Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260714_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)
=== ===== === ==== ==== === === === ====
Tue 07/14 12Z 0.61 2823  69  35  18 0.00
Tue 07/14 13Z 0.74 2726  69  34  18 0.00
Tue 07/14 14Z 0.75 2727  66  37  19 0.00
Tue 07/14 15Z 0.70 2726  68  35  20 0.00
Tue 07/14 16Z 0.70 2726  69  30  20 0.00
Tue 07/14 17Z 0.79 2726  75  24  20 0.00
Tue 07/14 18Z 0.92 2626  76  23  20 0.00
Tue 07/14 19Z 1.31 2624  79  19  20 0.00
Tue 07/14 20Z 4.51 2624  79  19  20 0.00
Tue 07/14 21Z 4.72 2625  79  21  20 0.00
Tue 07/14 22Z 3.89 2627  81  31  20 0.00
Tue 07/14 23Z 2.15 2629  84  37  20 0.00
Wed 07/15 00Z 1.59 2731  85  40  20 0.00
Wed 07/15 01Z 1.38 2732  87  48  20 0.00
Wed 07/15 02Z 1.21 2733  87  46  20 0.00
Wed 07/15 03Z 1.11 2835  88  51  20 0.00
Wed 07/15 04Z 1.03 2834  89  57  20 0.00
Wed 07/15 05Z 1.00 2934  93  69  19 0.04
Wed 07/15 06Z 0.82 3030  92  60  18 0.04
Wed 07/15 07Z 0.74 3027  94  79  17 0.02
Wed 07/15 08Z 0.58 3124  93  86  17 0.02
Wed 07/15 09Z 0.41 3221  93  89  16 0.04
Wed 07/15 10Z 0.35 3323  83  76  15 0.08
Wed 07/15 11Z 0.29 3421  74  56  14 0.01
Wed 07/15 12Z 0.40 3319  68  29  14 0.00
Wed 07/15 13Z 0.54 3219  63  24  14 0.00
Wed 07/15 14Z 0.82 3119  58  26  13 0.00
Wed 07/15 15Z 3.01 3019  61  28  13 0.00
Wed 07/15 16Z 7.59 2919  69  30  13 0.00
Wed 07/15 17Z 10.68 2922  71  44  13 0.00
Wed 07/15 18Z 12.67 2924  63  50  13 0.00
Wed 07/15 19Z 14.81 3025  62  49  13 0.00
Wed 07/15 20Z 11.10 3025  65  64  13 0.01
Wed 07/15 21Z 6.65 3027  66  60  13 0.02
Wed 07/15 22Z 3.06 3026  71  57  12 0.00
Wed 07/15 23Z 1.83 3126  69  50  12 0.00
Thu 07/16 00Z 1.68 3127  65  45  12 0.00
Thu 07/16 01Z 1.51 3128  63  40  12 0.00
Thu 07/16 02Z 1.43 3128  64  38  12 0.00
Thu 07/16 03Z 1.18 3127  65  29  12 0.00
Thu 07/16 04Z 0.93 3225  64  26  12 0.00
Thu 07/16 05Z 0.88 3223  64  28  12 0.00
Thu 07/16 06Z 0.91 3121  66  30  11 0.00
Thu 07/16 07Z 0.94 3121  68  34  11 0.00
Thu 07/16 08Z 0.91 3121  71  35  11 0.00
Thu 07/16 09Z 0.85 3121  72  42  11 0.00
Thu 07/16 10Z 0.80 3021  72  37  11 0.00
Thu 07/16 11Z 0.78 3021  71  44  11 0.00
Thu 07/16 12Z 0.78 2921  72  40  11 0.00
Thu 07/16 13Z 0.85 2921  72  39  11 0.00
Thu 07/16 14Z 1.18 2821  74  33  11 0.00
Thu 07/16 15Z 2.46 2721  77  35  11 0.00
Thu 07/16 16Z 9.38 2622  78  36  12 0.00
Thu 07/16 17Z 11.93 2622  77  33  12 0.00
Thu 07/16 18Z 11.15 2623  72  52  13 0.00
Thu 07/16 19Z 12.55 2625  68  54  13 0.00
Thu 07/16 20Z 13.50 2627  69  56  13 0.01
Thu 07/16 21Z 7.60 2828  70  62  13 0.13
Thu 07/16 22Z 2.49 3127  69  64  13 0.08
Thu 07/16 23Z 0.74 3226  73  61  11 0.07

Run total areal avg QPF for the greens is: 0.57 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