NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260919_0600
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)
=== ===== === ==== ==== === === === ====
Sat 09/19 06Z 0.07 0014  75   7   4 0.00
Sat 09/19 07Z 0.05 0014  71   6   4 0.00
Sat 09/19 08Z 0.04 0013  65   6   4 0.00
Sat 09/19 09Z 0.03 0011  59   6   5 0.00
Sat 09/19 10Z 0.03 3510  54   6   6 0.00
Sat 09/19 11Z 0.02 3510  51   6   6 0.00
Sat 09/19 12Z 0.02 0009  47   6   6 0.00
Sat 09/19 13Z 0.02 0008  45   6   6 0.00
Sat 09/19 14Z 0.02 0006  46   6   6 0.00
Sat 09/19 15Z 0.02 0004  50   6   6 0.00
Sat 09/19 16Z 0.02 0002  56   5   5 0.00
Sat 09/19 17Z 0.02 0001  62   5   5 0.00
Sat 09/19 18Z 0.03 3000  67   5   5 0.00
Sat 09/19 19Z 0.05 1901  70   5   5 0.00
Sat 09/19 20Z 0.10 2401  71   5   5 0.00
Sat 09/19 21Z 0.06 2301  68   5   6 0.00
Sat 09/19 22Z 0.04 2002  65   5   6 0.00
Sat 09/19 23Z 0.03 1805  63   5   6 0.00
Sun 09/20 00Z 0.06 1907  60   5   6 0.00
Sun 09/20 01Z 0.08 1908  58   5   6 0.00
Sun 09/20 02Z 0.04 1810  57   6   7 0.00
Sun 09/20 03Z 0.11 1912  62   6   6 0.00
Sun 09/20 04Z 0.20 2015  68   7   6 0.00
Sun 09/20 05Z 0.24 2017  76   9   6 0.00
Sun 09/20 06Z 0.29 2018  82   9   6 0.00
Sun 09/20 07Z 0.27 2118  86   8   6 0.00
Sun 09/20 08Z 0.28 2118  88  11   6 0.00
Sun 09/20 09Z 0.26 2018  91  16   6 0.00
Sun 09/20 10Z 0.24 2018  94  28   6 0.01
Sun 09/20 11Z 0.19 2017  95  43   6 0.01
Sun 09/20 12Z 0.15 1918  96  67   6 0.01
Sun 09/20 13Z 0.14 1919  96  85   7 0.02
Sun 09/20 14Z 0.14 1920  97  98   7 0.03
Sun 09/20 15Z 0.11 1921  97  99   7 0.05
Sun 09/20 16Z 0.09 1922  98  99   8 0.09
Sun 09/20 17Z 0.12 1923  98  99   8 0.14
Sun 09/20 18Z 0.13 1923  98  99   8 0.14
Sun 09/20 19Z 0.15 1923  98  98   8 0.14
Sun 09/20 20Z 0.15 1921  98  99   8 0.15
Sun 09/20 21Z 0.13 1919  98  96   8 0.11
Sun 09/20 22Z 0.11 1915  99  92   8 0.10
Sun 09/20 23Z 0.08 1911  98  74   8 0.07
Mon 09/21 00Z 0.08 2007  99  64   7 0.04
Mon 09/21 01Z 0.07 2402  99  60   7 0.03
Mon 09/21 02Z 0.04 3303  99  58   6 0.01
Mon 09/21 03Z 0.03 0006  98  41   6 0.01
Mon 09/21 04Z 0.05 0108  96  40   6 0.00
Mon 09/21 05Z 0.04 0009  93  23   6 0.00
Mon 09/21 06Z 0.04 0011  91  10   6 0.00
Mon 09/21 07Z 0.04 0014  87   2   5 0.00
Mon 09/21 08Z 0.03 0017  82   2   5 0.00
Mon 09/21 09Z 0.04 0018  83   2   5 0.01
Mon 09/21 10Z 0.05 0019  82   3   4 0.01
Mon 09/21 11Z 0.06 0019  83   3   4 0.01
Mon 09/21 12Z 0.07 0019  82   3   3 0.00
Mon 09/21 13Z 0.07 0018  82   2   3 0.00
Mon 09/21 14Z 0.06 3517  77   2   3 0.00
Mon 09/21 15Z 0.04 0018  71   1   4 0.00
Mon 09/21 16Z 0.04 0017  65   1   4 0.00
Mon 09/21 17Z 0.05 0016  60   1   4 0.00

Run total areal avg QPF for the greens is: 1.19 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