Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260218_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)
=== ===== === ==== ==== === === === ====
Wed 02/18 12Z 0.40 3017 83 36 -5 0.00
Wed 02/18 13Z 0.38 3119 72 40 -5 0.00
Wed 02/18 14Z 0.31 3118 64 42 -5 0.00
Wed 02/18 15Z 0.26 3116 55 39 -5 0.00
Wed 02/18 16Z 0.23 3215 47 34 -4 0.00
Wed 02/18 17Z 0.19 3213 41 33 -5 0.00
Wed 02/18 18Z 0.11 3311 37 31 -5 0.00
Wed 02/18 19Z 0.09 3309 37 30 -5 0.00
Wed 02/18 20Z 0.06 3408 37 26 -5 0.00
Wed 02/18 21Z 0.04 3508 39 24 -5 0.00
Wed 02/18 22Z 0.04 0009 39 15 -5 0.00
Wed 02/18 23Z 0.08 0110 35 9 -5 0.00
Thu 02/19 00Z 0.12 0211 32 9 -5 0.00
Thu 02/19 01Z 0.14 0312 32 11 -5 0.00
Thu 02/19 02Z 0.15 0312 32 13 -5 0.00
Thu 02/19 03Z 0.14 0312 33 14 -6 0.00
Thu 02/19 04Z 0.12 0211 32 18 -6 0.00
Thu 02/19 05Z 0.10 0211 30 22 -5 0.00
Thu 02/19 06Z 0.12 0211 28 23 -5 0.00
Thu 02/19 07Z 0.14 0311 27 27 -5 0.00
Thu 02/19 08Z 0.10 0308 25 35 -6 0.00
Thu 02/19 09Z 0.09 0306 23 39 -6 0.00
Thu 02/19 10Z 0.09 0405 22 39 -6 0.00
Thu 02/19 11Z 0.09 0404 20 40 -5 0.00
Thu 02/19 12Z 0.08 0404 20 36 -5 0.00
Thu 02/19 13Z 0.05 0502 19 29 -5 0.00
Thu 02/19 14Z 0.04 0701 19 28 -5 0.00
Thu 02/19 15Z 0.02 1200 21 26 -4 0.00
Thu 02/19 16Z 0.02 1800 24 31 -4 0.00
Thu 02/19 17Z 0.03 2101 28 34 -4 0.00
Thu 02/19 18Z 0.04 2202 33 38 -4 0.00
Thu 02/19 19Z 0.05 2103 38 39 -4 0.00
Thu 02/19 20Z 0.07 2204 41 35 -3 0.00
Thu 02/19 21Z 0.06 2203 44 34 -3 0.00
Thu 02/19 22Z 0.04 2003 47 36 -3 0.00
Thu 02/19 23Z 0.03 2003 51 34 -3 0.00
Fri 02/20 00Z 0.04 2004 56 30 -3 0.00
Fri 02/20 01Z 0.03 2003 61 30 -3 0.00
Fri 02/20 02Z 0.02 1804 65 35 -3 0.00
Fri 02/20 03Z 0.05 1907 69 35 -4 0.00
Fri 02/20 04Z 0.04 1907 75 30 -4 0.00
Fri 02/20 05Z 0.07 1908 80 31 -4 0.00
Fri 02/20 06Z 0.09 2009 84 31 -4 0.00
Fri 02/20 07Z 0.12 2010 87 32 -3 0.00
Fri 02/20 08Z 0.11 2010 87 31 -3 0.00
Fri 02/20 09Z 0.08 2009 85 27 -2 0.00
Fri 02/20 10Z 0.07 2008 84 21 -2 0.00
Fri 02/20 11Z 0.06 2006 85 22 -2 0.00
Fri 02/20 12Z 0.04 1806 84 26 -1 0.00
Fri 02/20 13Z 0.03 1707 84 29 -1 0.00
Fri 02/20 14Z 0.04 1608 82 29 0 0.00
Fri 02/20 15Z 0.05 1610 81 37 0 0.00
Fri 02/20 16Z 0.08 1612 81 57 0 0.00
Fri 02/20 17Z 0.12 1514 85 73 0 0.00
Fri 02/20 18Z 0.18 1417 90 82 0 0.01
Fri 02/20 19Z 0.26 1321 93 91 0 0.02
Fri 02/20 20Z 0.31 1323 95 97 0 0.04
Fri 02/20 21Z 0.35 1324 96 97 -1 0.12
Fri 02/20 22Z 0.40 1224 95 98 -2 0.15
Fri 02/20 23Z 0.42 1224 96 98 -3 0.12
Run total areal avg QPF for the greens is: 0.46 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