NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260416_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 04/16 18Z 1.06 2212  75  72  13 0.00
Thu 04/16 19Z 1.08 2215  69  73  14 0.00
Thu 04/16 20Z 1.40 2319  67  62  14 0.00
Thu 04/16 21Z 2.55 2221  74  47  14 0.00
Thu 04/16 22Z 1.56 2222  77  52  14 0.00
Thu 04/16 23Z 1.20 2321  81  64  14 0.00
Fri 04/17 00Z 0.69 2518  89  83  13 0.05
Fri 04/17 01Z 0.72 2821  91  63  12 0.14
Fri 04/17 02Z 0.44 3018  84  90  12 0.22
Fri 04/17 03Z 0.45 2917  86  89  11 0.01
Fri 04/17 04Z 0.47 2917  95  89  10 0.04
Fri 04/17 05Z 0.44 2715  91  81  10 0.04
Fri 04/17 06Z 0.43 2714  94  80  10 0.01
Fri 04/17 07Z 0.34 2913  96  85  10 0.02
Fri 04/17 08Z 0.26 3113  97  90   9 0.02
Fri 04/17 09Z 0.13 3313  96  88   9 0.02
Fri 04/17 10Z 0.06 3513  94  93   9 0.01
Fri 04/17 11Z 0.09 0013  93  86   9 0.01
Fri 04/17 12Z 0.10 0013  92  80   9 0.00
Fri 04/17 13Z 0.12 0113  91  76   8 0.00
Fri 04/17 14Z 0.12 0111  88  71   8 0.00
Fri 04/17 15Z 0.15 0111  85  63   7 0.00
Fri 04/17 16Z 0.22 0213  79  54   7 0.00
Fri 04/17 17Z 0.30 0213  71  44   7 0.00
Fri 04/17 18Z 0.44 0213  65  36   8 0.00
Fri 04/17 19Z 0.63 0311  61  28   8 0.00
Fri 04/17 20Z 0.62 0311  59  18   8 0.00
Fri 04/17 21Z 0.50 0310  57  12   8 0.00
Fri 04/17 22Z 0.40 0310  57   9   8 0.00
Fri 04/17 23Z 0.37 0510  59   8   8 0.00
Sat 04/18 00Z 0.41 0610  64   9   8 0.00
Sat 04/18 01Z 0.39 0709  72   8   7 0.00
Sat 04/18 02Z 0.34 0810  76   8   7 0.00
Sat 04/18 03Z 0.29 1009  81   7   7 0.00
Sat 04/18 04Z 0.27 1210  84   7   7 0.00
Sat 04/18 05Z 0.33 1214  77   5   7 0.00
Sat 04/18 06Z 0.45 1219  71   4   7 0.00
Sat 04/18 07Z 0.39 1219  72   6   7 0.00
Sat 04/18 08Z 0.28 1318  73   6   7 0.00
Sat 04/18 09Z 0.22 1418  72   6   7 0.00
Sat 04/18 10Z 0.25 1320  68   5   8 0.00
Sat 04/18 11Z 0.22 1420  69   5   8 0.00
Sat 04/18 12Z 0.25 1423  71   8   8 0.01
Sat 04/18 13Z 0.24 1422  78  15   7 0.01
Sat 04/18 14Z 0.19 1421  79  21   7 0.00
Sat 04/18 15Z 0.21 1422  83  21   7 0.00
Sat 04/18 16Z 0.24 1423  87  13   7 0.01
Sat 04/18 17Z 0.19 1422  84   6   7 0.00
Sat 04/18 18Z 0.14 1521  81   7   8 0.00
Sat 04/18 19Z 0.09 1520  79   9   8 0.00
Sat 04/18 20Z 0.06 1620  79   5   9 0.00
Sat 04/18 21Z 0.05 1620  79   8   9 0.00
Sat 04/18 22Z 0.03 1621  77  13  10 0.00
Sat 04/18 23Z 0.03 1722  72  47  10 0.00
Sun 04/19 00Z 0.08 1823  69  46  11 0.00
Sun 04/19 01Z 0.09 1824  64  40  12 0.00
Sun 04/19 02Z 0.15 1925  66  42  12 0.00
Sun 04/19 03Z 0.28 2027  73  38  11 0.00
Sun 04/19 04Z 0.41 2130  85  91  10 0.00
Sun 04/19 05Z 0.42 2129  92  91   9 0.01

Run total areal avg QPF for the Central_Greens is: 0.63 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