Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260409_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 04/09 18Z 0.64 1918 31 30 2 0.00
Thu 04/09 19Z 0.69 1921 32 23 3 0.00
Thu 04/09 20Z 0.64 1923 32 26 3 0.00
Thu 04/09 21Z 0.52 1926 30 36 4 0.00
Thu 04/09 22Z 0.46 2027 30 44 5 0.00
Fri 04/10 00Z 0.41 2129 33 53 7 0.00
Fri 04/10 01Z 0.48 2230 38 52 7 0.00
Fri 04/10 02Z 0.53 2331 43 64 7 0.00
Fri 04/10 03Z 0.58 2432 50 69 7 0.00
Fri 04/10 04Z 0.64 2433 62 67 6 0.00
Fri 04/10 05Z 0.65 2432 69 84 6 0.00
Fri 04/10 06Z 0.64 2532 70 57 6 0.00
Fri 04/10 07Z 0.60 2629 71 35 6 0.00
Fri 04/10 08Z 0.55 2625 72 7 5 0.00
Fri 04/10 09Z 0.53 2624 76 5 5 0.00
Fri 04/10 10Z 0.51 2522 83 4 5 0.00
Fri 04/10 11Z 0.53 2522 85 8 5 0.00
Fri 04/10 13Z 0.47 2420 85 20 6 0.00
Fri 04/10 14Z 0.46 2421 86 66 6 0.00
Fri 04/10 15Z 0.45 2321 83 86 7 0.00
Fri 04/10 16Z 0.49 2323 84 94 7 0.00
Fri 04/10 17Z 0.57 2324 83 80 7 0.00
Fri 04/10 18Z 0.64 2324 79 49 8 0.00
Fri 04/10 19Z 0.70 2325 76 36 8 0.00
Fri 04/10 20Z 0.79 2228 71 31 8 0.00
Fri 04/10 22Z 0.96 2231 71 62 8 0.00
Fri 04/10 23Z 1.14 2234 78 94 7 0.00
Sat 04/11 00Z 1.04 2433 95 96 6 0.00
Sat 04/11 01Z 0.92 2532 98 94 5 0.00
Sat 04/11 02Z 0.75 2626 98 95 5 0.01
Sat 04/11 03Z 0.56 2722 98 88 4 0.09
Sat 04/11 04Z 0.37 2818 99 94 3 0.13
Sat 04/11 05Z 0.35 3021 97 92 1 0.07
Sat 04/11 06Z 0.39 3024 96 55 0 0.04
Sat 04/11 07Z 0.46 3127 92 20 -2 0.03
Sat 04/11 08Z 0.46 3127 85 8 -3 0.03
Sat 04/11 09Z 0.49 3129 85 3 -3 0.01
Sat 04/11 10Z 0.52 3029 84 3 -4 0.01
Sat 04/11 11Z 0.48 3128 80 3 -4 0.01
Sat 04/11 12Z 0.45 3127 79 6 -5 0.01
Sat 04/11 13Z 0.46 3127 78 8 -5 0.01
Sat 04/11 14Z 0.46 3127 76 8 -6 0.01
Sat 04/11 15Z 0.50 3126 79 7 -6 0.01
Sat 04/11 16Z 0.51 3124 81 9 -6 0.00
Sat 04/11 17Z 0.54 3122 81 10 -6 0.00
Sat 04/11 18Z 0.57 3121 81 10 -6 0.00
Sat 04/11 19Z 0.74 3120 81 9 -6 0.00
Sat 04/11 21Z 1.63 3119 79 8 -6 0.00
Sat 04/11 22Z 1.23 3119 79 6 -6 0.00
Sat 04/11 23Z 0.94 3119 77 7 -6 0.00
Sun 04/12 00Z 0.78 3121 75 8 -5 0.00
Sun 04/12 01Z 0.52 3221 72 7 -5 0.00
Sun 04/12 02Z 0.33 3221 67 8 -5 0.00
Sun 04/12 03Z 0.25 3221 61 7 -4 0.00
Sun 04/12 04Z 0.23 3220 60 8 -4 0.00
Sun 04/12 05Z 0.19 3218 59 8 -4 0.00
Run total areal avg QPF for the Central_Greens is: 0.47 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