Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260205_0000
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)
=== ===== === ==== ==== === === === ====
Thu 02/05 00Z 0.45 3016 82 35 -12 0.00
Thu 02/05 01Z 0.39 3118 81 34 -12 0.00
Thu 02/05 02Z 0.39 3018 85 36 -12 0.00
Thu 02/05 03Z 0.38 3017 86 37 -12 0.00
Thu 02/05 04Z 0.35 3016 86 39 -12 0.00
Thu 02/05 05Z 0.39 2917 86 41 -12 0.00
Thu 02/05 06Z 0.42 2918 88 39 -13 0.00
Thu 02/05 07Z 0.45 2918 88 42 -13 0.00
Thu 02/05 08Z 0.49 2919 86 50 -13 0.00
Thu 02/05 09Z 0.52 2920 86 56 -14 0.01
Thu 02/05 10Z 0.52 2920 86 67 -14 0.01
Thu 02/05 11Z 0.51 2920 88 78 -15 0.00
Thu 02/05 12Z 0.51 3020 89 52 -15 0.00
Thu 02/05 13Z 0.47 3020 87 9 -16 0.00
Thu 02/05 14Z 0.40 3119 83 2 -16 0.00
Thu 02/05 15Z 0.35 3118 81 2 -16 0.00
Thu 02/05 16Z 0.33 3117 80 2 -16 0.00
Thu 02/05 17Z 0.30 3115 77 3 -16 0.00
Thu 02/05 18Z 0.27 3113 74 3 -16 0.00
Thu 02/05 19Z 0.25 3112 69 4 -15 0.00
Thu 02/05 20Z 0.21 3112 63 3 -14 0.00
Thu 02/05 21Z 0.19 3112 59 3 -14 0.00
Thu 02/05 22Z 0.18 3112 55 3 -13 0.00
Thu 02/05 23Z 0.15 3212 52 4 -12 0.00
Fri 02/06 00Z 0.11 3210 50 4 -12 0.00
Fri 02/06 01Z 0.11 3210 50 5 -12 0.00
Fri 02/06 02Z 0.08 3309 46 6 -12 0.00
Fri 02/06 03Z 0.04 3407 40 7 -11 0.00
Fri 02/06 04Z 0.03 3405 36 8 -11 0.00
Fri 02/06 05Z 0.02 3403 34 10 -10 0.00
Fri 02/06 06Z 0.02 3302 32 11 -10 0.00
Fri 02/06 07Z 0.01 3000 31 10 -10 0.00
Fri 02/06 08Z 0.02 2201 30 9 -11 0.00
Fri 02/06 09Z 0.02 2002 28 9 -10 0.00
Fri 02/06 10Z 0.03 2003 27 8 -10 0.00
Fri 02/06 11Z 0.03 2004 26 7 -10 0.00
Fri 02/06 12Z 0.04 2103 26 8 -10 0.00
Fri 02/06 13Z 0.05 2203 26 13 -10 0.00
Fri 02/06 14Z 0.04 2203 29 31 -11 0.00
Fri 02/06 15Z 0.04 2004 34 50 -11 0.00
Fri 02/06 16Z 0.06 2104 38 67 -11 0.00
Fri 02/06 17Z 0.07 2104 41 79 -11 0.00
Fri 02/06 18Z 0.06 2104 44 85 -11 0.00
Fri 02/06 19Z 0.07 2004 49 87 -11 0.00
Fri 02/06 20Z 0.11 2104 54 87 -11 0.00
Fri 02/06 21Z 0.13 2205 57 87 -12 0.00
Fri 02/06 22Z 0.14 2205 57 87 -12 0.00
Fri 02/06 23Z 0.15 2206 52 89 -12 0.00
Sat 02/07 00Z 0.16 2207 52 90 -11 0.00
Sat 02/07 01Z 0.17 2307 55 88 -12 0.00
Sat 02/07 02Z 0.20 2308 64 88 -12 0.00
Sat 02/07 03Z 0.20 2208 79 88 -12 0.00
Sat 02/07 04Z 0.14 2206 87 88 -12 0.00
Sat 02/07 05Z 0.12 2205 89 87 -12 0.01
Sat 02/07 06Z 0.13 2404 90 87 -12 0.01
Sat 02/07 07Z 0.15 2604 90 85 -12 0.01
Sat 02/07 08Z 0.16 2905 91 87 -13 0.01
Sat 02/07 09Z 0.16 3106 91 85 -13 0.01
Sat 02/07 10Z 0.21 3210 90 83 -13 0.02
Sat 02/07 11Z 0.15 3416 90 81 -14 0.02
Run total areal avg QPF for the greens is: 0.11 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