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_0600
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 06Z 0.53 2612  58  40   0 0.00
Sat 05/09 07Z 0.59 2612  55  35   0 0.00
Sat 05/09 08Z 0.52 2610  53  35   0 0.00
Sat 05/09 09Z 0.39 2508  49  34   0 0.00
Sat 05/09 10Z 0.36 2308  49  39   0 0.00
Sat 05/09 11Z 0.31 2010  51  38   0 0.00
Sat 05/09 12Z 0.31 1913  60  35   0 0.00
Sat 05/09 13Z 0.40 1812  70  34   0 0.00
Sat 05/09 14Z 0.32 1611  76  46   0 0.00
Sat 05/09 15Z 0.61 1612  82  66   1 0.00
Sat 05/09 16Z 0.53 1615  89  82   0 0.00
Sat 05/09 17Z 0.22 1618  94  89   0 0.02
Sat 05/09 18Z 0.16 1520  96  88   1 0.05
Sat 05/09 19Z 0.11 1620  97  85   1 0.04
Sat 05/09 20Z 0.08 1719  97  85   2 0.04
Sat 05/09 21Z 0.06 1717  98  85   3 0.02
Sat 05/09 22Z 0.11 1816  98  89   3 0.01
Sat 05/09 23Z 0.16 1817  97  80   3 0.01
Sun 05/10 00Z 0.22 1919  98  58   3 0.01
Sun 05/10 01Z 0.35 2021  98  44   3 0.01
Sun 05/10 02Z 0.43 2023  98  25   3 0.01
Sun 05/10 03Z 0.45 2023  95  18   4 0.01
Sun 05/10 04Z 0.54 2125  93  21   4 0.01
Sun 05/10 05Z 0.44 2124  86  21   5 0.01
Sun 05/10 06Z 0.46 2126  83  32   6 0.01
Sun 05/10 07Z 0.63 2229  88  60   5 0.01
Sun 05/10 08Z 0.68 2327  88  83   6 0.00
Sun 05/10 09Z 0.71 2327  90  90   6 0.00
Sun 05/10 10Z 0.77 2426  95  86   5 0.02
Sun 05/10 11Z 0.77 2524  94  66   4 0.01
Sun 05/10 12Z 0.81 2621  97  74   3 0.02
Sun 05/10 13Z 0.92 2619  94  67   2 0.03
Sun 05/10 14Z 0.89 2619  83  36   1 0.02
Sun 05/10 15Z 3.04 2519  81  13   1 0.00
Sun 05/10 16Z 5.67 2517  78  11   1 0.00
Sun 05/10 17Z 11.29 2516  64  15   1 0.00
Sun 05/10 18Z 12.07 2516  52  17   2 0.00
Sun 05/10 19Z 12.12 2516  44  17   2 0.00
Sun 05/10 20Z 12.05 2616  43  19   2 0.00
Sun 05/10 21Z 12.59 2617  43  22   2 0.00
Sun 05/10 22Z 12.02 2618  45  20   2 0.00
Sun 05/10 23Z 7.61 2720  47  22   1 0.00
Mon 05/11 00Z 2.51 2723  48  19   0 0.00
Mon 05/11 01Z 1.74 2723  45  20   0 0.00
Mon 05/11 02Z 1.38 2822  47  22  -1 0.00
Mon 05/11 03Z 1.15 2920  59  19  -2 0.00
Mon 05/11 04Z 0.88 2920  71  21  -2 0.00
Mon 05/11 05Z 0.78 2921  76  21  -2 0.00
Mon 05/11 06Z 0.69 3019  77  19  -3 0.00
Mon 05/11 07Z 0.58 3017  74  16  -3 0.00
Mon 05/11 08Z 0.54 3016  75  18  -3 0.00
Mon 05/11 09Z 0.49 3015  72  17  -3 0.00
Mon 05/11 10Z 0.50 2915  69  18  -3 0.00
Mon 05/11 11Z 0.55 2915  68  18  -3 0.00
Mon 05/11 12Z 0.70 2816  61  16  -3 0.00
Mon 05/11 13Z 2.76 2916  59  16  -4 0.00
Mon 05/11 14Z 7.65 2814  62  21  -3 0.00
Mon 05/11 15Z 9.02 2813  61  23  -3 0.00
Mon 05/11 16Z 8.18 2812  57  22  -2 0.00
Mon 05/11 17Z 7.37 2811  55  23  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.37 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