NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260522_1200
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)
=== ===== === ==== ==== === === === ====
Fri 05/22 12Z 0.11 0208  58   4   0 0.00
Fri 05/22 13Z 0.14 0208  57   5   0 0.00
Fri 05/22 14Z 0.22 0306  57   6   0 0.00
Fri 05/22 15Z 0.80 0305  58   7   0 0.00
Fri 05/22 16Z 1.04 0303  57  10   1 0.00
Fri 05/22 17Z 0.67 0201  56  13   2 0.00
Fri 05/22 18Z 0.44 0001  56  16   2 0.00
Fri 05/22 19Z 0.37 3501  58  19   3 0.00
Fri 05/22 20Z 0.32 3502  59  22   3 0.00
Fri 05/22 21Z 0.24 0002  60  24   3 0.00
Fri 05/22 22Z 0.18 3502  60  25   4 0.00
Fri 05/22 23Z 0.11 0103  58  25   4 0.00
Sat 05/23 00Z 0.14 0203  55  25   4 0.00
Sat 05/23 01Z 0.18 0403  52  25   4 0.00
Sat 05/23 02Z 0.19 0404  49  24   4 0.00
Sat 05/23 03Z 0.19 0504  48  23   4 0.00
Sat 05/23 04Z 0.24 0605  48  21   4 0.00
Sat 05/23 05Z 0.29 0706  49  20   4 0.00
Sat 05/23 06Z 0.35 0707  49  17   4 0.00
Sat 05/23 07Z 0.45 0708  46  14   4 0.00
Sat 05/23 08Z 0.51 0809  44  12   3 0.00
Sat 05/23 09Z 0.58 0910  47   9   3 0.00
Sat 05/23 10Z 0.57 1012  49   6   3 0.00
Sat 05/23 11Z 0.57 1113  48   5   3 0.00
Sat 05/23 12Z 0.55 1214  48   5   3 0.00
Sat 05/23 13Z 0.52 1214  49   4   3 0.00
Sat 05/23 14Z 0.56 1214  52   4   3 0.00
Sat 05/23 15Z 0.90 1213  54   4   3 0.00
Sat 05/23 16Z 0.83 1212  57   4   3 0.00
Sat 05/23 17Z 0.70 1312  58   4   4 0.00
Sat 05/23 18Z 0.71 1312  59   3   4 0.00
Sat 05/23 19Z 0.55 1412  61   3   4 0.00
Sat 05/23 20Z 0.43 1413  63   3   4 0.00
Sat 05/23 21Z 0.39 1414  64   3   4 0.00
Sat 05/23 22Z 0.36 1415  64   2   4 0.00
Sat 05/23 23Z 0.39 1418  61   3   4 0.00
Sun 05/24 00Z 0.40 1420  57   4   4 0.00
Sun 05/24 01Z 0.42 1422  54   6   4 0.00
Sun 05/24 02Z 0.41 1423  51  13   4 0.00
Sun 05/24 03Z 0.39 1424  51  25   4 0.00
Sun 05/24 04Z 0.38 1426  49  39   5 0.00
Sun 05/24 05Z 0.37 1528  48  59   5 0.00
Sun 05/24 06Z 0.34 1529  49  67   5 0.00
Sun 05/24 07Z 0.34 1530  55  73   5 0.01
Sun 05/24 08Z 0.38 1432  61  80   5 0.02
Sun 05/24 09Z 0.40 1434  66  92   5 0.02
Sun 05/24 10Z 0.40 1435  74  98   5 0.03
Sun 05/24 11Z 0.40 1437  81  99   5 0.06
Sun 05/24 12Z 0.39 1439  83  99   5 0.07
Sun 05/24 13Z 0.37 1540  86  99   5 0.08
Sun 05/24 14Z 0.32 1541  88  98   5 0.08
Sun 05/24 15Z 0.27 1541  92  97   5 0.10
Sun 05/24 16Z 0.22 1640  94  98   5 0.11
Sun 05/24 17Z 0.18 1639  96  98   5 0.11
Sun 05/24 18Z 0.15 1638  96  98   5 0.09
Sun 05/24 19Z 0.11 1737  96  96   5 0.05
Sun 05/24 20Z 0.08 1737  97  88   6 0.03
Sun 05/24 21Z 0.08 1737  97  81   6 0.03
Sun 05/24 22Z 0.08 1737  97  78   7 0.02
Sun 05/24 23Z 0.07 1736  97  63   8 0.03

Run total areal avg QPF for the greens is: 0.94 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