NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260911_0600
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)
=== ===== === ==== ==== === === === ====
Fri 09/11 06Z 0.20 3213  86   6   8 0.00
Fri 09/11 07Z 0.31 3116  84   5   7 0.00
Fri 09/11 08Z 0.32 3118  86   4   7 0.00
Fri 09/11 09Z 0.34 3120  87   3   6 0.00
Fri 09/11 10Z 0.41 3122  87   2   6 0.00
Fri 09/11 11Z 0.42 3023  85   2   6 0.00
Fri 09/11 12Z 0.42 3023  82   2   6 0.00
Fri 09/11 13Z 0.41 3023  79   3   6 0.00
Fri 09/11 14Z 0.37 3121  73   4   6 0.00
Fri 09/11 15Z 0.36 3120  70   6   6 0.00
Fri 09/11 16Z 0.40 3119  73   8   6 0.00
Fri 09/11 17Z 0.45 3117  76  10   6 0.00
Fri 09/11 18Z 0.51 3016  78  12   6 0.00
Fri 09/11 19Z 0.53 3015  76  14   6 0.00
Fri 09/11 20Z 0.54 3015  75  16   6 0.00
Fri 09/11 21Z 0.53 3015  74  18   7 0.00
Fri 09/11 22Z 0.44 3115  71  19   7 0.00
Fri 09/11 23Z 0.38 3116  67  22   7 0.00
Sat 09/12 00Z 0.31 3116  62  26   8 0.00
Sat 09/12 01Z 0.21 3216  57  31   9 0.00
Sat 09/12 02Z 0.16 3215  54  37   9 0.00
Sat 09/12 03Z 0.13 3213  51  41  10 0.00
Sat 09/12 04Z 0.11 3212  48  42  11 0.00
Sat 09/12 05Z 0.07 3311  43  39  11 0.00
Sat 09/12 06Z 0.03 3409  40  37  12 0.00
Sat 09/12 07Z 0.01 3407  37  34  12 0.00
Sat 09/12 08Z 0.01 3505  36  32  12 0.00
Sat 09/12 09Z 0.02 0004  35  30  13 0.00
Sat 09/12 10Z 0.02 0201  35  28  13 0.00
Sat 09/12 11Z 0.01 1501  36  27  12 0.00
Sat 09/12 12Z 0.01 1603  36  24  12 0.00
Sat 09/12 13Z 0.02 1706  37  22  11 0.00
Sat 09/12 14Z 0.07 1908  39  22  11 0.00
Sat 09/12 15Z 0.10 1908  40  21  12 0.00
Sat 09/12 16Z 0.12 1909  46  22  12 0.00
Sat 09/12 17Z 0.14 1909  49  24  12 0.00
Sat 09/12 18Z 0.19 1910  51  28  12 0.00
Sat 09/12 19Z 0.22 1911  55  26  11 0.00
Sat 09/12 20Z 0.25 1913  58  23  12 0.00
Sat 09/12 21Z 0.24 1915  58  18  12 0.00
Sat 09/12 22Z 0.28 2017  57  13  12 0.00
Sat 09/12 23Z 0.33 2018  54   6  13 0.00
Sun 09/13 00Z 0.40 2120  57   9  13 0.00
Sun 09/13 01Z 0.40 2220  65   5  13 0.00
Sun 09/13 02Z 0.41 2221  69   5  14 0.00
Sun 09/13 03Z 0.45 2222  78  15  13 0.00
Sun 09/13 04Z 0.46 2222  85  43  13 0.00
Sun 09/13 05Z 0.49 2224  88  79  13 0.00
Sun 09/13 06Z 0.48 2224  90  86  14 0.00
Sun 09/13 07Z 0.48 2223  92  88  14 0.00
Sun 09/13 08Z 0.48 2224  93  89  14 0.00
Sun 09/13 09Z 0.48 2225  95  88  14 0.06
Sun 09/13 10Z 0.49 2225  94  86  14 0.04
Sun 09/13 11Z 0.52 2226  96  83  14 0.03
Sun 09/13 12Z 0.49 2225  96  89  14 0.05
Sun 09/13 13Z 0.44 2224  94  89  14 0.03
Sun 09/13 14Z 0.44 2126  92  89  14 0.02
Sun 09/13 15Z 0.44 2225  94  95  14 0.03
Sun 09/13 16Z 0.47 2226  97  90  14 0.02
Sun 09/13 17Z 0.50 2224  98  82  13 0.03

Run total areal avg QPF for the Central_Greens is: 0.31 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