Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260429_1800
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 04/29 18Z 1.67 1608 71 72 7 0.00
Wed 04/29 19Z 2.91 1511 72 62 7 0.00
Wed 04/29 20Z 4.03 1515 74 58 7 0.00
Wed 04/29 21Z 3.51 1518 76 54 6 0.00
Wed 04/29 22Z 2.14 1520 79 65 6 0.00
Wed 04/29 23Z 0.49 1522 83 80 6 0.00
Thu 04/30 00Z 0.16 1622 86 90 6 0.00
Thu 04/30 01Z 0.10 1721 88 93 6 0.00
Thu 04/30 02Z 0.10 1623 87 94 6 0.00
Thu 04/30 03Z 0.12 1625 85 92 7 0.00
Thu 04/30 04Z 0.12 1627 84 93 7 0.00
Thu 04/30 05Z 0.07 1727 88 98 5 0.01
Thu 04/30 06Z 0.03 1727 92 98 4 0.06
Thu 04/30 07Z 0.06 1728 94 99 4 0.12
Thu 04/30 08Z 0.06 1728 95 98 4 0.11
Thu 04/30 09Z 0.06 1828 96 97 3 0.08
Thu 04/30 10Z 0.12 1926 96 97 3 0.05
Thu 04/30 11Z 0.16 1921 97 98 3 0.03
Thu 04/30 12Z 0.16 2017 97 97 3 0.02
Thu 04/30 13Z 0.19 2114 97 93 3 0.02
Thu 04/30 14Z 0.22 2112 98 88 3 0.01
Thu 04/30 15Z 0.18 2208 98 87 3 0.02
Thu 04/30 16Z 0.10 2304 98 91 3 0.03
Thu 04/30 17Z 0.05 2102 98 92 3 0.01
Thu 04/30 18Z 0.04 2002 99 92 2 0.02
Thu 04/30 19Z 0.06 2202 99 94 2 0.02
Thu 04/30 20Z 0.08 2602 99 93 2 0.03
Thu 04/30 21Z 0.12 2903 99 89 2 0.02
Thu 04/30 22Z 0.19 3006 99 87 2 0.02
Thu 04/30 23Z 0.26 3109 99 91 2 0.02
Fri 05/01 00Z 0.34 3113 98 96 1 0.02
Fri 05/01 01Z 0.41 3215 96 96 1 0.03
Fri 05/01 02Z 0.44 3117 95 97 0 0.02
Fri 05/01 03Z 0.42 3117 94 96 0 0.02
Fri 05/01 04Z 0.43 3117 94 94 0 0.02
Fri 05/01 05Z 0.43 3117 94 89 0 0.01
Fri 05/01 06Z 0.40 3118 91 87 0 0.01
Fri 05/01 07Z 0.38 3018 88 84 0 0.01
Fri 05/01 08Z 0.40 3019 85 74 0 0.00
Fri 05/01 09Z 0.42 3020 84 73 0 0.00
Fri 05/01 10Z 0.43 3020 82 71 0 0.00
Fri 05/01 11Z 0.42 3020 80 72 -1 0.00
Fri 05/01 12Z 0.44 3020 80 72 -1 0.00
Fri 05/01 13Z 0.47 3119 80 71 -1 0.00
Fri 05/01 14Z 0.55 3118 77 73 -2 0.00
Fri 05/01 15Z 2.12 3116 76 71 -2 0.00
Fri 05/01 16Z 4.66 3114 75 71 -2 0.00
Fri 05/01 17Z 7.12 3012 76 70 -2 0.00
Fri 05/01 18Z 6.89 2911 77 70 -1 0.00
Fri 05/01 19Z 5.63 2912 81 66 -1 0.00
Fri 05/01 20Z 5.06 2912 80 58 -1 0.01
Fri 05/01 21Z 5.08 2911 79 57 -1 0.00
Fri 05/01 22Z 4.37 3011 79 64 -1 0.00
Fri 05/01 23Z 2.75 3012 78 68 -1 0.01
Sat 05/02 00Z 1.65 3013 78 65 -1 0.00
Sat 05/02 01Z 2.08 3013 78 66 -2 0.00
Sat 05/02 02Z 1.56 3013 79 65 -2 0.00
Sat 05/02 03Z 1.21 3013 78 65 -2 0.00
Sat 05/02 04Z 1.31 3013 78 65 -2 0.00
Sat 05/02 05Z 0.87 3014 80 62 -2 0.00
Run total areal avg QPF for the greens is: 0.86 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