Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260703_0600
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)
=== ===== === ==== ==== === === === ====
Fri 07/03 06Z 0.50 3122  87  56  18 0.00
Fri 07/03 07Z 0.57 3024  86  62  18 0.00
Fri 07/03 08Z 0.59 3023  85  63  17 0.00
Fri 07/03 09Z 0.60 3023  84  58  17 0.00
Fri 07/03 10Z 0.55 3023  77  48  17 0.00
Fri 07/03 11Z 0.53 3024  70  34  18 0.00
Fri 07/03 12Z 0.52 3023  67  29  18 0.00
Fri 07/03 13Z 0.57 2922  68  24  18 0.00
Fri 07/03 14Z 0.62 2921  70  22  17 0.00
Fri 07/03 15Z 0.67 2920  72  23  17 0.00
Fri 07/03 16Z 0.79 2917  75  29  17 0.00
Fri 07/03 17Z 2.04 2915  77  35  17 0.00
Fri 07/03 18Z 6.24 2714  78  45  17 0.00
Fri 07/03 19Z 8.86 2714  74  49  17 0.00
Fri 07/03 20Z 8.90 2716  69  62  18 0.00
Fri 07/03 21Z 5.55 2816  69  69  18 0.00
Fri 07/03 22Z 2.56 2716  71  73  18 0.00
Fri 07/03 23Z 1.21 2816  73  68  18 0.00
Sat 07/04 00Z 0.93 2915  70  66  18 0.00
Sat 07/04 01Z 0.85 2917  74  63  17 0.00
Sat 07/04 02Z 0.79 2917  74  66  17 0.00
Sat 07/04 03Z 0.66 2918  73  65  17 0.00
Sat 07/04 04Z 0.54 3020  74  68  17 0.00
Sat 07/04 05Z 0.47 3121  78  63  17 0.00
Sat 07/04 06Z 0.41 3121  79  63  17 0.00
Sat 07/04 07Z 0.40 3122  82  58  16 0.00
Sat 07/04 08Z 0.39 3121  88  59  16 0.00
Sat 07/04 09Z 0.42 3121  90  57  16 0.00
Sat 07/04 10Z 0.40 3121  89  60  16 0.00
Sat 07/04 11Z 0.42 3121  91  63  15 0.00
Sat 07/04 12Z 0.41 3120  95  63  15 0.00
Sat 07/04 13Z 0.39 3119  96  61  14 0.01
Sat 07/04 14Z 0.37 3119  96  57  14 0.00
Sat 07/04 15Z 0.39 3119  93  54  13 0.00
Sat 07/04 16Z 0.45 3119  88  65  13 0.02
Sat 07/04 17Z 0.64 3018  83  52  13 0.02
Sat 07/04 18Z 0.85 3117  79  44  13 0.00
Sat 07/04 19Z 0.92 3117  77  31  13 0.00
Sat 07/04 20Z 0.86 3116  72  23  13 0.00
Sat 07/04 21Z 0.82 3117  68  18  13 0.00
Sat 07/04 22Z 0.56 3116  64  14  13 0.00
Sat 07/04 23Z 0.35 3215  61   9  13 0.00
Sun 07/05 00Z 0.22 3316  60   7  12 0.00
Sun 07/05 01Z 0.17 3316  61   6  12 0.00
Sun 07/05 02Z 0.10 3415  60   7  12 0.00
Sun 07/05 03Z 0.05 3414  58   6  12 0.00
Sun 07/05 04Z 0.04 3510  57   6  12 0.00
Sun 07/05 05Z 0.04 3509  58   7  12 0.00
Sun 07/05 06Z 0.09 0008  58   7  12 0.00
Sun 07/05 07Z 0.11 0106  58   6  12 0.00
Sun 07/05 08Z 0.11 0203  59   7  12 0.00
Sun 07/05 09Z 0.09 0402  59   8  12 0.00
Sun 07/05 10Z 0.07 0901  59   7  12 0.00
Sun 07/05 11Z 0.06 1302  58   7  12 0.00
Sun 07/05 12Z 0.03 1603  57  10  12 0.00
Sun 07/05 13Z 0.03 1603  58  16  12 0.00
Sun 07/05 14Z 0.05 1402  62  15  12 0.00
Sun 07/05 15Z 0.12 1503  69   9  11 0.00
Sun 07/05 16Z 0.22 1502  74   7  11 0.00
Sun 07/05 17Z 0.27 1401  76   7  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.05 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