Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260802_0000
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)
=== ===== === ==== ==== === === === ====
Sun 08/02 00Z 0.20 2106  76  28  15 0.00
Sun 08/02 01Z 0.18 2007  74  27  15 0.00
Sun 08/02 02Z 0.19 1909  74  32  15 0.00
Sun 08/02 03Z 0.24 2012  74  42  15 0.00
Sun 08/02 04Z 0.38 2014  75  53  15 0.00
Sun 08/02 05Z 0.52 2118  82  64  15 0.00
Sun 08/02 06Z 0.48 2120  87  68  15 0.01
Sun 08/02 07Z 0.41 2122  87  67  15 0.00
Sun 08/02 08Z 0.39 2122  85  69  15 0.00
Sun 08/02 09Z 0.45 2123  86  82  15 0.00
Sun 08/02 10Z 0.51 2222  88  80  15 0.00
Sun 08/02 11Z 0.51 2221  88  71  15 0.00
Sun 08/02 12Z 0.46 2219  87  68  15 0.00
Sun 08/02 13Z 0.41 2216  88  53  15 0.00
Sun 08/02 14Z 0.44 2116  92  50  14 0.00
Sun 08/02 15Z 0.43 2115  95  72  14 0.01
Sun 08/02 16Z 0.34 2115  93  83  14 0.03
Sun 08/02 17Z 0.38 2015  92  79  14 0.01
Sun 08/02 18Z 0.38 2017  92  70  15 0.00
Sun 08/02 19Z 0.45 2017  90  59  15 0.02
Sun 08/02 20Z 0.50 2017  88  56  15 0.03
Sun 08/02 21Z 0.51 2017  87  34  15 0.00
Sun 08/02 22Z 0.29 1917  81  33  15 0.00
Sun 08/02 23Z 0.24 1919  81  39  15 0.00
Mon 08/03 00Z 0.22 1920  78  60  15 0.00
Mon 08/03 01Z 0.20 1920  79  72  15 0.00
Mon 08/03 02Z 0.22 1921  78  83  15 0.00
Mon 08/03 03Z 0.18 1921  71  84  15 0.00
Mon 08/03 04Z 0.17 1921  65  90  15 0.00
Mon 08/03 05Z 0.18 1922  67  86  16 0.00
Mon 08/03 06Z 0.24 1923  76  74  15 0.00
Mon 08/03 07Z 0.21 1922  85  64  15 0.01
Mon 08/03 08Z 0.19 1922  86  89  16 0.01
Mon 08/03 09Z 0.17 1921  83  94  15 0.02
Mon 08/03 10Z 0.09 1821  80  90  16 0.01
Mon 08/03 11Z 0.08 1823  82  89  17 0.00
Mon 08/03 12Z 0.09 1825  87  84  17 0.01
Mon 08/03 13Z 0.15 1926  93  82  17 0.01
Mon 08/03 14Z 0.19 1927  96  80  17 0.01
Mon 08/03 15Z 0.26 1925  98  84  16 0.04
Mon 08/03 16Z 0.31 2023  98  79  17 0.15
Mon 08/03 17Z 0.36 2022  98  81  17 0.07
Mon 08/03 18Z 0.34 2020  96  85  17 0.13
Mon 08/03 19Z 0.41 1921  97  77  17 0.04
Mon 08/03 20Z 0.36 1921  96  63  17 0.05
Mon 08/03 21Z 0.61 2221  93  74  17 0.43
Mon 08/03 22Z 0.73 2523  94  37  15 0.37
Mon 08/03 23Z 0.84 2524  94  58  14 0.02
Tue 08/04 00Z 0.74 2623  96  68  13 0.04
Tue 08/04 01Z 0.60 2720  98  69  13 0.03
Tue 08/04 02Z 0.50 2919  98  67  13 0.05
Tue 08/04 03Z 0.50 3123  98  83  12 0.05
Tue 08/04 04Z 0.40 3330  98  85  11 0.07
Tue 08/04 05Z 0.30 3332  94  69  12 0.03
Tue 08/04 06Z 0.26 3431  87  33  12 0.01
Tue 08/04 07Z 0.23 3429  82   8  12 0.01
Tue 08/04 08Z 0.23 3426  80   2  12 0.01
Tue 08/04 09Z 0.28 3324  82   2  11 0.00
Tue 08/04 10Z 0.24 3322  73   2  12 0.00
Tue 08/04 11Z 0.21 3321  60   2  12 0.00

Run total areal avg QPF for the greens is: 1.79 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