NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260911_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)
=== ===== === ==== ==== === === === ====
Fri 09/11 12Z 0.32 3118  86   4   6 0.00
Fri 09/11 13Z 0.34 3119  82   5   6 0.00
Fri 09/11 14Z 0.35 3118  82   6   6 0.00
Fri 09/11 15Z 0.36 3117  80   8   6 0.00
Fri 09/11 16Z 0.39 3116  75  11   6 0.00
Fri 09/11 17Z 0.46 3016  77  14   6 0.00
Fri 09/11 18Z 0.46 3015  76  16   6 0.00
Fri 09/11 19Z 0.51 3015  74  18   7 0.00
Fri 09/11 20Z 0.59 2915  76  18   7 0.00
Fri 09/11 21Z 0.56 3016  73  18   7 0.00
Fri 09/11 22Z 0.48 3016  70  19   7 0.00
Fri 09/11 23Z 0.35 3116  65  20   8 0.00
Sat 09/12 00Z 0.29 3116  62  23   8 0.00
Sat 09/12 01Z 0.22 3216  57  26   9 0.00
Sat 09/12 02Z 0.15 3215  51  32  10 0.00
Sat 09/12 03Z 0.12 3214  47  35  11 0.00
Sat 09/12 04Z 0.08 3313  43  34  11 0.00
Sat 09/12 05Z 0.05 3311  40  34  11 0.00
Sat 09/12 06Z 0.03 3409  37  33  12 0.00
Sat 09/12 07Z 0.02 3406  35  33  12 0.00
Sat 09/12 08Z 0.02 3404  33  33  12 0.00
Sat 09/12 09Z 0.02 3403  33  31  12 0.00
Sat 09/12 10Z 0.02 0002  33  30  12 0.00
Sat 09/12 11Z 0.02 1000  32  28  12 0.00
Sat 09/12 12Z 0.02 1803  32  28  12 0.00
Sat 09/12 13Z 0.04 1806  34  24  12 0.00
Sat 09/12 14Z 0.08 1907  36  22  12 0.00
Sat 09/12 15Z 0.12 2008  39  22  12 0.00
Sat 09/12 16Z 0.17 2109  42  24  12 0.00
Sat 09/12 17Z 0.20 2010  43  27  12 0.00
Sat 09/12 18Z 0.20 2011  44  27  12 0.00
Sat 09/12 19Z 0.20 1911  47  23  12 0.00
Sat 09/12 20Z 0.24 1912  51  15  12 0.00
Sat 09/12 21Z 0.26 1914  53   6  12 0.00
Sat 09/12 22Z 0.29 2016  52   7  13 0.00
Sat 09/12 23Z 0.34 2017  55   7  13 0.00
Sun 09/13 00Z 0.38 2119  63  22  13 0.00
Sun 09/13 01Z 0.38 2120  73  71  13 0.00
Sun 09/13 02Z 0.43 2122  82  84  13 0.00
Sun 09/13 03Z 0.48 2223  89  98  13 0.01
Sun 09/13 04Z 0.42 2121  91  80  13 0.01
Sun 09/13 05Z 0.42 2122  98  88  13 0.06
Sun 09/13 06Z 0.43 2124  97  85  13 0.14
Sun 09/13 07Z 0.44 2224  96  89  14 0.05
Sun 09/13 08Z 0.44 2223  97  96  14 0.05
Sun 09/13 09Z 0.40 2221  95  92  14 0.10
Sun 09/13 10Z 0.36 2220  95  93  14 0.05
Sun 09/13 11Z 0.42 2124  96  93  14 0.07
Sun 09/13 12Z 0.43 2123  97  94  14 0.19
Sun 09/13 13Z 0.44 2126  98  92  14 0.15
Sun 09/13 14Z 0.44 2126  99  94  14 0.25
Sun 09/13 15Z 0.52 2223  99  86  13 0.08
Sun 09/13 16Z 0.49 2419  98  73  14 0.03
Sun 09/13 17Z 0.42 2515  94  51  14 0.01
Sun 09/13 18Z 0.45 2615  91  39  14 0.00
Sun 09/13 19Z 0.46 2613  90  40  14 0.00
Sun 09/13 20Z 0.56 2614  92  39  14 0.00
Sun 09/13 21Z 0.70 2617  96  26  14 0.01
Sun 09/13 22Z 0.82 2619  95  22  14 0.04
Sun 09/13 23Z 0.76 2721  91  25  13 0.02

Run total areal avg QPF for the Central_Greens is: 1.32 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