NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260719_1800
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 07/19 18Z 5.53 3216  78  10   8 0.00
Sun 07/19 19Z 5.61 3117  76   9   8 0.00
Sun 07/19 20Z 7.39 3018  77  11   8 0.00
Sun 07/19 21Z 7.54 3018  74  12   9 0.00
Sun 07/19 22Z 6.40 3018  70  11   9 0.00
Sun 07/19 23Z 3.72 3019  71  10   9 0.00
Mon 07/20 00Z 2.68 3021  75   9   8 0.00
Mon 07/20 01Z 1.75 3122  78   7   8 0.00
Mon 07/20 02Z 1.20 3123  81   6   8 0.00
Mon 07/20 03Z 1.08 3123  83   6   7 0.00
Mon 07/20 04Z 0.86 3123  82   7   7 0.00
Mon 07/20 05Z 0.71 3123  84  19   7 0.00
Mon 07/20 06Z 0.60 3123  84  17   8 0.00
Mon 07/20 07Z 0.50 3122  86  12   8 0.00
Mon 07/20 08Z 0.47 3120  85  14   8 0.00
Mon 07/20 09Z 0.40 3118  83  19   8 0.00
Mon 07/20 10Z 0.33 3116  80  22   8 0.00
Mon 07/20 11Z 0.31 3115  75  32   8 0.00
Mon 07/20 12Z 0.30 3114  73  42   8 0.00
Mon 07/20 13Z 0.31 3011  73  45   8 0.00
Mon 07/20 14Z 0.37 3009  73  44   8 0.00
Mon 07/20 15Z 0.71 2907  72  49   8 0.00
Mon 07/20 16Z 1.15 2805  71  53   9 0.00
Mon 07/20 17Z 1.44 2505  67  49  10 0.00
Mon 07/20 18Z 1.74 2406  66  47  10 0.00
Mon 07/20 19Z 2.11 2307  67  47  11 0.00
Mon 07/20 20Z 2.46 2308  70  49  11 0.00
Mon 07/20 21Z 1.82 2208  71  46  11 0.00
Mon 07/20 22Z 0.81 2209  71  39  11 0.00
Mon 07/20 23Z 0.45 2111  68  31  12 0.00
Tue 07/21 00Z 0.39 2113  61  23  12 0.00
Tue 07/21 01Z 0.34 2014  53  24  13 0.00
Tue 07/21 02Z 0.36 2016  55  21  13 0.00
Tue 07/21 03Z 0.43 2118  57  15  13 0.00
Tue 07/21 04Z 0.50 2121  59  14  13 0.00
Tue 07/21 05Z 0.62 2123  63  13  12 0.00
Tue 07/21 06Z 0.68 2224  70  11  12 0.00
Tue 07/21 07Z 0.70 2225  70   9  12 0.00
Tue 07/21 08Z 0.57 2124  72   6  12 0.00
Tue 07/21 09Z 0.55 2124  81   3  12 0.00
Tue 07/21 10Z 0.56 2125  89   2  12 0.00
Tue 07/21 11Z 0.56 2125  91   1  12 0.00
Tue 07/21 12Z 0.47 2024  95   2  12 0.00
Tue 07/21 13Z 0.41 2025  98  11  12 0.01
Tue 07/21 14Z 0.41 2025  98  30  12 0.02
Tue 07/21 15Z 0.37 1925  97  33  12 0.01
Tue 07/21 16Z 0.37 1924  97  51  12 0.01
Tue 07/21 17Z 0.26 1823  95  66  13 0.00
Tue 07/21 18Z 0.19 1823  94  53  13 0.00
Tue 07/21 19Z 0.12 1724  93  74  13 0.01
Tue 07/21 20Z 0.08 1625  93  87  13 0.03
Tue 07/21 21Z 0.12 1626  91  51  14 0.02
Tue 07/21 22Z 0.10 1628  92  58  14 0.02
Tue 07/21 23Z 0.09 1628  92  66  15 0.01
Wed 07/22 00Z 0.06 1726  96  62  15 0.00
Wed 07/22 01Z 0.16 1826  95  85  15 0.09
Wed 07/22 02Z 0.21 1825  91  62  15 0.19
Wed 07/22 03Z 0.39 2025  90  58  14 0.02
Wed 07/22 04Z 0.48 2223  85  60  14 0.01
Wed 07/22 05Z 0.59 2226  80  61  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.45 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