NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260525_1800
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)
=== ===== === ==== ==== === === === ====
Mon 05/25 18Z 0.48 2914  97  14   9 0.00
Mon 05/25 19Z 0.54 2916  98   1   9 0.01
Mon 05/25 20Z 0.69 2819  97   4   8 0.02
Mon 05/25 21Z 0.81 2821  95   5   9 0.02
Mon 05/25 22Z 0.72 2922  88  10   9 0.01
Mon 05/25 23Z 0.59 3021  79   5   9 0.01
Tue 05/26 00Z 0.56 3022  75   4   9 0.01
Tue 05/26 01Z 0.55 3123  68   3   9 0.00
Tue 05/26 02Z 0.53 3124  66   4   9 0.00
Tue 05/26 03Z 0.48 3222  66   5   9 0.00
Tue 05/26 04Z 0.44 3221  66   7   9 0.00
Tue 05/26 05Z 0.54 3120  73  11   9 0.00
Tue 05/26 06Z 0.65 3121  79   9   9 0.01
Tue 05/26 07Z 0.63 3022  82  16   9 0.00
Tue 05/26 08Z 0.63 3023  85  13   9 0.00
Tue 05/26 09Z 0.59 3022  83  15   9 0.01
Tue 05/26 10Z 0.54 3022  87  15  10 0.01
Tue 05/26 11Z 0.47 3120  92  17  10 0.01
Tue 05/26 12Z 0.41 3119  91  18  10 0.01
Tue 05/26 13Z 0.34 3116  85  16  11 0.00
Tue 05/26 14Z 0.36 3015  83  15  11 0.00
Tue 05/26 15Z 0.43 2914  75  20  11 0.00
Tue 05/26 16Z 0.55 2913  80  18  11 0.00
Tue 05/26 17Z 0.84 2813  78  34  11 0.00
Tue 05/26 18Z 1.25 2612  80  42  11 0.00
Tue 05/26 19Z 2.29 2513  79  28  12 0.00
Tue 05/26 20Z 3.06 2414  76  26  12 0.00
Tue 05/26 21Z 2.54 2416  76  31  12 0.00
Tue 05/26 22Z 1.78 2319  77  36  12 0.00
Tue 05/26 23Z 1.20 2322  77  32  12 0.00
Wed 05/27 00Z 1.14 2425  68  44  12 0.00
Wed 05/27 01Z 1.27 2427  64  47  12 0.00
Wed 05/27 02Z 1.24 2428  65  47  12 0.00
Wed 05/27 03Z 1.12 2529  65  48  13 0.00
Wed 05/27 04Z 1.11 2630  64  52  12 0.00
Wed 05/27 05Z 1.17 2630  64  59  12 0.00
Wed 05/27 06Z 1.14 2729  64  65  12 0.00
Wed 05/27 07Z 1.10 2729  68  61  12 0.01
Wed 05/27 08Z 0.92 2826  73  62  12 0.01
Wed 05/27 09Z 0.75 2823  78  59  11 0.00
Wed 05/27 10Z 0.63 2920  84  54  11 0.00
Wed 05/27 11Z 0.54 2818  88  49  11 0.00
Wed 05/27 12Z 0.52 2917  90  47  10 0.01
Wed 05/27 13Z 0.48 2815  91  43  10 0.00
Wed 05/27 14Z 0.48 2814  89  37  10 0.00
Wed 05/27 15Z 0.66 2913  85  38  10 0.00
Wed 05/27 16Z 0.85 2912  83  30  10 0.00
Wed 05/27 17Z 1.29 3012  84  25  10 0.00
Wed 05/27 18Z 1.54 3013  82  21   9 0.01
Wed 05/27 19Z 2.80 3113  80  24   9 0.00
Wed 05/27 20Z 3.27 3113  77  25   9 0.00
Wed 05/27 21Z 2.62 3112  76  24   9 0.00
Wed 05/27 22Z 2.13 3113  77  27   9 0.00
Wed 05/27 23Z 1.29 3115  76  28   8 0.00
Thu 05/28 00Z 1.03 3217  77  27   8 0.00
Thu 05/28 01Z 0.75 3218  78  22   7 0.00
Thu 05/28 02Z 0.66 3319  80  18   7 0.00
Thu 05/28 03Z 0.55 3319  82  26   6 0.00
Thu 05/28 04Z 0.35 3319  82  33   6 0.00
Thu 05/28 05Z 0.28 3318  82  37   5 0.00

Run total areal avg QPF for the greens is: 0.17 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