NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260725_1800
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)
=== ===== === ==== ==== === === === ====
Sat 07/25 18Z 1.11 1503  71  30  13 0.00
Sat 07/25 19Z 1.47 1404  69  27  13 0.00
Sat 07/25 20Z 0.76 1504  69  24  14 0.00
Sat 07/25 21Z 0.63 1504  71  22  14 0.00
Sat 07/25 22Z 0.45 1505  73  21  13 0.00
Sat 07/25 23Z 0.29 1607  74  20  13 0.00
Sun 07/26 00Z 0.15 1708  76  19  13 0.00
Sun 07/26 01Z 0.12 1710  77  17  13 0.00
Sun 07/26 02Z 0.09 1811  78  15  12 0.00
Sun 07/26 03Z 0.09 1811  79  12  12 0.00
Sun 07/26 04Z 0.14 1911  80  11  12 0.00
Sun 07/26 05Z 0.21 2010  81  12  12 0.00
Sun 07/26 06Z 0.26 2108  82  12  12 0.00
Sun 07/26 07Z 0.31 2208  84  12  12 0.00
Sun 07/26 08Z 0.30 2307  85  12  11 0.00
Sun 07/26 09Z 0.22 2305  85  14  11 0.00
Sun 07/26 10Z 0.18 2204  84  16  11 0.00
Sun 07/26 11Z 0.13 2104  84  15  11 0.00
Sun 07/26 12Z 0.08 1903  83  14  11 0.00
Sun 07/26 13Z 0.08 1702  83  12  11 0.00
Sun 07/26 14Z 0.25 1503  85  12  11 0.00
Sun 07/26 15Z 0.60 1404  86  11  11 0.00
Sun 07/26 16Z 0.94 1405  84  10  11 0.00
Sun 07/26 17Z 0.84 1504  80  10  12 0.00
Sun 07/26 18Z 0.86 1504  79  10  12 0.00
Sun 07/26 19Z 0.46 1703  77  11  13 0.00
Sun 07/26 20Z 0.28 1803  77  13  13 0.00
Sun 07/26 21Z 0.16 1804  78  14  13 0.00
Sun 07/26 22Z 0.14 1704  78  15  13 0.00
Sun 07/26 23Z 0.09 1805  79  21  13 0.00
Mon 07/27 00Z 0.10 1905  80  29  13 0.00
Mon 07/27 01Z 0.08 1906  80  32  12 0.00
Mon 07/27 02Z 0.14 1907  79  32  12 0.00
Mon 07/27 03Z 0.24 2008  79  32  12 0.00
Mon 07/27 04Z 0.28 2108  79  31  12 0.00
Mon 07/27 05Z 0.34 2209  81  32  12 0.00
Mon 07/27 06Z 0.34 2308  80  31  12 0.00
Mon 07/27 07Z 0.27 2307  79  29  12 0.00
Mon 07/27 08Z 0.26 2307  79  28  12 0.00
Mon 07/27 09Z 0.23 2306  81  27  12 0.00
Mon 07/27 10Z 0.19 2305  81  26  12 0.00
Mon 07/27 11Z 0.15 2105  81  26  12 0.00
Mon 07/27 12Z 0.16 2106  81  28  12 0.00
Mon 07/27 13Z 0.17 2106  82  30  12 0.00
Mon 07/27 14Z 0.18 2004  83  33  12 0.00
Mon 07/27 15Z 0.42 2004  85  35  12 0.00
Mon 07/27 16Z 0.21 1803  84  38  12 0.00
Mon 07/27 17Z 0.26 1704  84  44  13 0.00
Mon 07/27 18Z 0.20 1705  83  53  13 0.00
Mon 07/27 19Z 0.37 1906  83  65  13 0.00
Mon 07/27 20Z 0.46 1906  83  69  13 0.00
Mon 07/27 21Z 0.27 1907  84  68  13 0.00
Mon 07/27 22Z 0.27 1907  85  66  13 0.01
Mon 07/27 23Z 0.17 1908  85  60  13 0.00
Tue 07/28 00Z 0.23 2009  87  62  13 0.00
Tue 07/28 01Z 0.21 2010  90  65  13 0.00
Tue 07/28 02Z 0.24 2011  92  71  13 0.00
Tue 07/28 03Z 0.28 2013  93  74  13 0.01
Tue 07/28 04Z 0.28 2014  94  69  13 0.02
Tue 07/28 05Z 0.28 2014  94  67  13 0.03

Run total areal avg QPF for the greens is: 0.07 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