Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260613_0600
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 06Z 0.78 2923 74 10 12 0.00
Sat 06/13 07Z 0.77 3028 74 10 12 0.00
Sat 06/13 08Z 0.57 3027 72 10 12 0.00
Sat 06/13 09Z 0.43 3126 70 9 12 0.00
Sat 06/13 10Z 0.40 3127 72 8 12 0.00
Sat 06/13 11Z 0.39 3228 71 9 11 0.00
Sat 06/13 12Z 0.35 3226 69 10 11 0.00
Sat 06/13 13Z 0.36 3222 71 12 11 0.00
Sat 06/13 14Z 0.38 3219 70 12 11 0.00
Sat 06/13 15Z 0.46 3115 71 12 11 0.00
Sat 06/13 16Z 1.22 3012 73 13 11 0.00
Sat 06/13 17Z 3.21 2911 77 13 11 0.00
Sat 06/13 18Z 4.46 2810 80 13 12 0.00
Sat 06/13 19Z 4.49 2710 82 14 12 0.00
Sat 06/13 20Z 3.42 2710 77 15 12 0.00
Sat 06/13 21Z 3.35 2612 77 12 12 0.00
Sat 06/13 22Z 3.14 2613 74 10 12 0.00
Sat 06/13 23Z 1.76 2615 75 13 12 0.00
Sun 06/14 00Z 0.93 2615 72 30 13 0.00
Sun 06/14 01Z 0.94 2618 70 39 13 0.00
Sun 06/14 02Z 1.03 2520 65 51 13 0.00
Sun 06/14 03Z 0.98 2521 61 52 13 0.00
Sun 06/14 04Z 0.84 2621 62 52 13 0.00
Sun 06/14 05Z 0.80 2523 74 57 13 0.00
Sun 06/14 06Z 0.79 2522 72 59 13 0.00
Sun 06/14 07Z 0.74 2522 67 42 14 0.00
Sun 06/14 08Z 0.77 2522 69 57 13 0.00
Sun 06/14 09Z 0.89 2524 75 61 13 0.00
Sun 06/14 10Z 1.02 2526 80 29 13 0.00
Sun 06/14 11Z 0.98 2525 82 25 12 0.01
Sun 06/14 12Z 0.83 2522 82 23 13 0.01
Sun 06/14 13Z 0.77 2419 81 22 13 0.01
Sun 06/14 14Z 0.89 2318 79 30 13 0.00
Sun 06/14 15Z 1.93 2216 78 29 13 0.00
Sun 06/14 16Z 3.89 2117 75 28 14 0.00
Sun 06/14 17Z 3.77 2118 71 33 14 0.00
Sun 06/14 18Z 4.57 2018 68 41 14 0.00
Sun 06/14 19Z 3.60 2020 68 46 15 0.00
Sun 06/14 20Z 6.15 2023 71 61 15 0.01
Sun 06/14 21Z 1.45 2124 74 42 15 0.02
Sun 06/14 22Z 1.53 2126 76 37 15 0.00
Sun 06/14 23Z 1.29 2026 79 54 15 0.00
Mon 06/15 00Z 1.06 2130 84 81 15 0.05
Mon 06/15 01Z 0.87 2030 83 66 15 0.03
Mon 06/15 02Z 0.94 2132 81 85 15 0.00
Mon 06/15 03Z 1.04 2132 84 90 14 0.00
Mon 06/15 04Z 1.11 2231 91 95 13 0.01
Mon 06/15 05Z 0.98 2230 95 97 13 0.04
Mon 06/15 06Z 0.70 2225 97 91 13 0.10
Mon 06/15 07Z 0.69 2320 99 97 12 0.20
Mon 06/15 08Z 0.58 2717 98 98 11 0.26
Mon 06/15 09Z 0.42 2816 97 91 11 0.05
Mon 06/15 10Z 0.55 2820 97 53 9 0.02
Mon 06/15 11Z 0.51 2819 92 30 8 0.01
Mon 06/15 12Z 0.41 2918 82 7 7 0.00
Mon 06/15 13Z 0.34 3017 81 2 7 0.00
Mon 06/15 14Z 0.30 3014 75 1 7 0.00
Mon 06/15 15Z 0.34 3014 75 1 7 0.00
Mon 06/15 16Z 0.67 2913 83 1 6 0.00
Mon 06/15 17Z 2.33 2913 88 8 6 0.00
Run total areal avg QPF for the Central_Greens is: 0.83 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