Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260807_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 08/07 06Z 0.19 2906 89 75 17 0.00
Fri 08/07 07Z 0.25 2908 88 73 16 0.00
Fri 08/07 08Z 0.24 2908 88 69 16 0.00
Fri 08/07 09Z 0.23 2908 86 62 16 0.00
Fri 08/07 10Z 0.21 3008 84 53 16 0.00
Fri 08/07 11Z 0.18 3108 81 57 16 0.00
Fri 08/07 12Z 0.16 3208 84 61 16 0.00
Fri 08/07 13Z 0.13 3307 85 57 16 0.00
Fri 08/07 14Z 0.09 3406 86 55 15 0.00
Fri 08/07 15Z 0.06 3404 88 51 15 0.00
Fri 08/07 16Z 0.06 3502 88 46 16 0.00
Fri 08/07 17Z 0.08 3201 87 48 16 0.02
Fri 08/07 18Z 0.11 2601 86 48 16 0.03
Fri 08/07 19Z 0.19 2702 86 50 16 0.02
Fri 08/07 20Z 0.15 2701 85 51 17 0.01
Fri 08/07 21Z 0.16 2702 84 55 17 0.00
Fri 08/07 22Z 0.12 2602 83 54 17 0.00
Fri 08/07 23Z 0.06 2401 81 55 17 0.00
Sat 08/08 00Z 0.04 2201 79 56 17 0.00
Sat 08/08 01Z 0.03 2001 79 57 17 0.00
Sat 08/08 02Z 0.03 1902 79 60 17 0.00
Sat 08/08 03Z 0.03 1902 79 61 17 0.00
Sat 08/08 04Z 0.05 1903 80 66 16 0.00
Sat 08/08 05Z 0.05 1803 80 68 16 0.00
Sat 08/08 06Z 0.07 1704 81 69 16 0.00
Sat 08/08 07Z 0.06 1605 83 73 16 0.00
Sat 08/08 08Z 0.08 1606 82 77 16 0.00
Sat 08/08 09Z 0.09 1706 82 84 16 0.00
Sat 08/08 10Z 0.04 1706 83 85 16 0.00
Sat 08/08 11Z 0.06 1907 83 84 16 0.00
Sat 08/08 12Z 0.15 2008 86 85 16 0.00
Sat 08/08 13Z 0.19 2109 89 80 16 0.00
Sat 08/08 14Z 0.27 2111 93 82 16 0.00
Sat 08/08 15Z 0.29 2211 93 79 16 0.00
Sat 08/08 16Z 0.43 2313 90 61 16 0.03
Sat 08/08 17Z 0.47 2413 84 58 16 0.03
Sat 08/08 18Z 0.58 2414 88 63 16 0.01
Sat 08/08 19Z 0.70 2415 92 53 16 0.02
Sat 08/08 20Z 0.81 2518 91 53 16 0.10
Sat 08/08 21Z 0.85 2617 90 53 16 0.07
Sat 08/08 22Z 0.83 2616 91 59 16 0.03
Sat 08/08 23Z 0.77 2615 89 55 16 0.00
Sun 08/09 00Z 0.68 2614 89 57 16 0.00
Sun 08/09 01Z 0.59 2614 87 64 16 0.00
Sun 08/09 02Z 0.53 2613 85 69 16 0.00
Sun 08/09 03Z 0.48 2613 87 76 16 0.02
Sun 08/09 04Z 0.44 2713 86 73 16 0.08
Sun 08/09 05Z 0.44 2713 91 81 16 0.00
Sun 08/09 06Z 0.42 2713 90 68 16 0.00
Sun 08/09 07Z 0.43 2714 89 51 16 0.00
Sun 08/09 08Z 0.38 2714 86 34 16 0.00
Sun 08/09 09Z 0.38 2714 82 42 16 0.00
Sun 08/09 10Z 0.41 2715 85 47 16 0.00
Sun 08/09 11Z 0.43 2715 87 43 16 0.01
Sun 08/09 12Z 0.47 2716 91 40 15 0.01
Sun 08/09 13Z 0.50 2716 94 50 15 0.01
Sun 08/09 14Z 0.51 2715 96 52 15 0.01
Sun 08/09 15Z 0.57 2715 96 44 14 0.01
Sun 08/09 16Z 0.67 2715 97 38 14 0.01
Sun 08/09 17Z 0.69 2716 95 31 14 0.04
Run total areal avg QPF for the greens is: 0.57 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