Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260206_1200
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 02/06 12Z 0.04 1710  63  56 -11 0.00
Fri 02/06 13Z 0.10 1912  65  64 -11 0.00
Fri 02/06 14Z 0.17 2012  66  68 -11 0.00
Fri 02/06 15Z 0.15 2010  65  76 -11 0.00
Fri 02/06 16Z 0.12 1909  67  82 -11 0.00
Fri 02/06 17Z 0.15 1907  68  82 -11 0.00
Fri 02/06 18Z 0.22 2007  68  84 -11 0.00
Fri 02/06 19Z 0.25 2006  70  84 -11 0.00
Fri 02/06 20Z 0.22 2006  72  78 -11 0.00
Fri 02/06 21Z 0.13 1906  75  74 -11 0.00
Fri 02/06 22Z 0.05 1708  79  74 -11 0.00
Fri 02/06 23Z 0.05 1711  85  67 -11 0.00
Sat 02/07 01Z 0.19 1912  91  79 -12 0.00
Sat 02/07 04Z 0.44 2213  93  69 -12 0.00
Sat 02/07 05Z 0.38 2212  92  80 -12 0.00
Sat 02/07 06Z 0.25 2109  93  89 -12 0.00
Sat 02/07 07Z 0.14 2006  92  87 -12 0.00
Sat 02/07 08Z 0.07 1905  92  86 -12 0.00
Sat 02/07 09Z 0.04 1705  92  86 -12 0.00
Sat 02/07 10Z 0.04 1705  92  86 -12 0.01
Sat 02/07 11Z 0.03 1704  93  85 -12 0.02
Sat 02/07 12Z 0.03 1901  93  86 -12 0.02
Sat 02/07 13Z 0.06 3304  92  83 -13 0.01
Sat 02/07 14Z 0.16 3409  90  80 -13 0.01
Sat 02/07 15Z 0.11 3414  88  80 -14 0.01
Sat 02/07 16Z 0.05 3416  86  80 -15 0.02
Sat 02/07 17Z 0.06 3417  84  81 -15 0.03
Sat 02/07 18Z 0.07 3318  84  82 -16 0.02
Sat 02/07 19Z 0.10 3320  84  83 -17 0.01
Sat 02/07 20Z 0.11 3321  84  83 -17 0.01
Sat 02/07 21Z 0.11 3323  84  83 -18 0.01
Sat 02/07 22Z 0.11 3324  84  81 -19 0.01
Sat 02/07 23Z 0.12 3325  85  78 -19 0.01
Sun 02/08 00Z 0.12 3326  84  78 -20 0.01
Sun 02/08 01Z 0.11 3326  84  77 -20 0.00
Sun 02/08 02Z 0.11 3326  84  76 -20 0.00
Sun 02/08 03Z 0.10 3325  84  75 -20 0.00
Sun 02/08 04Z 0.10 3324  83  77 -20 0.00
Sun 02/08 05Z 0.09 3323  82  78 -19 0.00
Sun 02/08 06Z 0.07 3323  82  79 -19 0.00
Sun 02/08 07Z 0.08 3323  81  77 -19 0.00
Sun 02/08 08Z 0.09 3324  81  76 -20 0.00
Sun 02/08 09Z 0.09 3325  81  75 -20 0.00
Sun 02/08 10Z 0.08 3324  80  75 -20 0.00
Sun 02/08 11Z 0.06 3424  80  75 -19 0.00
Sun 02/08 12Z 0.03 3423  80  76 -19 0.00
Sun 02/08 13Z 0.02 3523  79  76 -18 0.00
Sun 02/08 14Z 0.02 3522  79  75 -17 0.00
Sun 02/08 15Z 0.02 3422  78  72 -17 0.00
Sun 02/08 16Z 0.02 3423  76  69 -17 0.00
Sun 02/08 17Z 0.02 3423  75  65 -16 0.00
Sun 02/08 18Z 0.03 3424  72  61 -16 0.00
Sun 02/08 19Z 0.04 3424  68  55 -15 0.00
Sun 02/08 20Z 0.05 3425  64  41 -15 0.00
Sun 02/08 21Z 0.07 3326  59  24 -15 0.00
Sun 02/08 22Z 0.07 3427  55  20 -14 0.00
Sun 02/08 23Z 0.06 3427  51  19 -13 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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