Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260917_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)
=== ===== === ==== ==== === === === ====
Thu 09/17 06Z 0.05 3203 98 18 12 0.00
Thu 09/17 07Z 0.04 3302 98 26 12 0.00
Thu 09/17 08Z 0.03 0400 98 38 12 0.00
Thu 09/17 09Z 0.04 1401 98 45 12 0.00
Thu 09/17 10Z 0.04 1503 98 43 11 0.00
Thu 09/17 11Z 0.04 1606 98 37 11 0.00
Thu 09/17 12Z 0.04 1709 98 32 11 0.01
Thu 09/17 13Z 0.09 1809 96 30 12 0.00
Thu 09/17 14Z 0.15 2009 95 44 12 0.00
Thu 09/17 15Z 0.20 2110 95 66 12 0.00
Thu 09/17 16Z 0.23 2210 95 84 12 0.00
Thu 09/17 17Z 0.25 2309 95 93 12 0.00
Thu 09/17 18Z 0.21 2208 92 92 13 0.00
Thu 09/17 19Z 0.22 2208 93 94 13 0.00
Thu 09/17 20Z 0.23 2209 96 97 13 0.00
Thu 09/17 21Z 0.23 2109 97 99 12 0.01
Thu 09/17 22Z 0.20 2107 99 99 12 0.03
Thu 09/17 23Z 0.11 2005 99 99 12 0.05
Fri 09/18 00Z 0.07 1806 99 99 12 0.10
Fri 09/18 01Z 0.11 1908 98 98 13 0.13
Fri 09/18 02Z 0.14 2008 99 95 13 0.08
Fri 09/18 03Z 0.24 2309 100 95 13 0.05
Fri 09/18 04Z 0.26 2810 100 97 13 0.04
Fri 09/18 05Z 0.24 3216 99 95 12 0.06
Fri 09/18 06Z 0.21 3220 95 95 12 0.03
Fri 09/18 07Z 0.25 3221 87 92 11 0.02
Fri 09/18 08Z 0.28 3221 75 75 11 0.00
Fri 09/18 09Z 0.28 3223 77 66 10 0.01
Fri 09/18 10Z 0.27 3223 77 43 10 0.01
Fri 09/18 11Z 0.24 3224 78 49 9 0.01
Fri 09/18 12Z 0.24 3225 80 37 8 0.01
Fri 09/18 13Z 0.23 3326 73 17 8 0.00
Fri 09/18 14Z 0.23 3325 72 13 7 0.00
Fri 09/18 15Z 0.42 3223 83 10 6 0.00
Fri 09/18 16Z 0.95 3222 81 5 6 0.00
Fri 09/18 17Z 1.20 3321 77 1 6 0.00
Fri 09/18 18Z 0.80 3319 71 1 5 0.00
Fri 09/18 19Z 1.00 3320 62 1 5 0.00
Fri 09/18 20Z 0.61 3319 57 1 5 0.00
Fri 09/18 21Z 0.26 3319 56 1 5 0.00
Fri 09/18 22Z 0.15 3319 53 1 5 0.00
Fri 09/18 23Z 0.13 3421 53 2 5 0.00
Sat 09/19 00Z 0.07 3422 51 2 5 0.00
Sat 09/19 01Z 0.05 3422 57 2 5 0.00
Sat 09/19 02Z 0.02 3522 59 2 4 0.00
Sat 09/19 03Z 0.05 3520 58 2 4 0.00
Sat 09/19 04Z 0.03 3519 54 2 5 0.00
Sat 09/19 05Z 0.04 3518 47 2 6 0.00
Sat 09/19 06Z 0.04 3517 42 3 6 0.00
Sat 09/19 07Z 0.03 3516 36 3 6 0.00
Sat 09/19 08Z 0.03 3515 32 3 6 0.00
Sat 09/19 09Z 0.05 3515 30 2 6 0.00
Sat 09/19 10Z 0.05 0013 30 2 6 0.00
Sat 09/19 11Z 0.06 0012 30 2 6 0.00
Sat 09/19 12Z 0.05 0010 30 2 5 0.00
Sat 09/19 13Z 0.04 0008 30 3 5 0.00
Sat 09/19 14Z 0.05 0007 32 3 5 0.00
Sat 09/19 15Z 0.03 0004 35 4 5 0.00
Sat 09/19 16Z 0.02 3504 39 4 5 0.00
Sat 09/19 17Z 0.02 3503 46 4 4 0.00
Run total areal avg QPF for the Central_Greens is: 0.65 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