Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20260402_1800
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 04/02 18Z 0.14 1508  89  46  -1 0.00
Thu 04/02 19Z 0.22 1511  89  56  -1 0.00
Thu 04/02 20Z 0.24 1513  90  73  -1 0.00
Thu 04/02 21Z 0.27 1514  90  86   0 0.00
Thu 04/02 22Z 0.28 1517  93  95   0 0.00
Thu 04/02 23Z 0.29 1521  93  99   0 0.00
Fri 04/03 00Z 0.25 1624  96  99   0 0.01
Fri 04/03 02Z 0.22 1728  96  97   2 0.06
Fri 04/03 03Z 0.20 1732  96  96   2 0.04
Fri 04/03 04Z 0.16 1835  96  96   3 0.03
Fri 04/03 05Z 0.11 1838  96  92   5 0.08
Fri 04/03 06Z 0.05 1938  96  82   7 0.07
Fri 04/03 07Z 0.04 2039  96  75   9 0.03
Fri 04/03 08Z 0.07 2039  95  66  10 0.03
Fri 04/03 09Z 0.09 2041  94  78  11 0.03
Fri 04/03 10Z 0.12 2145  93  87  11 0.02
Fri 04/03 11Z 0.16 2145  91  86  12 0.03
Fri 04/03 12Z 0.24 2245  94  85  11 0.02
Fri 04/03 13Z 0.28 2241  94  97  11 0.01
Fri 04/03 14Z 0.32 2242  97  93  10 0.02
Fri 04/03 15Z 0.39 2341  93  83  11 0.05
Fri 04/03 16Z 0.45 2341  92  77  11 0.05
Fri 04/03 17Z 0.52 2440  96  91  11 0.01
Fri 04/03 18Z 0.59 2441  94  67  11 0.03
Fri 04/03 19Z 0.67 2540  94  69  10 0.01
Fri 04/03 20Z 0.72 2539  94  37  10 0.00
Fri 04/03 21Z 0.86 2540  94  39  10 0.00
Fri 04/03 22Z 0.92 2541  92  30  10 0.00
Fri 04/03 23Z 0.95 2542  93  24  10 0.00
Sat 04/04 00Z 1.04 2542  96  12   9 0.00
Sat 04/04 01Z 1.26 2542  96  10   8 0.01
Sat 04/04 02Z 1.32 2641  90   9   7 0.02
Sat 04/04 03Z 1.22 2737  93   8   6 0.02
Sat 04/04 04Z 0.86 2734  93   9   4 0.02
Sat 04/04 05Z 0.74 2834  91  17   3 0.04
Sat 04/04 06Z 0.66 2831  92  23   2 0.02
Sat 04/04 07Z 0.57 2929  93  15   1 0.02
Sat 04/04 08Z 0.46 3124  94  19   0 0.02
Sat 04/04 09Z 0.33 3219  95  26   0 0.02
Sat 04/04 10Z 0.18 3415  95  30   0 0.02
Sat 04/04 11Z 0.08 0013  96  29   0 0.02
Sat 04/04 12Z 0.07 0211  96  29   0 0.01
Sat 04/04 13Z 0.11 0411  94  27   0 0.01
Sat 04/04 14Z 0.17 0611  91  25   0 0.00
Sat 04/04 15Z 0.20 0811  91  25   0 0.00
Sat 04/04 16Z 0.22 1110  93  26   0 0.00
Sat 04/04 17Z 0.25 1212  93  30   1 0.00
Sat 04/04 18Z 0.29 1414  92  40   1 0.00
Sat 04/04 19Z 0.31 1517  92  50   1 0.00
Sat 04/04 20Z 0.38 1519  90  52   1 0.00
Sat 04/04 21Z 0.45 1521  88  37   1 0.00
Sat 04/04 22Z 0.41 1625  83  49   2 0.00
Sat 04/04 23Z 0.30 1629  77  98   5 0.00
Sun 04/05 00Z 0.23 1733  81  99   6 0.00
Sun 04/05 01Z 0.21 1736  82  95   7 0.01
Sun 04/05 02Z 0.18 1839  82  92   8 0.01
Sun 04/05 03Z 0.17 1840  83  87   9 0.00
Sun 04/05 04Z 0.14 1843  87  82   9 0.00
Sun 04/05 05Z 0.13 1845  90  79  10 0.00

Run total areal avg QPF for the Northern_Greens is: 0.90 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