Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260714_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 07/14 12Z 0.53 2822  70  35  18 0.00
Tue 07/14 13Z 0.64 2825  69  31  18 0.00
Tue 07/14 14Z 0.66 2726  67  35  19 0.00
Tue 07/14 15Z 0.62 2724  69  32  19 0.00
Tue 07/14 16Z 0.63 2725  70  29  20 0.00
Tue 07/14 17Z 0.70 2725  75  23  20 0.00
Tue 07/14 18Z 0.80 2626  75  18  21 0.00
Tue 07/14 19Z 1.01 2625  76  14  21 0.00
Tue 07/14 20Z 2.96 2526  77  15  20 0.00
Tue 07/14 21Z 4.04 2527  78  15  20 0.00
Tue 07/14 22Z 4.31 2628  82  16  20 0.00
Tue 07/14 23Z 2.34 2630  83  25  20 0.00
Wed 07/15 00Z 1.77 2731  83  34  20 0.00
Wed 07/15 01Z 1.50 2733  86  42  19 0.00
Wed 07/15 02Z 1.22 2733  87  39  20 0.00
Wed 07/15 03Z 1.04 2834  89  40  20 0.00
Wed 07/15 04Z 0.92 2833  89  50  20 0.00
Wed 07/15 05Z 0.88 2933  93  62  19 0.00
Wed 07/15 06Z 0.72 2930  94  55  19 0.01
Wed 07/15 07Z 0.68 3028  94  75  18 0.02
Wed 07/15 08Z 0.59 3025  95  83  17 0.02
Wed 07/15 09Z 0.46 3122  96  92  16 0.05
Wed 07/15 10Z 0.23 3323  92  91  16 0.12
Wed 07/15 11Z 0.07 3420  84  70  15 0.01
Wed 07/15 12Z 0.21 3319  75  36  14 0.00
Wed 07/15 13Z 0.38 3220  64  16  14 0.00
Wed 07/15 14Z 0.56 3120  54  18  14 0.00
Wed 07/15 15Z 1.14 3119  56  20  14 0.00
Wed 07/15 16Z 3.55 3017  67  24  13 0.00
Wed 07/15 17Z 6.67 2920  72  44  13 0.00
Wed 07/15 18Z 8.47 3022  61  47  13 0.00
Wed 07/15 19Z 11.97 3023  58  44  13 0.00
Wed 07/15 20Z 9.49 2923  64  66  13 0.01
Wed 07/15 21Z 3.91 3027  67  61  13 0.02
Wed 07/15 22Z 0.93 3126  75  56  13 0.00
Wed 07/15 23Z 0.93 3125  72  51  13 0.00
Thu 07/16 00Z 1.07 3125  68  48  12 0.00
Thu 07/16 01Z 0.99 3126  64  39  13 0.00
Thu 07/16 02Z 1.08 3127  65  39  12 0.00
Thu 07/16 03Z 0.89 3127  67  29  12 0.00
Thu 07/16 04Z 0.67 3225  65  26  12 0.00
Thu 07/16 05Z 0.63 3223  64  24  12 0.00
Thu 07/16 06Z 0.66 3121  66  25  12 0.00
Thu 07/16 07Z 0.70 3120  68  30  11 0.00
Thu 07/16 08Z 0.69 3120  70  30  11 0.00
Thu 07/16 09Z 0.63 3120  70  35  11 0.00
Thu 07/16 10Z 0.62 3120  71  36  11 0.00
Thu 07/16 11Z 0.60 3020  68  42  11 0.00
Thu 07/16 12Z 0.65 3020  69  40  11 0.00
Thu 07/16 13Z 0.77 2921  69  38  11 0.00
Thu 07/16 14Z 1.13 2821  71  32  12 0.00
Thu 07/16 15Z 2.60 2721  74  32  12 0.00
Thu 07/16 16Z 11.57 2621  75  28  12 0.00
Thu 07/16 17Z 13.65 2622  74  25  13 0.00
Thu 07/16 18Z 11.69 2623  71  37  13 0.00
Thu 07/16 19Z 11.70 2624  69  46  13 0.00
Thu 07/16 20Z 12.06 2627  69  42  13 0.00
Thu 07/16 21Z 10.16 2631  62  44  14 0.00
Thu 07/16 22Z 3.41 2924  73  62  14 0.02
Thu 07/16 23Z 0.75 3224  81  74  12 0.11

Run total areal avg QPF for the Central_Greens is: 0.39 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