Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260718_0600
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)
=== ===== === ==== ==== === === === ====
Sat 07/18 06Z 0.30 2208 59 16 12 0.00
Sat 07/18 07Z 0.47 2311 61 51 12 0.00
Sat 07/18 08Z 0.36 2310 62 89 12 0.00
Sat 07/18 09Z 0.43 2313 61 98 12 0.00
Sat 07/18 10Z 0.49 2315 68 90 11 0.01
Sat 07/18 11Z 0.46 2315 65 96 12 0.00
Sat 07/18 12Z 0.41 2119 70 94 13 0.02
Sat 07/18 13Z 0.47 2122 71 66 14 0.01
Sat 07/18 14Z 0.50 2123 73 59 15 0.00
Sat 07/18 15Z 0.62 2127 81 58 15 0.00
Sat 07/18 16Z 0.75 2127 90 84 15 0.00
Sat 07/18 17Z 0.72 2229 96 78 15 0.41
Sat 07/18 18Z 0.73 2231 93 71 16 0.10
Sat 07/18 19Z 0.84 2231 95 77 16 0.01
Sat 07/18 20Z 0.90 2227 95 77 16 0.02
Sat 07/18 21Z 0.89 2227 94 69 16 0.05
Sat 07/18 22Z 0.89 2227 93 73 16 0.01
Sat 07/18 23Z 0.82 2326 93 79 15 0.01
Sun 07/19 00Z 0.77 2429 95 79 15 0.11
Sun 07/19 01Z 0.78 2528 95 73 15 0.02
Sun 07/19 02Z 0.81 2527 96 62 15 0.03
Sun 07/19 03Z 0.86 2528 95 50 15 0.02
Sun 07/19 04Z 0.90 2629 96 60 14 0.04
Sun 07/19 05Z 0.90 2928 98 63 12 0.05
Sun 07/19 06Z 0.61 3128 94 39 11 0.03
Sun 07/19 07Z 0.40 3229 92 20 10 0.02
Sun 07/19 08Z 0.31 3228 88 17 9 0.01
Sun 07/19 09Z 0.30 3228 86 16 9 0.01
Sun 07/19 10Z 0.30 3229 87 10 8 0.01
Sun 07/19 11Z 0.34 3228 89 6 8 0.01
Sun 07/19 12Z 0.33 3226 89 9 8 0.01
Sun 07/19 13Z 0.32 3224 90 8 7 0.01
Sun 07/19 14Z 0.30 3221 89 4 7 0.00
Sun 07/19 15Z 0.29 3220 85 4 7 0.00
Sun 07/19 16Z 0.38 3218 80 7 7 0.00
Sun 07/19 17Z 2.73 3117 76 8 7 0.00
Sun 07/19 18Z 6.70 3017 71 7 7 0.00
Sun 07/19 19Z 8.47 3017 68 10 8 0.00
Sun 07/19 20Z 8.52 3016 66 11 8 0.00
Sun 07/19 21Z 8.45 3017 63 10 9 0.00
Sun 07/19 22Z 6.62 3018 65 8 9 0.00
Sun 07/19 23Z 3.23 3019 66 7 9 0.00
Mon 07/20 00Z 1.93 3022 64 8 8 0.00
Mon 07/20 01Z 1.53 3123 66 7 8 0.00
Mon 07/20 02Z 1.50 3123 71 7 8 0.00
Mon 07/20 03Z 1.12 3224 73 5 7 0.00
Mon 07/20 04Z 0.72 3224 73 5 7 0.00
Mon 07/20 05Z 0.51 3223 74 5 7 0.00
Mon 07/20 06Z 0.40 3320 75 5 7 0.00
Mon 07/20 07Z 0.31 3318 73 6 7 0.00
Mon 07/20 08Z 0.31 3217 73 7 7 0.00
Mon 07/20 09Z 0.26 3215 74 9 7 0.00
Mon 07/20 10Z 0.22 3213 72 13 8 0.00
Mon 07/20 11Z 0.25 3111 73 22 8 0.00
Mon 07/20 12Z 0.29 3011 73 23 8 0.00
Mon 07/20 13Z 0.33 2909 74 27 8 0.00
Mon 07/20 14Z 0.42 2707 74 35 8 0.00
Mon 07/20 15Z 0.96 2607 74 45 8 0.00
Mon 07/20 16Z 1.64 2507 71 49 8 0.00
Mon 07/20 17Z 1.77 2607 67 58 9 0.00
Run total areal avg QPF for the Central_Greens is: 1.03 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