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_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 08/28 12Z 0.27 2607  91  86  12 0.00
Fri 08/28 13Z 0.33 2609  91  77  12 0.00
Fri 08/28 14Z 0.38 2510  90  66  12 0.00
Fri 08/28 15Z 0.44 2510  90  59  12 0.00
Fri 08/28 16Z 0.47 2610  89  53  12 0.00
Fri 08/28 17Z 0.50 2511  86  49  12 0.00
Fri 08/28 18Z 0.49 2813  86  41  12 0.11
Fri 08/28 19Z 0.54 2815  89  21  12 0.07
Fri 08/28 20Z 0.45 3017  93  46  10 0.05
Fri 08/28 21Z 0.41 3017  88  16  10 0.01
Fri 08/28 22Z 0.39 3117  89  19   9 0.00
Fri 08/28 23Z 0.39 3018  81  23   9 0.00
Sat 08/29 00Z 0.34 3119  85  20   8 0.00
Sat 08/29 01Z 0.30 3219  90  12   8 0.00
Sat 08/29 02Z 0.27 3219  87   5   7 0.00
Sat 08/29 03Z 0.24 3219  81   4   7 0.00
Sat 08/29 04Z 0.21 3220  75   4   7 0.00
Sat 08/29 05Z 0.19 3220  73   5   7 0.00
Sat 08/29 06Z 0.17 3320  69   5   7 0.00
Sat 08/29 07Z 0.15 3320  65   5   7 0.00
Sat 08/29 08Z 0.15 3320  64   5   7 0.00
Sat 08/29 09Z 0.14 3319  66   5   7 0.00
Sat 08/29 10Z 0.14 3318  67   7   7 0.00
Sat 08/29 11Z 0.14 3316  67   9   7 0.00
Sat 08/29 12Z 0.19 3214  69   9   7 0.00
Sat 08/29 13Z 0.24 3113  67  11   7 0.00
Sat 08/29 14Z 0.29 3012  66  13   8 0.00
Sat 08/29 15Z 0.30 2910  63  10   8 0.00
Sat 08/29 16Z 0.32 2910  59   9   8 0.00
Sat 08/29 17Z 0.40 2908  60   9   8 0.00
Sat 08/29 18Z 0.61 2908  64  28   9 0.00
Sat 08/29 19Z 0.75 2708  67  45   9 0.00
Sat 08/29 20Z 0.92 2611  73  44   9 0.00
Sat 08/29 21Z 0.85 2612  78  26   9 0.00
Sat 08/29 22Z 0.75 2513  79  10   9 0.00
Sat 08/29 23Z 0.74 2515  79  24  10 0.00
Sun 08/30 00Z 0.91 2519  78  16  10 0.00
Sun 08/30 01Z 1.03 2522  77  12  10 0.00
Sun 08/30 02Z 1.18 2624  76  19  10 0.00
Sun 08/30 03Z 1.23 2626  76  25  10 0.00
Sun 08/30 04Z 1.14 2626  78  35  10 0.00
Sun 08/30 05Z 1.27 2628  78  28  10 0.00
Sun 08/30 06Z 1.39 2629  76  31  10 0.00
Sun 08/30 07Z 1.31 2628  74  36  11 0.00
Sun 08/30 08Z 1.29 2728  74  29  11 0.00
Sun 08/30 09Z 1.17 2727  74  28  11 0.00
Sun 08/30 10Z 1.08 2726  73  40  11 0.00
Sun 08/30 11Z 1.02 2724  75  32  11 0.00
Sun 08/30 12Z 0.89 2722  73  31  11 0.00
Sun 08/30 13Z 0.82 2721  73  38  11 0.00
Sun 08/30 14Z 0.82 2720  72  42  11 0.00
Sun 08/30 15Z 0.78 2718  75  43  11 0.00
Sun 08/30 16Z 0.87 2616  71  38  11 0.00
Sun 08/30 17Z 1.11 2613  67  33  12 0.00
Sun 08/30 18Z 1.76 2512  68  30  12 0.00
Sun 08/30 19Z 2.26 2412  73  30  12 0.00
Sun 08/30 20Z 1.62 2412  75  32  12 0.00
Sun 08/30 21Z 0.90 2314  79  31  12 0.00
Sun 08/30 22Z 0.77 2416  77  46  12 0.00
Sun 08/30 23Z 0.81 2519  82  64  12 0.01

Run total areal avg QPF for the Central_Greens is: 0.25 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