NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260317_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)
=== ===== === ==== ==== === === === ====
Tue 03/17 06Z 0.48 2023  99  98   5 0.00
Tue 03/17 07Z 1.68 2630  96  89  -4 0.05
Tue 03/17 08Z 1.28 2631  95  93  -6 0.05
Tue 03/17 09Z 1.02 2529  91  83  -7 0.01
Tue 03/17 10Z 2.60 2533  93  24 -10 0.00
Tue 03/17 11Z 8.27 2533  84  22 -11 0.00
Tue 03/17 12Z 9.15 2534  76  26 -12 0.00
Tue 03/17 13Z 15.91 2537  69  21 -14 0.00
Tue 03/17 14Z 21.66 2534  74  18 -15 0.00
Tue 03/17 15Z 21.64 2532  74  17 -15 0.00
Tue 03/17 16Z 20.92 2530  76  17 -15 0.00
Tue 03/17 17Z 19.91 2529  74  20 -15 0.00
Tue 03/17 18Z 20.38 2529  69  17 -15 0.00
Tue 03/17 19Z 20.63 2529  67  21 -14 0.00
Tue 03/17 20Z 19.19 2527  72  25 -14 0.00
Tue 03/17 21Z 16.84 2626  76  31 -15 0.00
Tue 03/17 22Z 12.14 2626  79  41 -15 0.00
Tue 03/17 23Z 14.07 2728  75  50 -16 0.00
Wed 03/18 00Z 10.26 2727  80  48 -17 0.00
Wed 03/18 01Z 6.62 2824  87  41 -18 0.00
Wed 03/18 02Z 4.55 2823  82  43 -18 0.00
Wed 03/18 03Z 1.90 2822  82  52 -18 0.00
Wed 03/18 04Z 1.21 2822  83  52 -18 0.00
Wed 03/18 05Z 0.97 2823  80  48 -18 0.00
Wed 03/18 06Z 1.02 2823  80  29 -18 0.00
Wed 03/18 07Z 1.15 2823  78  18 -18 0.00
Wed 03/18 08Z 1.20 2824  73   9 -19 0.00
Wed 03/18 09Z 1.09 2824  66   7 -19 0.00
Wed 03/18 10Z 0.95 2823  62   5 -19 0.00
Wed 03/18 11Z 0.73 2920  61   5 -19 0.00
Wed 03/18 12Z 0.50 2917  59   5 -19 0.00
Wed 03/18 13Z 0.44 2915  58   5 -18 0.00
Wed 03/18 14Z 0.37 2913  50   6 -18 0.00
Wed 03/18 15Z 0.34 2810  43   7 -17 0.00
Wed 03/18 16Z 0.41 2808  39   8 -16 0.00
Wed 03/18 17Z 0.82 2707  37   8 -16 0.00
Wed 03/18 18Z 1.00 2605  35   8 -15 0.00
Wed 03/18 19Z 0.99 2504  33   8 -14 0.00
Wed 03/18 20Z 0.84 2404  33   8 -14 0.00
Wed 03/18 21Z 0.45 2104  33   7 -13 0.00
Wed 03/18 22Z 0.24 1906  35   8 -13 0.00
Wed 03/18 23Z 0.17 1810  37   7 -12 0.00
Thu 03/19 00Z 0.23 1813  39  10 -12 0.00
Thu 03/19 01Z 0.30 1915  37  11 -12 0.00
Thu 03/19 02Z 0.42 2016  40  22 -12 0.00
Thu 03/19 03Z 0.51 2018  45  31 -11 0.00
Thu 03/19 04Z 0.59 2119  51  71 -11 0.00
Thu 03/19 05Z 0.61 2120  53  89 -11 0.00
Thu 03/19 06Z 0.60 2121  60  87 -11 0.00
Thu 03/19 09Z 0.58 2220  66  88 -10 0.00
Thu 03/19 10Z 0.54 2120  73  85 -10 0.00
Thu 03/19 11Z 0.51 2120  80  89 -10 0.00
Thu 03/19 12Z 0.44 2121  84  88 -10 0.00
Thu 03/19 13Z 0.41 2120  88  90  -9 0.00
Thu 03/19 14Z 0.44 2120  89  89  -9 0.00
Thu 03/19 15Z 0.49 2019  87  81  -9 0.00
Thu 03/19 16Z 0.95 2018  83  71  -8 0.00
Thu 03/19 17Z 1.72 2017  79  51  -8 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