Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260802_0600
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 06Z 0.43 2117  82  82  15 0.00
Sun 08/02 07Z 0.51 2120  84  86  15 0.00
Sun 08/02 08Z 0.54 2121  85  71  15 0.00
Sun 08/02 09Z 0.49 2119  86  52  15 0.00
Sun 08/02 10Z 0.51 2119  89  35  15 0.00
Sun 08/02 11Z 0.59 2120  89  34  14 0.00
Sun 08/02 12Z 0.53 2120  88  35  15 0.00
Sun 08/02 13Z 0.49 2119  85  33  15 0.00
Sun 08/02 14Z 0.47 2117  83  39  15 0.00
Sun 08/02 15Z 0.48 2015  84  52  15 0.00
Sun 08/02 16Z 0.69 2014  83  66  15 0.00
Sun 08/02 17Z 0.79 1915  76  79  15 0.00
Sun 08/02 18Z 0.50 1817  69  61  15 0.00
Sun 08/02 19Z 0.90 1818  72  38  15 0.00
Sun 08/02 20Z 0.70 1818  71  34  15 0.00
Sun 08/02 21Z 0.37 1819  72  31  15 0.00
Sun 08/02 22Z 0.34 1821  68  25  15 0.00
Sun 08/02 23Z 0.23 1823  64  32  15 0.00
Mon 08/03 00Z 0.18 1823  70  28  15 0.00
Mon 08/03 01Z 0.16 1824  71  32  15 0.00
Mon 08/03 02Z 0.22 1823  75  17  15 0.00
Mon 08/03 03Z 0.27 1923  76  27  15 0.00
Mon 08/03 04Z 0.27 1923  73  63  15 0.00
Mon 08/03 05Z 0.34 1924  72  89  15 0.00
Mon 08/03 06Z 0.33 1923  79  93  15 0.01
Mon 08/03 07Z 0.32 1923  81  87  16 0.00
Mon 08/03 08Z 0.36 2025  83  86  16 0.00
Mon 08/03 09Z 0.41 2025  89  91  16 0.01
Mon 08/03 10Z 0.43 2026  92  94  16 0.01
Mon 08/03 11Z 0.44 2025  91  95  16 0.01
Mon 08/03 12Z 0.32 1925  88  79  16 0.00
Mon 08/03 13Z 0.45 2025  89  85  16 0.01
Mon 08/03 14Z 0.55 2026  95  86  16 0.01
Mon 08/03 15Z 0.61 2025  99  87  16 0.12
Mon 08/03 16Z 0.91 2325  98  83  16 0.11
Mon 08/03 17Z 0.98 2422  97  87  15 0.02
Mon 08/03 18Z 0.96 2622  97  82  15 0.10
Mon 08/03 19Z 0.76 2925  90  61  14 0.03
Mon 08/03 20Z 0.63 3126  79  33  13 0.00
Mon 08/03 21Z 0.64 3125  81  21  13 0.00
Mon 08/03 22Z 0.85 3123  85  11  12 0.00
Mon 08/03 23Z 0.84 3222  81   6  11 0.00
Tue 08/04 00Z 0.35 3321  73   4  11 0.00
Tue 08/04 01Z 0.15 3320  62   6  11 0.00
Tue 08/04 02Z 0.32 3217  61   8  12 0.00
Tue 08/04 03Z 0.58 3017  65  11  11 0.00
Tue 08/04 04Z 0.75 2819  81  23  11 0.00
Tue 08/04 05Z 0.71 2920  86   8  11 0.00
Tue 08/04 06Z 0.57 2921  85   6  11 0.00
Tue 08/04 07Z 0.53 2921  82   5  11 0.00
Tue 08/04 08Z 0.47 3020  77   4  11 0.00
Tue 08/04 09Z 0.46 3020  71   3  12 0.00
Tue 08/04 10Z 0.42 3020  66   2  12 0.00
Tue 08/04 11Z 0.39 3018  62   2  12 0.00
Tue 08/04 12Z 0.37 3018  58   2  13 0.00
Tue 08/04 13Z 0.35 3017  57   2  13 0.00
Tue 08/04 14Z 0.32 3015  56   1  13 0.00
Tue 08/04 15Z 0.31 3014  53   2  13 0.00
Tue 08/04 16Z 0.25 3011  49   2  14 0.00
Tue 08/04 17Z 0.27 2909  47   2  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.44 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