Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260604_1800
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)
=== ===== === ==== ==== === === === ====
Thu 06/04 18Z 4.33 2707 50 33 13 0.00
Thu 06/04 19Z 4.87 2709 53 29 14 0.00
Thu 06/04 20Z 4.18 2710 55 24 14 0.00
Thu 06/04 21Z 2.13 2711 56 20 14 0.00
Thu 06/04 22Z 1.10 2613 57 19 14 0.00
Thu 06/04 23Z 0.97 2715 53 19 14 0.00
Fri 06/05 00Z 1.17 2816 48 20 14 0.00
Fri 06/05 01Z 1.08 2818 46 18 14 0.00
Fri 06/05 02Z 0.94 2920 42 16 13 0.00
Fri 06/05 03Z 0.84 2920 44 13 13 0.00
Fri 06/05 04Z 0.77 3021 51 12 13 0.00
Fri 06/05 05Z 0.67 3121 59 10 13 0.00
Fri 06/05 06Z 0.62 3119 62 8 13 0.00
Fri 06/05 07Z 0.57 3119 59 8 13 0.00
Fri 06/05 08Z 0.52 3118 54 7 13 0.00
Fri 06/05 09Z 0.47 3115 50 11 13 0.00
Fri 06/05 10Z 0.47 3015 50 12 13 0.00
Fri 06/05 11Z 0.45 3013 51 14 12 0.00
Fri 06/05 12Z 0.39 3011 51 16 12 0.00
Fri 06/05 13Z 0.37 2909 51 15 12 0.00
Fri 06/05 14Z 0.42 2909 52 15 12 0.00
Fri 06/05 15Z 0.94 2808 53 15 12 0.00
Fri 06/05 16Z 1.49 2808 53 16 13 0.00
Fri 06/05 17Z 2.34 2708 53 13 13 0.00
Fri 06/05 18Z 3.83 2708 55 9 13 0.00
Fri 06/05 19Z 4.21 2608 58 10 13 0.00
Fri 06/05 20Z 4.20 2609 63 15 14 0.00
Fri 06/05 21Z 2.93 2509 65 17 14 0.00
Fri 06/05 22Z 2.11 2511 67 29 14 0.00
Fri 06/05 23Z 1.28 2512 70 31 14 0.00
Sat 06/06 00Z 1.03 2514 68 16 14 0.00
Sat 06/06 01Z 1.30 2515 64 20 14 0.00
Sat 06/06 02Z 1.47 2517 62 24 14 0.00
Sat 06/06 03Z 1.72 2619 63 24 13 0.00
Sat 06/06 04Z 1.73 2520 69 25 13 0.00
Sat 06/06 05Z 1.65 2520 75 24 13 0.00
Sat 06/06 06Z 1.27 2520 79 30 12 0.00
Sat 06/06 07Z 1.14 2520 82 29 12 0.00
Sat 06/06 08Z 1.02 2520 82 33 12 0.01
Sat 06/06 09Z 0.84 2420 86 46 12 0.00
Sat 06/06 10Z 0.82 2421 88 53 12 0.00
Sat 06/06 11Z 0.78 2321 90 31 12 0.00
Sat 06/06 12Z 0.71 2319 88 48 12 0.00
Sat 06/06 13Z 0.69 2320 84 43 12 0.00
Sat 06/06 14Z 0.78 2220 86 56 12 0.00
Sat 06/06 15Z 1.76 2219 87 76 12 0.00
Sat 06/06 16Z 1.15 2120 83 95 12 0.01
Sat 06/06 17Z 0.79 2123 89 94 12 0.02
Sat 06/06 18Z 0.80 2227 97 85 13 0.06
Sat 06/06 19Z 1.00 2329 98 86 13 0.09
Sat 06/06 20Z 1.19 2530 98 70 13 0.08
Sat 06/06 21Z 1.18 2627 97 67 13 0.05
Sat 06/06 22Z 1.02 2725 95 72 13 0.02
Sat 06/06 23Z 1.01 2725 95 47 13 0.01
Sun 06/07 00Z 0.94 2725 93 36 13 0.01
Sun 06/07 01Z 0.97 2727 94 45 13 0.01
Sun 06/07 02Z 0.85 2824 95 51 12 0.01
Sun 06/07 03Z 0.79 2823 95 55 12 0.02
Sun 06/07 04Z 0.65 2921 95 57 12 0.02
Sun 06/07 05Z 0.57 2919 95 58 12 0.02
Run total areal avg QPF for the greens is: 0.44 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