Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260225_1200
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 02/25 12Z 0.28 1928 90 85 -10 0.00
Wed 02/25 13Z 0.35 2027 94 86 -10 0.01
Wed 02/25 14Z 0.45 2125 96 90 -10 0.01
Wed 02/25 15Z 0.51 2222 95 86 -9 0.01
Wed 02/25 16Z 0.57 2220 95 77 -9 0.00
Wed 02/25 17Z 0.70 2218 92 67 -8 0.00
Wed 02/25 18Z 1.45 2117 90 50 -8 0.00
Wed 02/25 19Z 4.88 2216 86 34 -7 0.00
Wed 02/25 20Z 5.55 2317 86 43 -7 0.00
Wed 02/25 21Z 1.55 2216 87 68 -7 0.00
Wed 02/25 22Z 0.76 2117 87 63 -6 0.00
Wed 02/25 23Z 0.55 2020 88 67 -6 0.00
Thu 02/26 00Z 0.53 2023 90 82 -5 0.00
Thu 02/26 01Z 0.65 2126 94 83 -5 0.00
Thu 02/26 02Z 0.79 2229 96 82 -5 0.01
Thu 02/26 03Z 1.07 2328 97 86 -5 0.02
Thu 02/26 04Z 1.37 2424 93 86 -7 0.02
Thu 02/26 05Z 1.06 2522 94 38 -7 0.01
Thu 02/26 07Z 1.46 2626 89 13 -9 0.02
Thu 02/26 08Z 1.44 2628 81 16 -11 0.02
Thu 02/26 09Z 1.55 2730 75 22 -12 0.00
Thu 02/26 10Z 1.29 2731 69 18 -13 0.00
Thu 02/26 11Z 1.13 2732 65 16 -13 0.00
Thu 02/26 12Z 1.01 2832 66 4 -13 0.00
Thu 02/26 13Z 1.06 2730 67 4 -14 0.00
Thu 02/26 14Z 1.39 2726 69 1 -15 0.00
Thu 02/26 15Z 2.92 2724 70 2 -15 0.00
Thu 02/26 16Z 2.38 2820 70 4 -14 0.00
Thu 02/26 17Z 4.47 2719 73 6 -14 0.00
Thu 02/26 18Z 8.81 2718 75 9 -14 0.00
Thu 02/26 19Z 8.35 2616 75 13 -14 0.00
Thu 02/26 20Z 7.59 2616 75 18 -13 0.00
Thu 02/26 21Z 5.47 2716 74 22 -13 0.00
Thu 02/26 22Z 2.44 2717 74 27 -13 0.00
Thu 02/26 23Z 1.77 2719 74 33 -13 0.00
Fri 02/27 00Z 1.28 2721 73 39 -13 0.00
Fri 02/27 01Z 0.96 2822 71 45 -14 0.00
Fri 02/27 02Z 0.69 2821 67 47 -14 0.00
Fri 02/27 03Z 0.52 2920 66 46 -13 0.00
Fri 02/27 04Z 0.42 2919 68 48 -13 0.00
Fri 02/27 05Z 0.37 2918 69 42 -13 0.00
Fri 02/27 06Z 0.32 2917 68 43 -12 0.00
Fri 02/27 07Z 0.29 2916 64 47 -11 0.00
Fri 02/27 08Z 0.27 2916 60 59 -11 0.00
Fri 02/27 09Z 0.28 2916 59 60 -10 0.00
Fri 02/27 10Z 0.32 2817 61 65 -10 0.00
Fri 02/27 11Z 0.32 2817 60 76 -10 0.00
Fri 02/27 12Z 0.34 2717 65 84 -9 0.00
Fri 02/27 13Z 0.37 2619 71 86 -8 0.00
Fri 02/27 14Z 0.42 2520 77 82 -8 0.00
Fri 02/27 15Z 0.47 2521 73 80 -7 0.00
Fri 02/27 17Z 0.52 2421 63 89 -5 0.00
Fri 02/27 18Z 0.55 2323 61 71 -5 0.00
Fri 02/27 19Z 0.64 2326 60 78 -5 0.00
Fri 02/27 20Z 0.72 2327 56 62 -4 0.00
Fri 02/27 21Z 0.85 2329 59 66 -4 0.00
Fri 02/27 22Z 0.90 2330 65 70 -4 0.00
Fri 02/27 23Z 0.85 2330 71 58 -4 0.00
Run total areal avg QPF for the Central_Greens is: 0.13 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