Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260314_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)
=== ===== === ==== ==== === === === ====
Sat 03/14 06Z 0.11 1922  97  84  -7 0.00
Sat 03/14 07Z 0.18 1923  96  92  -6 0.01
Sat 03/14 08Z 0.31 2023  96  93  -6 0.01
Sat 03/14 09Z 0.50 2224  96  88  -6 0.02
Sat 03/14 10Z 0.72 2324  95  85  -6 0.02
Sat 03/14 11Z 0.89 2324  94  83  -6 0.02
Sat 03/14 12Z 1.02 2424  95  83  -7 0.02
Sat 03/14 13Z 1.54 2524  95  81  -8 0.02
Sat 03/14 14Z 2.14 2522  94  80  -8 0.01
Sat 03/14 15Z 2.77 2520  93  79  -8 0.01
Sat 03/14 16Z 1.54 2520  93  83  -8 0.01
Sat 03/14 17Z 1.57 2519  93  84  -8 0.02
Sat 03/14 19Z 1.81 2727  95  85  -7 0.02
Sat 03/14 20Z 2.99 2832  91  80  -8 0.05
Sat 03/14 21Z 2.67 2833  90  77  -9 0.04
Sat 03/14 22Z 1.82 2833  91  76 -10 0.03
Sat 03/14 23Z 1.74 2835  94  77 -10 0.02
Sun 03/15 00Z 1.42 2935  95  65 -10 0.02
Sun 03/15 01Z 1.34 3033  96  55 -10 0.02
Sun 03/15 02Z 1.26 3031  96  36 -11 0.02
Sun 03/15 03Z 1.28 3030  96   9 -11 0.01
Sun 03/15 04Z 1.11 3028  94   4 -12 0.01
Sun 03/15 05Z 0.95 3027  90   7 -12 0.01
Sun 03/15 06Z 0.62 3024  80   6 -11 0.01
Sun 03/15 07Z 0.43 3021  66   7 -10 0.00
Sun 03/15 08Z 0.34 3120  53   7  -9 0.00
Sun 03/15 09Z 0.25 3117  38  10  -8 0.00
Sun 03/15 10Z 0.18 3214  25  12  -7 0.00
Sun 03/15 11Z 0.14 3210  17  24  -6 0.00
Sun 03/15 12Z 0.09 3207  14  74  -6 0.00
Sun 03/15 13Z 0.05 2902  15  87  -6 0.00
Sun 03/15 14Z 0.02 1803  17  94  -6 0.00
Sun 03/15 15Z 0.04 1709  23  96  -6 0.00
Sun 03/15 16Z 0.09 1615  41  97  -7 0.00
Sun 03/15 17Z 0.08 1721  63  95  -6 0.00
Sun 03/15 18Z 0.06 1727  59  93  -6 0.00
Sun 03/15 19Z 0.05 1731  41  76  -4 0.00
Sun 03/15 20Z 0.06 1835  32  65  -3 0.00
Sun 03/15 21Z 0.09 1837  38  73  -3 0.00
Sun 03/15 22Z 0.12 1839  39  61  -1 0.00
Sun 03/15 23Z 0.16 1942  34  33   0 0.00
Mon 03/16 00Z 0.21 1943  31  25   1 0.00
Mon 03/16 01Z 0.23 1945  29  35   3 0.00
Mon 03/16 02Z 0.25 1946  31  37   3 0.00
Mon 03/16 03Z 0.27 1947  49  37   4 0.00
Mon 03/16 04Z 0.26 1947  66  39   4 0.00
Mon 03/16 05Z 0.22 1948  78  33   4 0.00
Mon 03/16 06Z 0.17 1949  86  50   4 0.00
Mon 03/16 07Z 0.13 1850  89  70   5 0.00
Mon 03/16 08Z 0.09 1850  91  88   5 0.00
Mon 03/16 09Z 0.09 1849  91  94   5 0.01
Mon 03/16 10Z 0.11 1748  94  95   8 0.03
Mon 03/16 11Z 0.10 1750  95  99   9 0.08
Mon 03/16 12Z 0.06 1849  97  82   8 0.12
Mon 03/16 13Z 0.16 1944  96  28   8 0.07
Mon 03/16 14Z 0.24 1945  95  31   8 0.02
Mon 03/16 15Z 0.30 1944  96  30   8 0.01
Mon 03/16 16Z 0.33 1944  92  20   9 0.01
Mon 03/16 17Z 0.32 1944  93  31  10 0.01

Run total areal avg QPF for the greens is: 0.79 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