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