NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260318_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)
=== ===== === ==== ==== === === === ====
Wed 03/18 06Z 2.20 2716  83  70 -18 0.00
Wed 03/18 07Z 6.70 2722  87  60 -18 0.00
Wed 03/18 08Z 6.16 2821  89  43 -18 0.00
Wed 03/18 09Z 3.23 2919  86  25 -19 0.00
Wed 03/18 10Z 1.24 2917  84  11 -19 0.00
Wed 03/18 11Z 0.71 2916  82   6 -19 0.00
Wed 03/18 12Z 0.53 3014  81   3 -19 0.00
Wed 03/18 13Z 0.51 3012  78   4 -19 0.00
Wed 03/18 14Z 0.88 2909  73   5 -19 0.00
Wed 03/18 15Z 1.03 2808  65   6 -18 0.00
Wed 03/18 16Z 1.52 2706  60   6 -17 0.00
Wed 03/18 17Z 1.29 2604  55   5 -16 0.00
Wed 03/18 18Z 0.80 2903  48   5 -15 0.00
Wed 03/18 19Z 1.04 2903  45   5 -14 0.00
Wed 03/18 20Z 1.06 2503  44   3 -14 0.00
Wed 03/18 21Z 0.67 2204  43   2 -13 0.00
Wed 03/18 22Z 0.24 1905  45   2 -13 0.00
Wed 03/18 23Z 0.08 1708  46   4 -13 0.00
Thu 03/19 00Z 0.10 1710  48   4 -13 0.00
Thu 03/19 01Z 0.15 1813  49   7 -12 0.00
Thu 03/19 02Z 0.26 1913  49   8 -12 0.00
Thu 03/19 03Z 0.40 2013  48   6 -12 0.00
Thu 03/19 04Z 0.48 2014  54   6 -12 0.00
Thu 03/19 05Z 0.55 2115  58  20 -12 0.00
Thu 03/19 06Z 0.60 2116  63  33 -12 0.00
Thu 03/19 07Z 0.57 2116  62  39 -11 0.00
Thu 03/19 08Z 0.56 2116  57  82 -11 0.00
Thu 03/19 09Z 0.51 2116  61  88 -11 0.00
Thu 03/19 10Z 0.44 2115  62  93 -11 0.00
Thu 03/19 11Z 0.39 2015  66  90 -11 0.00
Thu 03/19 12Z 0.38 2016  69  87 -11 0.00
Thu 03/19 13Z 0.35 2016  69  87 -11 0.00
Thu 03/19 14Z 0.41 1915  68  88 -10 0.00
Thu 03/19 15Z 1.05 1914  69  93 -10 0.00
Thu 03/19 16Z 1.80 1813  70  93 -10 0.00
Thu 03/19 17Z 2.24 1813  69  89  -9 0.00
Thu 03/19 18Z 2.17 1813  70  89  -9 0.00
Thu 03/19 19Z 1.73 1914  74  88  -8 0.00
Thu 03/19 20Z 0.62 1915  82  89  -8 0.00
Thu 03/19 21Z 0.36 1915  87  91  -7 0.00
Thu 03/19 22Z 0.39 2016  91  84  -7 0.01
Thu 03/19 23Z 0.47 2118  94  73  -7 0.01
Fri 03/20 00Z 0.53 2119  97  53  -7 0.01
Fri 03/20 01Z 0.58 2220  98  50  -7 0.02
Fri 03/20 02Z 0.63 2419  98  34  -7 0.02
Fri 03/20 03Z 0.73 2519  98  25  -7 0.01
Fri 03/20 04Z 0.72 2616  96  13  -7 0.01
Fri 03/20 05Z 0.65 2615  98  10  -7 0.01
Fri 03/20 06Z 0.62 2615  98   7  -7 0.02
Fri 03/20 07Z 0.67 2715  98   9  -7 0.01
Fri 03/20 08Z 0.59 2714  96  17  -8 0.01
Fri 03/20 09Z 0.54 2714  94  16  -8 0.00
Fri 03/20 10Z 0.43 2713  88  14  -7 0.00
Fri 03/20 11Z 0.31 2812  76  22  -6 0.00
Fri 03/20 12Z 0.29 2712  69  18  -5 0.00
Fri 03/20 13Z 0.23 2610  60  22  -4 0.00
Fri 03/20 14Z 0.19 2508  52  36  -3 0.00
Fri 03/20 15Z 0.15 2207  44  42  -2 0.00
Fri 03/20 16Z 0.15 2009  40  65  -2 0.00
Fri 03/20 17Z 0.21 2012  40  48  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.14 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