Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260206_0000
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)
=== ===== === ==== ==== === === === ====
Fri 02/06 00Z 0.12 3006  58  17 -11 0.00
Fri 02/06 01Z 0.09 3106  59  18 -11 0.00
Fri 02/06 02Z 0.09 3105  63  20 -11 0.00
Fri 02/06 03Z 0.05 3203  65  20 -11 0.00
Fri 02/06 04Z 0.03 3302  63  21 -11 0.00
Fri 02/06 05Z 0.04 0400  59  21 -11 0.00
Fri 02/06 06Z 0.04 1602  55  20 -10 0.00
Fri 02/06 07Z 0.03 1604  51  17 -10 0.00
Fri 02/06 08Z 0.03 1707  52  13 -10 0.00
Fri 02/06 09Z 0.02 1708  54   9 -11 0.00
Fri 02/06 10Z 0.02 1809  55   6 -11 0.00
Fri 02/06 11Z 0.03 1809  57  11 -11 0.00
Fri 02/06 12Z 0.03 1811  61  29 -12 0.00
Fri 02/06 13Z 0.03 1812  65  47 -12 0.00
Fri 02/06 14Z 0.06 1914  68  58 -12 0.00
Fri 02/06 15Z 0.09 1913  70  64 -11 0.00
Fri 02/06 16Z 0.11 1912  71  73 -11 0.00
Fri 02/06 17Z 0.11 2010  74  84 -11 0.00
Fri 02/06 18Z 0.12 2008  78  87 -11 0.00
Fri 02/06 19Z 0.15 2007  81  88 -11 0.00
Fri 02/06 20Z 0.08 1907  83  90 -11 0.00
Fri 02/06 21Z 0.05 1807  85  89 -11 0.00
Fri 02/06 22Z 0.05 1808  85  86 -11 0.00
Fri 02/06 23Z 0.07 1910  85  85 -11 0.00
Sat 02/07 00Z 0.08 1910  86  88 -11 0.00
Sat 02/07 01Z 0.11 1912  89  90 -12 0.00
Sat 02/07 02Z 0.14 1912  92  87 -12 0.00
Sat 02/07 03Z 0.16 1913  92  87 -12 0.01
Sat 02/07 04Z 0.14 1913  92  87 -11 0.01
Sat 02/07 05Z 0.13 1913  92  86 -11 0.01
Sat 02/07 06Z 0.12 1913  91  85 -11 0.01
Sat 02/07 07Z 0.11 1912  92  85 -11 0.01
Sat 02/07 08Z 0.11 1911  91  84 -11 0.01
Sat 02/07 09Z 0.12 2009  92  84 -11 0.01
Sat 02/07 10Z 0.13 2106  92  84 -12 0.01
Sat 02/07 11Z 0.15 2304  93  84 -12 0.01
Sat 02/07 12Z 0.15 3106  92  82 -13 0.03
Sat 02/07 13Z 0.10 3310  89  82 -13 0.02
Sat 02/07 14Z 0.10 3414  88  82 -13 0.02
Sat 02/07 15Z 0.09 3415  87  82 -14 0.01
Sat 02/07 16Z 0.10 3315  85  82 -15 0.01
Sat 02/07 17Z 0.12 3316  84  83 -15 0.01
Sat 02/07 18Z 0.14 3317  84  83 -16 0.01
Sat 02/07 19Z 0.16 3319  83  83 -17 0.01
Sat 02/07 20Z 0.18 3321  84  82 -18 0.01
Sat 02/07 21Z 0.19 3323  85  80 -18 0.01
Sat 02/07 22Z 0.19 3325  86  78 -18 0.00
Sat 02/07 23Z 0.20 3326  86  75 -19 0.00
Sun 02/08 00Z 0.20 3327  86  72 -19 0.00
Sun 02/08 01Z 0.22 3328  85  72 -20 0.00
Sun 02/08 02Z 0.21 3327  84  71 -20 0.00
Sun 02/08 03Z 0.22 3226  84  73 -20 0.00
Sun 02/08 04Z 0.21 3225  83  74 -20 0.00
Sun 02/08 05Z 0.19 3224  82  74 -20 0.00
Sun 02/08 06Z 0.20 3225  81  68 -20 0.00
Sun 02/08 07Z 0.20 3225  81  63 -20 0.00
Sun 02/08 08Z 0.22 3226  80  61 -21 0.00
Sun 02/08 09Z 0.24 3227  78  57 -21 0.00
Sun 02/08 10Z 0.25 3229  76  53 -21 0.00
Sun 02/08 11Z 0.24 3229  73  42 -21 0.00

Run total areal avg QPF for the greens is: 0.23 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