Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260519_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)
=== ===== === ==== ==== === === === ====
Tue 05/19 12Z 0.85 2625 77 52 16 0.00
Tue 05/19 13Z 0.91 2624 76 63 16 0.00
Tue 05/19 14Z 1.13 2625 78 72 15 0.00
Tue 05/19 15Z 1.30 2524 83 86 15 0.01
Tue 05/19 16Z 2.55 2522 86 78 15 0.00
Tue 05/19 17Z 3.37 2420 88 78 15 0.00
Tue 05/19 18Z 4.40 2419 88 81 15 0.00
Tue 05/19 19Z 5.66 2521 86 81 15 0.02
Tue 05/19 20Z 4.70 2622 84 75 15 0.06
Tue 05/19 21Z 2.46 2625 81 66 15 0.08
Tue 05/19 22Z 1.19 2728 81 61 15 0.03
Tue 05/19 23Z 1.04 2729 79 44 16 0.00
Wed 05/20 00Z 1.00 2628 81 43 16 0.00
Wed 05/20 01Z 0.96 2628 76 66 17 0.00
Wed 05/20 02Z 1.04 2631 74 83 17 0.00
Wed 05/20 03Z 1.05 2531 72 74 17 0.00
Wed 05/20 04Z 1.30 2434 80 61 16 0.00
Wed 05/20 05Z 1.49 2438 85 59 16 0.01
Wed 05/20 06Z 1.32 2537 83 60 16 0.00
Wed 05/20 07Z 1.21 2536 86 56 16 0.01
Wed 05/20 08Z 1.12 2533 89 56 15 0.00
Wed 05/20 09Z 1.07 2632 91 55 14 0.00
Wed 05/20 10Z 1.03 2632 95 55 14 0.01
Wed 05/20 11Z 1.05 2631 94 48 13 0.01
Wed 05/20 12Z 1.06 2730 94 48 12 0.01
Wed 05/20 13Z 1.12 2729 96 51 12 0.01
Wed 05/20 14Z 1.32 2727 94 37 11 0.02
Wed 05/20 15Z 1.45 2727 89 32 10 0.02
Wed 05/20 16Z 4.35 2725 83 29 10 0.01
Wed 05/20 17Z 8.42 2824 74 28 9 0.01
Wed 05/20 18Z 9.49 2924 70 15 9 0.00
Wed 05/20 19Z 8.43 2924 72 13 8 0.00
Wed 05/20 20Z 6.20 2923 74 12 7 0.00
Wed 05/20 21Z 4.56 3024 74 11 6 0.00
Wed 05/20 22Z 1.70 3024 78 10 5 0.00
Wed 05/20 23Z 0.94 3025 80 10 4 0.00
Thu 05/21 00Z 0.84 3126 76 8 3 0.00
Thu 05/21 01Z 0.78 3126 74 7 2 0.00
Thu 05/21 02Z 0.82 3126 73 7 2 0.00
Thu 05/21 03Z 0.80 3127 74 6 1 0.00
Thu 05/21 04Z 0.64 3227 75 5 0 0.00
Thu 05/21 05Z 0.49 3226 72 4 0 0.00
Thu 05/21 06Z 0.39 3226 70 4 0 0.00
Thu 05/21 07Z 0.34 3227 65 3 0 0.00
Thu 05/21 08Z 0.29 3327 62 3 0 0.00
Thu 05/21 09Z 0.25 3326 59 4 0 0.00
Thu 05/21 10Z 0.21 3325 56 4 0 0.00
Thu 05/21 11Z 0.17 3323 54 4 0 0.00
Thu 05/21 12Z 0.15 3321 51 4 0 0.00
Thu 05/21 13Z 0.13 3419 50 5 0 0.00
Thu 05/21 14Z 0.14 3316 49 5 0 0.00
Thu 05/21 15Z 0.16 3315 49 5 0 0.00
Thu 05/21 16Z 0.17 3315 49 3 0 0.00
Thu 05/21 17Z 0.27 3314 47 3 0 0.00
Thu 05/21 18Z 0.36 3314 45 3 0 0.00
Thu 05/21 19Z 0.47 3314 42 4 0 0.00
Thu 05/21 20Z 0.44 3315 40 6 0 0.00
Thu 05/21 21Z 0.40 3316 39 8 0 0.00
Thu 05/21 22Z 0.37 3217 38 8 0 0.00
Thu 05/21 23Z 0.33 3318 39 7 1 0.00
Run total areal avg QPF for the greens is: 0.32 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