NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260426_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)
=== ===== === ==== ==== === === === ====
Sun 04/26 18Z 0.51 3504  60  17   3 0.00
Sun 04/26 19Z 0.60 0006  61  19   3 0.00
Sun 04/26 20Z 0.68 0006  63  18   3 0.00
Sun 04/26 21Z 0.52 0005  63  21   3 0.00
Sun 04/26 22Z 0.84 0205  64  22   3 0.00
Sun 04/26 23Z 0.41 0205  64  23   3 0.00
Mon 04/27 00Z 0.35 0306  64  20   3 0.00
Mon 04/27 01Z 0.45 0406  64  18   3 0.00
Mon 04/27 02Z 0.53 0407  64  17   3 0.00
Mon 04/27 03Z 0.54 0508  64  16   3 0.00
Mon 04/27 04Z 0.47 0507  65  17   3 0.00
Mon 04/27 05Z 0.44 0507  66  19   3 0.00
Mon 04/27 06Z 0.36 0507  67  23   3 0.00
Mon 04/27 07Z 0.37 0507  67  27   3 0.00
Mon 04/27 08Z 0.36 0607  67  34   3 0.00
Mon 04/27 09Z 0.34 0606  67  38   3 0.00
Mon 04/27 10Z 0.31 0606  68  39   3 0.00
Mon 04/27 11Z 0.34 0606  69  38   3 0.00
Mon 04/27 12Z 0.38 0706  69  37   3 0.00
Mon 04/27 13Z 0.49 0806  70  36   3 0.00
Mon 04/27 14Z 1.25 0905  70  35   3 0.00
Mon 04/27 15Z 1.76 1003  70  38   3 0.00
Mon 04/27 16Z 1.54 1002  68  37   4 0.00
Mon 04/27 17Z 1.04 0900  66  37   4 0.00
Mon 04/27 18Z 1.12 0501  66  35   5 0.00
Mon 04/27 19Z 0.64 0901  66  34   5 0.00
Mon 04/27 20Z 0.86 1001  65  32   5 0.00
Mon 04/27 21Z 1.53 1103  63  28   6 0.00
Mon 04/27 22Z 0.19 1602  64  32   6 0.00
Mon 04/27 23Z 0.30 1403  65  20   6 0.00
Tue 04/28 00Z 0.28 1405  65  16   5 0.00
Tue 04/28 01Z 0.21 1506  64  12   5 0.00
Tue 04/28 02Z 0.19 1507  64  11   5 0.00
Tue 04/28 03Z 0.14 1608  64  10   5 0.00
Tue 04/28 04Z 0.05 1709  63  10   5 0.00
Tue 04/28 05Z 0.04 1708  61  10   5 0.00
Tue 04/28 06Z 0.14 1608  59   9   5 0.00
Tue 04/28 07Z 0.20 1509  61   9   5 0.00
Tue 04/28 08Z 0.25 1511  62   8   5 0.00
Tue 04/28 09Z 0.19 1613  65   8   4 0.00
Tue 04/28 10Z 0.21 1615  65   7   4 0.00
Tue 04/28 11Z 0.10 1715  66   7   4 0.00
Tue 04/28 12Z 0.22 1618  65   8   4 0.00
Tue 04/28 13Z 0.26 1520  66   9   4 0.00
Tue 04/28 14Z 0.39 1520  68   9   4 0.00
Tue 04/28 15Z 0.65 1520  68   9   4 0.00
Tue 04/28 16Z 1.93 1518  68   9   3 0.00
Tue 04/28 17Z 3.02 1616  68   9   4 0.00
Tue 04/28 18Z 3.55 1516  67   9   4 0.00
Tue 04/28 19Z 3.51 1516  68   9   4 0.00
Tue 04/28 20Z 2.99 1516  68   8   4 0.00
Tue 04/28 21Z 2.08 1616  66   7   5 0.00
Tue 04/28 22Z 1.02 1617  65   5   5 0.00
Tue 04/28 23Z 0.18 1718  67   5   5 0.00
Wed 04/29 00Z 0.14 1720  70   6   5 0.00
Wed 04/29 01Z 0.14 1622  70   9   5 0.00
Wed 04/29 02Z 0.05 1821  74  22   5 0.00
Wed 04/29 03Z 0.05 1821  73  31   5 0.00
Wed 04/29 04Z 0.13 1921  76  37   4 0.00
Wed 04/29 05Z 0.20 2020  82  43   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