NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260515_1200
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)
=== ===== === ==== ==== === === === ====
Fri 05/15 12Z 0.31 0508  99  86   3 0.00
Fri 05/15 13Z 0.35 0509  99  82   3 0.01
Fri 05/15 14Z 0.42 0610  98  82   3 0.01
Fri 05/15 15Z 0.53 0712  98  90   3 0.00
Fri 05/15 16Z 0.56 0712  97  95   3 0.01
Fri 05/15 17Z 0.50 0611  97  93   3 0.01
Fri 05/15 18Z 0.42 0708  96  84   3 0.01
Fri 05/15 19Z 0.28 0605  95  77   3 0.00
Fri 05/15 20Z 0.25 0604  94  73   4 0.00
Fri 05/15 21Z 0.18 0603  94  74   4 0.00
Fri 05/15 22Z 0.11 0802  93  74   5 0.00
Fri 05/15 23Z 0.10 2101  93  79   5 0.01
Sat 05/16 00Z 0.12 2402  91  80   5 0.01
Sat 05/16 01Z 0.14 2603  87  74   5 0.00
Sat 05/16 02Z 0.12 2603  83  62   6 0.00
Sat 05/16 03Z 0.23 2607  85  59   5 0.00
Sat 05/16 04Z 0.30 2609  89  54   5 0.00
Sat 05/16 05Z 0.31 2510  89  55   6 0.00
Sat 05/16 06Z 0.33 2611  88  56   6 0.00
Sat 05/16 07Z 0.39 2614  88  53   6 0.00
Sat 05/16 08Z 0.38 2614  85  44   6 0.00
Sat 05/16 09Z 0.40 2816  82  37   6 0.00
Sat 05/16 10Z 0.43 2917  82  19   6 0.00
Sat 05/16 11Z 0.47 2817  78   9   5 0.00
Sat 05/16 12Z 0.54 2818  73  10   5 0.00
Sat 05/16 13Z 0.59 2717  66  28   5 0.00
Sat 05/16 14Z 0.65 2615  64  42   6 0.00
Sat 05/16 15Z 0.87 2616  61  57   6 0.00
Sat 05/16 16Z 1.09 2515  53  56   7 0.00
Sat 05/16 17Z 1.51 2413  51  34   7 0.00
Sat 05/16 18Z 2.28 2314  62  18   8 0.00
Sat 05/16 19Z 1.72 2316  67  12   8 0.00
Sat 05/16 20Z 1.53 2219  73  10   8 0.00
Sat 05/16 21Z 0.92 2219  74  10   9 0.00
Sat 05/16 22Z 0.80 2221  70   8  10 0.00
Sat 05/16 23Z 0.91 2125  71  28  10 0.00
Sun 05/17 00Z 0.99 2229  72  84  10 0.00
Sun 05/17 01Z 0.99 2232  74  83  10 0.00
Sun 05/17 02Z 1.14 2235  77  91  10 0.00
Sun 05/17 03Z 1.29 2336  82  87  10 0.01
Sun 05/17 04Z 1.23 2436  89  90  10 0.02
Sun 05/17 05Z 1.00 2534  94  87  11 0.05
Sun 05/17 06Z 0.90 2631  96  70  11 0.06
Sun 05/17 07Z 0.91 2731  96  30  10 0.04
Sun 05/17 08Z 0.84 2827  91   9   9 0.04
Sun 05/17 09Z 0.71 2928  68   4   9 0.03
Sun 05/17 10Z 0.67 3031  55   4   9 0.01
Sun 05/17 11Z 0.84 2936  47  15   9 0.00
Sun 05/17 12Z 0.91 2940  51  29   9 0.00
Sun 05/17 13Z 0.90 2937  62  34   8 0.00
Sun 05/17 14Z 0.92 2932  70  35   7 0.00
Sun 05/17 15Z 1.21 2928  75  35   7 0.00
Sun 05/17 16Z 4.87 3024  79  29   6 0.00
Sun 05/17 17Z 7.05 3022  81  25   6 0.00
Sun 05/17 18Z 7.08 3022  82  25   6 0.00
Sun 05/17 19Z 6.79 3021  83  23   6 0.00
Sun 05/17 20Z 3.85 3021  83  25   5 0.00
Sun 05/17 21Z 1.49 3021  82  24   5 0.00
Sun 05/17 22Z 0.76 3020  82  23   5 0.00
Sun 05/17 23Z 0.51 3120  81  19   6 0.00

Run total areal avg QPF for the Central_Greens is: 0.33 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