Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260727_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 07/27 12Z 0.09 2402 80 74 13 0.00
Mon 07/27 13Z 0.08 2402 80 71 13 0.00
Mon 07/27 14Z 0.10 2301 82 70 13 0.00
Mon 07/27 15Z 0.17 2302 85 72 13 0.00
Mon 07/27 16Z 0.33 2302 84 74 14 0.04
Mon 07/27 17Z 1.09 2605 83 73 14 0.08
Mon 07/27 18Z 1.12 2604 81 69 14 0.04
Mon 07/27 19Z 1.03 2503 81 66 14 0.02
Mon 07/27 20Z 0.80 2404 82 63 14 0.03
Mon 07/27 21Z 0.33 2203 84 60 14 0.04
Mon 07/27 22Z 0.10 2003 85 60 14 0.04
Mon 07/27 23Z 0.04 1704 85 66 14 0.04
Tue 07/28 00Z 0.23 2107 84 75 14 0.08
Tue 07/28 01Z 0.18 2009 79 73 14 0.05
Tue 07/28 02Z 0.15 2010 80 70 14 0.00
Tue 07/28 03Z 0.28 2111 82 69 14 0.00
Tue 07/28 04Z 0.25 2111 82 61 14 0.00
Tue 07/28 05Z 0.34 2113 84 61 14 0.00
Tue 07/28 06Z 0.36 2213 85 58 14 0.00
Tue 07/28 07Z 0.24 2111 86 51 14 0.00
Tue 07/28 08Z 0.16 2010 87 53 14 0.00
Tue 07/28 09Z 0.09 1910 86 60 14 0.00
Tue 07/28 10Z 0.08 1911 87 66 14 0.00
Tue 07/28 11Z 0.07 1813 89 66 14 0.00
Tue 07/28 12Z 0.04 1814 90 66 14 0.00
Tue 07/28 13Z 0.03 1815 92 72 14 0.00
Tue 07/28 14Z 0.08 1716 93 70 14 0.00
Tue 07/28 15Z 0.06 1716 94 69 14 0.00
Tue 07/28 16Z 0.09 1716 96 72 14 0.01
Tue 07/28 17Z 0.19 1616 95 69 14 0.01
Tue 07/28 18Z 0.23 1617 93 75 14 0.02
Tue 07/28 19Z 0.31 1516 94 72 14 0.03
Tue 07/28 20Z 0.29 1619 95 72 14 0.03
Tue 07/28 21Z 0.24 1718 96 78 14 0.07
Tue 07/28 22Z 0.14 1718 93 75 14 0.14
Tue 07/28 23Z 0.14 1717 93 83 14 0.04
Wed 07/29 00Z 0.11 1718 95 89 13 0.15
Wed 07/29 01Z 0.10 1717 95 90 13 0.22
Wed 07/29 02Z 0.08 1717 96 91 13 0.17
Wed 07/29 03Z 0.18 1621 97 95 13 0.17
Wed 07/29 04Z 0.19 1625 97 93 12 0.16
Wed 07/29 05Z 0.20 1627 95 94 12 0.09
Wed 07/29 06Z 0.25 1627 94 95 12 0.05
Wed 07/29 07Z 0.33 1526 94 96 12 0.03
Wed 07/29 08Z 0.41 1527 94 96 12 0.03
Wed 07/29 09Z 0.49 1429 93 94 12 0.05
Wed 07/29 10Z 0.64 1331 92 95 11 0.08
Wed 07/29 11Z 0.73 1331 92 95 11 0.13
Wed 07/29 12Z 0.71 1335 91 96 11 0.13
Wed 07/29 13Z 0.72 1236 90 95 11 0.08
Wed 07/29 14Z 0.78 1237 91 94 11 0.05
Wed 07/29 15Z 0.82 1237 92 93 11 0.05
Wed 07/29 16Z 0.86 1237 91 92 11 0.04
Wed 07/29 17Z 0.85 1237 92 93 11 0.03
Wed 07/29 18Z 0.82 1235 93 92 11 0.03
Wed 07/29 19Z 0.78 1233 92 93 11 0.03
Wed 07/29 20Z 0.77 1131 93 92 12 0.02
Wed 07/29 21Z 0.74 1129 93 94 12 0.02
Wed 07/29 22Z 0.69 1128 93 95 12 0.01
Wed 07/29 23Z 0.69 1128 92 95 12 0.01
Run total areal avg QPF for the greens is: 2.64 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