Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260619_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)
=== ===== === ==== ==== === === === ====
Fri 06/19 12Z 1.07 2724  93  57   7 0.00
Fri 06/19 13Z 1.44 2627  94  51   7 0.00
Fri 06/19 14Z 2.06 2628  94  52   8 0.00
Fri 06/19 15Z 2.14 2627  95  53   8 0.01
Fri 06/19 16Z 2.85 2627  95  57   8 0.01
Fri 06/19 17Z 4.78 2627  93  64   8 0.01
Fri 06/19 18Z 8.76 2626  91  57   8 0.00
Fri 06/19 19Z 11.22 2726  87  46   9 0.00
Fri 06/19 20Z 15.28 2725  82  38   9 0.00
Fri 06/19 21Z 15.85 2625  75  34   9 0.00
Fri 06/19 22Z 13.17 2625  75  38   9 0.00
Fri 06/19 23Z 7.48 2627  78  46   9 0.00
Sat 06/20 00Z 2.40 2728  81  63   9 0.01
Sat 06/20 01Z 2.13 2728  85  68   8 0.01
Sat 06/20 02Z 1.76 2729  88  69   8 0.01
Sat 06/20 03Z 1.53 2729  89  68   7 0.01
Sat 06/20 04Z 1.32 2729  91  69   7 0.01
Sat 06/20 05Z 1.11 2829  93  74   7 0.01
Sat 06/20 06Z 0.95 2830  95  90   7 0.05
Sat 06/20 07Z 0.89 2830  97  91   7 0.08
Sat 06/20 08Z 0.81 2828  97  92   7 0.08
Sat 06/20 09Z 0.76 2928  97  87   7 0.06
Sat 06/20 10Z 0.76 2929  96  81   7 0.03
Sat 06/20 11Z 0.72 3029  97  77   7 0.02
Sat 06/20 12Z 0.70 3028  97  71   7 0.01
Sat 06/20 13Z 0.68 3025  95  69   7 0.01
Sat 06/20 14Z 0.79 3022  96  70   7 0.01
Sat 06/20 15Z 1.05 2920  97  67   7 0.01
Sat 06/20 16Z 1.09 2920  96  69   8 0.01
Sat 06/20 17Z 0.97 2922  96  72   8 0.03
Sat 06/20 18Z 1.49 2922  95  65   8 0.02
Sat 06/20 19Z 2.17 2921  93  61   8 0.01
Sat 06/20 20Z 1.97 2919  91  60   8 0.00
Sat 06/20 21Z 2.10 2918  90  58   9 0.00
Sat 06/20 22Z 1.43 2918  91  58   9 0.00
Sat 06/20 23Z 0.71 3017  93  59   9 0.00
Sun 06/21 00Z 0.49 3017  95  64   9 0.01
Sun 06/21 01Z 0.40 3117  95  60   9 0.01
Sun 06/21 02Z 0.37 3117  95  59   9 0.01
Sun 06/21 03Z 0.36 3116  96  54   9 0.01
Sun 06/21 04Z 0.32 3115  96  63   8 0.03
Sun 06/21 05Z 0.27 3114  95  72   8 0.05
Sun 06/21 06Z 0.24 3113  96  72   8 0.02
Sun 06/21 07Z 0.27 3112  96  77   8 0.02
Sun 06/21 08Z 0.25 3011  93  72   9 0.01
Sun 06/21 09Z 0.24 3010  92  65   9 0.00
Sun 06/21 10Z 0.25 2910  91  64   9 0.00
Sun 06/21 11Z 0.25 2909  91  65   9 0.00
Sun 06/21 12Z 0.23 2808  89  66   9 0.01
Sun 06/21 13Z 0.24 2708  90  65   9 0.00
Sun 06/21 14Z 0.27 2708  90  59   9 0.00
Sun 06/21 15Z 0.32 2709  90  61   9 0.00
Sun 06/21 16Z 0.40 2809  91  64   9 0.00
Sun 06/21 17Z 0.75 2908  91  69   9 0.00
Sun 06/21 18Z 1.16 2908  91  70   9 0.00
Sun 06/21 19Z 1.34 2908  91  73   9 0.00
Sun 06/21 20Z 0.97 2908  90  76  10 0.00
Sun 06/21 21Z 0.33 3008  80  77  10 0.05
Sun 06/21 22Z 0.26 3007  78  66  10 0.01
Sun 06/21 23Z 0.36 2808  79  65  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.76 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