NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260429_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)
=== ===== === ==== ==== === === === ====
Wed 04/29 18Z 1.57 1507  71  70   7 0.00
Wed 04/29 19Z 2.53 1512  72  63   7 0.00
Wed 04/29 20Z 2.82 1515  74  62   7 0.00
Wed 04/29 21Z 2.56 1518  76  58   6 0.00
Wed 04/29 22Z 1.92 1519  79  78   6 0.00
Wed 04/29 23Z 0.37 1521  85  87   5 0.00
Thu 04/30 00Z 0.06 1621  88  93   6 0.00
Thu 04/30 01Z 0.05 1620  90  95   6 0.00
Thu 04/30 02Z 0.05 1622  89  95   6 0.00
Thu 04/30 03Z 0.06 1624  86  93   7 0.00
Thu 04/30 04Z 0.06 1626  86  92   7 0.00
Thu 04/30 05Z 0.06 1725  90  99   5 0.01
Thu 04/30 06Z 0.07 1725  93  99   4 0.07
Thu 04/30 07Z 0.04 1725  96  99   3 0.14
Thu 04/30 08Z 0.06 1726  97  99   4 0.12
Thu 04/30 09Z 0.17 1825  98  97   3 0.10
Thu 04/30 10Z 0.23 1923  97  97   3 0.06
Thu 04/30 11Z 0.24 2018  97  97   3 0.02
Thu 04/30 12Z 0.22 2015  98  97   3 0.01
Thu 04/30 13Z 0.23 2112  98  94   3 0.02
Thu 04/30 14Z 0.24 2210  98  92   3 0.01
Thu 04/30 15Z 0.20 2208  98  95   3 0.02
Thu 04/30 16Z 0.09 2303  98  95   3 0.04
Thu 04/30 17Z 0.03 1901  98  94   3 0.01
Thu 04/30 18Z 0.03 1802  99  96   2 0.01
Thu 04/30 19Z 0.06 2102  99  98   2 0.03
Thu 04/30 20Z 0.06 2601  99  95   2 0.03
Thu 04/30 21Z 0.10 3003  99  87   2 0.02
Thu 04/30 22Z 0.15 3106  99  83   2 0.01
Thu 04/30 23Z 0.17 3108  99  89   2 0.01
Fri 05/01 00Z 0.22 3211  99  96   1 0.02
Fri 05/01 01Z 0.21 3315  97  97   1 0.03
Fri 05/01 02Z 0.27 3216  95  98   0 0.02
Fri 05/01 03Z 0.28 3216  95  97   0 0.02
Fri 05/01 04Z 0.33 3217  96  96   0 0.02
Fri 05/01 05Z 0.35 3117  95  87   0 0.01
Fri 05/01 06Z 0.32 3117  92  86   0 0.01
Fri 05/01 07Z 0.31 3118  89  83   0 0.01
Fri 05/01 08Z 0.33 3119  85  70   0 0.00
Fri 05/01 09Z 0.35 3120  82  68   0 0.00
Fri 05/01 10Z 0.35 3120  80  68   0 0.00
Fri 05/01 11Z 0.33 3120  78  69  -1 0.00
Fri 05/01 12Z 0.36 3120  78  70  -1 0.00
Fri 05/01 13Z 0.39 3118  78  70  -1 0.00
Fri 05/01 14Z 0.45 3117  76  73  -2 0.00
Fri 05/01 15Z 2.18 3215  76  71  -2 0.00
Fri 05/01 16Z 3.89 3112  74  75  -2 0.00
Fri 05/01 17Z 4.72 3010  74  73  -1 0.00
Fri 05/01 18Z 4.71 2909  78  70  -1 0.00
Fri 05/01 19Z 3.25 2910  86  66  -1 0.01
Fri 05/01 20Z 2.52 2911  85  61  -1 0.01
Fri 05/01 21Z 2.84 3010  82  59  -1 0.00
Fri 05/01 22Z 2.03 3010  83  68  -1 0.00
Fri 05/01 23Z 0.92 3011  81  74  -1 0.01
Sat 05/02 00Z 0.66 3111  81  69  -1 0.01
Sat 05/02 01Z 0.72 3112  81  70  -1 0.00
Sat 05/02 02Z 0.68 3011  83  73  -2 0.00
Sat 05/02 03Z 0.50 3011  82  73  -2 0.00
Sat 05/02 04Z 0.49 3012  81  71  -2 0.00
Sat 05/02 05Z 0.52 3012  84  66  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.92 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