Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260805_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)
=== ===== === ==== ==== === === === ====
Wed 08/05 06Z 0.28 2710 67 35 17 0.00
Wed 08/05 07Z 0.27 2710 68 37 17 0.00
Wed 08/05 08Z 0.27 2709 69 38 16 0.00
Wed 08/05 09Z 0.28 2810 69 37 16 0.00
Wed 08/05 10Z 0.26 2809 69 36 16 0.00
Wed 08/05 11Z 0.22 2808 68 33 15 0.00
Wed 08/05 12Z 0.16 2906 67 30 16 0.00
Wed 08/05 13Z 0.11 2804 65 27 16 0.00
Wed 08/05 14Z 0.11 2503 66 23 16 0.00
Wed 08/05 15Z 0.12 2303 68 18 15 0.00
Wed 08/05 16Z 0.19 2204 69 10 15 0.00
Wed 08/05 17Z 0.43 2205 66 4 15 0.00
Wed 08/05 18Z 0.55 2206 62 2 16 0.00
Wed 08/05 19Z 0.59 2106 58 1 16 0.00
Wed 08/05 20Z 0.46 2106 56 1 16 0.00
Wed 08/05 21Z 0.37 2207 54 9 17 0.00
Wed 08/05 22Z 0.34 2208 55 27 17 0.00
Wed 08/05 23Z 0.34 2209 57 46 17 0.00
Thu 08/06 00Z 0.39 2309 62 58 16 0.00
Thu 08/06 01Z 0.42 2410 68 63 16 0.00
Thu 08/06 02Z 0.43 2410 71 73 16 0.00
Thu 08/06 03Z 0.39 2311 74 77 16 0.00
Thu 08/06 04Z 0.35 2211 78 74 16 0.00
Thu 08/06 05Z 0.34 2212 78 83 16 0.00
Thu 08/06 06Z 0.33 2212 77 89 16 0.00
Thu 08/06 07Z 0.34 2212 77 93 16 0.00
Thu 08/06 08Z 0.31 2211 75 92 16 0.00
Thu 08/06 09Z 0.27 2110 74 91 16 0.00
Thu 08/06 10Z 0.22 2009 76 94 16 0.00
Thu 08/06 11Z 0.15 1909 79 90 17 0.00
Thu 08/06 12Z 0.18 2010 85 92 16 0.00
Thu 08/06 13Z 0.16 2010 88 92 16 0.00
Thu 08/06 14Z 0.19 2010 91 88 16 0.00
Thu 08/06 15Z 0.21 2110 93 85 16 0.00
Thu 08/06 16Z 0.24 2110 95 85 17 0.01
Thu 08/06 17Z 0.33 2112 98 88 16 0.00
Thu 08/06 18Z 0.35 2212 99 88 17 0.01
Thu 08/06 19Z 0.33 2211 97 82 17 0.01
Thu 08/06 20Z 0.42 2311 95 78 17 0.00
Thu 08/06 21Z 0.33 2308 95 77 17 0.00
Thu 08/06 22Z 0.34 2408 95 80 17 0.01
Thu 08/06 23Z 0.32 2608 94 77 17 0.00
Fri 08/07 00Z 0.28 2607 95 74 17 0.01
Fri 08/07 01Z 0.22 2606 91 69 17 0.01
Fri 08/07 02Z 0.23 2607 89 69 18 0.01
Fri 08/07 03Z 0.25 2708 84 68 18 0.00
Fri 08/07 04Z 0.26 2808 86 67 18 0.00
Fri 08/07 05Z 0.29 2810 85 66 17 0.00
Fri 08/07 06Z 0.27 2910 88 62 17 0.00
Fri 08/07 07Z 0.26 2909 90 53 17 0.00
Fri 08/07 08Z 0.23 3009 93 37 17 0.00
Fri 08/07 09Z 0.17 3007 93 37 17 0.00
Fri 08/07 10Z 0.13 3106 91 37 17 0.00
Fri 08/07 11Z 0.14 3107 92 37 17 0.00
Fri 08/07 12Z 0.12 3006 91 33 17 0.00
Fri 08/07 13Z 0.12 3005 90 55 17 0.00
Fri 08/07 14Z 0.14 2805 87 54 17 0.00
Fri 08/07 15Z 0.16 2705 85 49 17 0.00
Fri 08/07 16Z 0.17 2705 82 55 17 0.00
Fri 08/07 17Z 0.21 2706 80 60 17 0.00
Run total areal avg QPF for the Central_Greens is: 0.07 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