Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260907_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)
=== ===== === ==== ==== === === === ====
Mon 09/07 12Z 0.19 3421 82 20 8 0.00
Mon 09/07 13Z 0.22 3422 79 15 8 0.00
Mon 09/07 14Z 0.21 3425 75 11 8 0.00
Mon 09/07 15Z 0.20 3424 70 9 9 0.00
Mon 09/07 16Z 0.21 3422 67 7 9 0.00
Mon 09/07 17Z 0.29 3419 67 5 9 0.00
Mon 09/07 18Z 0.55 3319 68 4 9 0.00
Mon 09/07 19Z 1.24 3318 68 4 9 0.00
Mon 09/07 20Z 2.41 3316 68 6 9 0.00
Mon 09/07 21Z 2.10 3217 69 8 9 0.00
Mon 09/07 22Z 1.09 3116 71 12 9 0.00
Mon 09/07 23Z 1.67 3118 72 14 9 0.00
Tue 09/08 00Z 1.53 3118 73 21 9 0.00
Tue 09/08 01Z 1.54 3119 75 26 9 0.00
Tue 09/08 02Z 1.04 3119 76 36 9 0.00
Tue 09/08 03Z 0.68 3216 76 52 9 0.00
Tue 09/08 04Z 0.52 3215 74 60 10 0.00
Tue 09/08 05Z 0.54 3115 74 67 10 0.00
Tue 09/08 06Z 0.65 3118 76 71 9 0.00
Tue 09/08 07Z 0.63 3117 75 60 10 0.00
Tue 09/08 08Z 0.65 3017 75 59 10 0.00
Tue 09/08 09Z 0.64 3017 75 61 10 0.00
Tue 09/08 10Z 0.67 3019 77 65 9 0.00
Tue 09/08 11Z 0.60 3118 78 71 9 0.00
Tue 09/08 12Z 0.46 3116 81 77 9 0.01
Tue 09/08 13Z 0.36 3115 83 84 9 0.01
Tue 09/08 14Z 0.31 3113 84 88 10 0.01
Tue 09/08 15Z 0.32 3113 87 83 9 0.01
Tue 09/08 16Z 0.29 3213 90 59 9 0.01
Tue 09/08 17Z 0.22 3312 89 42 9 0.00
Tue 09/08 18Z 0.15 3311 87 37 10 0.00
Tue 09/08 19Z 0.15 3309 81 35 10 0.00
Tue 09/08 20Z 0.14 3309 77 53 10 0.00
Tue 09/08 21Z 0.11 3307 72 64 10 0.00
Tue 09/08 22Z 0.11 3307 66 66 11 0.00
Tue 09/08 23Z 0.10 3205 62 62 11 0.00
Wed 09/09 00Z 0.12 3004 60 61 11 0.00
Wed 09/09 01Z 0.13 3004 63 64 11 0.00
Wed 09/09 02Z 0.16 2804 67 69 11 0.00
Wed 09/09 03Z 0.20 2605 73 73 11 0.00
Wed 09/09 04Z 0.21 2506 80 75 11 0.00
Wed 09/09 05Z 0.21 2307 87 72 11 0.00
Wed 09/09 06Z 0.22 2209 92 66 11 0.00
Wed 09/09 07Z 0.22 2111 93 60 11 0.00
Wed 09/09 08Z 0.29 2213 94 58 11 0.00
Wed 09/09 09Z 0.32 2215 94 60 11 0.00
Wed 09/09 10Z 0.29 2115 90 56 12 0.00
Wed 09/09 11Z 0.34 2118 89 63 12 0.00
Wed 09/09 12Z 0.40 2120 88 58 12 0.00
Wed 09/09 13Z 0.43 2221 87 52 11 0.00
Wed 09/09 14Z 0.43 2220 85 55 11 0.00
Wed 09/09 15Z 0.43 2121 82 45 12 0.00
Wed 09/09 16Z 0.46 2120 86 24 12 0.00
Wed 09/09 17Z 0.46 2121 86 11 12 0.00
Wed 09/09 18Z 0.44 2122 86 41 12 0.00
Wed 09/09 19Z 0.47 2124 88 58 12 0.00
Wed 09/09 20Z 0.48 2127 93 74 13 0.01
Wed 09/09 21Z 0.59 2129 93 73 13 0.02
Wed 09/09 22Z 0.70 2232 94 66 14 0.01
Wed 09/09 23Z 0.73 2233 93 57 14 0.03
Run total areal avg QPF for the greens is: 0.12 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