Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260219_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)
=== ===== === ==== ==== === === === ====
Thu 02/19 00Z 0.11 0110 44 41 -5 0.00
Thu 02/19 01Z 0.20 0213 48 61 -5 0.00
Thu 02/19 02Z 0.25 0314 53 71 -6 0.00
Thu 02/19 03Z 0.24 0314 53 72 -6 0.00
Thu 02/19 04Z 0.21 0313 50 65 -6 0.00
Thu 02/19 05Z 0.14 0210 44 58 -6 0.00
Thu 02/19 06Z 0.15 0310 39 54 -5 0.00
Thu 02/19 07Z 0.14 0309 34 48 -5 0.00
Thu 02/19 08Z 0.12 0307 30 48 -5 0.00
Thu 02/19 09Z 0.09 0305 28 37 -5 0.00
Thu 02/19 10Z 0.07 0304 25 24 -5 0.00
Thu 02/19 11Z 0.06 0304 23 15 -5 0.00
Thu 02/19 12Z 0.08 0404 23 15 -4 0.00
Thu 02/19 13Z 0.06 0403 24 17 -4 0.00
Thu 02/19 14Z 0.06 0602 25 18 -4 0.00
Thu 02/19 15Z 0.05 0802 26 17 -4 0.00
Thu 02/19 16Z 0.03 1101 29 32 -4 0.00
Thu 02/19 17Z 0.01 1701 33 42 -4 0.00
Thu 02/19 18Z 0.03 1803 36 48 -4 0.00
Thu 02/19 19Z 0.04 1903 39 59 -4 0.00
Thu 02/19 20Z 0.07 2003 45 53 -4 0.00
Thu 02/19 21Z 0.09 2104 49 50 -4 0.00
Thu 02/19 22Z 0.15 2306 54 48 -4 0.00
Thu 02/19 23Z 0.13 2305 60 47 -4 0.00
Fri 02/20 00Z 0.07 2203 70 40 -3 0.00
Fri 02/20 01Z 0.03 1803 76 28 -3 0.00
Fri 02/20 02Z 0.07 1905 79 10 -4 0.00
Fri 02/20 03Z 0.11 2006 84 12 -4 0.00
Fri 02/20 04Z 0.11 2007 88 13 -5 0.00
Fri 02/20 05Z 0.13 2007 92 10 -5 0.00
Fri 02/20 06Z 0.14 2107 92 10 -5 0.00
Fri 02/20 07Z 0.13 2007 89 8 -4 0.00
Fri 02/20 08Z 0.11 2007 86 10 -4 0.00
Fri 02/20 09Z 0.08 2006 82 16 -3 0.00
Fri 02/20 10Z 0.08 1906 79 30 -3 0.00
Fri 02/20 11Z 0.05 1806 77 33 -2 0.00
Fri 02/20 12Z 0.02 1707 78 35 -2 0.00
Fri 02/20 13Z 0.03 1609 79 35 -2 0.00
Fri 02/20 14Z 0.02 1612 82 31 -2 0.00
Fri 02/20 15Z 0.03 1613 81 31 -2 0.00
Fri 02/20 16Z 0.02 1615 81 36 -3 0.00
Fri 02/20 17Z 0.05 1615 75 40 -2 0.00
Fri 02/20 18Z 0.05 1616 71 65 -1 0.00
Fri 02/20 19Z 0.11 1516 77 91 0 0.00
Fri 02/20 20Z 0.14 1417 90 97 -1 0.02
Fri 02/20 21Z 0.19 1421 96 98 0 0.08
Fri 02/20 22Z 0.25 1323 95 99 -1 0.14
Fri 02/20 23Z 0.31 1327 95 99 -1 0.14
Sat 02/21 00Z 0.32 1329 95 99 -1 0.10
Sat 02/21 01Z 0.32 1329 95 97 -2 0.06
Sat 02/21 02Z 0.30 1328 96 78 -2 0.03
Sat 02/21 03Z 0.27 1425 96 95 -3 0.04
Sat 02/21 04Z 0.24 1422 95 93 -4 0.06
Sat 02/21 05Z 0.17 1519 95 94 -6 0.05
Sat 02/21 06Z 0.10 1517 95 93 -6 0.02
Sat 02/21 07Z 0.04 1715 96 93 -6 0.02
Sat 02/21 08Z 0.09 1812 96 93 -6 0.02
Sat 02/21 09Z 0.15 1911 96 94 -6 0.02
Sat 02/21 10Z 0.20 2010 97 96 -7 0.02
Sat 02/21 11Z 0.25 2111 98 98 -7 0.02
Run total areal avg QPF for the Central_Greens is: 0.84 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