Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260801_1200
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)
=== ===== === ==== ==== === === === ====
Sat 08/01 12Z 0.15 2304  85  69  14 0.00
Sat 08/01 13Z 0.14 2105  86  61  14 0.00
Sat 08/01 14Z 0.22 2206  87  50  14 0.00
Sat 08/01 15Z 0.45 2105  86  36  14 0.00
Sat 08/01 16Z 1.07 2106  82  29  14 0.00
Sat 08/01 17Z 1.55 2206  77  31  15 0.00
Sat 08/01 18Z 1.94 2306  75  24  15 0.00
Sat 08/01 19Z 1.66 2205  72  18  15 0.00
Sat 08/01 20Z 1.49 2105  70  16  16 0.00
Sat 08/01 21Z 0.79 2105  69  16  16 0.00
Sat 08/01 22Z 0.36 2006  68  17  16 0.00
Sat 08/01 23Z 0.21 2007  67  19  16 0.00
Sun 08/02 00Z 0.23 2009  67  23  16 0.00
Sun 08/02 01Z 0.37 2011  71  33  16 0.00
Sun 08/02 02Z 0.46 2015  73  39  15 0.00
Sun 08/02 03Z 0.49 2118  75  47  15 0.00
Sun 08/02 04Z 0.55 2119  78  48  15 0.00
Sun 08/02 05Z 0.55 2120  82  37  15 0.00
Sun 08/02 06Z 0.54 2121  82  48  15 0.00
Sun 08/02 07Z 0.58 2221  79  51  15 0.00
Sun 08/02 08Z 0.60 2222  79  37  15 0.00
Sun 08/02 09Z 0.61 2222  78  40  15 0.00
Sun 08/02 10Z 0.65 2222  82  43  15 0.00
Sun 08/02 11Z 0.61 2221  83  40  14 0.00
Sun 08/02 12Z 0.52 2219  85  42  14 0.00
Sun 08/02 13Z 0.50 2219  88  40  14 0.00
Sun 08/02 14Z 0.45 2118  87  39  14 0.00
Sun 08/02 15Z 0.45 2016  89  30  14 0.00
Sun 08/02 16Z 0.39 1916  90  34  14 0.00
Sun 08/02 17Z 0.42 1918  90  30  14 0.01
Sun 08/02 18Z 0.63 1920  87  34  14 0.01
Sun 08/02 19Z 0.65 1922  85  27  15 0.01
Sun 08/02 20Z 0.36 1923  83  27  15 0.01
Sun 08/02 21Z 0.21 1823  87  37  15 0.00
Sun 08/02 22Z 0.24 1925  88  54  15 0.01
Sun 08/02 23Z 0.24 1925  80  52  15 0.01
Mon 08/03 00Z 0.20 1926  74  49  16 0.00
Mon 08/03 01Z 0.21 1926  69  39  16 0.00
Mon 08/03 02Z 0.24 1926  68  36  16 0.00
Mon 08/03 03Z 0.26 1926  73  37  16 0.00
Mon 08/03 04Z 0.27 1926  85  60  16 0.00
Mon 08/03 05Z 0.25 1926  93  76  16 0.01
Mon 08/03 06Z 0.23 1926  96  73  16 0.02
Mon 08/03 07Z 0.25 1928  96  76  16 0.02
Mon 08/03 08Z 0.33 2029  93  86  16 0.03
Mon 08/03 09Z 0.31 2029  88  92  16 0.02
Mon 08/03 10Z 0.31 2029  83  85  16 0.01
Mon 08/03 11Z 0.34 2030  89  90  16 0.01
Mon 08/03 12Z 0.45 2028  98  98  16 0.05
Mon 08/03 13Z 0.46 2124  95  89  16 0.34
Mon 08/03 14Z 0.53 2220  92  79  15 0.24
Mon 08/03 15Z 0.64 2320  96  84  15 0.02
Mon 08/03 16Z 0.72 2420  98  81  15 0.02
Mon 08/03 17Z 0.81 2618  98  80  14 0.02
Mon 08/03 18Z 0.72 2719  97  69  14 0.09
Mon 08/03 19Z 0.63 2818  95  48  14 0.05
Mon 08/03 20Z 0.52 3018  94  31  14 0.02
Mon 08/03 21Z 0.43 3118  91  21  14 0.01
Mon 08/03 22Z 0.31 3218  84  14  13 0.00
Mon 08/03 23Z 0.28 3318  81   8  13 0.00

Run total areal avg QPF for the greens is: 1.04 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