Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260802_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)
=== ===== === ==== ==== === === === ====
Sun 08/02 12Z 0.28 2013  83  65  15 0.00
Sun 08/02 13Z 0.30 2014  82  59  15 0.00
Sun 08/02 14Z 0.33 1913  86  54  15 0.00
Sun 08/02 15Z 0.56 1913  92  62  15 0.00
Sun 08/02 16Z 0.31 1814  94  72  15 0.01
Sun 08/02 17Z 0.52 1917  94  79  15 0.03
Sun 08/02 18Z 0.60 1918  93  77  15 0.04
Sun 08/02 19Z 0.68 1819  89  44  15 0.00
Sun 08/02 20Z 0.75 1820  86  23  15 0.00
Sun 08/02 21Z 0.50 1822  87  16  15 0.01
Sun 08/02 22Z 0.29 1823  83  14  16 0.00
Sun 08/02 23Z 0.23 1824  82   9  16 0.00
Mon 08/03 00Z 0.21 1824  81  13  16 0.00
Mon 08/03 01Z 0.22 1824  80  52  16 0.00
Mon 08/03 02Z 0.27 1924  76  79  16 0.00
Mon 08/03 03Z 0.30 1924  75  92  15 0.00
Mon 08/03 04Z 0.25 1922  78  92  16 0.00
Mon 08/03 05Z 0.31 1924  81  91  16 0.00
Mon 08/03 06Z 0.44 1926  90  92  15 0.02
Mon 08/03 07Z 0.32 1925  88  79  15 0.08
Mon 08/03 08Z 0.33 1925  81  82  16 0.01
Mon 08/03 09Z 0.20 1825  84  90  16 0.01
Mon 08/03 10Z 0.24 1828  93  96  16 0.03
Mon 08/03 11Z 0.30 1831  98  94  16 0.10
Mon 08/03 12Z 0.51 2031  96  83  16 0.13
Mon 08/03 13Z 0.66 2030  94  73  16 0.05
Mon 08/03 14Z 0.64 2028  98  74  16 0.02
Mon 08/03 15Z 0.78 2225  99  78  16 0.03
Mon 08/03 16Z 0.74 2223  99  78  16 0.04
Mon 08/03 17Z 0.80 2222  97  78  16 0.11
Mon 08/03 18Z 0.65 2317  95  86  16 0.16
Mon 08/03 19Z 0.57 2417  92  81  15 0.28
Mon 08/03 20Z 0.63 2319  94  69  15 0.02
Mon 08/03 21Z 0.93 2524  97  72  14 0.08
Mon 08/03 22Z 0.92 2827  97  67  12 0.08
Mon 08/03 23Z 0.69 3027  94  36  11 0.01
Tue 08/04 00Z 0.45 3129  92  25  12 0.01
Tue 08/04 01Z 0.33 3228  92  19  11 0.01
Tue 08/04 02Z 0.27 3226  88  18  11 0.00
Tue 08/04 03Z 0.31 3224  82   9  11 0.00
Tue 08/04 04Z 0.38 3124  81   4  11 0.00
Tue 08/04 05Z 0.44 3122  82   2  11 0.00
Tue 08/04 06Z 0.46 3022  82   3  11 0.00
Tue 08/04 07Z 0.47 3022  79   2  11 0.00
Tue 08/04 08Z 0.45 3022  76   2  11 0.00
Tue 08/04 09Z 0.41 3021  71   1  12 0.00
Tue 08/04 10Z 0.36 3020  64   2  13 0.00
Tue 08/04 11Z 0.33 3018  58   2  13 0.00
Tue 08/04 12Z 0.31 3018  56   2  13 0.00
Tue 08/04 13Z 0.29 3016  55   1  13 0.00
Tue 08/04 14Z 0.25 3115  52   1  13 0.00
Tue 08/04 15Z 0.23 3112  51   1  13 0.00
Tue 08/04 16Z 0.20 3109  47   1  14 0.00
Tue 08/04 17Z 0.20 3008  44   1  14 0.00
Tue 08/04 18Z 0.16 3006  42   2  15 0.00
Tue 08/04 19Z 0.15 2905  41   3  15 0.00
Tue 08/04 20Z 0.17 2804  39   5  16 0.00
Tue 08/04 21Z 0.15 2603  37   7  16 0.00
Tue 08/04 22Z 0.12 2503  35  10  17 0.00
Tue 08/04 23Z 0.13 2404  35  13  17 0.00

Run total areal avg QPF for the Central_Greens is: 1.37 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