Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260429_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 04/29 18Z 1.57 1507 71 70 7 0.00
Wed 04/29 19Z 2.53 1512 72 63 7 0.00
Wed 04/29 20Z 2.82 1515 74 62 7 0.00
Wed 04/29 21Z 2.56 1518 76 58 6 0.00
Wed 04/29 22Z 1.92 1519 79 78 6 0.00
Wed 04/29 23Z 0.37 1521 85 87 5 0.00
Thu 04/30 00Z 0.06 1621 88 93 6 0.00
Thu 04/30 01Z 0.05 1620 90 95 6 0.00
Thu 04/30 02Z 0.05 1622 89 95 6 0.00
Thu 04/30 03Z 0.06 1624 86 93 7 0.00
Thu 04/30 04Z 0.06 1626 86 92 7 0.00
Thu 04/30 05Z 0.06 1725 90 99 5 0.01
Thu 04/30 06Z 0.07 1725 93 99 4 0.07
Thu 04/30 07Z 0.04 1725 96 99 3 0.14
Thu 04/30 08Z 0.06 1726 97 99 4 0.12
Thu 04/30 09Z 0.17 1825 98 97 3 0.10
Thu 04/30 10Z 0.23 1923 97 97 3 0.06
Thu 04/30 11Z 0.24 2018 97 97 3 0.02
Thu 04/30 12Z 0.22 2015 98 97 3 0.01
Thu 04/30 13Z 0.23 2112 98 94 3 0.02
Thu 04/30 14Z 0.24 2210 98 92 3 0.01
Thu 04/30 15Z 0.20 2208 98 95 3 0.02
Thu 04/30 16Z 0.09 2303 98 95 3 0.04
Thu 04/30 17Z 0.03 1901 98 94 3 0.01
Thu 04/30 18Z 0.03 1802 99 96 2 0.01
Thu 04/30 19Z 0.06 2102 99 98 2 0.03
Thu 04/30 20Z 0.06 2601 99 95 2 0.03
Thu 04/30 21Z 0.10 3003 99 87 2 0.02
Thu 04/30 22Z 0.15 3106 99 83 2 0.01
Thu 04/30 23Z 0.17 3108 99 89 2 0.01
Fri 05/01 00Z 0.22 3211 99 96 1 0.02
Fri 05/01 01Z 0.21 3315 97 97 1 0.03
Fri 05/01 02Z 0.27 3216 95 98 0 0.02
Fri 05/01 03Z 0.28 3216 95 97 0 0.02
Fri 05/01 04Z 0.33 3217 96 96 0 0.02
Fri 05/01 05Z 0.35 3117 95 87 0 0.01
Fri 05/01 06Z 0.32 3117 92 86 0 0.01
Fri 05/01 07Z 0.31 3118 89 83 0 0.01
Fri 05/01 08Z 0.33 3119 85 70 0 0.00
Fri 05/01 09Z 0.35 3120 82 68 0 0.00
Fri 05/01 10Z 0.35 3120 80 68 0 0.00
Fri 05/01 11Z 0.33 3120 78 69 -1 0.00
Fri 05/01 12Z 0.36 3120 78 70 -1 0.00
Fri 05/01 13Z 0.39 3118 78 70 -1 0.00
Fri 05/01 14Z 0.45 3117 76 73 -2 0.00
Fri 05/01 15Z 2.18 3215 76 71 -2 0.00
Fri 05/01 16Z 3.89 3112 74 75 -2 0.00
Fri 05/01 17Z 4.72 3010 74 73 -1 0.00
Fri 05/01 18Z 4.71 2909 78 70 -1 0.00
Fri 05/01 19Z 3.25 2910 86 66 -1 0.01
Fri 05/01 20Z 2.52 2911 85 61 -1 0.01
Fri 05/01 21Z 2.84 3010 82 59 -1 0.00
Fri 05/01 22Z 2.03 3010 83 68 -1 0.00
Fri 05/01 23Z 0.92 3011 81 74 -1 0.01
Sat 05/02 00Z 0.66 3111 81 69 -1 0.01
Sat 05/02 01Z 0.72 3112 81 70 -1 0.00
Sat 05/02 02Z 0.68 3011 83 73 -2 0.00
Sat 05/02 03Z 0.50 3011 82 73 -2 0.00
Sat 05/02 04Z 0.49 3012 81 71 -2 0.00
Sat 05/02 05Z 0.52 3012 84 66 -2 0.00
Run total areal avg QPF for the Central_Greens is: 0.92 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