NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260308_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 03/08 00Z 0.61 2339  76  90  12 0.00
Sun 03/08 01Z 0.70 2344  80  82  12 0.02
Sun 03/08 02Z 0.73 2344  88  89  11 0.01
Sun 03/08 03Z 0.74 2442  95  90  10 0.09
Sun 03/08 04Z 0.76 2441  95  92   9 0.14
Sun 03/08 05Z 0.75 2538  94  86   9 0.05
Sun 03/08 06Z 0.78 2539  94  86   9 0.01
Sun 03/08 07Z 0.76 2438  96  92   9 0.02
Sun 03/08 08Z 0.84 2539  94  89   8 0.04
Sun 03/08 09Z 0.93 2540  96  72   7 0.03
Sun 03/08 10Z 0.93 2638  94  47   7 0.02
Sun 03/08 11Z 1.03 2636  92  44   5 0.01
Sun 03/08 12Z 1.22 2636  94  28   4 0.01
Sun 03/08 13Z 1.21 2635  93   9   3 0.01
Sun 03/08 14Z 1.12 2632  93   9   1 0.01
Sun 03/08 15Z 0.98 2629  91  10   1 0.01
Sun 03/08 16Z 0.93 2727  91  11   0 0.01
Sun 03/08 17Z 0.90 2625  91  12   0 0.01
Sun 03/08 18Z 0.89 2625  90  11   0 0.01
Sun 03/08 19Z 1.00 2625  90   7   0 0.00
Sun 03/08 20Z 1.00 2525  88   8   0 0.00
Sun 03/08 21Z 1.04 2527  88  12  -1 0.00
Sun 03/08 22Z 0.87 2529  83  17   0 0.00
Sun 03/08 23Z 0.86 2532  74  35   0 0.00
Mon 03/09 00Z 0.76 2535  65  71   1 0.00
Mon 03/09 01Z 0.91 2638  70  39   0 0.00
Mon 03/09 02Z 1.21 2640  84  21  -2 0.00
Mon 03/09 03Z 1.36 2641  91  15  -2 0.00
Mon 03/09 04Z 1.34 2639  91  10  -2 0.00
Mon 03/09 05Z 1.17 2739  84   8  -1 0.01
Mon 03/09 06Z 1.01 2737  76  10   0 0.00
Mon 03/09 07Z 0.96 2736  69  22   0 0.00
Mon 03/09 08Z 0.89 2735  63  43   0 0.00
Mon 03/09 09Z 0.78 2733  55  68   1 0.00
Mon 03/09 10Z 0.67 2630  49  77   3 0.00
Mon 03/09 11Z 0.68 2531  52  76   3 0.00
Mon 03/09 12Z 0.76 2533  54  74   3 0.00
Mon 03/09 13Z 0.75 2436  49  71   4 0.00
Mon 03/09 14Z 0.78 2440  50  67   6 0.00
Mon 03/09 15Z 0.87 2442  37  72   7 0.00
Mon 03/09 16Z 0.96 2443  34  65   7 0.00
Mon 03/09 17Z 0.99 2443  34  59   7 0.00
Mon 03/09 18Z 1.02 2442  35  55   7 0.00
Mon 03/09 19Z 1.02 2441  37  55   7 0.00
Mon 03/09 20Z 1.01 2439  39  53   7 0.00
Mon 03/09 21Z 1.00 2438  41  50   7 0.00
Mon 03/09 22Z 0.94 2437  43  50   7 0.00
Mon 03/09 23Z 0.91 2437  42  49   7 0.00
Tue 03/10 00Z 0.92 2437  41  45   7 0.00
Tue 03/10 01Z 0.98 2438  42  44   7 0.00
Tue 03/10 02Z 1.01 2438  43  45   7 0.00
Tue 03/10 03Z 0.93 2537  41  42   8 0.00
Tue 03/10 04Z 0.99 2537  40  45   7 0.00
Tue 03/10 05Z 1.04 2635  42  45   6 0.00
Tue 03/10 06Z 1.07 2634  45  43   6 0.00
Tue 03/10 07Z 1.08 2631  49  45   5 0.00
Tue 03/10 09Z 0.91 2727  53  47   5 0.00
Tue 03/10 10Z 0.73 2624  53  45   5 0.00

Run total areal avg QPF for the greens is: 0.52 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