Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260518_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)
=== ===== === ==== ==== === === === ====
Mon 05/18 12Z 0.25 1916 65 74 13 0.00
Mon 05/18 13Z 0.32 1920 66 62 13 0.00
Mon 05/18 14Z 0.40 2022 68 41 14 0.00
Mon 05/18 15Z 0.50 2023 68 27 14 0.00
Mon 05/18 16Z 0.72 2121 72 26 15 0.00
Mon 05/18 17Z 0.87 2219 74 24 15 0.00
Mon 05/18 18Z 2.34 2217 74 21 15 0.00
Mon 05/18 19Z 6.56 2318 76 22 15 0.00
Mon 05/18 20Z 5.34 2418 80 34 15 0.01
Mon 05/18 21Z 2.16 2317 84 25 15 0.01
Mon 05/18 22Z 1.42 2318 86 28 15 0.01
Mon 05/18 23Z 0.88 2319 86 42 16 0.01
Tue 05/19 00Z 0.96 2321 87 27 16 0.02
Tue 05/19 01Z 0.99 2323 85 34 16 0.00
Tue 05/19 02Z 0.91 2325 83 26 16 0.00
Tue 05/19 03Z 1.02 2328 78 27 16 0.00
Tue 05/19 04Z 1.15 2331 75 20 17 0.00
Tue 05/19 05Z 1.47 2436 75 21 17 0.00
Tue 05/19 06Z 1.77 2540 76 17 16 0.00
Tue 05/19 07Z 1.73 2539 78 17 15 0.02
Tue 05/19 08Z 1.74 2538 78 10 15 0.00
Tue 05/19 09Z 1.48 2638 79 14 15 0.03
Tue 05/19 10Z 1.39 2637 85 23 15 0.03
Tue 05/19 11Z 1.14 2537 73 42 16 0.01
Tue 05/19 12Z 1.08 2635 77 59 16 0.00
Tue 05/19 13Z 1.09 2633 86 55 15 0.00
Tue 05/19 14Z 1.15 2629 92 67 14 0.00
Tue 05/19 15Z 1.20 2626 93 72 14 0.00
Tue 05/19 16Z 1.34 2623 92 79 14 0.00
Tue 05/19 17Z 1.49 2621 91 76 14 0.00
Tue 05/19 18Z 1.78 2521 90 81 14 0.00
Tue 05/19 19Z 3.75 2622 88 84 14 0.00
Tue 05/19 20Z 2.15 2624 88 83 14 0.02
Tue 05/19 21Z 3.43 2622 84 76 14 0.00
Tue 05/19 22Z 3.70 2622 84 68 14 0.00
Tue 05/19 23Z 1.73 2623 84 68 15 0.00
Wed 05/20 00Z 0.97 2624 83 72 15 0.00
Wed 05/20 01Z 0.80 2626 79 61 16 0.00
Wed 05/20 02Z 0.95 2630 80 64 16 0.00
Wed 05/20 03Z 1.26 2535 88 70 16 0.00
Wed 05/20 04Z 1.10 2535 84 73 16 0.02
Wed 05/20 05Z 1.20 2535 91 75 16 0.00
Wed 05/20 06Z 1.23 2535 92 84 15 0.14
Wed 05/20 07Z 1.24 2535 91 80 15 0.10
Wed 05/20 08Z 1.22 2535 92 65 15 0.02
Wed 05/20 09Z 1.09 2533 91 54 15 0.00
Wed 05/20 10Z 1.04 2632 93 55 15 0.00
Wed 05/20 11Z 1.04 2631 92 72 15 0.01
Wed 05/20 12Z 1.03 2530 93 72 14 0.01
Wed 05/20 13Z 1.12 2528 95 81 13 0.01
Wed 05/20 14Z 1.13 2627 95 85 13 0.02
Wed 05/20 15Z 1.18 2627 96 92 13 0.04
Wed 05/20 16Z 1.07 2726 96 92 12 0.06
Wed 05/20 17Z 1.14 2727 93 91 11 0.06
Wed 05/20 18Z 4.75 2726 84 68 10 0.02
Wed 05/20 19Z 10.15 2822 78 39 9 0.00
Wed 05/20 20Z 8.69 2922 78 17 8 0.01
Wed 05/20 21Z 7.37 2924 81 15 8 0.00
Wed 05/20 22Z 2.73 3025 86 5 6 0.00
Wed 05/20 23Z 1.21 3026 89 2 5 0.00
Run total areal avg QPF for the Central_Greens is: 0.69 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