NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260515_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 05/15 18Z 0.43 0806  98  69   3 0.00
Fri 05/15 19Z 0.43 1007  96  73   4 0.01
Fri 05/15 20Z 0.24 1106  96  76   4 0.01
Fri 05/15 21Z 0.14 1404  93  81   5 0.01
Fri 05/15 22Z 0.08 2002  90  85   5 0.01
Fri 05/15 23Z 0.10 2602  86  79   6 0.00
Sat 05/16 00Z 0.13 2603  83  66   6 0.00
Sat 05/16 01Z 0.22 2606  83  53   6 0.00
Sat 05/16 02Z 0.25 2708  83  45   6 0.00
Sat 05/16 03Z 0.32 2710  86  55   6 0.00
Sat 05/16 04Z 0.37 2612  90  67   6 0.00
Sat 05/16 05Z 0.36 2511  90  63   6 0.00
Sat 05/16 06Z 0.43 2614  94  52   6 0.01
Sat 05/16 07Z 0.43 2714  92  44   6 0.01
Sat 05/16 08Z 0.46 2715  84  31   6 0.00
Sat 05/16 09Z 0.51 2716  79  13   6 0.00
Sat 05/16 10Z 0.59 2719  79   8   5 0.00
Sat 05/16 11Z 0.61 2819  77   6   5 0.00
Sat 05/16 12Z 0.54 2716  74  22   5 0.00
Sat 05/16 13Z 0.54 2615  73  52   5 0.00
Sat 05/16 14Z 0.70 2517  71  40   5 0.00
Sat 05/16 15Z 0.94 2419  67  45   6 0.00
Sat 05/16 16Z 0.90 2418  52  54   7 0.00
Sat 05/16 17Z 1.23 2415  55  40   8 0.00
Sat 05/16 18Z 1.83 2315  64  38   8 0.00
Sat 05/16 19Z 3.03 2216  74  19   8 0.00
Sat 05/16 20Z 2.71 2118  75  10   8 0.00
Sat 05/16 21Z 1.94 2121  77   9   9 0.00
Sat 05/16 22Z 1.24 2123  73  11   9 0.00
Sat 05/16 23Z 0.91 2125  70  35  10 0.00
Sun 05/17 00Z 1.10 2230  74  92  10 0.00
Sun 05/17 01Z 1.21 2334  72  82  10 0.00
Sun 05/17 02Z 1.53 2337  75  79  10 0.00
Sun 05/17 03Z 1.61 2436  83  75  10 0.00
Sun 05/17 04Z 1.42 2534  87  64  10 0.01
Sun 05/17 05Z 1.19 2633  93  41  10 0.03
Sun 05/17 06Z 0.99 2730  93  40   9 0.02
Sun 05/17 07Z 0.89 2829  85  17   9 0.01
Sun 05/17 08Z 0.79 2929  74   6   9 0.00
Sun 05/17 09Z 0.77 2930  77   7   8 0.00
Sun 05/17 10Z 0.68 2932  58  24   8 0.00
Sun 05/17 11Z 0.68 3034  62  24   8 0.00
Sun 05/17 12Z 0.70 3033  66  31   8 0.00
Sun 05/17 13Z 0.74 3032  69  61   8 0.00
Sun 05/17 14Z 0.83 3030  74  55   7 0.00
Sun 05/17 15Z 1.31 3026  80  59   6 0.00
Sun 05/17 16Z 7.40 2923  84  45   6 0.00
Sun 05/17 17Z 9.37 2921  85  36   6 0.00
Sun 05/17 18Z 7.41 2921  86  30   6 0.00
Sun 05/17 19Z 6.27 2920  86  27   6 0.00
Sun 05/17 20Z 2.52 2920  87  27   6 0.00
Sun 05/17 21Z 1.88 3020  87  27   5 0.00
Sun 05/17 22Z 1.26 3020  86  27   5 0.00
Sun 05/17 23Z 0.62 3019  83  20   6 0.00
Mon 05/18 00Z 0.44 3119  80  11   6 0.00
Mon 05/18 01Z 0.34 3120  76   5   6 0.00
Mon 05/18 02Z 0.29 3219  75   2   6 0.00
Mon 05/18 03Z 0.26 3219  72   1   6 0.00
Mon 05/18 04Z 0.18 3217  65   2   7 0.00
Mon 05/18 05Z 0.14 3214  59   3   7 0.00

Run total areal avg QPF for the Central_Greens is: 0.13 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