NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260824_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)
=== ===== === ==== ==== === === === ====
Mon 08/24 00Z 0.40 2215  89  82  12 0.00
Mon 08/24 01Z 0.47 2315  87  83  12 0.00
Mon 08/24 02Z 0.57 2415  87  78  11 0.00
Mon 08/24 03Z 0.65 2515  86  78  11 0.00
Mon 08/24 04Z 0.56 2514  81  69  11 0.00
Mon 08/24 05Z 0.44 2512  78  68  11 0.00
Mon 08/24 06Z 0.35 2411  74  69  11 0.00
Mon 08/24 07Z 0.33 2312  74  69  10 0.00
Mon 08/24 08Z 0.33 2213  76  70  10 0.00
Mon 08/24 09Z 0.32 2214  77  67  10 0.00
Mon 08/24 10Z 0.33 2215  79  64  10 0.00
Mon 08/24 11Z 0.32 2116  80  64  10 0.00
Mon 08/24 12Z 0.29 2115  82  63   9 0.00
Mon 08/24 13Z 0.31 2115  84  55   9 0.00
Mon 08/24 14Z 0.30 2014  85  53   9 0.00
Mon 08/24 15Z 0.51 2113  84  47   9 0.00
Mon 08/24 16Z 1.23 2112  83  52   9 0.00
Mon 08/24 17Z 1.85 2011  81  55   9 0.00
Mon 08/24 18Z 1.84 1911  81  56  10 0.00
Mon 08/24 19Z 2.10 2014  80  69  10 0.05
Mon 08/24 20Z 1.08 2117  78  49  10 0.04
Mon 08/24 21Z 0.87 2116  73  40  10 0.00
Mon 08/24 22Z 0.65 2214  78  36  10 0.00
Mon 08/24 23Z 0.50 2213  79  45  10 0.00
Tue 08/25 00Z 0.55 2214  83  48  10 0.00
Tue 08/25 01Z 0.67 2215  83  56   9 0.00
Tue 08/25 02Z 0.71 2316  85  60   9 0.00
Tue 08/25 03Z 0.66 2315  89  65   9 0.01
Tue 08/25 04Z 0.56 2315  88  70   9 0.00
Tue 08/25 05Z 0.50 2316  89  83   9 0.00
Tue 08/25 06Z 0.45 2315  91  91   9 0.00
Tue 08/25 07Z 0.41 2315  93  92   9 0.01
Tue 08/25 08Z 0.38 2313  94  84   8 0.01
Tue 08/25 09Z 0.40 2413  96  81   8 0.00
Tue 08/25 10Z 0.40 2413  95  78   8 0.00
Tue 08/25 11Z 0.39 2412  94  78   8 0.00
Tue 08/25 12Z 0.36 2511  95  74   8 0.00
Tue 08/25 13Z 0.39 2511  96  75   8 0.00
Tue 08/25 14Z 0.39 2510  96  80   8 0.00
Tue 08/25 15Z 0.35 2608  96  79   8 0.00
Tue 08/25 16Z 0.32 2706  96  74   8 0.00
Tue 08/25 17Z 0.37 2706  95  70   8 0.00
Tue 08/25 18Z 0.41 2706  95  69   9 0.00
Tue 08/25 19Z 0.43 2707  95  72   9 0.01
Tue 08/25 20Z 0.37 2808  95  80   9 0.02
Tue 08/25 21Z 0.37 2910  93  73   9 0.02
Tue 08/25 22Z 0.37 3011  93  66   9 0.02
Tue 08/25 23Z 0.35 3011  92  59   9 0.01
Wed 08/26 00Z 0.33 3111  94  55   9 0.00
Wed 08/26 01Z 0.33 3112  95  54   9 0.02
Wed 08/26 02Z 0.31 3112  93  48   9 0.01
Wed 08/26 03Z 0.29 3112  93  48   9 0.01
Wed 08/26 04Z 0.29 3112  94  43   9 0.01
Wed 08/26 05Z 0.30 3111  94  39   9 0.01
Wed 08/26 06Z 0.30 3011  93  34   9 0.01
Wed 08/26 07Z 0.29 3112  92  34   9 0.01
Wed 08/26 08Z 0.28 3112  91  32   9 0.01
Wed 08/26 09Z 0.28 3111  92  34   9 0.01
Wed 08/26 10Z 0.26 3111  94  36   9 0.01
Wed 08/26 11Z 0.25 3110  93  41   9 0.01

Run total areal avg QPF for the greens is: 0.32 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