Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260520_1200
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 05/20 12Z 0.90 2722 92 68 13 0.00
Wed 05/20 13Z 0.97 2724 88 68 13 0.00
Wed 05/20 14Z 1.13 2724 92 80 13 0.00
Wed 05/20 15Z 1.40 2624 96 80 13 0.02
Wed 05/20 16Z 1.18 2626 96 81 14 0.04
Wed 05/20 17Z 1.59 2725 94 71 13 0.04
Wed 05/20 18Z 1.19 2723 94 66 12 0.02
Wed 05/20 19Z 1.57 2821 91 59 11 0.01
Wed 05/20 20Z 2.42 2920 92 59 11 0.01
Wed 05/20 21Z 1.99 3020 89 57 10 0.01
Wed 05/20 22Z 0.52 3121 78 58 9 0.00
Wed 05/20 23Z 0.48 3122 77 55 8 0.00
Thu 05/21 00Z 0.45 3123 73 47 7 0.00
Thu 05/21 01Z 0.34 3223 69 32 6 0.00
Thu 05/21 02Z 0.29 3223 69 19 5 0.00
Thu 05/21 03Z 0.28 3223 66 11 5 0.00
Thu 05/21 04Z 0.23 3223 63 8 4 0.00
Thu 05/21 05Z 0.19 3323 57 8 4 0.00
Thu 05/21 06Z 0.17 3324 56 5 3 0.00
Thu 05/21 07Z 0.17 3327 58 2 2 0.00
Thu 05/21 08Z 0.14 3326 61 1 2 0.00
Thu 05/21 09Z 0.11 3325 61 1 2 0.00
Thu 05/21 10Z 0.10 3324 55 2 2 0.00
Thu 05/21 11Z 0.09 3323 48 3 2 0.00
Thu 05/21 12Z 0.08 3321 45 3 2 0.00
Thu 05/21 13Z 0.06 3419 44 4 1 0.00
Thu 05/21 14Z 0.07 3317 43 4 1 0.00
Thu 05/21 15Z 0.07 3416 42 4 1 0.00
Thu 05/21 16Z 0.07 3414 43 4 0 0.00
Thu 05/21 17Z 0.09 3313 42 4 0 0.00
Thu 05/21 18Z 0.20 3314 41 4 0 0.00
Thu 05/21 19Z 0.22 3313 38 4 1 0.00
Thu 05/21 20Z 0.16 3414 35 4 1 0.00
Thu 05/21 21Z 0.11 3314 34 4 1 0.00
Thu 05/21 22Z 0.08 3414 33 4 1 0.00
Thu 05/21 23Z 0.07 3415 33 3 1 0.00
Fri 05/22 00Z 0.03 3417 32 3 1 0.00
Fri 05/22 01Z 0.05 3518 32 3 1 0.00
Fri 05/22 02Z 0.11 0018 34 4 1 0.00
Fri 05/22 03Z 0.12 0016 35 4 1 0.00
Fri 05/22 04Z 0.15 0115 34 3 1 0.00
Fri 05/22 05Z 0.17 0114 34 3 1 0.00
Fri 05/22 06Z 0.20 0113 36 2 0 0.00
Fri 05/22 07Z 0.21 0113 39 2 0 0.00
Fri 05/22 08Z 0.28 0214 40 3 0 0.00
Fri 05/22 09Z 0.29 0312 35 3 1 0.00
Fri 05/22 10Z 0.22 0310 32 4 1 0.00
Fri 05/22 11Z 0.25 0411 29 4 1 0.00
Fri 05/22 12Z 0.26 0411 31 6 1 0.00
Fri 05/22 13Z 0.26 0409 36 7 1 0.00
Fri 05/22 14Z 0.28 0407 39 7 1 0.00
Fri 05/22 15Z 0.47 0305 42 7 1 0.00
Fri 05/22 16Z 0.62 0203 45 9 1 0.00
Fri 05/22 17Z 0.38 0002 48 11 2 0.00
Fri 05/22 18Z 0.37 3202 50 12 3 0.00
Fri 05/22 19Z 0.41 3203 52 14 3 0.00
Fri 05/22 20Z 0.82 3103 53 15 4 0.00
Fri 05/22 21Z 0.65 3104 50 17 4 0.00
Fri 05/22 22Z 0.27 3305 47 19 4 0.00
Fri 05/22 23Z 0.09 3406 44 21 4 0.00
Run total areal avg QPF for the Central_Greens is: 0.15 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