NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260725_0600
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 06Z 0.04 1903  61  39  13 0.00
Sat 07/25 07Z 0.04 1704  61  36  13 0.00
Sat 07/25 08Z 0.04 1804  62  34  13 0.00
Sat 07/25 09Z 0.04 1804  63  32  12 0.00
Sat 07/25 10Z 0.02 1705  64  31  12 0.00
Sat 07/25 11Z 0.04 1705  64  31  12 0.00
Sat 07/25 12Z 0.07 1607  64  31  12 0.00
Sat 07/25 13Z 0.04 1709  64  31  12 0.00
Sat 07/25 14Z 0.08 1809  66  30  12 0.00
Sat 07/25 15Z 0.19 1907  70  30  12 0.00
Sat 07/25 16Z 0.22 1806  74  30  12 0.00
Sat 07/25 17Z 0.36 1805  76  29  12 0.00
Sat 07/25 18Z 0.29 1705  78  30  13 0.00
Sat 07/25 19Z 0.63 1606  77  29  13 0.00
Sat 07/25 20Z 0.60 1607  76  28  13 0.00
Sat 07/25 21Z 0.49 1608  74  28  13 0.00
Sat 07/25 22Z 0.34 1609  71  24  13 0.00
Sat 07/25 23Z 0.29 1611  69  22  13 0.00
Sun 07/26 00Z 0.16 1712  70  22  13 0.00
Sun 07/26 01Z 0.10 1813  71  23  13 0.00
Sun 07/26 02Z 0.15 1814  73  23  12 0.00
Sun 07/26 03Z 0.24 1915  74  23  12 0.00
Sun 07/26 04Z 0.27 1914  75  23  12 0.00
Sun 07/26 05Z 0.33 2013  77  22  12 0.00
Sun 07/26 06Z 0.35 2012  78  21  12 0.00
Sun 07/26 07Z 0.38 2112  79  21  11 0.00
Sun 07/26 08Z 0.37 2110  78  20  11 0.00
Sun 07/26 09Z 0.30 2109  77  18  11 0.00
Sun 07/26 10Z 0.31 2208  75  17  11 0.00
Sun 07/26 11Z 0.26 2107  73  15  11 0.00
Sun 07/26 12Z 0.16 2006  73  13  11 0.00
Sun 07/26 13Z 0.09 1806  74  11  11 0.00
Sun 07/26 14Z 0.16 1706  76  10  11 0.00
Sun 07/26 15Z 0.38 1706  78  10  11 0.00
Sun 07/26 16Z 0.66 1706  78  10  12 0.00
Sun 07/26 17Z 0.69 1705  78  10  12 0.00
Sun 07/26 18Z 0.49 1705  78  11  12 0.00
Sun 07/26 19Z 0.43 1706  77  14  13 0.00
Sun 07/26 20Z 0.40 1706  77  18  13 0.00
Sun 07/26 21Z 0.41 1707  77  23  13 0.00
Sun 07/26 22Z 0.27 1708  77  32  13 0.00
Sun 07/26 23Z 0.13 1708  77  42  13 0.00
Mon 07/27 00Z 0.12 1809  77  48  13 0.00
Mon 07/27 01Z 0.11 1810  77  56  12 0.00
Mon 07/27 02Z 0.13 1911  77  61  12 0.00
Mon 07/27 03Z 0.19 2010  77  64  12 0.00
Mon 07/27 04Z 0.26 2109  77  68  12 0.00
Mon 07/27 05Z 0.30 2209  78  71  12 0.00
Mon 07/27 06Z 0.34 2209  79  70  12 0.00
Mon 07/27 07Z 0.35 2309  79  69  12 0.00
Mon 07/27 08Z 0.29 2208  79  67  12 0.00
Mon 07/27 09Z 0.25 2207  80  65  12 0.00
Mon 07/27 10Z 0.18 2206  81  61  12 0.00
Mon 07/27 11Z 0.11 2104  81  58  12 0.00
Mon 07/27 12Z 0.04 1904  81  57  12 0.00
Mon 07/27 13Z 0.03 1704  81  58  12 0.00
Mon 07/27 14Z 0.03 1805  82  61  12 0.00
Mon 07/27 15Z 0.09 1705  82  61  12 0.00
Mon 07/27 16Z 0.26 1706  83  61  12 0.00
Mon 07/27 17Z 0.31 1706  84  63  12 0.00

Run total areal avg QPF for the greens is: 0.00 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