Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260802_0000
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)
=== ===== === ==== ==== === === === ====
Sun 08/02 00Z 0.31 2107  75  14  15 0.00
Sun 08/02 01Z 0.33 2108  73  14  15 0.00
Sun 08/02 02Z 0.36 2010  72  25  15 0.00
Sun 08/02 03Z 0.40 2012  73  40  15 0.00
Sun 08/02 04Z 0.55 2015  75  56  15 0.00
Sun 08/02 05Z 0.71 2119  85  68  15 0.00
Sun 08/02 06Z 0.56 2121  91  70  15 0.02
Sun 08/02 07Z 0.48 2123  88  75  15 0.01
Sun 08/02 08Z 0.47 2123  85  76  16 0.00
Sun 08/02 09Z 0.55 2223  90  84  15 0.00
Sun 08/02 10Z 0.64 2322  91  77  14 0.00
Sun 08/02 11Z 0.60 2222  87  64  15 0.00
Sun 08/02 12Z 0.51 2219  86  61  15 0.00
Sun 08/02 13Z 0.45 2217  87  45  15 0.00
Sun 08/02 14Z 0.55 2117  91  53  14 0.00
Sun 08/02 15Z 0.48 2116  96  87  14 0.01
Sun 08/02 16Z 0.41 2114  93  85  14 0.04
Sun 08/02 17Z 0.56 2115  92  78  14 0.00
Sun 08/02 18Z 0.54 2015  92  71  15 0.00
Sun 08/02 19Z 0.63 1916  91  49  15 0.03
Sun 08/02 20Z 0.72 2017  88  46  15 0.05
Sun 08/02 21Z 0.78 1916  87  21  15 0.00
Sun 08/02 22Z 0.51 1919  77  35  15 0.00
Sun 08/02 23Z 0.42 1921  76  47  15 0.00
Mon 08/03 00Z 0.34 1920  77  61  15 0.00
Mon 08/03 01Z 0.30 1920  78  61  15 0.00
Mon 08/03 02Z 0.31 1920  77  81  15 0.01
Mon 08/03 03Z 0.25 1921  68  80  16 0.00
Mon 08/03 04Z 0.27 1920  62  91  16 0.00
Mon 08/03 05Z 0.29 1921  66  85  16 0.00
Mon 08/03 06Z 0.35 2022  85  64  15 0.00
Mon 08/03 07Z 0.28 1920  93  48  15 0.01
Mon 08/03 08Z 0.28 1922  89  90  16 0.01
Mon 08/03 09Z 0.25 1919  81  94  16 0.02
Mon 08/03 10Z 0.17 1820  81  88  17 0.01
Mon 08/03 11Z 0.17 1823  86  85  17 0.00
Mon 08/03 12Z 0.22 1825  91  79  17 0.01
Mon 08/03 13Z 0.31 1926  95  78  17 0.01
Mon 08/03 14Z 0.37 1926  96  82  17 0.01
Mon 08/03 15Z 0.42 2024  98  83  17 0.05
Mon 08/03 16Z 0.45 2022  98  73  17 0.10
Mon 08/03 17Z 0.48 2020  98  74  17 0.06
Mon 08/03 18Z 0.46 2020  97  84  17 0.13
Mon 08/03 19Z 0.74 2023  97  71  17 0.04
Mon 08/03 20Z 0.64 2025  95  54  17 0.01
Mon 08/03 21Z 0.73 2224  91  68  17 0.23
Mon 08/03 22Z 0.75 2523  93  35  15 0.16
Mon 08/03 23Z 0.92 2524  96  47  13 0.02
Tue 08/04 00Z 0.78 2623  96  63  13 0.02
Tue 08/04 01Z 0.67 2622  97  65  13 0.02
Tue 08/04 02Z 0.60 2822  98  57  12 0.04
Tue 08/04 03Z 0.54 3025  98  78  11 0.04
Tue 08/04 04Z 0.37 3229  98  78  11 0.04
Tue 08/04 05Z 0.18 3332  96  76  12 0.02
Tue 08/04 06Z 0.16 3332  89  48  12 0.01
Tue 08/04 07Z 0.14 3330  81  10  12 0.01
Tue 08/04 08Z 0.12 3327  77   1  12 0.00
Tue 08/04 09Z 0.17 3325  79   2  12 0.00
Tue 08/04 10Z 0.15 3323  73   2  12 0.00
Tue 08/04 11Z 0.11 3321  60   2  13 0.00

Run total areal avg QPF for the Central_Greens is: 1.25 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