Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260117_1800
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 01/17 18Z 0.29 2118 96 86 -6 0.00
Sat 01/17 19Z 0.35 2119 96 87 -6 0.02
Sat 01/17 20Z 0.44 2219 97 86 -7 0.01
Sat 01/17 21Z 0.55 2420 97 82 -7 0.01
Sat 01/17 22Z 0.56 2520 94 78 -7 0.01
Sat 01/17 23Z 0.62 2521 93 72 -7 0.01
Sun 01/18 00Z 0.65 2622 91 57 -7 0.01
Sun 01/18 01Z 0.59 2621 86 59 -7 0.00
Sun 01/18 02Z 0.57 2521 84 49 -6 0.00
Sun 01/18 03Z 0.56 2521 87 41 -6 0.00
Sun 01/18 04Z 0.64 2423 89 46 -7 0.00
Sun 01/18 05Z 0.75 2425 94 48 -7 0.00
Sun 01/18 06Z 0.77 2424 94 42 -7 0.00
Sun 01/18 07Z 0.79 2423 94 25 -8 0.01
Sun 01/18 08Z 0.81 2424 94 32 -8 0.01
Sun 01/18 09Z 0.75 2423 92 60 -8 0.01
Sun 01/18 10Z 0.69 2421 91 65 -8 0.00
Sun 01/18 11Z 0.64 2420 87 86 -8 0.00
Sun 01/18 12Z 0.66 2319 91 88 -9 0.00
Sun 01/18 13Z 0.81 2319 93 83 -9 0.01
Sun 01/18 14Z 1.08 2420 96 74 -10 0.01
Sun 01/18 15Z 0.87 2418 97 66 -10 0.01
Sun 01/18 16Z 0.76 2417 97 64 -10 0.01
Sun 01/18 17Z 0.67 2415 96 62 -10 0.01
Sun 01/18 18Z 0.60 2413 94 69 -10 0.00
Sun 01/18 19Z 0.56 2412 90 68 -10 0.00
Sun 01/18 20Z 0.47 2510 89 70 -10 0.00
Sun 01/18 21Z 0.34 2607 88 67 -10 0.00
Sun 01/18 22Z 0.21 2505 85 86 -10 0.00
Sun 01/18 23Z 0.08 2301 82 79 -10 0.00
Mon 01/19 00Z 0.04 2300 84 73 -9 0.00
Mon 01/19 01Z 0.05 2801 86 71 -9 0.00
Mon 01/19 02Z 0.05 3202 86 84 -9 0.00
Mon 01/19 03Z 0.03 3202 87 82 -10 0.00
Mon 01/19 04Z 0.05 3203 87 85 -10 0.01
Mon 01/19 05Z 0.02 3404 89 87 -10 0.01
Mon 01/19 06Z 0.03 3404 91 86 -10 0.01
Mon 01/19 07Z 0.05 3204 92 78 -11 0.00
Mon 01/19 08Z 0.05 3103 92 62 -11 0.00
Mon 01/19 09Z 0.07 2702 93 49 -11 0.00
Mon 01/19 10Z 0.10 2503 92 39 -11 0.00
Mon 01/19 11Z 0.14 2405 92 34 -11 0.00
Mon 01/19 12Z 0.19 2307 92 40 -11 0.00
Mon 01/19 13Z 0.20 2208 91 46 -11 0.00
Mon 01/19 14Z 0.23 2110 91 71 -12 0.00
Mon 01/19 15Z 0.32 2112 91 86 -12 0.00
Mon 01/19 16Z 0.55 2215 92 87 -13 0.00
Mon 01/19 17Z 1.40 2215 90 81 -13 0.00
Mon 01/19 18Z 2.64 2217 88 77 -14 0.00
Mon 01/19 19Z 6.22 2319 89 80 -14 0.00
Mon 01/19 20Z 3.57 2321 90 80 -14 0.01
Mon 01/19 21Z 3.19 2423 92 77 -14 0.01
Mon 01/19 22Z 1.91 2425 85 71 -14 0.01
Mon 01/19 23Z 1.49 2427 86 67 -14 0.00
Tue 01/20 00Z 1.64 2329 87 65 -14 0.00
Tue 01/20 01Z 1.75 2431 85 63 -14 0.00
Tue 01/20 02Z 2.30 2433 87 57 -14 0.00
Tue 01/20 03Z 3.15 2433 89 49 -15 0.00
Tue 01/20 04Z 3.94 2433 85 51 -16 0.00
Tue 01/20 05Z 1.93 2434 87 77 -16 0.00
Run total areal avg QPF for the Central_Greens is: 0.21 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