NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260319_0000
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)
=== ===== === ==== ==== === === === ====
Thu 03/19 00Z 0.17 1810  61   7 -12 0.00
Thu 03/19 01Z 0.21 1812  58  13 -12 0.00
Thu 03/19 02Z 0.26 1815  53  13 -12 0.00
Thu 03/19 03Z 0.38 1916  51   5 -12 0.00
Thu 03/19 04Z 0.52 1917  50   4 -11 0.00
Thu 03/19 05Z 0.56 2017  53  14 -11 0.00
Thu 03/19 06Z 0.52 2016  55  40 -11 0.00
Thu 03/19 07Z 0.57 2016  58  68 -11 0.00
Thu 03/19 08Z 0.66 2117  59  76 -11 0.00
Thu 03/19 09Z 0.56 2117  59  88 -11 0.00
Thu 03/19 10Z 0.52 2117  62  89 -11 0.00
Thu 03/19 11Z 0.45 2116  65  88 -11 0.00
Thu 03/19 12Z 0.38 2016  65  90 -11 0.00
Thu 03/19 13Z 0.35 1916  66  91 -11 0.00
Thu 03/19 14Z 0.45 1916  70  93 -10 0.00
Thu 03/19 15Z 0.84 1915  73  91 -10 0.00
Thu 03/19 16Z 1.92 1914  74  86 -10 0.00
Thu 03/19 17Z 2.54 1915  77  88  -9 0.00
Thu 03/19 18Z 1.32 1916  83  92  -8 0.00
Thu 03/19 19Z 0.69 2015  86  91  -8 0.00
Thu 03/19 20Z 0.78 2015  86  87  -7 0.00
Thu 03/19 21Z 0.84 2116  85  66  -7 0.00
Thu 03/19 22Z 0.73 2117  86  29  -7 0.00
Thu 03/19 23Z 0.65 2219  90  20  -6 0.00
Fri 03/20 00Z 0.65 2320  94   9  -6 0.01
Fri 03/20 01Z 0.63 2322  96   4  -6 0.01
Fri 03/20 02Z 0.77 2523  98   5  -6 0.02
Fri 03/20 03Z 0.85 2621  96   5  -7 0.01
Fri 03/20 04Z 0.81 2719  97   7  -7 0.01
Fri 03/20 05Z 0.74 2818  96   8  -8 0.01
Fri 03/20 06Z 0.62 2816  93   9  -8 0.01
Fri 03/20 07Z 0.40 2814  85   9  -7 0.00
Fri 03/20 08Z 0.34 2813  78  16  -7 0.00
Fri 03/20 09Z 0.35 2815  75  27  -7 0.00
Fri 03/20 10Z 0.32 2814  69  34  -6 0.00
Fri 03/20 11Z 0.24 2712  57  49  -5 0.00
Fri 03/20 12Z 0.24 2712  48  68  -4 0.00
Fri 03/20 13Z 0.21 2610  43  86  -3 0.00
Fri 03/20 14Z 0.18 2408  41  91  -3 0.00
Fri 03/20 15Z 0.24 2111  49  95  -5 0.00
Fri 03/20 16Z 0.23 1913  87  93  -6 0.00
Fri 03/20 17Z 0.22 1918  94  95  -5 0.05
Fri 03/20 18Z 0.27 1921  92  96  -6 0.08
Fri 03/20 19Z 0.08 1722  96  97  -3 0.09
Fri 03/20 20Z 0.13 1821  97  96  -3 0.10
Fri 03/20 21Z 0.20 1921  97  97  -3 0.06
Fri 03/20 22Z 0.28 2020  98  97  -2 0.09
Fri 03/20 23Z 0.31 2117  99  97  -1 0.11
Sat 03/21 00Z 0.31 2215  99  97   0 0.10
Sat 03/21 01Z 0.28 2312  99  95   0 0.09
Sat 03/21 02Z 0.26 2410  99  90   0 0.05
Sat 03/21 03Z 0.23 2609 100  87   0 0.02
Sat 03/21 04Z 0.19 2808 100  79  -1 0.01
Sat 03/21 05Z 0.13 3007  99  46  -1 0.01
Sat 03/21 06Z 0.09 3107  98  16  -1 0.00
Sat 03/21 07Z 0.09 3106  98   3  -1 0.00
Sat 03/21 08Z 0.14 3009  99   4  -2 0.00
Sat 03/21 09Z 0.18 3112  99  16  -3 0.01
Sat 03/21 10Z 0.15 3213  97  15  -3 0.01
Sat 03/21 11Z 0.08 3209  94  26  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.96 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