NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260911_1200
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)
=== ===== === ==== ==== === === === ====
Fri 09/11 12Z 0.43 3119  87   4   5 0.00
Fri 09/11 13Z 0.45 3120  82   5   5 0.00
Fri 09/11 14Z 0.46 3119  82   6   5 0.00
Fri 09/11 15Z 0.48 3018  80   9   5 0.00
Fri 09/11 16Z 0.51 3017  77  11   5 0.00
Fri 09/11 17Z 0.57 3017  79  13   5 0.00
Fri 09/11 18Z 0.56 2916  78  15   6 0.00
Fri 09/11 19Z 0.59 3017  76  17   6 0.00
Fri 09/11 20Z 0.64 2916  76  19   6 0.00
Fri 09/11 21Z 0.61 3017  73  20   7 0.00
Fri 09/11 22Z 0.55 3017  70  21   7 0.00
Fri 09/11 23Z 0.44 3117  64  24   8 0.00
Sat 09/12 00Z 0.38 3117  61  28   8 0.00
Sat 09/12 01Z 0.31 3117  56  34   9 0.00
Sat 09/12 02Z 0.24 3216  52  38  10 0.00
Sat 09/12 03Z 0.20 3215  49  38  10 0.00
Sat 09/12 04Z 0.16 3314  45  36  11 0.00
Sat 09/12 05Z 0.12 3312  42  36  11 0.00
Sat 09/12 06Z 0.07 3309  39  35  11 0.00
Sat 09/12 07Z 0.05 3306  36  34  11 0.00
Sat 09/12 08Z 0.03 3404  35  34  11 0.00
Sat 09/12 09Z 0.02 3403  34  32  12 0.00
Sat 09/12 10Z 0.02 3502  35  31  12 0.00
Sat 09/12 11Z 0.03 0801  34  29  12 0.00
Sat 09/12 12Z 0.03 1703  34  29  12 0.00
Sat 09/12 13Z 0.03 1706  34  26  12 0.00
Sat 09/12 14Z 0.04 1808  36  24  12 0.00
Sat 09/12 15Z 0.08 1909  38  23  12 0.00
Sat 09/12 16Z 0.12 2010  42  23  12 0.00
Sat 09/12 17Z 0.15 2010  44  24  12 0.00
Sat 09/12 18Z 0.14 2011  45  26  12 0.00
Sat 09/12 19Z 0.14 1912  46  25  12 0.00
Sat 09/12 20Z 0.15 1913  50  19  12 0.00
Sat 09/12 21Z 0.18 1915  51  11  12 0.00
Sat 09/12 22Z 0.21 2017  50   7  13 0.00
Sat 09/12 23Z 0.26 2019  52   7  13 0.00
Sun 09/13 00Z 0.32 2120  60  16  13 0.00
Sun 09/13 01Z 0.32 2121  69  48  13 0.00
Sun 09/13 02Z 0.35 2122  77  63  13 0.00
Sun 09/13 03Z 0.41 2124  85  87  13 0.00
Sun 09/13 04Z 0.37 2123  87  83  13 0.01
Sun 09/13 05Z 0.36 2123  90  89  13 0.04
Sun 09/13 06Z 0.37 2125  94  83  13 0.09
Sun 09/13 07Z 0.39 2224  96  87  14 0.04
Sun 09/13 08Z 0.39 2224  95  93  14 0.04
Sun 09/13 09Z 0.37 2221  93  94  14 0.07
Sun 09/13 10Z 0.33 2220  91  94  14 0.03
Sun 09/13 11Z 0.35 2122  94  94  14 0.05
Sun 09/13 12Z 0.34 2122  96  93  13 0.13
Sun 09/13 13Z 0.33 2123  97  89  14 0.11
Sun 09/13 14Z 0.34 2123  98  90  14 0.17
Sun 09/13 15Z 0.41 2221  98  78  14 0.06
Sun 09/13 16Z 0.43 2417  98  63  14 0.02
Sun 09/13 17Z 0.41 2515  94  47  14 0.01
Sun 09/13 18Z 0.46 2615  92  45  14 0.00
Sun 09/13 19Z 0.48 2513  92  48  14 0.00
Sun 09/13 20Z 0.58 2514  94  45  14 0.01
Sun 09/13 21Z 0.77 2618  96  27  13 0.03
Sun 09/13 22Z 0.81 2620  93  21  13 0.04
Sun 09/13 23Z 0.78 2721  87  24  13 0.03

Run total areal avg QPF for the greens is: 0.98 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