NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260524_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)
=== ===== === ==== ==== === === === ====
Sun 05/24 06Z 0.34 1527  77  96   4 0.00
Sun 05/24 07Z 0.41 1530  76  97   4 0.00
Sun 05/24 08Z 0.48 1431  74  98   4 0.01
Sun 05/24 09Z 0.57 1432  76  98   3 0.02
Sun 05/24 10Z 0.61 1435  82  98   3 0.05
Sun 05/24 11Z 0.64 1436  87  99   3 0.05
Sun 05/24 12Z 0.65 1437  89  99   2 0.05
Sun 05/24 13Z 0.60 1437  90  98   3 0.07
Sun 05/24 14Z 0.51 1537  91  98   3 0.07
Sun 05/24 15Z 0.43 1537  92  98   4 0.08
Sun 05/24 16Z 0.34 1535  93  98   4 0.08
Sun 05/24 17Z 0.28 1533  93  98   5 0.05
Sun 05/24 18Z 0.24 1533  94  98   6 0.04
Sun 05/24 19Z 0.22 1635  94  98   5 0.04
Sun 05/24 20Z 0.21 1635  95  97   6 0.05
Sun 05/24 21Z 0.21 1636  94  97   6 0.04
Sun 05/24 22Z 0.21 1637  94  98   6 0.02
Sun 05/24 23Z 0.19 1636  94  87   7 0.02
Mon 05/25 00Z 0.16 1635  94  80   7 0.01
Mon 05/25 01Z 0.14 1633  95  79   8 0.01
Mon 05/25 02Z 0.12 1630  95  76   8 0.01
Mon 05/25 03Z 0.08 1728  95  77   8 0.01
Mon 05/25 04Z 0.05 1725  96  80   9 0.01
Mon 05/25 05Z 0.04 1723  96  78  10 0.01
Mon 05/25 06Z 0.04 1820  96  81  10 0.01
Mon 05/25 07Z 0.05 1818  97  89  10 0.02
Mon 05/25 08Z 0.07 1917  98  93  10 0.06
Mon 05/25 09Z 0.13 2017  99  98   9 0.08
Mon 05/25 10Z 0.21 2116  99  96   9 0.13
Mon 05/25 11Z 0.29 2316  99  98   8 0.10
Mon 05/25 12Z 0.29 2513  99  95   8 0.07
Mon 05/25 13Z 0.27 2712  97  90   8 0.02
Mon 05/25 14Z 0.23 3012  96  89   9 0.01
Mon 05/25 15Z 0.21 3113  93  84   9 0.00
Mon 05/25 16Z 0.22 3113  92  78   9 0.00
Mon 05/25 17Z 0.29 3014  92  69   9 0.00
Mon 05/25 18Z 0.37 3016  92  60   9 0.00
Mon 05/25 19Z 0.46 2916  92  34   9 0.00
Mon 05/25 20Z 0.55 2917  94  28   8 0.00
Mon 05/25 21Z 0.63 2918  96  22   8 0.01
Mon 05/25 22Z 0.62 2918  94  13   8 0.01
Mon 05/25 23Z 0.53 2918  85   7   8 0.01
Tue 05/26 00Z 0.45 3018  81   8   9 0.00
Tue 05/26 01Z 0.38 3117  73   8   9 0.00
Tue 05/26 02Z 0.32 3117  66   8   9 0.00
Tue 05/26 03Z 0.33 3117  64  10   9 0.00
Tue 05/26 04Z 0.32 3116  64  14   9 0.00
Tue 05/26 05Z 0.35 3116  65  15   9 0.00
Tue 05/26 06Z 0.37 3116  70  13   8 0.00
Tue 05/26 07Z 0.38 3115  71  12   8 0.00
Tue 05/26 08Z 0.45 3116  75  14   8 0.00
Tue 05/26 09Z 0.42 3015  74  15   8 0.00
Tue 05/26 10Z 0.40 3013  70  21   9 0.00
Tue 05/26 11Z 0.38 2912  65  25   9 0.00
Tue 05/26 12Z 0.38 2811  62  26  10 0.00
Tue 05/26 13Z 0.40 2710  61  29  10 0.00
Tue 05/26 14Z 0.39 2609  60  41  10 0.00
Tue 05/26 15Z 0.45 2409  60  52  10 0.00
Tue 05/26 16Z 0.88 2410  60  55  10 0.00
Tue 05/26 17Z 1.11 2411  58  62  11 0.00

Run total areal avg QPF for the greens is: 1.33 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