Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260915_0000
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 09/15 00Z 0.57 3221 85 22 4 0.00
Tue 09/15 01Z 0.52 3323 84 23 4 0.00
Tue 09/15 02Z 0.15 3422 81 18 4 0.00
Tue 09/15 03Z 0.02 3520 79 14 5 0.00
Tue 09/15 04Z 0.07 3518 76 10 6 0.00
Tue 09/15 05Z 0.05 3516 75 8 6 0.00
Tue 09/15 06Z 0.13 0013 72 7 6 0.00
Tue 09/15 07Z 0.09 0109 68 6 7 0.00
Tue 09/15 08Z 0.08 0107 65 7 7 0.00
Tue 09/15 09Z 0.04 0005 67 8 6 0.00
Tue 09/15 10Z 0.03 0001 65 10 6 0.00
Tue 09/15 11Z 0.02 1100 63 12 7 0.00
Tue 09/15 12Z 0.03 1603 62 13 7 0.00
Tue 09/15 13Z 0.03 1803 59 15 7 0.00
Tue 09/15 14Z 0.05 1904 61 16 7 0.00
Tue 09/15 15Z 0.06 1905 62 16 8 0.00
Tue 09/15 16Z 0.10 2006 65 16 8 0.00
Tue 09/15 17Z 0.09 1907 65 15 9 0.00
Tue 09/15 18Z 0.15 2009 65 16 9 0.00
Tue 09/15 19Z 0.17 2009 63 15 10 0.00
Tue 09/15 20Z 0.20 2011 61 15 10 0.00
Tue 09/15 21Z 0.20 2012 57 13 11 0.00
Tue 09/15 22Z 0.22 2014 50 45 12 0.00
Tue 09/15 23Z 0.28 2116 48 83 12 0.00
Wed 09/16 00Z 0.22 2016 40 91 14 0.00
Wed 09/16 01Z 0.21 2019 36 90 15 0.00
Wed 09/16 02Z 0.26 2120 37 86 15 0.00
Wed 09/16 03Z 0.33 2222 38 88 15 0.00
Wed 09/16 04Z 0.37 2223 43 91 15 0.00
Wed 09/16 05Z 0.42 2323 47 94 15 0.00
Wed 09/16 06Z 0.46 2423 51 96 14 0.00
Wed 09/16 07Z 0.48 2423 50 95 14 0.00
Wed 09/16 08Z 0.46 2522 52 91 14 0.00
Wed 09/16 09Z 0.46 2522 57 79 14 0.00
Wed 09/16 10Z 0.48 2622 69 75 14 0.00
Wed 09/16 11Z 0.46 2721 82 68 14 0.00
Wed 09/16 12Z 0.43 2719 90 68 14 0.00
Wed 09/16 13Z 0.41 2818 92 76 14 0.00
Wed 09/16 14Z 0.42 2717 92 72 14 0.00
Wed 09/16 15Z 0.41 2716 91 75 14 0.00
Wed 09/16 16Z 0.42 2716 92 80 14 0.00
Wed 09/16 17Z 0.40 2615 94 82 15 0.00
Wed 09/16 18Z 0.37 2614 96 86 15 0.00
Wed 09/16 19Z 0.35 2713 97 84 15 0.01
Wed 09/16 20Z 0.32 2812 97 57 14 0.01
Wed 09/16 21Z 0.28 2811 96 58 14 0.00
Wed 09/16 22Z 0.26 2811 95 49 14 0.00
Wed 09/16 23Z 0.25 2911 94 38 14 0.00
Thu 09/17 00Z 0.18 2909 91 19 14 0.00
Thu 09/17 01Z 0.15 3008 89 20 14 0.00
Thu 09/17 02Z 0.14 3007 87 16 14 0.00
Thu 09/17 03Z 0.12 3007 82 18 14 0.00
Thu 09/17 04Z 0.11 3006 79 15 14 0.00
Thu 09/17 05Z 0.07 2903 77 27 14 0.00
Thu 09/17 06Z 0.09 2703 78 41 14 0.00
Thu 09/17 07Z 0.10 2404 79 41 14 0.00
Thu 09/17 08Z 0.13 2306 80 47 14 0.00
Thu 09/17 09Z 0.14 2306 81 54 14 0.00
Thu 09/17 10Z 0.16 2307 87 73 14 0.00
Thu 09/17 11Z 0.16 2307 91 80 14 0.00
Run total areal avg QPF for the Central_Greens is: 0.02 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