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_0000
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 00Z 0.53 2120  92  80  13 0.00
Fri 08/28 01Z 0.60 2122  94  73  13 0.00
Fri 08/28 02Z 0.62 2224  94  75  14 0.01
Fri 08/28 03Z 0.63 2224  86  74  14 0.01
Fri 08/28 04Z 0.68 2422  88  63  14 0.01
Fri 08/28 05Z 0.64 2521  94  69  14 0.01
Fri 08/28 06Z 0.61 2519  92  61  13 0.02
Fri 08/28 07Z 0.53 2616  88  51  13 0.01
Fri 08/28 08Z 0.40 2613  86  51  13 0.00
Fri 08/28 09Z 0.32 2711  84  53  13 0.00
Fri 08/28 10Z 0.28 2810  86  54  12 0.00
Fri 08/28 11Z 0.24 2908  86  60  12 0.00
Fri 08/28 12Z 0.20 2907  86  61  12 0.00
Fri 08/28 13Z 0.18 2806  86  56  12 0.00
Fri 08/28 14Z 0.20 2706  86  39  12 0.00
Fri 08/28 15Z 0.23 2706  87  35  12 0.00
Fri 08/28 16Z 0.28 2807  87  35  11 0.00
Fri 08/28 17Z 0.32 2807  87  31  11 0.00
Fri 08/28 18Z 0.36 2807  87  33  11 0.00
Fri 08/28 19Z 0.38 2908  88  21  11 0.01
Fri 08/28 20Z 0.37 2909  91  36  12 0.02
Fri 08/28 21Z 0.23 3010  89  22  11 0.02
Fri 08/28 22Z 0.24 3010  86  21  11 0.00
Fri 08/28 23Z 0.24 3011  79  19  11 0.00
Sat 08/29 00Z 0.20 3112  73  19  11 0.00
Sat 08/29 01Z 0.17 3113  70  15  10 0.00
Sat 08/29 02Z 0.15 3213  67   8  10 0.00
Sat 08/29 03Z 0.15 3213  64   6  10 0.00
Sat 08/29 04Z 0.14 3214  61   6   9 0.00
Sat 08/29 05Z 0.13 3215  59   6   9 0.00
Sat 08/29 06Z 0.12 3214  58   7   9 0.00
Sat 08/29 07Z 0.12 3214  59   7   9 0.00
Sat 08/29 08Z 0.12 3212  57   9   9 0.00
Sat 08/29 09Z 0.13 3213  54  12   9 0.00
Sat 08/29 10Z 0.13 3214  52  14   9 0.00
Sat 08/29 11Z 0.13 3213  50  12   9 0.00
Sat 08/29 12Z 0.13 3213  51  11   9 0.00
Sat 08/29 13Z 0.13 3211  53  11   9 0.00
Sat 08/29 14Z 0.14 3108  57  22   8 0.00
Sat 08/29 15Z 0.18 3007  61  29   8 0.00
Sat 08/29 16Z 0.21 2906  61  24   8 0.00
Sat 08/29 17Z 0.32 2907  59  18   8 0.00
Sat 08/29 18Z 0.39 2908  58   8   9 0.00
Sat 08/29 19Z 0.36 2908  62  12   9 0.00
Sat 08/29 20Z 0.44 2808  70   9   9 0.00
Sat 08/29 21Z 0.55 2709  76  15   9 0.00
Sat 08/29 22Z 0.58 2610  81  16   9 0.00
Sat 08/29 23Z 0.62 2612  84   5   9 0.00
Sun 08/30 00Z 0.73 2615  86   5   9 0.00
Sun 08/30 01Z 0.90 2618  88   8   9 0.00
Sun 08/30 02Z 1.03 2618  88  13   9 0.00
Sun 08/30 03Z 0.92 2720  83  16   9 0.00
Sun 08/30 04Z 0.84 2821  79  17   9 0.00
Sun 08/30 05Z 0.91 2821  85  24   9 0.00
Sun 08/30 06Z 0.90 2721  86  25   9 0.00
Sun 08/30 07Z 1.03 2622  86  26   9 0.00
Sun 08/30 08Z 1.01 2623  88  28   9 0.00
Sun 08/30 09Z 1.03 2623  86  26  10 0.00
Sun 08/30 10Z 1.10 2624  85  27   9 0.00
Sun 08/30 11Z 1.02 2624  84  22  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.12 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