NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260815_1200
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 12Z 0.16 3310  84  13   8 0.00
Sat 08/15 13Z 0.10 3409  85  10   8 0.00
Sat 08/15 14Z 0.18 3309  85  11   7 0.00
Sat 08/15 15Z 0.23 3310  84  13   7 0.00
Sat 08/15 16Z 0.32 3308  86  16   7 0.00
Sat 08/15 17Z 0.57 3208  85  15   7 0.00
Sat 08/15 18Z 0.75 3109  82  15   7 0.00
Sat 08/15 19Z 0.89 3211  79  17   8 0.00
Sat 08/15 20Z 0.76 3211  78  19   8 0.00
Sat 08/15 21Z 0.46 3311  79  16   8 0.00
Sat 08/15 22Z 0.21 3410  76  13   8 0.00
Sat 08/15 23Z 0.13 3410  74  11   8 0.00
Sun 08/16 00Z 0.06 3510  71  10   8 0.00
Sun 08/16 01Z 0.06 3510  68  10   8 0.00
Sun 08/16 02Z 0.02 0010  63  10   9 0.00
Sun 08/16 03Z 0.03 0008  63  10   9 0.00
Sun 08/16 04Z 0.04 0006  61  11   9 0.00
Sun 08/16 05Z 0.04 3505  60  11   9 0.00
Sun 08/16 06Z 0.04 0004  58  10   9 0.00
Sun 08/16 07Z 0.04 0003  56  10   9 0.00
Sun 08/16 08Z 0.05 0102  54   9  10 0.00
Sun 08/16 09Z 0.04 0202  54   8  10 0.00
Sun 08/16 10Z 0.04 0301  52   8  10 0.00
Sun 08/16 11Z 0.03 2000  51   8  10 0.00
Sun 08/16 12Z 0.06 2103  51   7  10 0.00
Sun 08/16 13Z 0.07 2005  52   7  10 0.00
Sun 08/16 14Z 0.08 2005  56   6  10 0.00
Sun 08/16 15Z 0.12 2006  61   6  10 0.00
Sun 08/16 16Z 0.20 2007  68   6  10 0.00
Sun 08/16 17Z 0.28 2007  71   7  10 0.00
Sun 08/16 18Z 0.28 1908  73   7  10 0.00
Sun 08/16 19Z 0.24 1909  74   7  11 0.00
Sun 08/16 20Z 0.14 1810  75   7  11 0.00
Sun 08/16 21Z 0.18 1912  81  10  11 0.00
Sun 08/16 22Z 0.20 1914  86  25  11 0.00
Sun 08/16 23Z 0.21 1916  91  40  11 0.00
Mon 08/17 00Z 0.21 1918  94  65  12 0.00
Mon 08/17 01Z 0.20 1922  96  81  12 0.01
Mon 08/17 02Z 0.23 1924  98  78  12 0.02
Mon 08/17 03Z 0.31 2027  97  86  13 0.02
Mon 08/17 04Z 0.31 2028  97  97  13 0.02
Mon 08/17 05Z 0.33 2029  96  98  13 0.02
Mon 08/17 06Z 0.35 2030  95  97  12 0.02
Mon 08/17 07Z 0.32 2029  98  96  12 0.05
Mon 08/17 08Z 0.31 2027  98  97  12 0.06
Mon 08/17 09Z 0.29 2024  99  96  12 0.09
Mon 08/17 10Z 0.27 2024  98  93  12 0.08
Mon 08/17 11Z 0.25 2023  98  95  12 0.08
Mon 08/17 12Z 0.25 2023  99  94  12 0.06
Mon 08/17 13Z 0.25 2022  99  95  12 0.04
Mon 08/17 14Z 0.24 2019  99  95  12 0.03
Mon 08/17 15Z 0.21 2016  99  94  12 0.02
Mon 08/17 16Z 0.19 2014  99  90  12 0.02
Mon 08/17 17Z 0.16 2110  99  84  13 0.01
Mon 08/17 18Z 0.12 2106  98  72  13 0.01
Mon 08/17 19Z 0.13 2405  97  63  14 0.00
Mon 08/17 20Z 0.13 2805  96  54  14 0.00
Mon 08/17 21Z 0.13 3105  96  50  14 0.00
Mon 08/17 22Z 0.12 3206  96  39  14 0.00
Mon 08/17 23Z 0.11 3206  96  41  14 0.00

Run total areal avg QPF for the greens is: 0.66 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