NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250313_1800
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 03/13 18Z 0.07 1915  71  22  -3 0.00
Thu 03/13 19Z 0.15 1917  68  15  -3 0.00
Thu 03/13 20Z 0.16 1816  72  12  -3 0.00
Thu 03/13 21Z 0.14 1819  75   6  -3 0.00
Thu 03/13 22Z 0.08 1921  74   4  -3 0.00
Thu 03/13 23Z 0.08 2022  73   3  -2 0.00
Fri 03/14 00Z 0.12 2121  73   2  -2 0.00
Fri 03/14 01Z 0.16 2120  72   2  -1 0.00
Fri 03/14 02Z 0.19 2220  71   4  -1 0.00
Fri 03/14 03Z 0.24 2220  70   5  -1 0.00
Fri 03/14 04Z 0.27 2220  68   5  -1 0.00
Fri 03/14 05Z 0.32 2321  66   5  -1 0.00
Fri 03/14 06Z 0.34 2319  65   6   0 0.00
Fri 03/14 07Z 0.40 2417  64   9   0 0.00
Fri 03/14 08Z 0.44 2516  66  13   0 0.00
Fri 03/14 09Z 0.45 2615  68  18   0 0.00
Fri 03/14 10Z 0.38 2513  68  28   0 0.00
Fri 03/14 11Z 0.31 2512  65  37   0 0.00
Fri 03/14 12Z 0.27 2511  61  41   0 0.00
Fri 03/14 13Z 0.30 2512  61  48   0 0.00
Fri 03/14 14Z 0.24 2511  57  45   1 0.00
Fri 03/14 15Z 0.22 2410  53  42   1 0.00
Fri 03/14 16Z 0.18 2410  50  39   2 0.00
Fri 03/14 17Z 0.14 2309  48  36   2 0.00
Fri 03/14 18Z 0.07 2109  45  33   3 0.00
Fri 03/14 19Z 0.03 2011  43  31   4 0.00
Fri 03/14 20Z 0.06 2014  44  31   4 0.00
Fri 03/14 21Z 0.08 2116  40  29   4 0.00
Fri 03/14 22Z 0.11 2119  37  31   5 0.00
Fri 03/14 23Z 0.12 2120  34  39   6 0.00
Sat 03/15 00Z 0.13 2121  34  38   6 0.00
Sat 03/15 01Z 0.17 2122  39  36   6 0.00
Sat 03/15 02Z 0.16 2122  39  37   7 0.00
Sat 03/15 03Z 0.17 2222  38  43   8 0.00
Sat 03/15 04Z 0.17 2221  36  40   8 0.00
Sat 03/15 05Z 0.16 2220  35  42   8 0.00
Sat 03/15 06Z 0.16 2220  34  40   9 0.00
Sat 03/15 07Z 0.16 2122  32  36   9 0.00
Sat 03/15 08Z 0.18 2125  37  30   8 0.00
Sat 03/15 09Z 0.21 2127  43  25   8 0.00
Sat 03/15 10Z 0.22 2129  44  22   8 0.00
Sat 03/15 11Z 0.25 2131  44  24   9 0.00
Sat 03/15 12Z 0.27 2233  43  36   9 0.00
Sat 03/15 13Z 0.27 2234  43  32   9 0.00
Sat 03/15 14Z 0.27 2234  42  26   9 0.00
Sat 03/15 15Z 0.24 2134  42  29   9 0.00
Sat 03/15 16Z 0.21 2134  41  41  10 0.00
Sat 03/15 17Z 0.17 2132  39  34  10 0.00
Sat 03/15 18Z 0.19 2132  41  33  10 0.00
Sat 03/15 19Z 0.21 2132  47  36  10 0.00
Sat 03/15 20Z 0.20 2133  48  33  10 0.00
Sat 03/15 21Z 0.18 2133  50  35  10 0.00
Sat 03/15 22Z 0.15 2135  53  34  10 0.00
Sat 03/15 23Z 0.13 2038  50  28  11 0.00
Sun 03/16 00Z 0.11 2040  43  17  11 0.00
Sun 03/16 01Z 0.14 2042  37  16  11 0.00
Sun 03/16 02Z 0.20 2143  37  50  11 0.00
Sun 03/16 03Z 0.20 2144  40  58  12 0.00
Sun 03/16 04Z 0.22 2143  45  73  12 0.00
Sun 03/16 05Z 0.24 2140  51  81  12 0.00

Run total areal avg QPF for the Northern_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