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_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)
=== ===== === ==== ==== === === === ====
Fri 09/11 18Z 0.81 3011  85  10   7 0.00
Fri 09/11 19Z 0.58 3013  81  14   7 0.00
Fri 09/11 20Z 0.54 3014  80  18   7 0.00
Fri 09/11 21Z 0.49 3015  78  20   8 0.00
Fri 09/11 22Z 0.40 3115  72  19   8 0.00
Fri 09/11 23Z 0.35 3116  66  17   9 0.00
Sat 09/12 00Z 0.29 3115  62  16   9 0.00
Sat 09/12 01Z 0.23 3216  57  18  10 0.00
Sat 09/12 02Z 0.16 3214  53  22  10 0.00
Sat 09/12 03Z 0.11 3212  51  27  11 0.00
Sat 09/12 04Z 0.07 3310  48  31  11 0.00
Sat 09/12 05Z 0.06 3308  45  34  11 0.00
Sat 09/12 06Z 0.05 3205  42  35  11 0.00
Sat 09/12 07Z 0.05 3103  39  36  12 0.00
Sat 09/12 08Z 0.05 3003  36  36  12 0.00
Sat 09/12 09Z 0.06 2802  34  36  12 0.00
Sat 09/12 10Z 0.04 2601  33  35  12 0.00
Sat 09/12 11Z 0.04 2002  33  34  12 0.00
Sat 09/12 12Z 0.03 1804  34  33  12 0.00
Sat 09/12 13Z 0.05 1806  35  30  12 0.00
Sat 09/12 14Z 0.09 1909  39  28  12 0.00
Sat 09/12 15Z 0.16 2010  45  25  12 0.00
Sat 09/12 16Z 0.20 2010  52  20  11 0.00
Sat 09/12 17Z 0.19 2011  55  16  12 0.00
Sat 09/12 18Z 0.19 1910  60  15  12 0.00
Sat 09/12 19Z 0.23 1912  65  13  12 0.00
Sat 09/12 20Z 0.24 1913  67   9  12 0.00
Sat 09/12 21Z 0.31 2015  69   4  12 0.00
Sat 09/12 22Z 0.32 2016  65   5  12 0.00
Sat 09/12 23Z 0.34 2017  63  12  12 0.00
Sun 09/13 00Z 0.38 2118  66  22  13 0.00
Sun 09/13 01Z 0.40 2119  72  18  13 0.00
Sun 09/13 02Z 0.45 2120  79  28  13 0.00
Sun 09/13 03Z 0.44 2220  81  42  13 0.00
Sun 09/13 04Z 0.45 2220  85  54  13 0.00
Sun 09/13 05Z 0.46 2222  90  69  13 0.00
Sun 09/13 06Z 0.43 2223  96  94  13 0.05
Sun 09/13 07Z 0.46 2224  96  92  13 0.14
Sun 09/13 08Z 0.46 2323  94  91  14 0.02
Sun 09/13 09Z 0.43 2223  95  87  14 0.02
Sun 09/13 10Z 0.43 2223  97  91  14 0.04
Sun 09/13 11Z 0.45 2322  97  82  14 0.05
Sun 09/13 12Z 0.44 2321  97  89  14 0.05
Sun 09/13 13Z 0.42 2220  96  93  14 0.08
Sun 09/13 14Z 0.45 2221  97  87  14 0.10
Sun 09/13 15Z 0.50 2321  98  81  14 0.19
Sun 09/13 16Z 0.49 2220  95  63  14 0.07
Sun 09/13 17Z 0.46 2220  96  55  14 0.01
Sun 09/13 18Z 0.40 2218  95  48  14 0.01
Sun 09/13 19Z 0.38 2215  95  43  14 0.01
Sun 09/13 20Z 0.41 2314  91  51  14 0.01
Sun 09/13 21Z 0.42 2413  89  49  14 0.00
Sun 09/13 22Z 0.50 2615  90  30  14 0.00
Sun 09/13 23Z 0.64 2718  94  28  13 0.01
Mon 09/14 00Z 0.64 2719  87  33  13 0.01
Mon 09/14 01Z 0.75 2722  90  35  13 0.02
Mon 09/14 02Z 0.61 2822  77  45  13 0.02
Mon 09/14 03Z 0.73 2824  71  35  11 0.00
Mon 09/14 04Z 0.67 2923  70  47  11 0.00
Mon 09/14 05Z 0.70 2924  78  49  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.91 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