NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260507_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)
=== ===== === ==== ==== === === === ====
Thu 05/07 06Z 0.34 2912  86  81   0 0.00
Thu 05/07 07Z 0.44 2914  91  78   0 0.01
Thu 05/07 08Z 0.47 2814  94  60   0 0.01
Thu 05/07 09Z 0.61 2817  93  63   0 0.01
Thu 05/07 10Z 0.73 2820  96  60  -1 0.01
Thu 05/07 11Z 0.66 2720  82  53  -1 0.01
Thu 05/07 12Z 0.64 2821  63  32  -2 0.00
Thu 05/07 13Z 0.82 2821  66  19  -2 0.00
Thu 05/07 14Z 2.53 2818  76  26  -3 0.00
Thu 05/07 15Z 9.62 2816  82  31  -3 0.00
Thu 05/07 16Z 10.92 2816  77  40  -2 0.00
Thu 05/07 17Z 11.30 2817  68  35  -1 0.00
Thu 05/07 18Z 11.45 2817  62  38  -1 0.00
Thu 05/07 19Z 11.29 2816  55  34   0 0.00
Thu 05/07 20Z 11.08 2816  49  32   0 0.00
Thu 05/07 21Z 10.64 2816  47  32   0 0.00
Thu 05/07 22Z 9.36 2815  47  28   0 0.00
Thu 05/07 23Z 5.67 2816  50  22   0 0.00
Fri 05/08 00Z 1.63 2917  52  16   0 0.00
Fri 05/08 01Z 1.16 2918  56  15   0 0.00
Fri 05/08 02Z 1.00 2917  61  19  -1 0.00
Fri 05/08 03Z 1.03 2917  66  30  -1 0.00
Fri 05/08 04Z 1.13 2817  69  60  -2 0.00
Fri 05/08 05Z 1.02 2818  71  55  -2 0.00
Fri 05/08 06Z 0.93 2819  71  61  -2 0.00
Fri 05/08 07Z 0.90 2820  67  60  -2 0.00
Fri 05/08 08Z 0.82 2821  60  51  -2 0.00
Fri 05/08 09Z 0.77 2820  64  52  -2 0.00
Fri 05/08 10Z 0.71 2819  66  63  -2 0.00
Fri 05/08 11Z 0.69 2817  68  73  -2 0.00
Fri 05/08 12Z 0.84 2814  67  77  -2 0.00
Fri 05/08 13Z 3.80 2711  67  86  -2 0.00
Fri 05/08 14Z 5.83 2609  68  84  -2 0.00
Fri 05/08 15Z 4.79 2507  67  67  -1 0.00
Fri 05/08 16Z 5.11 2507  68  83  -1 0.00
Fri 05/08 17Z 5.94 2409  74  77  -1 0.00
Fri 05/08 18Z 5.03 2411  83  82   0 0.00
Fri 05/08 19Z 1.17 2515  92  77  -1 0.04
Fri 05/08 20Z 1.11 2613  90  68  -1 0.01
Fri 05/08 21Z 1.68 2812  86  51   0 0.00
Fri 05/08 22Z 1.64 2812  86  46  -1 0.00
Fri 05/08 23Z 0.90 2812  84  45  -1 0.01
Sat 05/09 00Z 0.74 2913  79  18  -1 0.00
Sat 05/09 01Z 0.93 2914  77   8  -1 0.00
Sat 05/09 02Z 1.06 2914  72   8  -1 0.00
Sat 05/09 03Z 1.14 2914  66  19  -2 0.00
Sat 05/09 04Z 1.01 2814  65  25  -2 0.00
Sat 05/09 05Z 0.78 2814  60  21  -2 0.00
Sat 05/09 06Z 0.59 2813  58  15  -2 0.00
Sat 05/09 07Z 0.53 2913  63  16  -2 0.00
Sat 05/09 08Z 0.48 2911  66  27  -2 0.00
Sat 05/09 09Z 0.44 2810  65  28  -2 0.00
Sat 05/09 10Z 0.42 2709  69  18  -2 0.00
Sat 05/09 11Z 0.43 2608  76  16  -2 0.00
Sat 05/09 12Z 0.53 2608  78  12  -2 0.00
Sat 05/09 13Z 1.91 2407  75  13  -2 0.00
Sat 05/09 14Z 3.05 2207  72  13  -1 0.00
Sat 05/09 15Z 4.06 2109  67  19   0 0.00
Sat 05/09 16Z 3.64 2010  63  19   0 0.00
Sat 05/09 17Z 3.07 1910  60  21   1 0.00

Run total areal avg QPF for the Central_Greens is: 0.11 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