Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260719_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)
=== ===== === ==== ==== === === === ====
Sun 07/19 00Z 0.62 2327 95 87 15 0.00
Sun 07/19 01Z 0.87 2429 94 90 15 0.11
Sun 07/19 02Z 1.01 2530 96 75 14 0.12
Sun 07/19 03Z 1.05 2629 99 75 14 0.06
Sun 07/19 04Z 0.94 2725 98 76 13 0.08
Sun 07/19 05Z 0.96 2825 98 74 13 0.10
Sun 07/19 06Z 0.99 3028 98 46 11 0.08
Sun 07/19 07Z 0.81 3028 97 22 10 0.03
Sun 07/19 08Z 0.68 3130 96 13 8 0.03
Sun 07/19 09Z 0.59 3231 95 15 8 0.02
Sun 07/19 10Z 0.54 3231 94 18 7 0.02
Sun 07/19 11Z 0.53 3231 94 17 7 0.02
Sun 07/19 12Z 0.54 3230 94 14 7 0.02
Sun 07/19 13Z 0.56 3228 94 10 6 0.01
Sun 07/19 14Z 0.51 3226 91 7 7 0.01
Sun 07/19 15Z 0.53 3224 87 8 7 0.01
Sun 07/19 16Z 0.97 3123 84 11 7 0.00
Sun 07/19 17Z 5.43 3121 79 13 7 0.00
Sun 07/19 18Z 10.38 3020 75 12 7 0.00
Sun 07/19 19Z 11.92 3020 71 13 7 0.00
Sun 07/19 20Z 13.04 2921 68 13 8 0.00
Sun 07/19 21Z 12.84 3022 67 14 8 0.00
Sun 07/19 22Z 10.62 3023 67 15 8 0.00
Sun 07/19 23Z 4.90 3024 66 15 8 0.00
Mon 07/20 00Z 3.06 3125 68 18 8 0.00
Mon 07/20 01Z 2.38 3126 72 20 7 0.00
Mon 07/20 02Z 2.46 3126 77 18 7 0.00
Mon 07/20 03Z 1.46 3126 77 16 7 0.00
Mon 07/20 04Z 1.28 3126 76 15 7 0.00
Mon 07/20 05Z 1.18 3125 77 14 7 0.00
Mon 07/20 06Z 0.86 3223 78 12 7 0.00
Mon 07/20 07Z 0.66 3221 79 18 7 0.00
Mon 07/20 08Z 0.60 3220 82 24 7 0.00
Mon 07/20 09Z 0.53 3219 79 32 7 0.00
Mon 07/20 10Z 0.57 3219 77 29 7 0.00
Mon 07/20 11Z 0.55 3118 77 34 7 0.00
Mon 07/20 12Z 0.50 3116 75 39 8 0.00
Mon 07/20 13Z 0.54 3115 75 49 8 0.00
Mon 07/20 14Z 0.64 3011 75 43 8 0.00
Mon 07/20 15Z 1.67 2909 76 47 8 0.00
Mon 07/20 16Z 2.66 2808 76 49 8 0.00
Mon 07/20 17Z 3.52 2608 75 51 9 0.00
Mon 07/20 18Z 3.57 2507 76 49 9 0.00
Mon 07/20 19Z 3.23 2407 76 48 10 0.00
Mon 07/20 20Z 2.72 2308 76 48 10 0.00
Mon 07/20 21Z 1.72 2208 76 44 11 0.00
Mon 07/20 22Z 0.70 2209 73 38 11 0.00
Mon 07/20 23Z 0.36 2110 70 34 11 0.00
Tue 07/21 00Z 0.38 2113 65 30 12 0.00
Tue 07/21 01Z 0.36 2015 59 26 12 0.00
Tue 07/21 02Z 0.35 2017 58 25 12 0.00
Tue 07/21 03Z 0.39 2019 60 23 12 0.00
Tue 07/21 04Z 0.47 2121 59 21 12 0.00
Tue 07/21 05Z 0.52 2123 64 18 12 0.00
Tue 07/21 06Z 0.51 2123 65 17 12 0.00
Tue 07/21 07Z 0.47 2123 66 16 12 0.00
Tue 07/21 08Z 0.45 2123 62 14 12 0.00
Tue 07/21 09Z 0.41 2123 63 14 11 0.00
Tue 07/21 10Z 0.34 2023 70 14 11 0.00
Tue 07/21 11Z 0.34 2025 76 10 11 0.00
Run total areal avg QPF for the greens is: 0.72 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