Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260604_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)
=== ===== === ==== ==== === === === ====
Thu 06/04 12Z 0.31 2709 50 44 13 0.00
Thu 06/04 13Z 0.35 2810 49 46 13 0.00
Thu 06/04 14Z 0.38 2810 50 46 13 0.00
Thu 06/04 15Z 0.44 2710 51 44 13 0.00
Thu 06/04 16Z 0.63 2812 49 40 13 0.00
Thu 06/04 17Z 1.25 2812 48 33 13 0.00
Thu 06/04 18Z 2.02 2711 50 26 13 0.00
Thu 06/04 19Z 3.59 2711 55 23 13 0.00
Thu 06/04 20Z 6.65 2713 59 21 13 0.00
Thu 06/04 21Z 4.95 2713 58 20 13 0.00
Thu 06/04 22Z 1.83 2713 56 19 14 0.00
Thu 06/04 23Z 1.10 2814 52 21 14 0.00
Fri 06/05 00Z 0.99 2814 46 23 13 0.00
Fri 06/05 01Z 0.98 2817 45 23 13 0.00
Fri 06/05 02Z 0.88 2919 44 24 13 0.00
Fri 06/05 03Z 0.76 2921 41 22 13 0.00
Fri 06/05 04Z 0.70 3022 41 19 13 0.00
Fri 06/05 05Z 0.64 3022 51 15 13 0.00
Fri 06/05 06Z 0.64 3022 64 12 12 0.00
Fri 06/05 07Z 0.57 3121 64 10 12 0.00
Fri 06/05 08Z 0.57 3121 58 9 12 0.00
Fri 06/05 09Z 0.65 3021 59 8 12 0.00
Fri 06/05 10Z 0.76 3020 64 9 11 0.00
Fri 06/05 11Z 0.76 2919 61 10 12 0.00
Fri 06/05 12Z 0.76 2819 60 9 12 0.00
Fri 06/05 13Z 0.67 2817 56 8 12 0.00
Fri 06/05 14Z 0.76 2816 54 7 12 0.00
Fri 06/05 15Z 1.68 2915 56 6 12 0.00
Fri 06/05 16Z 3.35 2913 56 6 12 0.00
Fri 06/05 17Z 6.73 2812 63 6 12 0.00
Fri 06/05 18Z 7.55 2611 70 5 13 0.00
Fri 06/05 19Z 7.15 2512 73 8 13 0.00
Fri 06/05 20Z 6.02 2512 72 9 13 0.00
Fri 06/05 21Z 5.17 2412 71 10 13 0.00
Fri 06/05 22Z 3.58 2514 65 17 14 0.00
Fri 06/05 23Z 1.38 2515 58 21 14 0.00
Sat 06/06 00Z 1.18 2516 54 24 14 0.00
Sat 06/06 01Z 1.64 2519 58 21 14 0.00
Sat 06/06 02Z 1.59 2518 66 17 14 0.00
Sat 06/06 03Z 1.67 2520 71 20 13 0.00
Sat 06/06 04Z 1.39 2521 75 21 13 0.00
Sat 06/06 05Z 1.37 2522 80 20 12 0.00
Sat 06/06 06Z 1.32 2522 79 23 12 0.00
Sat 06/06 07Z 1.37 2521 80 26 12 0.00
Sat 06/06 08Z 1.14 2421 82 26 12 0.00
Sat 06/06 09Z 1.05 2423 84 22 12 0.00
Sat 06/06 10Z 1.08 2425 86 11 12 0.00
Sat 06/06 11Z 1.02 2325 84 13 12 0.00
Sat 06/06 12Z 0.93 2424 86 27 12 0.01
Sat 06/06 13Z 0.98 2324 89 73 12 0.01
Sat 06/06 14Z 0.95 2323 86 95 13 0.01
Sat 06/06 15Z 1.22 2324 91 97 13 0.06
Sat 06/06 16Z 1.25 2325 97 98 13 0.13
Sat 06/06 17Z 1.06 2528 98 97 12 0.16
Sat 06/06 18Z 1.04 2526 98 79 12 0.07
Sat 06/06 19Z 1.02 2724 98 43 13 0.04
Sat 06/06 20Z 0.90 2822 96 30 13 0.02
Sat 06/06 21Z 0.94 2821 94 44 13 0.01
Sat 06/06 22Z 0.99 2821 93 52 13 0.00
Sat 06/06 23Z 0.90 2721 94 58 13 0.01
Run total areal avg QPF for the Central_Greens is: 0.53 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