NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260515_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 05/15 12Z 0.37 0710  98  90   3 0.00
Fri 05/15 13Z 0.37 0710  96  88   3 0.01
Fri 05/15 14Z 0.41 0811  95  88   3 0.01
Fri 05/15 15Z 0.48 0812  96  91   3 0.00
Fri 05/15 16Z 0.49 0811  96  95   3 0.01
Fri 05/15 17Z 0.43 0809  96  93   3 0.01
Fri 05/15 18Z 0.33 0806  95  87   4 0.01
Fri 05/15 19Z 0.21 0603  94  81   4 0.00
Fri 05/15 20Z 0.17 0502  93  77   4 0.01
Fri 05/15 21Z 0.13 0402  94  77   5 0.01
Fri 05/15 22Z 0.10 0501  94  77   5 0.02
Fri 05/15 23Z 0.13 2702  95  81   5 0.02
Sat 05/16 00Z 0.18 2703  92  81   5 0.01
Sat 05/16 01Z 0.18 2705  89  76   5 0.00
Sat 05/16 02Z 0.18 2605  87  65   6 0.00
Sat 05/16 03Z 0.30 2608  89  62   5 0.01
Sat 05/16 04Z 0.35 2610  92  51   5 0.01
Sat 05/16 05Z 0.34 2511  91  53   6 0.02
Sat 05/16 06Z 0.35 2512  90  57   6 0.01
Sat 05/16 07Z 0.40 2614  90  57   6 0.00
Sat 05/16 08Z 0.40 2615  86  44   6 0.00
Sat 05/16 09Z 0.48 2816  84  33   6 0.00
Sat 05/16 10Z 0.57 2818  81  16   5 0.00
Sat 05/16 11Z 0.61 2818  77   9   5 0.00
Sat 05/16 12Z 0.67 2818  71  16   5 0.00
Sat 05/16 13Z 0.67 2718  65  35   5 0.00
Sat 05/16 14Z 0.70 2616  65  50   6 0.00
Sat 05/16 15Z 0.95 2616  62  61   6 0.00
Sat 05/16 16Z 1.11 2515  53  56   7 0.00
Sat 05/16 17Z 1.61 2413  50  39   7 0.00
Sat 05/16 18Z 1.92 2313  60  17   8 0.00
Sat 05/16 19Z 1.92 2315  65  11   8 0.00
Sat 05/16 20Z 1.60 2217  70  11   9 0.00
Sat 05/16 21Z 1.04 2219  72  11   9 0.00
Sat 05/16 22Z 0.69 2121  70  10  10 0.00
Sat 05/16 23Z 0.75 2125  72  37  10 0.00
Sun 05/17 00Z 0.86 2229  73  86  10 0.00
Sun 05/17 01Z 0.86 2232  74  87  10 0.00
Sun 05/17 02Z 1.01 2235  78  91  10 0.01
Sun 05/17 03Z 1.14 2337  83  87  10 0.01
Sun 05/17 04Z 1.12 2436  90  88  10 0.02
Sun 05/17 05Z 1.01 2533  95  78  10 0.04
Sun 05/17 06Z 0.98 2631  97  57  10 0.05
Sun 05/17 07Z 0.96 2730  96  22   9 0.04
Sun 05/17 08Z 0.90 2828  89   8   9 0.03
Sun 05/17 09Z 0.78 2929  68   6   9 0.02
Sun 05/17 10Z 0.81 2932  53   7   9 0.01
Sun 05/17 11Z 1.04 2936  51  15   8 0.00
Sun 05/17 12Z 1.12 2938  61  32   7 0.00
Sun 05/17 13Z 0.99 2935  72  33   7 0.00
Sun 05/17 14Z 0.92 2930  78  34   7 0.00
Sun 05/17 15Z 1.16 3026  82  34   6 0.00
Sun 05/17 16Z 3.93 3024  85  30   5 0.00
Sun 05/17 17Z 5.57 3022  86  24   5 0.01
Sun 05/17 18Z 5.68 3023  86  25   5 0.00
Sun 05/17 19Z 5.57 3022  87  22   5 0.00
Sun 05/17 20Z 3.25 3022  87  23   5 0.01
Sun 05/17 21Z 1.48 3022  86  19   5 0.01
Sun 05/17 22Z 0.96 3021  85  17   4 0.00
Sun 05/17 23Z 0.86 3120  83  13   5 0.00

Run total areal avg QPF for the greens is: 0.43 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