Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260828_0600
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)
=== ===== === ==== ==== === === === ====
Fri 08/28 06Z 0.51 2416 90 75 13 0.00
Fri 08/28 07Z 0.53 2516 90 75 13 0.00
Fri 08/28 08Z 0.57 2517 92 75 13 0.00
Fri 08/28 09Z 0.59 2617 94 67 12 0.00
Fri 08/28 10Z 0.57 2715 93 52 12 0.01
Fri 08/28 11Z 0.54 2814 92 46 12 0.01
Fri 08/28 12Z 0.47 2812 93 40 12 0.01
Fri 08/28 13Z 0.43 2811 91 39 11 0.00
Fri 08/28 14Z 0.41 2710 90 36 11 0.00
Fri 08/28 15Z 0.46 2709 90 46 11 0.00
Fri 08/28 16Z 0.49 2709 91 47 11 0.01
Fri 08/28 17Z 0.53 2811 92 60 11 0.02
Fri 08/28 18Z 0.63 2914 91 55 11 0.03
Fri 08/28 19Z 0.47 2914 90 34 11 0.02
Fri 08/28 20Z 0.41 2914 86 26 10 0.02
Fri 08/28 21Z 0.42 2914 82 20 10 0.00
Fri 08/28 22Z 0.40 3014 81 24 9 0.00
Fri 08/28 23Z 0.37 3014 79 27 9 0.00
Sat 08/29 00Z 0.37 3015 78 21 9 0.00
Sat 08/29 01Z 0.37 3017 76 14 9 0.00
Sat 08/29 02Z 0.36 3118 76 9 8 0.00
Sat 08/29 03Z 0.32 3117 77 7 8 0.00
Sat 08/29 04Z 0.32 3117 77 6 8 0.00
Sat 08/29 05Z 0.29 3217 75 7 7 0.00
Sat 08/29 06Z 0.26 3216 74 7 7 0.00
Sat 08/29 07Z 0.24 3216 70 7 7 0.00
Sat 08/29 08Z 0.23 3216 65 7 7 0.00
Sat 08/29 09Z 0.21 3315 65 6 7 0.00
Sat 08/29 10Z 0.23 3315 66 5 6 0.00
Sat 08/29 11Z 0.24 3214 66 5 7 0.00
Sat 08/29 12Z 0.26 3212 66 6 7 0.00
Sat 08/29 13Z 0.29 3112 67 7 7 0.00
Sat 08/29 14Z 0.30 3010 68 6 7 0.00
Sat 08/29 15Z 0.32 2909 68 7 7 0.00
Sat 08/29 16Z 0.31 2808 65 9 8 0.00
Sat 08/29 17Z 0.46 2708 66 10 8 0.00
Sat 08/29 18Z 0.69 2710 69 12 8 0.00
Sat 08/29 19Z 0.69 2709 71 13 8 0.00
Sat 08/29 20Z 0.63 2608 73 10 8 0.00
Sat 08/29 21Z 0.62 2609 75 11 9 0.00
Sat 08/29 22Z 0.59 2511 77 19 9 0.00
Sat 08/29 23Z 0.67 2514 79 24 9 0.00
Sun 08/30 00Z 0.77 2517 78 16 9 0.00
Sun 08/30 01Z 0.79 2618 76 11 9 0.00
Sun 08/30 02Z 0.76 2718 75 12 10 0.00
Sun 08/30 03Z 0.86 2720 76 13 10 0.00
Sun 08/30 04Z 0.98 2721 75 18 10 0.00
Sun 08/30 05Z 1.09 2822 77 24 9 0.00
Sun 08/30 06Z 1.10 2723 78 27 9 0.00
Sun 08/30 07Z 1.12 2723 80 29 9 0.01
Sun 08/30 08Z 1.03 2724 81 34 10 0.01
Sun 08/30 09Z 1.00 2723 82 35 10 0.00
Sun 08/30 10Z 0.94 2722 81 41 10 0.00
Sun 08/30 11Z 0.85 2721 80 44 10 0.00
Sun 08/30 12Z 0.85 2721 82 51 10 0.00
Sun 08/30 13Z 0.82 2720 83 54 10 0.01
Sun 08/30 14Z 0.82 2719 82 52 10 0.00
Sun 08/30 15Z 0.83 2617 79 62 10 0.00
Sun 08/30 16Z 0.83 2617 76 68 10 0.00
Sun 08/30 17Z 1.09 2516 76 85 10 0.00
Run total areal avg QPF for the greens is: 0.16 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