NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260715_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)
=== ===== === ==== ==== === === === ====
Wed 07/15 18Z 5.67 3023  76  29  13 0.00
Wed 07/15 19Z 11.49 3025  71  30  13 0.00
Wed 07/15 20Z 14.23 2927  63  43  13 0.00
Wed 07/15 21Z 12.95 3027  61  43  13 0.01
Wed 07/15 22Z 5.16 3028  61  41  13 0.03
Wed 07/15 23Z 1.86 3027  63  36  13 0.01
Thu 07/16 00Z 1.50 3027  65  33  13 0.00
Thu 07/16 01Z 1.62 3027  67  36  13 0.00
Thu 07/16 02Z 1.71 3127  68  41  13 0.00
Thu 07/16 03Z 1.96 3126  70  40  12 0.00
Thu 07/16 04Z 1.42 3125  70  44  12 0.00
Thu 07/16 05Z 1.14 3124  69  45  12 0.00
Thu 07/16 06Z 1.09 3024  69  42  12 0.00
Thu 07/16 07Z 0.93 3024  71  37  12 0.00
Thu 07/16 08Z 0.77 3124  71  40  12 0.00
Thu 07/16 09Z 0.68 3022  71  34  12 0.00
Thu 07/16 10Z 0.64 3021  70  40  12 0.00
Thu 07/16 11Z 0.62 2921  70  37  12 0.00
Thu 07/16 12Z 0.64 2921  71  39  11 0.00
Thu 07/16 13Z 0.71 2821  72  43  11 0.00
Thu 07/16 14Z 0.93 2821  72  43  11 0.00
Thu 07/16 15Z 2.37 2722  76  48  11 0.00
Thu 07/16 16Z 8.57 2723  79  55  11 0.00
Thu 07/16 17Z 6.92 2726  79  62  12 0.02
Thu 07/16 18Z 8.67 2725  74  41  12 0.00
Thu 07/16 19Z 10.81 2828  75  68  12 0.05
Thu 07/16 20Z 4.24 3029  76  65  11 0.07
Thu 07/16 21Z 0.71 3230  73  53  10 0.05
Thu 07/16 22Z 0.63 3230  73  28  10 0.03
Thu 07/16 23Z 0.74 3129  76  13   9 0.00
Fri 07/17 00Z 0.87 3128  77  10   8 0.00
Fri 07/17 01Z 1.41 3129  74  14   7 0.00
Fri 07/17 02Z 1.22 3132  68  18   7 0.00
Fri 07/17 03Z 1.42 3233  71  32   6 0.00
Fri 07/17 04Z 1.46 3233  74  35   6 0.00
Fri 07/17 05Z 1.48 3233  76  39   5 0.00
Fri 07/17 06Z 1.56 3233  77  47   5 0.00
Fri 07/17 07Z 1.37 3232  78  44   5 0.00
Fri 07/17 08Z 0.74 3230  77  33   5 0.00
Fri 07/17 09Z 0.51 3228  75  27   6 0.00
Fri 07/17 10Z 0.43 3227  74  22   6 0.00
Fri 07/17 11Z 0.38 3225  73  17   7 0.00
Fri 07/17 12Z 0.32 3223  67  16   7 0.00
Fri 07/17 13Z 0.31 3222  59  14   7 0.00
Fri 07/17 14Z 0.30 3320  53  13   8 0.00
Fri 07/17 15Z 0.29 3318  52  13   8 0.00
Fri 07/17 16Z 0.33 3316  54  13   8 0.00
Fri 07/17 17Z 0.53 3214  54  14   8 0.00
Fri 07/17 18Z 1.65 3113  53  17   8 0.00
Fri 07/17 19Z 2.49 3113  53  14   8 0.00
Fri 07/17 20Z 3.43 2912  57  11   9 0.00
Fri 07/17 21Z 2.90 2912  59  10   9 0.00
Fri 07/17 22Z 1.22 2812  60   7   9 0.00
Fri 07/17 23Z 0.84 2713  59   7  10 0.00
Sat 07/18 00Z 0.78 2714  58   7  10 0.00
Sat 07/18 01Z 0.77 2714  57   9  10 0.00
Sat 07/18 02Z 0.75 2714  54  11  10 0.00
Sat 07/18 03Z 0.66 2713  52  10  10 0.00
Sat 07/18 04Z 0.57 2612  50  10  11 0.00
Sat 07/18 05Z 0.53 2612  49  11  11 0.00

Run total areal avg QPF for the greens is: 0.27 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