Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260513_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)
=== ===== === ==== ==== === === === ====
Wed 05/13 12Z 0.04 1815 68 95 1 0.00
Wed 05/13 13Z 0.04 1817 72 91 2 0.00
Wed 05/13 14Z 0.04 1818 79 95 2 0.01
Wed 05/13 15Z 0.06 1719 85 97 2 0.01
Wed 05/13 16Z 0.07 1720 91 98 3 0.04
Wed 05/13 17Z 0.05 1719 90 84 4 0.06
Wed 05/13 18Z 0.06 1721 91 89 4 0.03
Wed 05/13 19Z 0.04 1723 94 96 4 0.04
Wed 05/13 20Z 0.05 1824 93 97 4 0.05
Wed 05/13 21Z 0.05 1825 95 98 5 0.04
Wed 05/13 22Z 0.09 1826 97 93 5 0.07
Wed 05/13 23Z 0.12 1827 97 80 6 0.04
Thu 05/14 00Z 0.19 1927 96 78 6 0.02
Thu 05/14 01Z 0.20 1926 93 72 6 0.01
Thu 05/14 02Z 0.18 1928 90 69 6 0.01
Thu 05/14 03Z 0.21 1930 83 64 7 0.01
Thu 05/14 04Z 0.25 1931 81 66 6 0.00
Thu 05/14 05Z 0.22 1930 83 85 6 0.01
Thu 05/14 06Z 0.18 1928 88 91 6 0.01
Thu 05/14 07Z 0.12 1828 94 92 5 0.01
Thu 05/14 08Z 0.08 1827 97 92 5 0.01
Thu 05/14 09Z 0.05 1826 97 96 5 0.05
Thu 05/14 10Z 0.05 1825 97 97 5 0.06
Thu 05/14 11Z 0.06 1723 98 94 5 0.05
Thu 05/14 12Z 0.08 1722 98 93 5 0.08
Thu 05/14 13Z 0.13 1621 98 97 5 0.06
Thu 05/14 14Z 0.21 1621 99 98 5 0.10
Thu 05/14 15Z 0.29 1522 97 99 5 0.12
Thu 05/14 16Z 0.32 1520 93 98 5 0.10
Thu 05/14 17Z 0.39 1417 97 98 5 0.11
Thu 05/14 18Z 0.51 1317 98 98 5 0.14
Thu 05/14 19Z 0.67 1219 98 98 5 0.14
Thu 05/14 20Z 0.76 1119 97 98 4 0.14
Thu 05/14 21Z 0.67 1018 96 96 4 0.10
Thu 05/14 22Z 0.61 0917 96 94 4 0.09
Thu 05/14 23Z 0.59 0817 98 96 4 0.08
Fri 05/15 00Z 0.62 0917 99 95 4 0.09
Fri 05/15 01Z 0.61 1018 98 96 4 0.09
Fri 05/15 02Z 0.63 1021 97 92 5 0.11
Fri 05/15 03Z 0.63 1022 97 89 5 0.08
Fri 05/15 04Z 0.76 0925 97 85 4 0.07
Fri 05/15 05Z 0.77 0924 97 92 4 0.07
Fri 05/15 06Z 0.84 0925 97 90 3 0.07
Fri 05/15 07Z 0.90 0926 96 75 3 0.04
Fri 05/15 08Z 0.85 1026 97 69 3 0.02
Fri 05/15 09Z 0.84 1025 97 61 2 0.02
Fri 05/15 10Z 0.75 1022 98 66 2 0.02
Fri 05/15 11Z 0.67 0919 98 71 2 0.04
Fri 05/15 12Z 0.62 0917 99 69 2 0.04
Fri 05/15 13Z 0.61 0816 99 73 2 0.03
Fri 05/15 14Z 0.66 0816 98 71 2 0.02
Fri 05/15 15Z 0.75 0816 98 70 1 0.02
Fri 05/15 16Z 0.81 0916 98 73 2 0.02
Fri 05/15 17Z 0.74 0915 98 80 2 0.01
Fri 05/15 18Z 0.59 1012 97 85 2 0.01
Fri 05/15 19Z 0.46 1009 95 83 3 0.00
Fri 05/15 20Z 0.26 1104 94 83 3 0.00
Fri 05/15 21Z 0.18 1103 93 78 3 0.01
Fri 05/15 22Z 0.09 1901 94 78 3 0.01
Fri 05/15 23Z 0.09 2302 91 75 4 0.02
Run total areal avg QPF for the greens is: 2.81 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