Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260716_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)
=== ===== === ==== ==== === === === ====
Thu 07/16 18Z 5.87 2925 79 83 13 0.00
Thu 07/16 19Z 4.47 3024 80 80 13 0.03
Thu 07/16 20Z 0.65 3223 89 79 12 0.08
Thu 07/16 21Z 0.57 3121 85 74 12 0.10
Thu 07/16 22Z 0.62 3024 89 74 11 0.17
Thu 07/16 23Z 0.58 3130 82 36 11 0.05
Fri 07/17 00Z 0.56 3232 79 14 10 0.01
Fri 07/17 01Z 0.66 3232 75 10 9 0.00
Fri 07/17 02Z 0.65 3232 71 20 9 0.00
Fri 07/17 03Z 0.58 3232 63 29 8 0.00
Fri 07/17 04Z 0.57 3231 61 31 8 0.00
Fri 07/17 05Z 0.58 3230 61 29 8 0.00
Fri 07/17 06Z 0.59 3229 61 28 7 0.00
Fri 07/17 07Z 0.62 3230 63 23 7 0.00
Fri 07/17 08Z 0.59 3229 67 17 7 0.00
Fri 07/17 09Z 0.57 3228 70 13 7 0.00
Fri 07/17 10Z 0.46 3228 72 12 7 0.00
Fri 07/17 11Z 0.37 3228 71 16 8 0.00
Fri 07/17 12Z 0.30 3226 67 19 9 0.00
Fri 07/17 13Z 0.21 3222 60 21 9 0.00
Fri 07/17 14Z 0.18 3219 56 17 9 0.00
Fri 07/17 15Z 0.19 3216 56 14 9 0.00
Fri 07/17 16Z 0.26 3214 55 17 9 0.00
Fri 07/17 17Z 0.37 3113 50 19 9 0.00
Fri 07/17 18Z 0.50 3013 49 20 10 0.00
Fri 07/17 19Z 0.79 2914 58 20 10 0.00
Fri 07/17 20Z 0.98 2813 60 18 10 0.00
Fri 07/17 21Z 1.31 2812 61 16 10 0.00
Fri 07/17 22Z 1.03 2811 59 12 11 0.00
Fri 07/17 23Z 0.69 2810 53 10 11 0.00
Sat 07/18 00Z 0.66 2810 47 9 11 0.00
Sat 07/18 01Z 0.64 2810 45 9 11 0.00
Sat 07/18 02Z 0.59 2710 45 10 11 0.00
Sat 07/18 03Z 0.58 2710 49 11 11 0.00
Sat 07/18 04Z 0.49 2609 50 10 11 0.00
Sat 07/18 05Z 0.49 2409 53 9 11 0.00
Sat 07/18 06Z 0.46 2410 56 11 11 0.00
Sat 07/18 07Z 0.49 2412 57 12 11 0.00
Sat 07/18 08Z 0.45 2414 44 22 12 0.00
Sat 07/18 09Z 0.52 2515 45 40 12 0.00
Sat 07/18 10Z 0.59 2416 59 78 12 0.00
Sat 07/18 11Z 0.61 2318 68 94 12 0.00
Sat 07/18 12Z 0.60 2220 67 81 13 0.00
Sat 07/18 13Z 0.66 2124 69 85 13 0.00
Sat 07/18 14Z 0.77 2125 69 64 14 0.00
Sat 07/18 15Z 0.98 2127 74 68 14 0.00
Sat 07/18 16Z 1.07 2128 78 64 15 0.00
Sat 07/18 17Z 4.74 2027 80 63 15 0.00
Sat 07/18 18Z 2.93 2129 86 84 15 0.01
Sat 07/18 19Z 0.88 2135 96 93 15 0.08
Sat 07/18 20Z 0.82 2135 98 91 15 0.13
Sat 07/18 21Z 0.79 2136 97 77 15 0.03
Sat 07/18 22Z 0.77 2138 97 78 15 0.02
Sat 07/18 23Z 0.80 2138 97 78 15 0.03
Sun 07/19 00Z 0.68 2133 96 65 16 0.02
Sun 07/19 01Z 0.70 2232 98 78 16 0.02
Sun 07/19 02Z 0.80 2232 96 84 16 0.22
Sun 07/19 03Z 0.87 2329 93 78 15 0.34
Sun 07/19 04Z 0.83 2327 95 75 15 0.05
Sun 07/19 05Z 0.79 2525 93 74 15 0.02
Run total areal avg QPF for the Central_Greens is: 1.41 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