NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261008_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)
=== ===== === ==== ==== === === === ====
Thu 10/08 12Z 0.59 2519  86  94   6 0.00
Thu 10/08 13Z 0.74 2621  87  92   5 0.01
Thu 10/08 14Z 0.85 2723  84  70   5 0.01
Thu 10/08 15Z 1.06 2722  80  61   4 0.00
Thu 10/08 16Z 3.32 2721  88  61   4 0.00
Thu 10/08 17Z 8.05 2720  86  64   4 0.00
Thu 10/08 18Z 7.80 2721  82  67   4 0.04
Thu 10/08 19Z 8.37 2722  78  60   4 0.02
Thu 10/08 20Z 10.61 2621  80  49   4 0.00
Thu 10/08 21Z 5.07 2622  79  47   4 0.00
Thu 10/08 22Z 2.18 2623  85  49   4 0.00
Thu 10/08 23Z 1.51 2624  86  50   3 0.00
Fri 10/09 00Z 1.34 2725  85  54   3 0.00
Fri 10/09 01Z 1.13 2726  87  54   3 0.00
Fri 10/09 02Z 0.92 2725  84  52   3 0.00
Fri 10/09 03Z 0.86 2725  79  48   3 0.00
Fri 10/09 04Z 0.89 2725  87  56   3 0.00
Fri 10/09 05Z 0.83 2824  87  39   3 0.00
Fri 10/09 06Z 0.77 2824  82  32   3 0.00
Fri 10/09 07Z 0.80 2825  78  27   2 0.00
Fri 10/09 08Z 0.86 2727  80  26   2 0.00
Fri 10/09 09Z 0.89 2728  83  29   2 0.00
Fri 10/09 10Z 0.99 2729  87  38   2 0.00
Fri 10/09 11Z 1.00 2728  87  33   1 0.00
Fri 10/09 12Z 1.09 2728  89  24   1 0.00
Fri 10/09 13Z 1.21 2728  92  24   0 0.01
Fri 10/09 14Z 1.16 2827  93  24   0 0.01
Fri 10/09 15Z 1.28 2924  92  22   0 0.01
Fri 10/09 16Z 4.72 2822  90  29   0 0.00
Fri 10/09 17Z 5.14 2821  90  41   0 0.00
Fri 10/09 18Z 4.22 2720  87  58   0 0.00
Fri 10/09 19Z 3.20 2720  86  53   0 0.00
Fri 10/09 20Z 1.84 2620  87  52   0 0.01
Fri 10/09 21Z 2.13 2623  87  68   1 0.01
Fri 10/09 22Z 2.11 2724  85  85   1 0.01
Fri 10/09 23Z 1.92 2728  87  93   1 0.02
Sat 10/10 00Z 1.16 2727  91  86   1 0.05
Sat 10/10 01Z 1.02 2827  94  67   1 0.02
Sat 10/10 02Z 0.92 2927  92  62   0 0.04
Sat 10/10 03Z 0.83 3027  89  21   0 0.01
Sat 10/10 04Z 0.60 3127  84  13   0 0.00
Sat 10/10 05Z 0.48 3127  76  11   0 0.00
Sat 10/10 06Z 0.44 3127  75   8   0 0.00
Sat 10/10 07Z 0.40 3127  73   6   0 0.01
Sat 10/10 08Z 0.37 3126  73   7   0 0.01
Sat 10/10 09Z 0.31 3125  71   7   0 0.00
Sat 10/10 10Z 0.26 3224  64   8   0 0.00
Sat 10/10 11Z 0.24 3224  57   9   0 0.00
Sat 10/10 12Z 0.22 3223  51  10   0 0.00
Sat 10/10 13Z 0.21 3220  49  14   0 0.00
Sat 10/10 14Z 0.21 3118  48  20   0 0.00
Sat 10/10 15Z 0.23 3116  46  21   0 0.00
Sat 10/10 16Z 0.21 3115  42  25   1 0.00
Sat 10/10 17Z 0.20 3115  39  36   2 0.00
Sat 10/10 18Z 0.24 3115  36  47   2 0.00
Sat 10/10 19Z 0.20 3116  31  53   4 0.00
Sat 10/10 20Z 0.20 3116  32  52   4 0.00
Sat 10/10 21Z 0.19 3114  33  59   4 0.00
Sat 10/10 22Z 0.17 3112  33  61   5 0.00
Sat 10/10 23Z 0.17 3011  33  51   5 0.00

Run total areal avg QPF for the Central_Greens is: 0.30 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