Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260519_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)
=== ===== === ==== ==== === === === ====
Tue 05/19 12Z 0.76 2624 76 34 16 0.00
Tue 05/19 13Z 0.84 2623 75 46 16 0.00
Tue 05/19 14Z 1.12 2623 77 59 16 0.00
Tue 05/19 15Z 1.49 2522 83 83 15 0.00
Tue 05/19 16Z 3.47 2421 85 75 15 0.00
Tue 05/19 17Z 4.80 2419 86 72 16 0.00
Tue 05/19 18Z 6.29 2419 86 80 16 0.00
Tue 05/19 19Z 7.53 2522 84 80 16 0.03
Tue 05/19 20Z 5.54 2623 82 79 16 0.07
Tue 05/19 21Z 2.87 2626 79 78 16 0.12
Tue 05/19 22Z 1.14 2730 80 69 15 0.05
Tue 05/19 23Z 0.99 2731 78 48 16 0.00
Wed 05/20 00Z 1.01 2628 81 43 16 0.00
Wed 05/20 01Z 0.97 2628 76 64 17 0.00
Wed 05/20 02Z 1.09 2630 76 81 17 0.00
Wed 05/20 03Z 1.07 2530 73 71 17 0.00
Wed 05/20 04Z 1.28 2433 77 56 17 0.00
Wed 05/20 05Z 1.57 2438 82 58 16 0.00
Wed 05/20 06Z 1.31 2537 82 56 16 0.00
Wed 05/20 07Z 1.16 2535 88 52 16 0.00
Wed 05/20 08Z 1.03 2533 88 57 16 0.00
Wed 05/20 09Z 1.08 2632 91 50 15 0.00
Wed 05/20 10Z 1.01 2631 94 55 14 0.01
Wed 05/20 11Z 1.01 2630 94 50 13 0.01
Wed 05/20 12Z 0.96 2730 93 50 13 0.01
Wed 05/20 13Z 1.04 2729 96 48 12 0.01
Wed 05/20 14Z 1.17 2727 97 44 11 0.02
Wed 05/20 15Z 1.27 2727 93 35 11 0.03
Wed 05/20 16Z 3.88 2725 80 30 10 0.01
Wed 05/20 17Z 10.63 2823 71 37 10 0.00
Wed 05/20 18Z 12.72 2822 66 21 10 0.00
Wed 05/20 19Z 10.55 2921 66 18 9 0.00
Wed 05/20 20Z 7.76 2921 69 17 9 0.00
Wed 05/20 21Z 5.22 3023 67 16 8 0.00
Wed 05/20 22Z 1.44 3023 76 14 7 0.00
Wed 05/20 23Z 0.63 3024 81 14 6 0.00
Thu 05/21 00Z 0.58 3125 79 11 4 0.00
Thu 05/21 01Z 0.50 3124 77 10 4 0.00
Thu 05/21 02Z 0.43 3124 73 9 3 0.00
Thu 05/21 03Z 0.43 3225 73 8 2 0.00
Thu 05/21 04Z 0.42 3226 74 7 1 0.00
Thu 05/21 05Z 0.32 3225 72 5 0 0.00
Thu 05/21 06Z 0.25 3226 68 4 0 0.00
Thu 05/21 07Z 0.22 3228 65 4 0 0.00
Thu 05/21 08Z 0.19 3328 61 4 0 0.00
Thu 05/21 09Z 0.16 3327 56 4 1 0.00
Thu 05/21 10Z 0.11 3326 52 4 1 0.00
Thu 05/21 11Z 0.08 3324 50 4 1 0.00
Thu 05/21 12Z 0.07 3422 47 4 1 0.00
Thu 05/21 13Z 0.06 3419 46 5 1 0.00
Thu 05/21 14Z 0.06 3416 47 5 0 0.00
Thu 05/21 15Z 0.07 3415 47 5 0 0.00
Thu 05/21 16Z 0.07 3415 46 4 0 0.00
Thu 05/21 17Z 0.17 3314 44 4 0 0.00
Thu 05/21 18Z 0.26 3314 41 4 0 0.00
Thu 05/21 19Z 0.30 3315 37 4 0 0.00
Thu 05/21 20Z 0.27 3316 34 5 1 0.00
Thu 05/21 21Z 0.26 3317 33 7 1 0.00
Thu 05/21 22Z 0.25 3318 35 6 1 0.00
Thu 05/21 23Z 0.19 3318 37 6 1 0.00
Run total areal avg QPF for the Central_Greens is: 0.37 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