Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260224_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)
=== ===== === ==== ==== === === === ====
Tue 02/24 06Z 0.36 3227 87 40 -13 0.00
Tue 02/24 07Z 0.40 3231 90 34 -13 0.00
Tue 02/24 08Z 0.30 3328 92 35 -14 0.00
Tue 02/24 09Z 0.25 3325 91 36 -14 0.00
Tue 02/24 10Z 0.26 3223 91 43 -14 0.00
Tue 02/24 11Z 0.29 3122 92 52 -15 0.00
Tue 02/24 12Z 0.27 3121 92 54 -15 0.00
Tue 02/24 13Z 0.24 3119 93 54 -15 0.00
Tue 02/24 14Z 0.26 3118 92 55 -15 0.00
Tue 02/24 15Z 0.32 3017 91 54 -16 0.00
Tue 02/24 16Z 0.36 3018 90 54 -16 0.00
Tue 02/24 17Z 0.36 3017 87 55 -16 0.00
Tue 02/24 18Z 0.42 3017 85 56 -16 0.00
Tue 02/24 19Z 0.61 3016 84 45 -16 0.00
Tue 02/24 20Z 0.60 3014 83 31 -15 0.00
Tue 02/24 22Z 0.67 2813 84 7 -15 0.00
Tue 02/24 23Z 0.72 2715 85 3 -15 0.00
Wed 02/25 00Z 0.66 2716 85 1 -15 0.00
Wed 02/25 01Z 0.51 2715 82 4 -15 0.00
Wed 02/25 02Z 0.40 2614 78 7 -14 0.00
Wed 02/25 03Z 0.29 2513 65 21 -12 0.00
Wed 02/25 04Z 0.23 2411 49 52 -11 0.00
Wed 02/25 05Z 0.25 2314 44 58 -11 0.00
Wed 02/25 06Z 0.31 2318 36 87 -10 0.00
Wed 02/25 07Z 0.31 2218 35 66 -10 0.00
Wed 02/25 08Z 0.25 2119 52 25 -9 0.00
Wed 02/25 09Z 0.25 1924 62 62 -9 0.00
Wed 02/25 10Z 0.28 1928 75 91 -9 0.00
Wed 02/25 11Z 0.30 1932 91 89 -9 0.00
Wed 02/25 12Z 0.31 1932 92 88 -8 0.01
Wed 02/25 13Z 0.38 2029 92 87 -9 0.05
Wed 02/25 14Z 0.44 2125 94 88 -9 0.06
Wed 02/25 15Z 0.50 2121 95 89 -9 0.04
Wed 02/25 16Z 0.61 2217 96 81 -8 0.03
Wed 02/25 17Z 0.86 2215 95 68 -8 0.01
Wed 02/25 18Z 1.91 2315 93 58 -8 0.00
Wed 02/25 19Z 4.38 2317 91 42 -8 0.00
Wed 02/25 20Z 2.85 2319 93 52 -8 0.00
Wed 02/25 21Z 1.27 2319 94 82 -8 0.00
Wed 02/25 22Z 1.01 2320 95 77 -7 0.00
Wed 02/25 23Z 0.87 2222 96 85 -7 0.00
Thu 02/26 00Z 0.99 2323 94 87 -7 0.01
Thu 02/26 01Z 1.42 2522 95 85 -8 0.03
Thu 02/26 02Z 1.65 2624 96 50 -9 0.03
Thu 02/26 03Z 1.42 2626 86 36 -10 0.01
Thu 02/26 04Z 1.11 2725 81 38 -11 0.01
Thu 02/26 05Z 0.87 2722 81 45 -11 0.00
Thu 02/26 06Z 0.90 2621 89 59 -11 0.00
Thu 02/26 07Z 0.91 2621 93 57 -11 0.00
Thu 02/26 08Z 1.12 2624 95 54 -12 0.00
Thu 02/26 09Z 1.35 2726 86 43 -13 0.01
Thu 02/26 10Z 1.24 2728 74 27 -14 0.01
Thu 02/26 11Z 1.30 2731 71 16 -14 0.00
Thu 02/26 12Z 1.29 2732 66 11 -15 0.00
Thu 02/26 13Z 1.46 2731 66 6 -15 0.00
Thu 02/26 14Z 1.96 2728 70 5 -16 0.00
Thu 02/26 15Z 9.40 2725 75 4 -16 0.00
Thu 02/26 16Z 15.67 2724 80 5 -16 0.00
Thu 02/26 17Z 15.68 2724 79 7 -16 0.00
Run total areal avg QPF for the Central_Greens is: 0.31 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