NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20251010_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 10/10 00Z 0.13 3411  62   6  -1 0.00
Fri 10/10 01Z 0.12 3411  59   7  -1 0.00
Fri 10/10 02Z 0.10 3510  55   8   0 0.00
Fri 10/10 03Z 0.09 3507  49   8   0 0.00
Fri 10/10 04Z 0.08 3405  45   8   0 0.00
Fri 10/10 05Z 0.06 3203  41   9   0 0.00
Fri 10/10 06Z 0.07 2902  38   9   1 0.00
Fri 10/10 07Z 0.08 2703  36   9   1 0.00
Fri 10/10 08Z 0.08 2403  34   9   1 0.00
Fri 10/10 09Z 0.10 2305  32   8   1 0.00
Fri 10/10 10Z 0.13 2306  32   8   2 0.00
Fri 10/10 11Z 0.16 2407  36   7   2 0.00
Fri 10/10 12Z 0.18 2408  38   7   2 0.00
Fri 10/10 13Z 0.18 2309  39   7   2 0.00
Fri 10/10 14Z 0.16 2209  40   7   2 0.00
Fri 10/10 15Z 0.15 2209  42   6   2 0.00
Fri 10/10 16Z 0.15 2109  44   6   2 0.00
Fri 10/10 17Z 0.16 2010  45   5   2 0.00
Fri 10/10 18Z 0.19 2010  45   5   2 0.00
Fri 10/10 19Z 0.20 2011  44   5   2 0.00
Fri 10/10 20Z 0.23 2013  42   5   3 0.00
Fri 10/10 21Z 0.24 2016  39   6   3 0.00
Fri 10/10 22Z 0.31 2119  35   6   4 0.00
Fri 10/10 23Z 0.36 2221  35   6   4 0.00
Sat 10/11 00Z 0.40 2221  39   7   5 0.00
Sat 10/11 01Z 0.44 2322  41   6   5 0.00
Sat 10/11 02Z 0.45 2322  45   8   5 0.00
Sat 10/11 03Z 0.46 2422  47   7   5 0.00
Sat 10/11 04Z 0.48 2422  53   8   5 0.00
Sat 10/11 05Z 0.47 2421  57   8   4 0.00
Sat 10/11 06Z 0.44 2420  60   9   4 0.00
Sat 10/11 07Z 0.41 2419  61   9   4 0.00
Sat 10/11 08Z 0.37 2417  62   9   4 0.00
Sat 10/11 09Z 0.31 2414  62   9   4 0.00
Sat 10/11 10Z 0.25 2412  62   8   4 0.00
Sat 10/11 11Z 0.20 2310  60   8   4 0.00
Sat 10/11 12Z 0.15 2308  58   8   4 0.00
Sat 10/11 13Z 0.12 2307  57   8   4 0.00
Sat 10/11 14Z 0.09 2205  55   8   4 0.00
Sat 10/11 15Z 0.06 2105  53   9   5 0.00
Sat 10/11 16Z 0.06 2104  52   8   6 0.00
Sat 10/11 17Z 0.06 2004  52   8   6 0.00
Sat 10/11 18Z 0.05 2004  52   7   6 0.00
Sat 10/11 19Z 0.06 2003  54   7   6 0.00
Sat 10/11 20Z 0.05 2002  57   6   6 0.00
Sat 10/11 21Z 0.05 1802  59   5   6 0.00
Sat 10/11 22Z 0.06 1603  59   5   6 0.00
Sat 10/11 23Z 0.07 1503  60   5   6 0.00
Sun 10/12 00Z 0.06 1603  57   5   7 0.00
Sun 10/12 01Z 0.06 1604  53   6   7 0.00
Sun 10/12 02Z 0.06 1703  52   7   7 0.00
Sun 10/12 03Z 0.06 1803  51   7   7 0.00
Sun 10/12 04Z 0.05 1802  50   7   7 0.00
Sun 10/12 05Z 0.04 1601  50   8   7 0.00
Sun 10/12 06Z 0.04 1402  51   9   7 0.00
Sun 10/12 07Z 0.05 1303  51  10   7 0.00
Sun 10/12 08Z 0.07 1304  51  12   7 0.00
Sun 10/12 09Z 0.10 1305  51  15   7 0.00
Sun 10/12 10Z 0.12 1307  51  27   8 0.00
Sun 10/12 11Z 0.12 1308  50  39   8 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