Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260215_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)
=== ===== === ==== ==== === === === ====
Sun 02/15 12Z 0.14 3315 73 9 -11 0.00
Sun 02/15 13Z 0.10 3415 57 11 -11 0.00
Sun 02/15 14Z 0.08 3513 43 12 -10 0.00
Sun 02/15 15Z 0.09 0111 35 14 -9 0.00
Sun 02/15 16Z 0.13 0310 33 18 -8 0.00
Sun 02/15 17Z 0.14 0508 31 23 -8 0.00
Sun 02/15 18Z 0.14 0806 31 30 -7 0.00
Sun 02/15 19Z 0.12 1005 31 38 -7 0.00
Sun 02/15 20Z 0.10 1205 30 44 -6 0.00
Sun 02/15 21Z 0.09 1306 28 45 -6 0.00
Sun 02/15 22Z 0.08 1507 26 41 -5 0.00
Sun 02/15 23Z 0.06 1609 25 36 -5 0.00
Mon 02/16 00Z 0.06 1611 25 36 -5 0.00
Mon 02/16 01Z 0.04 1712 30 37 -5 0.00
Mon 02/16 02Z 0.02 1713 36 36 -5 0.00
Mon 02/16 03Z 0.02 1814 44 36 -5 0.00
Mon 02/16 04Z 0.03 1814 53 41 -6 0.00
Mon 02/16 05Z 0.05 1815 62 50 -6 0.00
Mon 02/16 06Z 0.05 1815 70 68 -6 0.00
Mon 02/16 07Z 0.04 1816 73 84 -6 0.00
Mon 02/16 08Z 0.04 1816 76 89 -5 0.00
Mon 02/16 09Z 0.03 1814 81 90 -5 0.01
Mon 02/16 10Z 0.04 1814 84 92 -5 0.00
Mon 02/16 11Z 0.06 1914 85 89 -6 0.00
Mon 02/16 12Z 0.08 1914 88 91 -5 0.00
Mon 02/16 13Z 0.08 1913 89 83 -5 0.00
Mon 02/16 14Z 0.08 1913 90 73 -4 0.00
Mon 02/16 15Z 0.10 2013 91 61 -4 0.00
Mon 02/16 16Z 0.10 2011 92 54 -4 0.00
Mon 02/16 17Z 0.08 2010 92 46 -4 0.00
Mon 02/16 18Z 0.09 2010 92 40 -4 0.00
Mon 02/16 19Z 0.12 2011 91 36 -4 0.00
Mon 02/16 20Z 0.15 2112 91 35 -4 0.00
Mon 02/16 21Z 0.15 2012 91 39 -4 0.00
Mon 02/16 22Z 0.15 2013 90 38 -3 0.00
Mon 02/16 23Z 0.19 2115 92 34 -4 0.00
Tue 02/17 00Z 0.24 2116 93 48 -4 0.00
Tue 02/17 01Z 0.29 2218 93 86 -4 0.00
Tue 02/17 02Z 0.37 2220 94 90 -4 0.00
Tue 02/17 03Z 0.34 2318 88 90 -3 0.00
Tue 02/17 04Z 0.32 2416 87 91 -3 0.00
Tue 02/17 05Z 0.30 2415 85 94 -3 0.00
Tue 02/17 06Z 0.35 2417 87 92 -3 0.00
Tue 02/17 07Z 0.33 2415 90 92 -3 0.00
Tue 02/17 08Z 0.33 2415 94 94 -3 0.00
Tue 02/17 09Z 0.33 2415 94 91 -2 0.01
Tue 02/17 10Z 0.35 2514 91 92 -3 0.01
Tue 02/17 11Z 0.36 2514 91 87 -3 0.01
Tue 02/17 12Z 0.36 2613 93 74 -3 0.01
Tue 02/17 13Z 0.37 2614 95 62 -3 0.01
Tue 02/17 14Z 0.35 2713 96 50 -3 0.01
Tue 02/17 15Z 0.30 2711 96 37 -3 0.01
Tue 02/17 16Z 0.28 2810 96 19 -3 0.00
Tue 02/17 17Z 0.30 2811 96 13 -3 0.00
Tue 02/17 18Z 0.31 2811 95 22 -3 0.00
Tue 02/17 19Z 0.35 2812 95 23 -3 0.00
Tue 02/17 20Z 0.37 2913 92 24 -3 0.00
Tue 02/17 21Z 0.37 2813 88 24 -3 0.00
Tue 02/17 22Z 0.39 2814 81 22 -3 0.00
Tue 02/17 23Z 0.38 2814 72 19 -3 0.01
Run total areal avg QPF for the greens is: 0.09 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