Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260605_1200
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 06/05 12Z 0.27 3010 59 10 13 0.00
Fri 06/05 13Z 0.28 2909 58 10 13 0.00
Fri 06/05 14Z 0.31 2908 57 11 13 0.00
Fri 06/05 15Z 0.38 2808 57 12 13 0.00
Fri 06/05 16Z 0.63 2807 56 13 13 0.00
Fri 06/05 17Z 1.38 2808 55 14 13 0.00
Fri 06/05 18Z 2.02 2808 53 16 13 0.00
Fri 06/05 19Z 2.99 2708 55 17 13 0.00
Fri 06/05 20Z 3.14 2708 58 17 13 0.00
Fri 06/05 21Z 2.36 2708 59 13 14 0.00
Fri 06/05 22Z 1.04 2608 60 11 14 0.00
Fri 06/05 23Z 0.65 2608 58 8 14 0.00
Sat 06/06 00Z 0.79 2610 55 13 14 0.00
Sat 06/06 01Z 0.80 2510 58 10 14 0.00
Sat 06/06 02Z 0.78 2510 60 13 14 0.00
Sat 06/06 03Z 0.94 2412 59 14 14 0.00
Sat 06/06 04Z 1.19 2415 60 22 14 0.00
Sat 06/06 05Z 1.30 2517 62 27 14 0.00
Sat 06/06 06Z 1.24 2518 65 28 13 0.00
Sat 06/06 07Z 1.11 2517 68 24 13 0.00
Sat 06/06 08Z 1.04 2417 72 41 13 0.00
Sat 06/06 09Z 0.85 2316 75 54 13 0.01
Sat 06/06 10Z 0.75 2217 77 64 12 0.00
Sat 06/06 11Z 0.68 2218 77 62 12 0.00
Sat 06/06 12Z 0.67 2119 76 50 13 0.00
Sat 06/06 13Z 0.84 2121 77 57 13 0.00
Sat 06/06 14Z 0.94 2121 79 79 12 0.00
Sat 06/06 15Z 1.17 2122 85 92 12 0.00
Sat 06/06 16Z 0.68 2124 90 97 12 0.02
Sat 06/06 17Z 0.65 2127 92 97 12 0.04
Sat 06/06 18Z 0.63 2128 88 92 13 0.04
Sat 06/06 19Z 0.68 2129 93 90 13 0.03
Sat 06/06 20Z 0.69 2230 95 83 14 0.06
Sat 06/06 21Z 0.81 2329 96 78 14 0.05
Sat 06/06 22Z 0.93 2426 96 73 14 0.01
Sat 06/06 23Z 0.88 2424 95 76 14 0.04
Sun 06/07 00Z 0.92 2424 95 78 14 0.03
Sun 06/07 01Z 0.88 2425 92 73 13 0.08
Sun 06/07 02Z 0.98 2428 95 76 13 0.03
Sun 06/07 03Z 1.09 2528 96 68 12 0.05
Sun 06/07 04Z 1.05 2628 98 78 11 0.04
Sun 06/07 05Z 0.97 2829 98 86 11 0.07
Sun 06/07 06Z 0.92 2929 98 92 10 0.09
Sun 06/07 07Z 0.99 3032 98 93 10 0.11
Sun 06/07 08Z 0.98 3032 98 79 9 0.08
Sun 06/07 09Z 1.05 3033 98 70 9 0.09
Sun 06/07 10Z 1.05 3034 98 68 8 0.09
Sun 06/07 11Z 0.92 3133 98 73 8 0.06
Sun 06/07 12Z 0.79 3131 97 75 7 0.04
Sun 06/07 13Z 0.70 3228 98 76 7 0.04
Sun 06/07 14Z 0.60 3226 98 75 7 0.04
Sun 06/07 15Z 0.48 3225 98 75 6 0.04
Sun 06/07 16Z 0.36 3325 98 71 6 0.03
Sun 06/07 17Z 0.27 3325 97 70 5 0.02
Sun 06/07 18Z 0.21 3425 95 65 5 0.01
Sun 06/07 19Z 0.19 3525 94 49 4 0.00
Sun 06/07 20Z 0.16 3525 94 27 4 0.01
Sun 06/07 21Z 0.18 3525 92 11 4 0.00
Sun 06/07 22Z 0.28 0026 90 3 4 0.00
Sun 06/07 23Z 0.26 0029 86 2 4 0.00
Run total areal avg QPF for the greens is: 1.35 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