Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260403_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 04/03 00Z 0.07 1521  97  99   2 0.00
Fri 04/03 01Z 0.06 1623  96  92   3 0.03
Fri 04/03 02Z 0.03 1725  97  82   3 0.02
Fri 04/03 03Z 0.08 1728  97  77   3 0.02
Fri 04/03 04Z 0.14 1829  97  79   5 0.01
Fri 04/03 05Z 0.19 1930  97  74   6 0.01
Fri 04/03 06Z 0.23 1931  97  77   7 0.01
Fri 04/03 07Z 0.26 2031  97  83   8 0.01
Fri 04/03 08Z 0.30 2032  97  86   9 0.01
Fri 04/03 09Z 0.37 2136  97  94  10 0.02
Fri 04/03 10Z 0.39 2135  97  92  10 0.09
Fri 04/03 11Z 0.46 2237  97  93  10 0.06
Fri 04/03 12Z 0.54 2239  98  87  10 0.06
Fri 04/03 13Z 0.56 2337  97  91  10 0.04
Fri 04/03 14Z 0.57 2436  93  92  10 0.04
Fri 04/03 15Z 0.60 2335  95  95  10 0.03
Fri 04/03 16Z 0.68 2437  95  86  10 0.06
Fri 04/03 17Z 0.72 2438  93  84  10 0.00
Fri 04/03 18Z 0.76 2537  94  72  11 0.00
Fri 04/03 19Z 0.80 2536  94  67  11 0.00
Fri 04/03 20Z 0.86 2535  91  58  11 0.00
Fri 04/03 21Z 0.99 2535  91  48  10 0.00
Fri 04/03 22Z 1.03 2535  90  38  10 0.00
Fri 04/03 23Z 1.14 2438  94  21  10 0.00
Sat 04/04 00Z 1.24 2541  95  21  10 0.00
Sat 04/04 01Z 1.20 2541  97  16   9 0.01
Sat 04/04 02Z 1.27 2540  98  16   9 0.02
Sat 04/04 03Z 1.39 2640  97  14   8 0.04
Sat 04/04 04Z 1.40 2637  94  14   7 0.03
Sat 04/04 05Z 1.26 2735  91  13   6 0.02
Sat 04/04 06Z 0.85 2831  87  12   5 0.01
Sat 04/04 07Z 0.60 2928  88  10   4 0.01
Sat 04/04 08Z 0.45 2926  88  14   3 0.00
Sat 04/04 09Z 0.33 3024  90  15   2 0.01
Sat 04/04 10Z 0.22 3121  88  23   2 0.01
Sat 04/04 11Z 0.12 3218  84  29   3 0.00
Sat 04/04 12Z 0.06 3314  82  28   3 0.00
Sat 04/04 13Z 0.04 3509  81  30   4 0.00
Sat 04/04 14Z 0.05 0105  82  35   4 0.00
Sat 04/04 15Z 0.05 0702  81  38   5 0.00
Sat 04/04 16Z 0.05 1304  82  35   4 0.00
Sat 04/04 17Z 0.04 1506  82  32   4 0.00
Sat 04/04 18Z 0.06 1509  81  32   4 0.00
Sat 04/04 19Z 0.10 1512  80  38   4 0.00
Sat 04/04 20Z 0.13 1516  83  33   4 0.00
Sat 04/04 21Z 0.07 1620  85  51   5 0.00
Sat 04/04 22Z 0.05 1622  84  91   6 0.00
Sat 04/04 23Z 0.03 1624  89  94   5 0.01
Sun 04/05 00Z 0.04 1626  94  85   6 0.01
Sun 04/05 01Z 0.04 1627  94  85   7 0.01
Sun 04/05 02Z 0.04 1728  95  87   8 0.01
Sun 04/05 03Z 0.04 1730  97  91   8 0.02
Sun 04/05 04Z 0.06 1733  97  95   7 0.04
Sun 04/05 05Z 0.09 1736  97  91   8 0.10
Sun 04/05 06Z 0.11 1838  97  86   8 0.05
Sun 04/05 07Z 0.14 1838  97  86   9 0.03
Sun 04/05 08Z 0.16 1837  97  92  10 0.02
Sun 04/05 09Z 0.18 1838  96  90  10 0.02
Sun 04/05 10Z 0.22 1938  97  83  10 0.02
Sun 04/05 11Z 0.28 2037  97  64  10 0.02

Run total areal avg QPF for the Central_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