Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260422_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)
=== ===== === ==== ==== === === === ====
Wed 04/22 18Z 0.25 1906 92 73 0 0.00
Wed 04/22 19Z 0.14 1808 94 70 0 0.00
Wed 04/22 20Z 0.22 1911 96 52 0 0.00
Wed 04/22 21Z 0.23 2011 96 42 0 0.00
Wed 04/22 22Z 0.29 2112 98 80 0 0.00
Wed 04/22 23Z 0.25 2210 97 50 1 0.01
Thu 04/23 00Z 0.27 2410 97 51 1 0.00
Thu 04/23 01Z 0.26 2610 97 27 2 0.00
Thu 04/23 02Z 0.27 2711 96 24 2 0.00
Thu 04/23 03Z 0.27 2811 94 17 2 0.00
Thu 04/23 04Z 0.25 2911 92 38 2 0.00
Thu 04/23 05Z 0.27 2913 90 59 1 0.00
Thu 04/23 06Z 0.32 2914 89 71 1 0.00
Thu 04/23 07Z 0.35 3016 88 78 1 0.00
Thu 04/23 08Z 0.42 3018 87 80 1 0.00
Thu 04/23 09Z 0.42 3020 87 79 1 0.00
Thu 04/23 10Z 0.40 3122 88 74 0 0.00
Thu 04/23 11Z 0.34 3223 89 64 0 0.00
Thu 04/23 12Z 0.28 3223 88 28 -1 0.00
Thu 04/23 13Z 0.27 3323 89 8 -2 0.00
Thu 04/23 14Z 0.72 3323 90 8 -3 0.00
Thu 04/23 15Z 3.36 3223 85 10 -3 0.00
Thu 04/23 16Z 4.96 3223 86 9 -3 0.00
Thu 04/23 17Z 5.59 3223 81 10 -2 0.00
Thu 04/23 18Z 5.43 3222 72 8 -1 0.00
Thu 04/23 19Z 5.43 3221 67 8 -1 0.00
Thu 04/23 20Z 4.86 3220 63 7 -1 0.00
Thu 04/23 21Z 4.13 3220 57 6 -1 0.00
Thu 04/23 22Z 2.65 3321 54 5 -1 0.00
Thu 04/23 23Z 0.70 3322 53 3 -1 0.00
Fri 04/24 00Z 0.34 3423 54 2 -2 0.00
Fri 04/24 01Z 0.28 3423 54 1 -2 0.00
Fri 04/24 02Z 0.18 3421 54 2 -3 0.00
Fri 04/24 03Z 0.19 3418 58 3 -3 0.00
Fri 04/24 04Z 0.17 3514 62 4 -4 0.00
Fri 04/24 05Z 0.10 3511 69 6 -4 0.00
Fri 04/24 06Z 0.05 3410 74 8 -4 0.00
Fri 04/24 07Z 0.11 3311 76 9 -5 0.00
Fri 04/24 08Z 0.10 3412 76 10 -5 0.00
Fri 04/24 09Z 0.07 3414 76 11 -5 0.00
Fri 04/24 10Z 0.08 3416 73 12 -5 0.00
Fri 04/24 11Z 0.07 3417 70 10 -5 0.00
Fri 04/24 12Z 0.06 3416 73 9 -5 0.00
Fri 04/24 13Z 0.04 3413 76 18 -5 0.00
Fri 04/24 14Z 0.08 3511 74 33 -5 0.00
Fri 04/24 15Z 0.44 3309 73 45 -5 0.00
Fri 04/24 16Z 0.41 3409 70 45 -4 0.00
Fri 04/24 17Z 0.80 3308 66 43 -3 0.00
Fri 04/24 18Z 1.11 3309 61 38 -3 0.00
Fri 04/24 19Z 1.27 3310 56 29 -2 0.00
Fri 04/24 20Z 1.20 3311 47 27 -2 0.00
Fri 04/24 21Z 0.59 3413 39 28 -2 0.00
Fri 04/24 22Z 0.22 3413 39 27 -1 0.00
Fri 04/24 23Z 0.10 3512 46 16 -2 0.00
Sat 04/25 00Z 0.21 0012 55 9 -2 0.00
Sat 04/25 01Z 0.35 0213 63 6 -2 0.00
Sat 04/25 02Z 0.46 0312 65 4 -3 0.00
Sat 04/25 03Z 0.46 0411 69 7 -3 0.00
Sat 04/25 04Z 0.35 0509 71 20 -3 0.00
Sat 04/25 05Z 0.33 0610 70 30 -3 0.00
Run total areal avg QPF for the Central_Greens is: 0.01 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