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_1200
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 12Z 0.48 3010  78   6 -18 0.00
Wed 03/18 13Z 0.27 3107  76   8 -18 0.00
Wed 03/18 14Z 0.74 2805  73   5 -18 0.00
Wed 03/18 15Z 1.76 2506  70   5 -17 0.00
Wed 03/18 16Z 2.24 2506  65   6 -16 0.00
Wed 03/18 17Z 1.94 2606  56   6 -15 0.00
Wed 03/18 18Z 1.39 2604  48   6 -15 0.00
Wed 03/18 19Z 0.97 2603  45   5 -14 0.00
Wed 03/18 20Z 0.78 2303  45   5 -13 0.00
Wed 03/18 21Z 0.72 2104  46   4 -13 0.00
Wed 03/18 22Z 0.39 1906  47   5 -13 0.00
Wed 03/18 23Z 0.22 1909  49  12 -12 0.00
Thu 03/19 00Z 0.26 1911  50  10 -12 0.00
Thu 03/19 01Z 0.26 1912  51   5 -12 0.00
Thu 03/19 02Z 0.32 1912  52   5 -12 0.00
Thu 03/19 03Z 0.36 1914  53   8 -12 0.00
Thu 03/19 04Z 0.41 1915  54  14 -12 0.00
Thu 03/19 05Z 0.50 2016  58  30 -12 0.00
Thu 03/19 06Z 0.55 2016  62  48 -12 0.00
Thu 03/19 07Z 0.55 2117  66  69 -11 0.00
Thu 03/19 08Z 0.52 2117  70  86 -11 0.00
Thu 03/19 09Z 0.54 2117  72  91 -11 0.00
Thu 03/19 10Z 0.50 2117  72  90 -11 0.00
Thu 03/19 11Z 0.44 2117  74  89 -11 0.00
Thu 03/19 12Z 0.37 2017  74  89 -10 0.00
Thu 03/19 13Z 0.32 2017  70  90 -10 0.00
Thu 03/19 14Z 0.37 1916  70  90 -10 0.00
Thu 03/19 15Z 0.80 1915  74  91 -10 0.00
Thu 03/19 16Z 1.63 1814  75  95 -10 0.00
Thu 03/19 17Z 1.90 1814  75  96  -9 0.00
Thu 03/19 18Z 1.65 1815  78  96  -8 0.00
Thu 03/19 19Z 0.75 1915  84  94  -8 0.00
Thu 03/19 20Z 0.41 2015  90  92  -7 0.01
Thu 03/19 21Z 0.47 2116  92  88  -7 0.01
Thu 03/19 22Z 0.56 2118  92  68  -7 0.00
Thu 03/19 23Z 0.62 2220  95  42  -7 0.00
Fri 03/20 00Z 0.63 2321  96  28  -7 0.01
Fri 03/20 01Z 0.69 2421  97  17  -7 0.01
Fri 03/20 02Z 0.76 2521  97  10  -7 0.01
Fri 03/20 03Z 0.93 2621  97   9  -8 0.01
Fri 03/20 04Z 0.95 2620  97  12  -8 0.01
Fri 03/20 05Z 1.04 2620  98  18  -8 0.01
Fri 03/20 06Z 1.01 2719  96  23  -8 0.01
Fri 03/20 07Z 0.87 2719  95  24  -8 0.00
Fri 03/20 08Z 0.70 2818  92  22  -7 0.01
Fri 03/20 09Z 0.50 2818  84  22  -7 0.01
Fri 03/20 10Z 0.40 2817  74  15  -6 0.00
Fri 03/20 11Z 0.29 2915  63  14  -4 0.00
Fri 03/20 12Z 0.25 2813  58  12  -4 0.00
Fri 03/20 13Z 0.20 2810  53  15  -3 0.00
Fri 03/20 14Z 0.18 2609  48  30  -3 0.00
Fri 03/20 15Z 0.20 2409  43  34  -2 0.00
Fri 03/20 16Z 0.21 2211  36  48  -2 0.00
Fri 03/20 17Z 0.27 2114  32  79  -2 0.00
Fri 03/20 18Z 0.34 2017  30  93  -1 0.00
Fri 03/20 19Z 0.44 2021  31  91  -1 0.00
Fri 03/20 20Z 0.49 2023  36  94   0 0.00
Fri 03/20 21Z 0.44 1927  39  94   0 0.00
Fri 03/20 22Z 0.36 1932  66  90   1 0.00
Fri 03/20 23Z 0.49 1937  75  91   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.11 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