NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260508_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 05/08 00Z 0.60 2913  61  36   0 0.00
Fri 05/08 01Z 0.79 2915  59  43   0 0.00
Fri 05/08 02Z 1.01 2916  58  33  -1 0.00
Fri 05/08 03Z 1.21 2917  58  35  -1 0.00
Fri 05/08 04Z 1.14 2918  63  45  -1 0.00
Fri 05/08 05Z 0.94 2919  66  51  -2 0.00
Fri 05/08 06Z 0.85 2920  67  45  -2 0.00
Fri 05/08 07Z 0.79 2921  66  41  -2 0.00
Fri 05/08 08Z 0.74 2921  69  49  -2 0.00
Fri 05/08 09Z 0.67 3020  70  57  -3 0.00
Fri 05/08 10Z 0.61 3019  68  63  -3 0.00
Fri 05/08 11Z 0.61 2917  69  66  -3 0.00
Fri 05/08 12Z 0.92 2915  68  71  -3 0.00
Fri 05/08 13Z 4.26 2812  66  77  -3 0.00
Fri 05/08 14Z 6.95 2811  64  74  -3 0.00
Fri 05/08 15Z 7.06 2710  64  69  -2 0.00
Fri 05/08 16Z 7.25 2610  64  64  -1 0.00
Fri 05/08 17Z 7.49 2510  63  71  -1 0.00
Fri 05/08 18Z 6.78 2511  68  82  -1 0.00
Fri 05/08 19Z 5.86 2613  74  87  -1 0.00
Fri 05/08 20Z 5.22 2613  77  83  -1 0.01
Fri 05/08 21Z 5.95 2712  72  74  -1 0.00
Fri 05/08 22Z 5.12 2812  69  64   0 0.00
Fri 05/08 23Z 2.84 2812  69  59  -1 0.00
Sat 05/09 00Z 1.11 2812  69  39  -1 0.00
Sat 05/09 01Z 1.28 2814  69  33  -1 0.00
Sat 05/09 02Z 1.22 2914  70  34  -1 0.00
Sat 05/09 03Z 1.24 2814  67  23  -2 0.00
Sat 05/09 04Z 0.92 2814  66  20  -2 0.00
Sat 05/09 05Z 0.66 2813  63  24  -2 0.00
Sat 05/09 06Z 0.56 2812  63  21  -2 0.00
Sat 05/09 07Z 0.51 2811  63  14  -2 0.00
Sat 05/09 08Z 0.45 2809  62  12  -2 0.00
Sat 05/09 09Z 0.42 2708  60   9  -1 0.00
Sat 05/09 10Z 0.34 2506  60   6  -1 0.00
Sat 05/09 11Z 0.26 2206  58   6  -1 0.00
Sat 05/09 12Z 0.27 2008  55   9  -1 0.00
Sat 05/09 13Z 0.37 1811  53  12  -1 0.00
Sat 05/09 14Z 0.49 1712  51  27   0 0.00
Sat 05/09 15Z 0.74 1714  55  52  -1 0.00
Sat 05/09 16Z 0.28 1714  72  71  -1 0.00
Sat 05/09 17Z 0.08 1716  90  94   0 0.04
Sat 05/09 18Z 0.03 1719  96  95   0 0.05
Sat 05/09 19Z 0.06 1722  97  96   0 0.04
Sat 05/09 20Z 0.10 1822  97  95   1 0.03
Sat 05/09 21Z 0.14 1821  98  91   1 0.02
Sat 05/09 22Z 0.17 1822  98  76   2 0.02
Sat 05/09 23Z 0.24 1922  98  66   2 0.02
Sun 05/10 00Z 0.30 2023  98  36   3 0.02
Sun 05/10 01Z 0.36 2121  98  39   3 0.02
Sun 05/10 02Z 0.43 2121  98  59   3 0.01
Sun 05/10 03Z 0.50 2123  97  74   4 0.01
Sun 05/10 04Z 0.56 2225  94  72   5 0.01
Sun 05/10 05Z 0.58 2227  88  74   5 0.01
Sun 05/10 06Z 0.81 2330  95  90   5 0.01
Sun 05/10 07Z 0.90 2329  95  91   4 0.02
Sun 05/10 08Z 0.96 2427  94  81   3 0.05
Sun 05/10 09Z 0.89 2525  92  72   3 0.02
Sun 05/10 10Z 0.79 2524  77  68   3 0.01
Sun 05/10 11Z 0.68 2623  56  42   3 0.00

Run total areal avg QPF for the Central_Greens is: 0.42 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