Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260309_0600
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)
=== ===== === ==== ==== === === === ====
Mon 03/09 06Z 0.98 2733  61  25   1 0.00
Mon 03/09 07Z 0.97 2733  55  30   1 0.00
Mon 03/09 08Z 0.94 2633  52  37   2 0.00
Mon 03/09 09Z 0.95 2631  53  39   2 0.00
Mon 03/09 10Z 0.91 2630  54  77   2 0.00
Mon 03/09 11Z 0.86 2531  53  62   3 0.00
Mon 03/09 12Z 0.85 2532  49  43   3 0.00
Mon 03/09 13Z 0.88 2434  44  51   4 0.00
Mon 03/09 14Z 0.88 2437  34  44   6 0.00
Mon 03/09 15Z 0.84 2437  29  40   7 0.00
Mon 03/09 16Z 0.80 2336  28  37   7 0.00
Mon 03/09 17Z 0.80 2336  27  33   7 0.00
Mon 03/09 18Z 0.80 2236  27  30   7 0.00
Mon 03/09 19Z 0.80 2235  28  27   7 0.00
Mon 03/09 20Z 0.83 2235  31  30   7 0.00
Mon 03/09 21Z 0.88 2335  36  33   7 0.00
Mon 03/09 22Z 0.92 2336  41  33   7 0.00
Mon 03/09 23Z 0.95 2337  44  39   7 0.00
Tue 03/10 00Z 1.01 2437  44  44   7 0.00
Tue 03/10 01Z 1.08 2438  44  45   7 0.00
Tue 03/10 02Z 1.05 2438  44  54   7 0.00
Tue 03/10 03Z 1.08 2538  45  56   7 0.00
Tue 03/10 04Z 1.14 2539  49  55   7 0.00
Tue 03/10 05Z 1.25 2638  54  57   6 0.00
Tue 03/10 06Z 1.28 2735  60  56   6 0.00
Tue 03/10 07Z 1.12 2732  68  57   5 0.00
Tue 03/10 08Z 0.95 2729  73  58   5 0.00
Tue 03/10 09Z 0.79 2826  77  55   5 0.00
Tue 03/10 10Z 0.59 2822  79  57   5 0.00
Tue 03/10 11Z 0.45 2817  80  59   6 0.00
Tue 03/10 12Z 0.37 2615  78  56   7 0.00
Tue 03/10 13Z 0.35 2516  75  54   7 0.00
Tue 03/10 14Z 0.36 2417  74  46   8 0.00
Tue 03/10 15Z 0.40 2419  76  59   7 0.00
Tue 03/10 16Z 0.46 2420  80  57   7 0.00
Tue 03/10 17Z 0.52 2419  84  45   6 0.00
Tue 03/10 18Z 0.56 2418  88  41   6 0.00
Tue 03/10 19Z 0.56 2418  91  38   5 0.00
Tue 03/10 20Z 0.56 2417  93  39   5 0.00
Tue 03/10 21Z 0.57 2417  94  42   5 0.00
Tue 03/10 22Z 0.57 2417  96  43   6 0.01
Tue 03/10 23Z 0.54 2517  96  41   6 0.01
Wed 03/11 00Z 0.51 2616  96  40   6 0.01
Wed 03/11 01Z 0.44 2615  97  41   6 0.01
Wed 03/11 02Z 0.38 2613  97  44   6 0.01
Wed 03/11 03Z 0.33 2612  97  46   6 0.01
Wed 03/11 04Z 0.24 2509  98  53   6 0.01
Wed 03/11 05Z 0.19 2409  99  66   7 0.02
Wed 03/11 06Z 0.15 2407  99  76   7 0.01
Wed 03/11 07Z 0.11 2107  99  71   7 0.01
Wed 03/11 08Z 0.06 1908  99  73   7 0.01
Wed 03/11 09Z 0.04 1812  99  79   8 0.01
Wed 03/11 10Z 0.03 1717  99  73   8 0.02
Wed 03/11 11Z 0.03 1723  98  69   8 0.03
Wed 03/11 12Z 0.03 1727  98  58   8 0.03
Wed 03/11 13Z 0.03 1829  98  44   8 0.04
Wed 03/11 14Z 0.06 1833  98  37   8 0.02
Wed 03/11 15Z 0.10 1835  97  33   9 0.02
Wed 03/11 16Z 0.16 1936  98  49   9 0.03
Wed 03/11 17Z 0.19 1937  96  56  10 0.03

Run total areal avg QPF for the greens is: 0.35 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