat 05/23 08Z 0.44 0609  46   4   3 0.00
Sat 05/23 09Z 0.49 0810  46   4   3 0.00
Sat 05/23 10Z 0.54 0812  46   5   3 0.00
Sat 05/23 11Z 0.56 0913  46   6   3 0.00
Sat 05/23 12Z 0.55 1013  46   6   3 0.00
Sat 05/23 13Z 0.56 1014  47   5   3 0.00
Sat 05/23 14Z 0.55 1012  50   5   3 0.00
Sat 05/23 15Z 0.83 1011  54   4   3 0.00
Sat 05/23 16Z 1.28 1110  57   4   3 0.00
Sat 05/23 17Z 2.12 1209  58   4   4 0.00
Sat 05/23 18Z 2.42 1308  59   4   4 0.00
Sat 05/23 19Z 2.58 1309  61   3   4 0.00
Sat 05/23 20Z 1.83 1309  63   3   4 0.00
Sat 05/23 21Z 2.14 1311  66   3   4 0.00
Sat 05/23 22Z 1.39 1412  69   3   4 0.00
Sat 05/23 23Z 0.84 1414  69   2   4 0.00
Sun 05/24 00Z 0.55 1317  67   2   4 0.00
Sun 05/24 01Z 0.42 1318  61   3   5 0.00
Sun 05/24 02Z 0.40 1320  49   3   5 0.00
Sun 05/24 03Z 0.39 1323  36   3   6 0.00
Sun 05/24 04Z 0.38 1425  30   3   7 0.00
Sun 05/24 05Z 0.38 1427  27   3   7 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