NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260806_1200
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)
=== ===== === ==== ==== === === === ====
Thu 08/06 12Z 0.27 2707  84  42  16 0.00
Thu 08/06 13Z 0.24 2606  84  53  16 0.00
Thu 08/06 14Z 0.19 2605  85  66  16 0.00
Thu 08/06 15Z 0.16 2503  86  85  16 0.00
Thu 08/06 16Z 0.14 2303  87  91  16 0.00
Thu 08/06 17Z 0.20 2304  84  90  16 0.01
Thu 08/06 18Z 0.23 2303  83  89  17 0.01
Thu 08/06 19Z 0.22 2302  82  89  17 0.00
Thu 08/06 20Z 0.27 2603  85  90  17 0.02
Thu 08/06 21Z 0.16 2403  82  84  17 0.03
Thu 08/06 22Z 0.08 2103  79  81  17 0.00
Thu 08/06 23Z 0.09 2103  79  81  17 0.00
Fri 08/07 00Z 0.14 2105  80  78  17 0.00
Fri 08/07 01Z 0.27 2307  81  80  17 0.00
Fri 08/07 02Z 0.25 2307  80  74  17 0.00
Fri 08/07 03Z 0.26 2307  82  75  17 0.00
Fri 08/07 04Z 0.31 2409  89  74  17 0.00
Fri 08/07 05Z 0.30 2409  92  69  17 0.00
Fri 08/07 06Z 0.29 2608  93  71  17 0.01
Fri 08/07 07Z 0.21 2706  94  74  16 0.01
Fri 08/07 08Z 0.27 2909  96  78  16 0.14
Fri 08/07 09Z 0.22 3109  94  67  16 0.09
Fri 08/07 10Z 0.19 3108  90  66  16 0.02
Fri 08/07 11Z 0.18 3108  89  70  16 0.00
Fri 08/07 12Z 0.14 3106  85  65  16 0.00
Fri 08/07 13Z 0.13 3005  83  63  16 0.00
Fri 08/07 14Z 0.16 2905  79  66  16 0.00
Fri 08/07 15Z 0.17 2905  76  58  16 0.00
Fri 08/07 16Z 0.20 2905  78  56  16 0.00
Fri 08/07 17Z 0.27 2805  79  51  16 0.00
Fri 08/07 18Z 0.32 2805  79  44  16 0.00
Fri 08/07 19Z 0.35 2806  81  37  16 0.00
Fri 08/07 20Z 0.33 2806  82  29  16 0.00
Fri 08/07 21Z 0.29 2806  84  22  16 0.00
Fri 08/07 22Z 0.25 2806  84  12  17 0.00
Fri 08/07 23Z 0.23 2806  83  17  17 0.00
Sat 08/08 00Z 0.23 2806  84  29  17 0.00
Sat 08/08 01Z 0.19 2705  83  36  17 0.00
Sat 08/08 02Z 0.24 2607  83  42  17 0.00
Sat 08/08 03Z 0.24 2607  82  44  17 0.00
Sat 08/08 04Z 0.21 2506  81  46  17 0.00
Sat 08/08 05Z 0.19 2406  79  61  17 0.00
Sat 08/08 06Z 0.16 2405  79  75  17 0.00
Sat 08/08 07Z 0.17 2306  81  81  17 0.00
Sat 08/08 08Z 0.18 2207  83  79  17 0.00
Sat 08/08 09Z 0.15 2207  83  75  16 0.00
Sat 08/08 10Z 0.13 2107  84  78  16 0.00
Sat 08/08 11Z 0.12 2007  85  75  16 0.00
Sat 08/08 12Z 0.12 2007  84  73  16 0.00
Sat 08/08 13Z 0.13 2008  86  74  16 0.00
Sat 08/08 14Z 0.18 2009  92  81  16 0.00
Sat 08/08 15Z 0.20 2010  91  85  16 0.06
Sat 08/08 16Z 0.10 1909  83  81  16 0.10
Sat 08/08 17Z 0.09 1911  80  79  16 0.01
Sat 08/08 18Z 0.20 1912  82  73  17 0.00
Sat 08/08 19Z 0.45 2013  85  70  16 0.00
Sat 08/08 20Z 0.79 2014  85  71  17 0.00
Sat 08/08 21Z 0.90 2114  83  79  17 0.00
Sat 08/08 22Z 0.66 2213  87  69  17 0.03
Sat 08/08 23Z 0.60 2318  90  73  16 0.07

Run total areal avg QPF for the greens is: 0.61 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