NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260815_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 08/15 06Z 0.04 3508  81  16  10 0.00
Sat 08/15 07Z 0.06 3408  83  17   9 0.00
Sat 08/15 08Z 0.10 3308  83  17   9 0.00
Sat 08/15 09Z 0.10 3306  82  16   9 0.00
Sat 08/15 10Z 0.17 3208  81  17   9 0.00
Sat 08/15 11Z 0.21 3210  80  17   9 0.00
Sat 08/15 12Z 0.20 3211  80  16   9 0.00
Sat 08/15 13Z 0.20 3313  79  14   9 0.00
Sat 08/15 14Z 0.20 3313  79  14   9 0.00
Sat 08/15 15Z 0.24 3311  81  16   8 0.00
Sat 08/15 16Z 0.34 3210  81  19   8 0.00
Sat 08/15 17Z 0.77 3210  80  26   8 0.00
Sat 08/15 18Z 0.85 3211  77  30   8 0.00
Sat 08/15 19Z 0.90 3212  77  25   8 0.00
Sat 08/15 20Z 0.83 3212  79  26   8 0.00
Sat 08/15 21Z 0.45 3212  78  17   8 0.00
Sat 08/15 22Z 0.37 3212  79  10   8 0.00
Sat 08/15 23Z 0.27 3311  80  10   8 0.00
Sun 08/16 00Z 0.19 3310  79  10   8 0.00
Sun 08/16 01Z 0.20 3310  79  11   8 0.00
Sun 08/16 02Z 0.13 3308  75  10   8 0.00
Sun 08/16 03Z 0.18 3208  76  10   8 0.00
Sun 08/16 04Z 0.17 3207  76  10   8 0.00
Sun 08/16 05Z 0.13 3206  75  10   8 0.00
Sun 08/16 06Z 0.09 3305  74  10   9 0.00
Sun 08/16 07Z 0.08 3204  72  10   9 0.00
Sun 08/16 08Z 0.07 3102  72   9   9 0.00
Sun 08/16 09Z 0.08 2701  72   8   9 0.00
Sun 08/16 10Z 0.12 2403  73   8   8 0.00
Sun 08/16 11Z 0.10 2303  71   8   9 0.00
Sun 08/16 12Z 0.10 2104  70   8   9 0.00
Sun 08/16 13Z 0.09 2005  71   8   9 0.00
Sun 08/16 14Z 0.13 2007  73   7   9 0.00
Sun 08/16 15Z 0.24 2108  79   6   9 0.00
Sun 08/16 16Z 0.28 2009  85   6   9 0.00
Sun 08/16 17Z 0.24 2009  87   9  10 0.00
Sun 08/16 18Z 0.20 2009  86   8  10 0.00
Sun 08/16 19Z 0.14 1909  87  10  11 0.00
Sun 08/16 20Z 0.06 1811  86  14  11 0.00
Sun 08/16 21Z 0.06 1812  87  20  11 0.00
Sun 08/16 22Z 0.06 1815  89  34  12 0.00
Sun 08/16 23Z 0.07 1818  90  63  12 0.00
Mon 08/17 00Z 0.08 1820  93  78  12 0.00
Mon 08/17 01Z 0.10 1822  95  87  12 0.01
Mon 08/17 02Z 0.12 1822  95  95  12 0.01
Mon 08/17 03Z 0.14 1923  96  99  12 0.02
Mon 08/17 04Z 0.12 1824  96  96  13 0.02
Mon 08/17 05Z 0.15 1927  97  94  13 0.03
Mon 08/17 06Z 0.17 1929  97  89  13 0.03
Mon 08/17 07Z 0.17 1929  98  94  13 0.02
Mon 08/17 08Z 0.18 1928  98  98  13 0.02
Mon 08/17 09Z 0.18 1927  98  97  13 0.02
Mon 08/17 10Z 0.21 1925  98  95  13 0.03
Mon 08/17 11Z 0.22 2023  98  92  13 0.02
Mon 08/17 12Z 0.22 2020  99  92  13 0.03
Mon 08/17 13Z 0.18 2017  99  89  13 0.03
Mon 08/17 14Z 0.18 2114  99  85  14 0.02
Mon 08/17 15Z 0.16 2111  99  80  14 0.01
Mon 08/17 16Z 0.14 2208  98  83  15 0.01
Mon 08/17 17Z 0.15 2406  98  87  15 0.00

Run total areal avg QPF for the greens is: 0.33 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