NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260909_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)
=== ===== === ==== ==== === === === ====
Wed 09/09 18Z 0.37 2020  93  42  12 0.00
Wed 09/09 19Z 0.34 2020  93  70  13 0.02
Wed 09/09 20Z 0.21 1823  96  97  13 0.06
Wed 09/09 21Z 0.13 1730  97  99  13 0.09
Wed 09/09 22Z 0.36 1935  99  99  14 0.16
Wed 09/09 23Z 0.54 2035  99  98  14 0.22
Thu 09/10 00Z 0.84 2138  99  91  15 0.16
Thu 09/10 01Z 0.92 2334  97  92  15 0.16
Thu 09/10 02Z 1.10 2341  98  88  16 0.21
Thu 09/10 03Z 1.09 2338  97  97  15 0.13
Thu 09/10 04Z 1.03 2339  99  98  16 0.37
Thu 09/10 05Z 1.05 2534  99  82  16 0.31
Thu 09/10 06Z 1.02 2629  91  77  15 0.10
Thu 09/10 07Z 0.84 2727  78  78  15 0.01
Thu 09/10 08Z 0.77 2727  76  52  15 0.00
Thu 09/10 09Z 0.81 2728  83  28  14 0.00
Thu 09/10 10Z 0.94 2729  90  28  13 0.00
Thu 09/10 11Z 1.16 2730  86  41  12 0.01
Thu 09/10 12Z 1.04 2730  74  25  12 0.01
Thu 09/10 13Z 0.96 2831  63  12  13 0.00
Thu 09/10 14Z 1.02 2830  61   7  12 0.00
Thu 09/10 15Z 1.19 2828  61   7  11 0.00
Thu 09/10 16Z 2.69 2827  61   8  11 0.00
Thu 09/10 17Z 9.96 2727  63   8  10 0.00
Thu 09/10 18Z 16.68 2727  63   7  10 0.00
Thu 09/10 19Z 17.27 2726  60   3  11 0.00
Thu 09/10 20Z 16.55 2726  60   2  11 0.00
Thu 09/10 21Z 11.53 2826  62   3  11 0.00
Thu 09/10 22Z 3.22 2825  71   3  10 0.00
Thu 09/10 23Z 1.68 2924  79   4   9 0.00
Fri 09/11 00Z 1.21 3023  87   5   8 0.00
Fri 09/11 01Z 0.84 3023  93   4   7 0.01
Fri 09/11 02Z 0.60 3022  96   5   7 0.01
Fri 09/11 03Z 0.59 3024  94   3   6 0.01
Fri 09/11 04Z 0.59 3026  90   3   5 0.01
Fri 09/11 05Z 0.60 3027  87   2   4 0.00
Fri 09/11 06Z 0.51 3027  83   1   5 0.00
Fri 09/11 07Z 0.45 3126  80   1   5 0.00
Fri 09/11 08Z 0.40 3126  76   3   5 0.00
Fri 09/11 09Z 0.34 3125  72   3   6 0.00
Fri 09/11 10Z 0.32 3124  67   3   6 0.00
Fri 09/11 11Z 0.31 3124  64   2   6 0.00
Fri 09/11 12Z 0.28 3124  59   3   6 0.00
Fri 09/11 13Z 0.29 3123  55   2   6 0.00
Fri 09/11 14Z 0.29 3123  49   4   6 0.00
Fri 09/11 15Z 0.29 3122  48   5   6 0.00
Fri 09/11 16Z 0.32 3122  50   5   6 0.00
Fri 09/11 17Z 0.33 3120  53   6   6 0.00
Fri 09/11 18Z 0.35 3118  56   9   6 0.00
Fri 09/11 19Z 0.42 3116  58  14   6 0.00
Fri 09/11 20Z 0.54 3016  62  19   6 0.00
Fri 09/11 21Z 0.56 2915  61  23   6 0.00
Fri 09/11 22Z 0.53 2915  58  32   7 0.00
Fri 09/11 23Z 0.50 2916  53  44   8 0.00
Sat 09/12 00Z 0.42 3017  48  49   8 0.00
Sat 09/12 01Z 0.30 3117  44  47   9 0.00
Sat 09/12 02Z 0.22 3216  41  42  10 0.00
Sat 09/12 03Z 0.16 3214  40  44  10 0.00
Sat 09/12 04Z 0.13 3212  40  44  11 0.00
Sat 09/12 05Z 0.13 3210  40  46  11 0.00

Run total areal avg QPF for the Central_Greens is: 2.06 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