NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260522_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)
=== ===== === ==== ==== === === === ====
Fri 05/22 00Z 0.19 3412  65   3   1 0.00
Fri 05/22 01Z 0.18 3414  65   2   1 0.00
Fri 05/22 02Z 0.19 3415  62   2   1 0.00
Fri 05/22 03Z 0.16 3415  59   3   0 0.00
Fri 05/22 04Z 0.10 3514  59   2   0 0.00
Fri 05/22 05Z 0.06 0013  58   2   0 0.00
Fri 05/22 06Z 0.09 0111  56   2   0 0.00
Fri 05/22 07Z 0.11 0110  54   2   0 0.00
Fri 05/22 08Z 0.13 0111  54   3   0 0.00
Fri 05/22 09Z 0.19 0212  51   4   0 0.00
Fri 05/22 10Z 0.23 0213  46   5   0 0.00
Fri 05/22 11Z 0.27 0313  43   6   0 0.00
Fri 05/22 12Z 0.27 0311  40   6   0 0.00
Fri 05/22 13Z 0.28 0310  39   6   0 0.00
Fri 05/22 14Z 0.43 0307  39   7   0 0.00
Fri 05/22 15Z 0.80 0305  41   9   0 0.00
Fri 05/22 16Z 0.88 0303  42  12   0 0.00
Fri 05/22 17Z 0.60 0102  43  14   1 0.00
Fri 05/22 18Z 0.42 0201  45  13   2 0.00
Fri 05/22 19Z 0.27 3501  47  13   3 0.00
Fri 05/22 20Z 0.27 3301  49  14   3 0.00
Fri 05/22 21Z 0.23 3301  51  15   3 0.00
Fri 05/22 22Z 0.14 3202  52  15   4 0.00
Fri 05/22 23Z 0.07 0001  50  19   4 0.00
Sat 05/23 00Z 0.04 0002  47  20   4 0.00
Sat 05/23 01Z 0.07 0202  44  19   4 0.00
Sat 05/23 02Z 0.12 0304  42  19   4 0.00
Sat 05/23 03Z 0.23 0505  41  17   4 0.00
Sat 05/23 04Z 0.21 0504  40  16   4 0.00
Sat 05/23 05Z 0.29 0506  40  14   4 0.00
Sat 05/23 06Z 0.35 0607  42  10   4 0.00
Sat 05/23 07Z 0.44 0808  44   7   4 0.00
Sat 05/23 08Z 0.46 0808  44   6   3 0.00
Sat 05/23 09Z 0.48 0909  44   5   3 0.00
Sat 05/23 10Z 0.43 1009  44   4   3 0.00
Sat 05/23 11Z 0.43 1110  44   4   3 0.00
Sat 05/23 12Z 0.50 1212  43   4   3 0.00
Sat 05/23 13Z 0.50 1213  45   4   3 0.00
Sat 05/23 14Z 0.54 1213  48   5   3 0.00
Sat 05/23 15Z 0.78 1212  51   5   3 0.00
Sat 05/23 16Z 1.83 1212  54   4   4 0.00
Sat 05/23 17Z 3.12 1311  57   5   4 0.00
Sat 05/23 18Z 2.69 1411  58   5   4 0.00
Sat 05/23 19Z 2.16 1411  59   5   4 0.00
Sat 05/23 20Z 1.59 1412  62   4   4 0.00
Sat 05/23 21Z 1.14 1413  65   3   4 0.00
Sat 05/23 22Z 0.77 1415  64   3   4 0.00
Sat 05/23 23Z 0.50 1417  63   3   4 0.00
Sun 05/24 00Z 0.42 1418  62   4   4 0.00
Sun 05/24 01Z 0.40 1420  57   4   4 0.00
Sun 05/24 02Z 0.40 1422  52   6   4 0.00
Sun 05/24 03Z 0.40 1423  49  11   4 0.00
Sun 05/24 04Z 0.42 1424  46  19   4 0.00
Sun 05/24 05Z 0.42 1425  46  32   4 0.00
Sun 05/24 06Z 0.42 1426  44  39   4 0.00
Sun 05/24 07Z 0.41 1428  43  50   5 0.00
Sun 05/24 08Z 0.42 1430  43  63   5 0.00
Sun 05/24 09Z 0.44 1433  48  74   5 0.00
Sun 05/24 10Z 0.42 1435  57  86   6 0.01
Sun 05/24 11Z 0.40 1437  64  81   7 0.02

Run total areal avg QPF for the greens is: 0.03 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