Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260515_1800
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)
=== ===== === ==== ==== === === === ====
Fri 05/15 18Z 0.43 0806 98 69 3 0.00
Fri 05/15 19Z 0.43 1007 96 73 4 0.01
Fri 05/15 20Z 0.24 1106 96 76 4 0.01
Fri 05/15 21Z 0.14 1404 93 81 5 0.01
Fri 05/15 22Z 0.08 2002 90 85 5 0.01
Fri 05/15 23Z 0.10 2602 86 79 6 0.00
Sat 05/16 00Z 0.13 2603 83 66 6 0.00
Sat 05/16 01Z 0.22 2606 83 53 6 0.00
Sat 05/16 02Z 0.25 2708 83 45 6 0.00
Sat 05/16 03Z 0.32 2710 86 55 6 0.00
Sat 05/16 04Z 0.37 2612 90 67 6 0.00
Sat 05/16 05Z 0.36 2511 90 63 6 0.00
Sat 05/16 06Z 0.43 2614 94 52 6 0.01
Sat 05/16 07Z 0.43 2714 92 44 6 0.01
Sat 05/16 08Z 0.46 2715 84 31 6 0.00
Sat 05/16 09Z 0.51 2716 79 13 6 0.00
Sat 05/16 10Z 0.59 2719 79 8 5 0.00
Sat 05/16 11Z 0.61 2819 77 6 5 0.00
Sat 05/16 12Z 0.54 2716 74 22 5 0.00
Sat 05/16 13Z 0.54 2615 73 52 5 0.00
Sat 05/16 14Z 0.70 2517 71 40 5 0.00
Sat 05/16 15Z 0.94 2419 67 45 6 0.00
Sat 05/16 16Z 0.90 2418 52 54 7 0.00
Sat 05/16 17Z 1.23 2415 55 40 8 0.00
Sat 05/16 18Z 1.83 2315 64 38 8 0.00
Sat 05/16 19Z 3.03 2216 74 19 8 0.00
Sat 05/16 20Z 2.71 2118 75 10 8 0.00
Sat 05/16 21Z 1.94 2121 77 9 9 0.00
Sat 05/16 22Z 1.24 2123 73 11 9 0.00
Sat 05/16 23Z 0.91 2125 70 35 10 0.00
Sun 05/17 00Z 1.10 2230 74 92 10 0.00
Sun 05/17 01Z 1.21 2334 72 82 10 0.00
Sun 05/17 02Z 1.53 2337 75 79 10 0.00
Sun 05/17 03Z 1.61 2436 83 75 10 0.00
Sun 05/17 04Z 1.42 2534 87 64 10 0.01
Sun 05/17 05Z 1.19 2633 93 41 10 0.03
Sun 05/17 06Z 0.99 2730 93 40 9 0.02
Sun 05/17 07Z 0.89 2829 85 17 9 0.01
Sun 05/17 08Z 0.79 2929 74 6 9 0.00
Sun 05/17 09Z 0.77 2930 77 7 8 0.00
Sun 05/17 10Z 0.68 2932 58 24 8 0.00
Sun 05/17 11Z 0.68 3034 62 24 8 0.00
Sun 05/17 12Z 0.70 3033 66 31 8 0.00
Sun 05/17 13Z 0.74 3032 69 61 8 0.00
Sun 05/17 14Z 0.83 3030 74 55 7 0.00
Sun 05/17 15Z 1.31 3026 80 59 6 0.00
Sun 05/17 16Z 7.40 2923 84 45 6 0.00
Sun 05/17 17Z 9.37 2921 85 36 6 0.00
Sun 05/17 18Z 7.41 2921 86 30 6 0.00
Sun 05/17 19Z 6.27 2920 86 27 6 0.00
Sun 05/17 20Z 2.52 2920 87 27 6 0.00
Sun 05/17 21Z 1.88 3020 87 27 5 0.00
Sun 05/17 22Z 1.26 3020 86 27 5 0.00
Sun 05/17 23Z 0.62 3019 83 20 6 0.00
Mon 05/18 00Z 0.44 3119 80 11 6 0.00
Mon 05/18 01Z 0.34 3120 76 5 6 0.00
Mon 05/18 02Z 0.29 3219 75 2 6 0.00
Mon 05/18 03Z 0.26 3219 72 1 6 0.00
Mon 05/18 04Z 0.18 3217 65 2 7 0.00
Mon 05/18 05Z 0.14 3214 59 3 7 0.00
Run total areal avg QPF for the Central_Greens is: 0.13 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