NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260427_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)
=== ===== === ==== ==== === === === ====
Mon 04/27 06Z 0.18 0704  64  49   4 0.00
Mon 04/27 07Z 0.16 0604  64  47   4 0.00
Mon 04/27 08Z 0.13 0503  64  44   4 0.00
Mon 04/27 09Z 0.10 0303  65  44   4 0.00
Mon 04/27 10Z 0.10 0205  66  46   4 0.00
Mon 04/27 11Z 0.15 0305  66  44   4 0.00
Mon 04/27 12Z 0.17 0405  67  40   4 0.00
Mon 04/27 13Z 0.19 0505  67  34   4 0.00
Mon 04/27 14Z 0.35 0605  67  30   4 0.00
Mon 04/27 15Z 1.00 0704  66  27   4 0.00
Mon 04/27 16Z 1.97 0904  64  25   4 0.00
Mon 04/27 17Z 1.59 1002  63  23   5 0.00
Mon 04/27 18Z 0.67 2100  64  25   5 0.00
Mon 04/27 19Z 0.45 3500  66  26   5 0.00
Mon 04/27 20Z 0.30 0100  67  24   6 0.00
Mon 04/27 21Z 0.56 0601  67  22   6 0.00
Mon 04/27 22Z 0.54 1202  64  20   6 0.00
Mon 04/27 23Z 0.10 1602  64  22   6 0.00
Tue 04/28 00Z 0.17 1504  64  16   6 0.00
Tue 04/28 01Z 0.17 1606  62  13   6 0.00
Tue 04/28 02Z 0.09 1708  62  12   6 0.00
Tue 04/28 03Z 0.05 1709  61  12   5 0.00
Tue 04/28 04Z 0.03 1708  60  12   6 0.00
Tue 04/28 05Z 0.09 1609  58  12   6 0.00
Tue 04/28 06Z 0.13 1610  58  12   5 0.00
Tue 04/28 07Z 0.17 1611  58  11   5 0.00
Tue 04/28 08Z 0.12 1811  60  11   5 0.00
Tue 04/28 09Z 0.11 1811  60  11   5 0.00
Tue 04/28 10Z 0.11 1713  57  10   5 0.00
Tue 04/28 11Z 0.14 1715  56  10   5 0.00
Tue 04/28 12Z 0.23 1617  55  10   5 0.00
Tue 04/28 13Z 0.30 1619  56  10   5 0.00
Tue 04/28 14Z 0.75 1620  59   9   4 0.00
Tue 04/28 15Z 1.49 1618  61   9   4 0.00
Tue 04/28 16Z 2.52 1617  60   9   5 0.00
Tue 04/28 17Z 2.56 1616  59   8   5 0.00
Tue 04/28 18Z 2.46 1615  59   7   5 0.00
Tue 04/28 19Z 3.24 1615  60   7   6 0.00
Tue 04/28 20Z 2.13 1616  63   7   6 0.00
Tue 04/28 21Z 2.72 1617  65   7   5 0.00
Tue 04/28 22Z 0.74 1718  67   9   5 0.00
Tue 04/28 23Z 0.23 1719  69  12   5 0.00
Wed 04/29 00Z 0.09 1720  74  49   4 0.00
Wed 04/29 01Z 0.06 1720  76  76   4 0.00
Wed 04/29 02Z 0.05 1820  77  94   4 0.00
Wed 04/29 03Z 0.06 1819  78  97   4 0.00
Wed 04/29 04Z 0.10 1919  79  96   4 0.00
Wed 04/29 05Z 0.15 1919  78  93   4 0.00
Wed 04/29 06Z 0.16 1919  70  86   4 0.00
Wed 04/29 07Z 0.13 1918  62  82   4 0.00
Wed 04/29 08Z 0.16 1917  57  81   5 0.00
Wed 04/29 09Z 0.23 2019  59  82   4 0.00
Wed 04/29 10Z 0.31 2021  66  86   4 0.00
Wed 04/29 11Z 0.15 2018  65  80   5 0.00
Wed 04/29 12Z 0.12 1916  67  74   6 0.00
Wed 04/29 13Z 0.05 1814  69  54   6 0.00
Wed 04/29 14Z 0.04 1814  69  45   6 0.00
Wed 04/29 15Z 0.02 1813  68  44   6 0.00
Wed 04/29 16Z 0.07 1812  66  44   6 0.00
Wed 04/29 17Z 0.44 1712  65  38   6 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