Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260829_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)
=== ===== === ==== ==== === === === ====
Sat 08/29 18Z 3.75 2706 81 10 8 0.00
Sat 08/29 19Z 3.06 2607 82 10 8 0.00
Sat 08/29 20Z 1.73 2509 84 9 8 0.00
Sat 08/29 21Z 0.91 2410 85 10 8 0.00
Sat 08/29 22Z 0.73 2411 85 10 9 0.00
Sat 08/29 23Z 0.66 2414 81 9 9 0.00
Sun 08/30 00Z 0.81 2517 78 7 9 0.00
Sun 08/30 01Z 0.81 2518 74 6 10 0.00
Sun 08/30 02Z 0.85 2520 71 13 10 0.00
Sun 08/30 03Z 0.83 2622 65 25 11 0.00
Sun 08/30 04Z 0.65 2720 55 53 11 0.00
Sun 08/30 05Z 0.68 2722 61 61 12 0.00
Sun 08/30 06Z 0.79 2725 70 54 12 0.00
Sun 08/30 07Z 0.82 2725 75 68 12 0.00
Sun 08/30 08Z 0.92 2726 78 65 11 0.00
Sun 08/30 09Z 0.98 2727 79 54 11 0.00
Sun 08/30 10Z 0.97 2726 75 44 11 0.00
Sun 08/30 11Z 1.07 2727 73 40 11 0.00
Sun 08/30 12Z 1.02 2727 75 36 12 0.00
Sun 08/30 13Z 0.95 2725 75 64 12 0.00
Sun 08/30 14Z 0.92 2725 75 70 11 0.00
Sun 08/30 15Z 0.76 2720 78 64 11 0.00
Sun 08/30 16Z 0.72 2617 77 54 11 0.00
Sun 08/30 17Z 0.74 2516 78 45 12 0.00
Sun 08/30 18Z 0.75 2516 78 67 12 0.00
Sun 08/30 19Z 0.87 2416 81 76 12 0.00
Sun 08/30 20Z 0.86 2417 80 85 12 0.00
Sun 08/30 21Z 0.87 2318 86 98 12 0.01
Sun 08/30 22Z 0.99 2622 94 93 11 0.16
Sun 08/30 23Z 0.92 2823 89 79 11 0.04
Mon 08/31 00Z 0.90 2923 92 74 11 0.00
Mon 08/31 01Z 0.74 3023 95 74 11 0.01
Mon 08/31 02Z 0.57 3022 96 55 11 0.01
Mon 08/31 03Z 0.39 3222 90 58 11 0.01
Mon 08/31 04Z 0.23 3322 82 46 10 0.00
Mon 08/31 05Z 0.14 3320 78 37 10 0.01
Mon 08/31 06Z 0.10 3417 77 26 10 0.00
Mon 08/31 07Z 0.07 3414 79 16 10 0.00
Mon 08/31 08Z 0.07 3313 75 3 10 0.00
Mon 08/31 09Z 0.08 3313 67 4 10 0.00
Mon 08/31 10Z 0.06 3312 61 6 10 0.00
Mon 08/31 11Z 0.05 3310 52 7 10 0.00
Mon 08/31 12Z 0.06 3308 47 7 11 0.00
Mon 08/31 13Z 0.09 3209 44 7 11 0.00
Mon 08/31 14Z 0.08 3207 42 7 11 0.00
Mon 08/31 15Z 0.11 3106 46 8 11 0.00
Mon 08/31 16Z 0.13 3006 50 8 11 0.00
Mon 08/31 17Z 0.10 3004 52 7 11 0.00
Mon 08/31 18Z 0.25 2904 55 6 10 0.00
Mon 08/31 19Z 0.31 2804 52 6 11 0.00
Mon 08/31 20Z 0.19 2703 47 6 11 0.00
Mon 08/31 21Z 0.18 2703 45 4 11 0.00
Mon 08/31 22Z 0.14 2703 44 1 11 0.00
Mon 08/31 23Z 0.20 2604 48 1 11 0.00
Tue 09/01 00Z 0.23 2505 54 2 11 0.00
Tue 09/01 01Z 0.22 2505 61 4 11 0.00
Tue 09/01 02Z 0.15 2304 64 5 11 0.00
Tue 09/01 03Z 0.14 2104 68 6 11 0.00
Tue 09/01 04Z 0.18 2105 71 8 11 0.00
Tue 09/01 05Z 0.19 2206 74 10 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.25 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