NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260509_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)
=== ===== === ==== ==== === === === ====
Sat 05/09 12Z 0.17 1812  62  32   0 0.00
Sat 05/09 13Z 0.18 1813  65  34   0 0.00
Sat 05/09 14Z 0.20 1712  74  56   0 0.00
Sat 05/09 15Z 0.39 1612  84  71   0 0.01
Sat 05/09 16Z 0.26 1714  93  79   0 0.03
Sat 05/09 17Z 0.06 1614  95  89   0 0.05
Sat 05/09 18Z 0.06 1615  96  97   1 0.06
Sat 05/09 19Z 0.08 1617  97  96   1 0.07
Sat 05/09 20Z 0.10 1719  98  94   2 0.04
Sat 05/09 21Z 0.15 1817  97  92   2 0.02
Sat 05/09 22Z 0.07 1717  96  93   3 0.02
Sat 05/09 23Z 0.12 1817  97  80   3 0.04
Sun 05/10 00Z 0.18 1918  98  58   4 0.02
Sun 05/10 01Z 0.24 2016  98  46   4 0.01
Sun 05/10 02Z 0.27 2017  98  23   4 0.01
Sun 05/10 03Z 0.30 2117  96  20   4 0.01
Sun 05/10 04Z 0.37 2119  95  23   4 0.01
Sun 05/10 05Z 0.42 2122  91  42   5 0.01
Sun 05/10 06Z 0.34 2120  77  52   7 0.01
Sun 05/10 07Z 0.35 2121  71  63   7 0.01
Sun 05/10 08Z 0.39 2222  66  67   8 0.01
Sun 05/10 09Z 0.42 2223  69  73   7 0.01
Sun 05/10 10Z 0.54 2225  79  86   7 0.01
Sun 05/10 11Z 0.58 2322  89  91   6 0.01
Sun 05/10 12Z 0.71 2325  94  94   5 0.06
Sun 05/10 13Z 0.65 2421  92  94   4 0.04
Sun 05/10 14Z 0.69 2518  87  69   4 0.01
Sun 05/10 15Z 0.88 2518  83  60   3 0.00
Sun 05/10 16Z 3.75 2518  88  25   3 0.00
Sun 05/10 17Z 4.33 2417  89  11   3 0.01
Sun 05/10 18Z 5.90 2517  87  14   3 0.01
Sun 05/10 19Z 9.42 2516  71  18   3 0.00
Sun 05/10 20Z 12.15 2517  56  19   3 0.00
Sun 05/10 21Z 12.59 2617  47  19   3 0.00
Sun 05/10 22Z 11.92 2618  43  21   3 0.00
Sun 05/10 23Z 3.98 2719  43  22   2 0.00
Mon 05/11 00Z 1.99 2721  44  21   2 0.00
Mon 05/11 01Z 1.40 2822  42  21   1 0.00
Mon 05/11 02Z 1.01 2920  46  22   0 0.00
Mon 05/11 03Z 0.77 2919  55  25   0 0.00
Mon 05/11 04Z 0.60 3018  64  25   0 0.00
Mon 05/11 05Z 0.48 3017  75  23  -1 0.00
Mon 05/11 06Z 0.42 3116  83  21  -2 0.00
Mon 05/11 07Z 0.40 3115  84  20  -2 0.00
Mon 05/11 08Z 0.33 3114  85  17  -2 0.00
Mon 05/11 09Z 0.30 3113  84  15  -3 0.00
Mon 05/11 10Z 0.32 3113  84  17  -3 0.00
Mon 05/11 11Z 0.36 3112  86  20  -3 0.00
Mon 05/11 12Z 0.41 3011  88  24  -3 0.00
Mon 05/11 13Z 1.16 3010  86  26  -3 0.00
Mon 05/11 14Z 2.61 2909  79  27  -3 0.00
Mon 05/11 15Z 3.74 2909  70  27  -2 0.00
Mon 05/11 16Z 4.64 2908  72  31  -2 0.00
Mon 05/11 17Z 3.95 2809  79  40  -2 0.00
Mon 05/11 18Z 4.00 2809  77  44  -1 0.00
Mon 05/11 19Z 4.34 2909  71  47  -1 0.00
Mon 05/11 20Z 3.45 3009  69  45  -1 0.00
Mon 05/11 21Z 3.06 3109  69  43  -1 0.00
Mon 05/11 22Z 2.23 3111  72  48  -1 0.00
Mon 05/11 23Z 0.92 3212  76  52  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.60 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