Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260914_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)
=== ===== === ==== ==== === === === ====
Mon 09/14 18Z 4.39 3215 84 14 4 0.00
Mon 09/14 19Z 3.46 3217 83 18 4 0.00
Mon 09/14 20Z 1.99 3218 81 19 4 0.00
Mon 09/14 21Z 1.61 3218 82 18 4 0.00
Mon 09/14 22Z 0.87 3219 82 17 4 0.00
Mon 09/14 23Z 0.75 3221 80 16 4 0.00
Tue 09/15 00Z 0.55 3320 81 13 4 0.00
Tue 09/15 01Z 0.52 3321 83 12 4 0.00
Tue 09/15 02Z 0.39 3321 83 10 4 0.00
Tue 09/15 03Z 0.14 3419 81 9 4 0.00
Tue 09/15 04Z 0.04 3418 75 8 5 0.00
Tue 09/15 05Z 0.05 3513 66 7 7 0.00
Tue 09/15 06Z 0.05 3510 64 7 7 0.00
Tue 09/15 07Z 0.05 0008 62 7 7 0.00
Tue 09/15 08Z 0.05 3308 64 7 6 0.00
Tue 09/15 09Z 0.01 3408 62 6 6 0.00
Tue 09/15 10Z 0.04 0005 59 8 7 0.00
Tue 09/15 11Z 0.06 0602 56 10 7 0.00
Tue 09/15 12Z 0.05 1303 54 13 7 0.00
Tue 09/15 13Z 0.04 1704 55 14 7 0.00
Tue 09/15 14Z 0.05 1904 57 16 7 0.00
Tue 09/15 15Z 0.07 2004 58 17 8 0.00
Tue 09/15 16Z 0.06 1906 58 17 8 0.00
Tue 09/15 17Z 0.13 2008 59 16 9 0.00
Tue 09/15 18Z 0.16 1909 58 15 9 0.00
Tue 09/15 19Z 0.16 1910 59 13 9 0.00
Tue 09/15 20Z 0.25 2010 61 11 9 0.00
Tue 09/15 21Z 0.16 2013 49 17 12 0.00
Tue 09/15 22Z 0.18 2015 44 34 13 0.00
Tue 09/15 23Z 0.22 2017 42 72 14 0.00
Wed 09/16 00Z 0.25 2019 39 89 14 0.00
Wed 09/16 01Z 0.27 2120 34 88 15 0.00
Wed 09/16 02Z 0.26 2121 31 83 15 0.00
Wed 09/16 03Z 0.33 2121 35 86 15 0.00
Wed 09/16 04Z 0.36 2222 41 91 15 0.00
Wed 09/16 05Z 0.39 2322 45 88 15 0.00
Wed 09/16 06Z 0.40 2321 45 89 15 0.00
Wed 09/16 07Z 0.43 2423 46 90 15 0.00
Wed 09/16 08Z 0.48 2424 52 91 15 0.00
Wed 09/16 09Z 0.46 2423 53 90 15 0.00
Wed 09/16 10Z 0.47 2523 59 93 15 0.00
Wed 09/16 11Z 0.46 2522 62 92 15 0.00
Wed 09/16 12Z 0.45 2522 72 94 15 0.00
Wed 09/16 13Z 0.50 2523 77 90 15 0.01
Wed 09/16 14Z 0.52 2523 85 89 15 0.02
Wed 09/16 15Z 0.53 2622 92 79 15 0.00
Wed 09/16 16Z 0.49 2721 95 83 15 0.01
Wed 09/16 17Z 0.43 2819 97 88 15 0.02
Wed 09/16 18Z 0.35 2816 98 77 15 0.01
Wed 09/16 19Z 0.29 2913 98 81 14 0.01
Wed 09/16 20Z 0.22 2911 98 71 14 0.00
Wed 09/16 21Z 0.18 3009 99 78 14 0.01
Wed 09/16 22Z 0.16 3008 98 70 13 0.00
Wed 09/16 23Z 0.15 3008 97 41 13 0.00
Thu 09/17 00Z 0.13 3107 95 19 13 0.00
Thu 09/17 01Z 0.12 3106 94 17 12 0.00
Thu 09/17 02Z 0.10 3005 94 14 12 0.00
Thu 09/17 03Z 0.09 2904 94 13 12 0.00
Thu 09/17 04Z 0.09 2803 94 15 12 0.00
Thu 09/17 05Z 0.09 2703 94 12 12 0.00
Run total areal avg QPF for the Central_Greens is: 0.09 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