NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260828_1800
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 08/28 18Z 0.78 2808  92  57  12 0.00
Fri 08/28 19Z 0.60 2908  90  35  12 0.01
Fri 08/28 20Z 0.42 3008  91  49  11 0.02
Fri 08/28 21Z 0.27 3112  94  55  11 0.03
Fri 08/28 22Z 0.22 3215  95  26  11 0.01
Fri 08/28 23Z 0.21 3215  94  23  10 0.00
Sat 08/29 00Z 0.24 3218  93  26   9 0.00
Sat 08/29 01Z 0.24 3219  86  11   9 0.00
Sat 08/29 02Z 0.19 3217  82   9   8 0.00
Sat 08/29 03Z 0.18 3216  79   2   8 0.00
Sat 08/29 04Z 0.16 3216  79   2   8 0.00
Sat 08/29 05Z 0.15 3316  78   3   8 0.00
Sat 08/29 06Z 0.13 3316  78   3   7 0.00
Sat 08/29 07Z 0.11 3315  73   4   7 0.00
Sat 08/29 08Z 0.11 3315  70   4   7 0.00
Sat 08/29 09Z 0.12 3316  66   5   7 0.00
Sat 08/29 10Z 0.11 3315  63   5   8 0.00
Sat 08/29 11Z 0.11 3315  61   5   8 0.00
Sat 08/29 12Z 0.11 3315  61   5   8 0.00
Sat 08/29 13Z 0.13 3314  61   7   8 0.00
Sat 08/29 14Z 0.12 3311  64  11   8 0.00
Sat 08/29 15Z 0.12 3207  64  17   8 0.00
Sat 08/29 16Z 0.18 3106  63  14   8 0.00
Sat 08/29 17Z 0.27 2905  61  19   9 0.00
Sat 08/29 18Z 0.38 2905  58  22   9 0.00
Sat 08/29 19Z 0.33 2806  56  33   9 0.00
Sat 08/29 20Z 0.30 2806  56  35  10 0.00
Sat 08/29 21Z 0.28 2606  56  22  10 0.00
Sat 08/29 22Z 0.36 2608  58  16  10 0.00
Sat 08/29 23Z 0.44 2511  62  23  10 0.00
Sun 08/30 00Z 0.50 2513  65  30  11 0.00
Sun 08/30 01Z 0.48 2514  64  22  11 0.00
Sun 08/30 02Z 0.55 2516  68  28  11 0.00
Sun 08/30 03Z 0.59 2617  68  33  11 0.00
Sun 08/30 04Z 0.63 2718  64  24  11 0.00
Sun 08/30 05Z 0.76 2721  61  29  11 0.00
Sun 08/30 06Z 0.75 2721  70  27  11 0.00
Sun 08/30 07Z 0.79 2822  74  31  11 0.00
Sun 08/30 08Z 0.80 2821  74  36  11 0.00
Sun 08/30 09Z 0.79 2720  73  39  11 0.00
Sun 08/30 10Z 0.81 2721  73  38  11 0.00
Sun 08/30 11Z 0.77 2719  70  33  11 0.00
Sun 08/30 12Z 0.78 2619  70  35  11 0.00
Sun 08/30 13Z 0.79 2619  68  37  11 0.00
Sun 08/30 14Z 0.82 2519  65  35  11 0.00
Sun 08/30 15Z 0.85 2520  63  37  11 0.00
Sun 08/30 16Z 0.90 2519  63  44  11 0.00
Sun 08/30 17Z 1.07 2518  64  48  12 0.00
Sun 08/30 18Z 1.21 2518  66  43  12 0.00
Sun 08/30 19Z 1.21 2518  70  84  11 0.00
Sun 08/30 20Z 1.38 2520  75  70  11 0.00
Sun 08/30 21Z 1.66 2422  77  82  10 0.00
Sun 08/30 22Z 1.26 2424  71  87  10 0.00
Sun 08/30 23Z 1.02 2523  72  89   9 0.00
Mon 08/31 00Z 0.86 2722  75  92   9 0.00
Mon 08/31 01Z 0.76 2823  85  92   9 0.00
Mon 08/31 02Z 0.75 2723  86  92   9 0.00
Mon 08/31 03Z 0.60 2821  89  91  10 0.00
Mon 08/31 04Z 0.52 2920  93  91  10 0.00
Mon 08/31 05Z 0.36 3019  93  90  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.07 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