Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260701_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 07/01 18Z 0.77 2606  85  44  19 0.00
Wed 07/01 19Z 0.55 2507  83  38  20 0.00
Wed 07/01 20Z 0.40 2307  80  34  20 0.00
Wed 07/01 21Z 0.47 2309  81  32  20 0.00
Wed 07/01 22Z 0.62 2313  87  42  20 0.00
Wed 07/01 23Z 0.65 2418  89  51  20 0.00
Thu 07/02 00Z 0.73 2522  81  55  20 0.09
Thu 07/02 01Z 0.81 2523  86  56  20 0.02
Thu 07/02 02Z 0.80 2623  90  61  20 0.05
Thu 07/02 03Z 0.69 2623  82  49  20 0.05
Thu 07/02 04Z 0.56 2720  68  49  22 0.00
Thu 07/02 05Z 0.67 2625  61  56  21 0.00
Thu 07/02 06Z 0.72 2727  66  57  21 0.00
Thu 07/02 07Z 0.69 2827  70  52  20 0.00
Thu 07/02 08Z 0.59 2925  69  49  20 0.00
Thu 07/02 09Z 0.52 2923  66  49  20 0.00
Thu 07/02 10Z 0.51 2923  66  37  20 0.00
Thu 07/02 11Z 0.51 2924  61  44  20 0.00
Thu 07/02 12Z 0.52 2923  63  55  19 0.00
Thu 07/02 13Z 0.54 2923  79  57  19 0.00
Thu 07/02 14Z 0.55 2922  84  56  18 0.01
Thu 07/02 15Z 0.50 2920  83  57  19 0.01
Thu 07/02 16Z 0.48 2917  80  59  19 0.00
Thu 07/02 17Z 0.51 2815  79  64  20 0.00
Thu 07/02 18Z 0.58 2715  80  67  20 0.00
Thu 07/02 19Z 0.66 2616  81  66  20 0.00
Thu 07/02 20Z 0.83 2517  88  52  20 0.00
Thu 07/02 21Z 1.04 2519  90  40  19 0.00
Thu 07/02 22Z 1.20 2520  87  40  19 0.01
Thu 07/02 23Z 1.46 2625  83  51  20 0.02
Fri 07/03 00Z 1.18 2626  87  64  19 0.01
Fri 07/03 01Z 1.08 2627  84  56  20 0.01
Fri 07/03 02Z 1.07 2729  86  64  19 0.01
Fri 07/03 03Z 1.00 2729  85  61  19 0.00
Fri 07/03 04Z 0.95 2828  87  56  19 0.00
Fri 07/03 05Z 0.87 2928  81  54  19 0.01
Fri 07/03 06Z 0.78 2927  79  42  18 0.01
Fri 07/03 07Z 0.71 2927  81  43  18 0.01
Fri 07/03 08Z 0.60 3025  81  38  18 0.02
Fri 07/03 09Z 0.54 3024  79  36  18 0.02
Fri 07/03 10Z 0.49 3022  80  27  18 0.01
Fri 07/03 11Z 0.45 3020  77  23  18 0.01
Fri 07/03 12Z 0.41 2918  76  21  18 0.01
Fri 07/03 13Z 0.42 2917  74  17  18 0.01
Fri 07/03 14Z 0.48 2918  73  17  18 0.01
Fri 07/03 15Z 0.58 2819  75  15  18 0.00
Fri 07/03 16Z 0.69 2820  74  14  17 0.00
Fri 07/03 17Z 0.88 2821  75  14  17 0.00
Fri 07/03 18Z 2.24 2821  78  17  17 0.00
Fri 07/03 19Z 7.93 2821  75  21  17 0.00
Fri 07/03 20Z 9.79 2822  64  18  17 0.00
Fri 07/03 21Z 8.55 2822  62  22  17 0.00
Fri 07/03 22Z 4.09 2823  64  24  17 0.00
Fri 07/03 23Z 2.36 2823  66  25  17 0.00
Sat 07/04 00Z 1.77 2824  67  26  17 0.00
Sat 07/04 01Z 2.06 2926  71  22  16 0.01
Sat 07/04 02Z 1.45 2926  81  24  16 0.00
Sat 07/04 03Z 1.19 2925  83  24  16 0.01
Sat 07/04 04Z 1.04 3025  83  24  15 0.00
Sat 07/04 05Z 0.91 3023  81  23  15 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