Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260205_1800
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)
=== ===== === ==== ==== === === === ====
Thu 02/05 18Z 0.33 3106  82  14 -14 0.00
Thu 02/05 19Z 0.33 3107  79  14 -13 0.00
Thu 02/05 20Z 0.20 3108  75  14 -13 0.00
Thu 02/05 21Z 0.18 3109  71  14 -12 0.00
Thu 02/05 22Z 0.14 3109  69  14 -12 0.00
Thu 02/05 23Z 0.13 3109  68  14 -11 0.00
Fri 02/06 00Z 0.09 3208  68  15 -11 0.00
Fri 02/06 01Z 0.06 3207  67  18 -10 0.00
Fri 02/06 02Z 0.02 3406  67  21 -10 0.00
Fri 02/06 03Z 0.02 3505  66  24 -10 0.00
Fri 02/06 04Z 0.02 0101  65  24 -10 0.00
Fri 02/06 06Z 0.04 1404  63  19 -11 0.00
Fri 02/06 07Z 0.03 1504  59  17 -10 0.00
Fri 02/06 08Z 0.01 1704  57  14 -10 0.00
Fri 02/06 09Z 0.02 1709  61  10 -11 0.00
Fri 02/06 10Z 0.03 1712  62   8 -11 0.00
Fri 02/06 11Z 0.05 1811  63   8 -11 0.00
Fri 02/06 12Z 0.11 1911  66   9 -12 0.00
Fri 02/06 13Z 0.13 2011  72  14 -12 0.00
Fri 02/06 14Z 0.14 2010  77  37 -12 0.00
Fri 02/06 15Z 0.14 2108  77  66 -11 0.00
Fri 02/06 16Z 0.10 2006  77  84 -11 0.00
Fri 02/06 17Z 0.05 1806  80  87 -11 0.00
Fri 02/06 18Z 0.07 1708  85  88 -12 0.00
Fri 02/06 19Z 0.10 1808  88  87 -12 0.00
Fri 02/06 20Z 0.08 1807  91  86 -12 0.00
Fri 02/06 21Z 0.10 1907  91  84 -12 0.00
Fri 02/06 22Z 0.14 1907  90  83 -11 0.00
Fri 02/06 23Z 0.17 2008  89  86 -11 0.00
Sat 02/07 00Z 0.19 2009  91  89 -12 0.00
Sat 02/07 01Z 0.20 2009  93  88 -12 0.00
Sat 02/07 02Z 0.22 2010  93  89 -12 0.00
Sat 02/07 04Z 0.20 2010  92  88 -12 0.00
Sat 02/07 05Z 0.21 2010  92  87 -12 0.01
Sat 02/07 06Z 0.20 2010  92  87 -12 0.01
Sat 02/07 07Z 0.17 2009  92  86 -11 0.01
Sat 02/07 08Z 0.15 2008  92  86 -11 0.01
Sat 02/07 09Z 0.11 2006  92  86 -11 0.01
Sat 02/07 10Z 0.09 2004  92  85 -11 0.01
Sat 02/07 11Z 0.07 2102  92  84 -11 0.01
Sat 02/07 12Z 0.06 2601  92  84 -12 0.01
Sat 02/07 13Z 0.08 3204  92  83 -12 0.01
Sat 02/07 14Z 0.06 3408  91  81 -12 0.01
Sat 02/07 15Z 0.08 3411  89  81 -13 0.02
Sat 02/07 16Z 0.06 3514  89  81 -13 0.02
Sat 02/07 17Z 0.04 3415  86  82 -14 0.02
Sat 02/07 18Z 0.04 3416  85  83 -14 0.01
Sat 02/07 19Z 0.06 3318  84  83 -15 0.01
Sat 02/07 20Z 0.08 3321  84  81 -16 0.01
Sat 02/07 21Z 0.10 3323  84  82 -17 0.01
Sat 02/07 23Z 0.12 3327  85  79 -18 0.01
Sun 02/08 00Z 0.12 3328  84  74 -18 0.01
Sun 02/08 01Z 0.13 3328  83  69 -19 0.00
Sun 02/08 03Z 0.15 3327  82  64 -20 0.00
Sun 02/08 05Z 0.14 3326  80  65 -21 0.00

Run total areal avg QPF for the Central_Greens is: 0.22 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