Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260613_1200
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 06/13 12Z 0.38 3220 84 9 10 0.00
Sat 06/13 13Z 0.33 3219 84 12 11 0.00
Sat 06/13 14Z 0.31 3215 80 13 11 0.00
Sat 06/13 15Z 0.52 3112 79 13 11 0.00
Sat 06/13 16Z 1.30 3010 80 14 12 0.00
Sat 06/13 17Z 2.72 2911 84 15 12 0.00
Sat 06/13 18Z 3.45 2811 88 15 12 0.00
Sat 06/13 19Z 2.86 2712 87 15 12 0.01
Sat 06/13 20Z 2.52 2711 80 15 12 0.01
Sat 06/13 21Z 2.48 2712 79 15 12 0.00
Sat 06/13 22Z 1.76 2612 77 14 12 0.00
Sat 06/13 23Z 1.31 2515 76 20 12 0.00
Sun 06/14 00Z 1.42 2618 76 42 13 0.00
Sun 06/14 01Z 0.73 2717 68 41 13 0.00
Sun 06/14 02Z 0.77 2718 66 43 13 0.00
Sun 06/14 03Z 0.76 2618 71 44 13 0.00
Sun 06/14 04Z 0.63 2618 69 43 13 0.00
Sun 06/14 05Z 0.70 2520 68 42 13 0.00
Sun 06/14 06Z 0.76 2522 67 37 13 0.00
Sun 06/14 07Z 0.77 2423 57 35 14 0.00
Sun 06/14 08Z 0.86 2426 54 34 14 0.00
Sun 06/14 09Z 0.93 2427 62 37 14 0.00
Sun 06/14 10Z 0.96 2427 68 34 14 0.00
Sun 06/14 11Z 0.93 2426 70 21 14 0.00
Sun 06/14 12Z 0.91 2425 74 23 13 0.01
Sun 06/14 13Z 0.96 2422 77 29 13 0.00
Sun 06/14 14Z 1.11 2319 76 33 13 0.00
Sun 06/14 15Z 2.88 2320 79 36 13 0.00
Sun 06/14 16Z 4.72 2219 82 27 13 0.00
Sun 06/14 17Z 3.46 2218 80 30 14 0.00
Sun 06/14 18Z 4.29 2117 80 44 14 0.00
Sun 06/14 19Z 4.23 2118 78 48 14 0.00
Sun 06/14 20Z 1.81 2119 74 64 15 0.02
Sun 06/14 21Z 1.18 2123 77 82 15 0.03
Sun 06/14 22Z 0.80 2224 86 81 14 0.04
Sun 06/14 23Z 0.91 2326 91 87 14 0.03
Mon 06/15 00Z 0.70 2323 93 76 13 0.12
Mon 06/15 01Z 0.70 2324 91 81 13 0.01
Mon 06/15 02Z 0.61 2320 95 93 13 0.02
Mon 06/15 03Z 0.62 2419 99 95 12 0.08
Mon 06/15 04Z 0.55 2416 98 92 12 0.07
Mon 06/15 05Z 0.42 2813 99 98 11 0.13
Mon 06/15 06Z 0.43 2921 94 97 10 0.25
Mon 06/15 07Z 0.39 2917 89 98 10 0.05
Mon 06/15 08Z 0.50 2818 88 93 8 0.01
Mon 06/15 09Z 0.46 2817 87 76 8 0.01
Mon 06/15 10Z 0.42 2817 83 48 7 0.01
Mon 06/15 11Z 0.41 2918 78 12 7 0.00
Mon 06/15 12Z 0.39 2917 71 2 7 0.00
Mon 06/15 13Z 0.36 2917 76 2 7 0.00
Mon 06/15 14Z 0.32 3016 77 1 7 0.00
Mon 06/15 15Z 0.33 3016 79 3 6 0.00
Mon 06/15 16Z 0.41 3014 81 4 5 0.00
Mon 06/15 17Z 2.15 3014 84 6 4 0.00
Mon 06/15 18Z 5.09 3014 87 12 4 0.00
Mon 06/15 19Z 4.10 3013 87 15 5 0.00
Mon 06/15 20Z 3.06 3014 88 21 5 0.00
Mon 06/15 21Z 2.67 2914 89 20 5 0.00
Mon 06/15 22Z 1.41 3015 87 9 5 0.00
Mon 06/15 23Z 0.85 3016 85 4 5 0.00
Run total areal avg QPF for the Central_Greens is: 0.91 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