Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260617_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 06/17 18Z 1.77 1909  67  86  10 0.00
Wed 06/17 19Z 1.69 1909  65  82  10 0.01
Wed 06/17 20Z 1.88 1910  64  75  11 0.00
Wed 06/17 21Z 0.42 1709  63  60  11 0.00
Wed 06/17 22Z 0.46 1710  63  68  11 0.00
Wed 06/17 23Z 0.34 1812  63  89  11 0.00
Thu 06/18 00Z 0.34 1813  65  88  11 0.00
Thu 06/18 01Z 0.30 1814  67  79  11 0.00
Thu 06/18 02Z 0.37 1818  70  78  11 0.00
Thu 06/18 03Z 0.39 1820  78  84  11 0.00
Thu 06/18 04Z 0.34 1923  90  93  11 0.05
Thu 06/18 05Z 0.42 2023  93  63  11 0.07
Thu 06/18 06Z 0.42 2119  94  53  11 0.00
Thu 06/18 07Z 0.44 2120  96  63  11 0.01
Thu 06/18 08Z 0.45 2121  93  56  11 0.01
Thu 06/18 09Z 0.45 2122  92  83  11 0.01
Thu 06/18 10Z 0.44 2023  92  90  11 0.04
Thu 06/18 11Z 0.23 1922  89  90  12 0.02
Thu 06/18 12Z 0.10 1728  92  88  12 0.02
Thu 06/18 13Z 0.15 1734  92  98  13 0.04
Thu 06/18 14Z 0.25 1839  88  89  14 0.10
Thu 06/18 15Z 0.33 1842  88  88  14 0.02
Thu 06/18 16Z 0.35 1840  95  94  13 0.16
Thu 06/18 17Z 0.42 1936  97  71  13 0.13
Thu 06/18 18Z 0.46 1932  97  72  14 0.04
Thu 06/18 19Z 0.45 1929  96  55  15 0.03
Thu 06/18 20Z 1.11 2026  93  69  15 0.08
Thu 06/18 21Z 1.25 2533  91  73  14 0.53
Thu 06/18 22Z 1.61 2433  89  50  13 0.04
Thu 06/18 23Z 2.33 2433  87  57  12 0.01
Fri 06/19 00Z 2.82 2533  86  62  11 0.01
Fri 06/19 01Z 1.84 2532  89  69  10 0.00
Fri 06/19 02Z 1.73 2532  92  69  10 0.01
Fri 06/19 03Z 1.38 2532  93  65  10 0.01
Fri 06/19 04Z 1.22 2531  96  70   9 0.01
Fri 06/19 05Z 1.16 2630  96  74   9 0.01
Fri 06/19 06Z 1.15 2531  96  71   8 0.01
Fri 06/19 07Z 1.16 2632  97  73   8 0.01
Fri 06/19 08Z 1.12 2632  96  68   8 0.01
Fri 06/19 09Z 1.01 2732  94  61   8 0.01
Fri 06/19 10Z 0.90 2733  89  56   9 0.00
Fri 06/19 11Z 0.87 2633  91  51   9 0.00
Fri 06/19 12Z 0.86 2631  89  42   9 0.01
Fri 06/19 13Z 0.95 2630  91  48   9 0.01
Fri 06/19 14Z 0.98 2628  94  46   9 0.01
Fri 06/19 15Z 1.07 2628  95  45   9 0.01
Fri 06/19 16Z 1.26 2626  95  43   9 0.01
Fri 06/19 17Z 1.50 2625  94  48   9 0.01
Fri 06/19 18Z 2.98 2624  93  44   9 0.01
Fri 06/19 19Z 4.76 2624  91  49  10 0.01
Fri 06/19 20Z 6.18 2624  89  42  10 0.01
Fri 06/19 21Z 7.98 2525  86  41  10 0.00
Fri 06/19 22Z 7.91 2527  81  37  10 0.00
Fri 06/19 23Z 4.60 2529  76  34  10 0.00
Sat 06/20 00Z 3.16 2632  79  38   9 0.00
Sat 06/20 01Z 2.19 2731  85  43   8 0.03
Sat 06/20 02Z 1.76 2731  84  56   8 0.04
Sat 06/20 03Z 1.45 2730  84  64   8 0.01
Sat 06/20 04Z 1.33 2730  90  71   7 0.01
Sat 06/20 05Z 1.18 2629  93  67   7 0.01

Run total areal avg QPF for the Central_Greens is: 1.70 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