NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261009_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 10/09 00Z 1.24 2722  72  78   4 0.00
Fri 10/09 01Z 1.22 2723  79  82   4 0.00
Fri 10/09 02Z 1.11 2826  79  81   4 0.01
Fri 10/09 03Z 1.09 2829  80  62   3 0.00
Fri 10/09 04Z 1.05 2828  84  40   3 0.00
Fri 10/09 05Z 0.98 2827  87  30   3 0.00
Fri 10/09 06Z 0.88 2826  83  31   3 0.00
Fri 10/09 07Z 0.82 2824  81  35   3 0.00
Fri 10/09 08Z 0.85 2726  80  38   2 0.00
Fri 10/09 09Z 0.79 2726  76  39   3 0.00
Fri 10/09 10Z 0.80 2727  74  49   3 0.00
Fri 10/09 11Z 0.91 2728  79  53   2 0.00
Fri 10/09 12Z 1.04 2729  89  56   2 0.00
Fri 10/09 13Z 1.05 2729  89  48   2 0.01
Fri 10/09 14Z 1.00 2828  90  36   1 0.01
Fri 10/09 15Z 1.02 2825  90  30   1 0.00
Fri 10/09 16Z 1.22 2722  93  38   1 0.00
Fri 10/09 17Z 1.08 2722  88  66   1 0.01
Fri 10/09 18Z 1.44 2722  87  72   1 0.00
Fri 10/09 19Z 4.54 2721  84  69   1 0.00
Fri 10/09 20Z 4.01 2621  83  64   1 0.00
Fri 10/09 21Z 1.94 2622  78  45   2 0.01
Fri 10/09 22Z 2.10 2626  74  56   2 0.00
Fri 10/09 23Z 2.16 2532  85  61   2 0.01
Sat 10/10 00Z 1.91 2833  86  58   2 0.05
Sat 10/10 01Z 1.12 3031  79  48   0 0.02
Sat 10/10 02Z 0.84 3131  72  17   0 0.00
Sat 10/10 03Z 0.73 3130  75  10   0 0.00
Sat 10/10 04Z 0.60 3127  75   8   0 0.01
Sat 10/10 05Z 0.50 3127  72   9   0 0.01
Sat 10/10 06Z 0.45 3126  73   8   0 0.01
Sat 10/10 07Z 0.40 3126  72   7   0 0.00
Sat 10/10 08Z 0.41 3125  72   8   0 0.00
Sat 10/10 09Z 0.39 3125  67   9   0 0.00
Sat 10/10 10Z 0.36 3125  64   7   0 0.00
Sat 10/10 11Z 0.34 3126  58   6   0 0.00
Sat 10/10 12Z 0.32 3126  52   5   0 0.00
Sat 10/10 13Z 0.28 3225  45   6   0 0.00
Sat 10/10 14Z 0.24 3224  41   6   0 0.00
Sat 10/10 15Z 0.20 3222  39   6   1 0.00
Sat 10/10 16Z 0.17 3320  40   8   0 0.00
Sat 10/10 17Z 0.18 3218  40  14   1 0.00
Sat 10/10 18Z 0.14 3317  35  21   1 0.00
Sat 10/10 19Z 0.14 3317  31  26   2 0.00
Sat 10/10 20Z 0.12 3315  30  31   3 0.00
Sat 10/10 21Z 0.11 3314  29  47   3 0.00
Sat 10/10 22Z 0.12 3213  28  55   4 0.00
Sat 10/10 23Z 0.10 3211  29  55   5 0.00
Sun 10/11 00Z 0.09 3208  27  61   5 0.00
Sun 10/11 01Z 0.10 3107  27  70   6 0.00
Sun 10/11 02Z 0.12 2805  27  70   6 0.00
Sun 10/11 03Z 0.13 2706  24  60   7 0.00
Sun 10/11 04Z 0.11 2505  23  50   7 0.00
Sun 10/11 05Z 0.12 2405  22  48   7 0.00
Sun 10/11 06Z 0.13 2306  21  43   8 0.00
Sun 10/11 07Z 0.14 2206  20  39   8 0.00
Sun 10/11 08Z 0.17 2209  21  40   8 0.00
Sun 10/11 09Z 0.19 2211  20  41   8 0.00
Sun 10/11 10Z 0.22 2212  18  49   9 0.00
Sun 10/11 11Z 0.24 2214  17  64   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.16 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