Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260514_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 05/14 00Z 0.26 1826 85 64 5 0.00
Thu 05/14 01Z 0.25 1828 76 54 6 0.00
Thu 05/14 02Z 0.26 1928 75 53 6 0.00
Thu 05/14 03Z 0.22 1827 75 54 6 0.00
Thu 05/14 04Z 0.19 1825 73 59 7 0.00
Thu 05/14 05Z 0.21 1826 75 75 7 0.00
Thu 05/14 06Z 0.25 1927 80 84 6 0.00
Thu 05/14 07Z 0.21 1924 88 81 6 0.00
Thu 05/14 08Z 0.14 1824 94 85 5 0.02
Thu 05/14 09Z 0.07 1724 98 90 5 0.06
Thu 05/14 10Z 0.07 1725 98 91 5 0.03
Thu 05/14 11Z 0.10 1725 98 96 5 0.04
Thu 05/14 12Z 0.17 1823 98 98 5 0.06
Thu 05/14 13Z 0.17 1819 99 92 5 0.04
Thu 05/14 14Z 0.09 1715 99 89 5 0.03
Thu 05/14 15Z 0.10 1614 99 91 5 0.06
Thu 05/14 16Z 0.20 1415 99 99 5 0.14
Thu 05/14 17Z 0.32 1318 99 99 5 0.22
Thu 05/14 18Z 0.40 1217 99 99 5 0.21
Thu 05/14 19Z 0.48 1220 99 98 5 0.20
Thu 05/14 20Z 0.53 1118 99 98 5 0.16
Thu 05/14 21Z 0.46 1114 99 97 5 0.14
Thu 05/14 22Z 0.49 1114 99 98 5 0.13
Thu 05/14 23Z 0.48 0913 99 97 5 0.12
Fri 05/15 00Z 0.42 0911 97 97 4 0.11
Fri 05/15 01Z 0.50 0913 98 97 4 0.10
Fri 05/15 02Z 0.48 0914 96 96 4 0.10
Fri 05/15 03Z 0.60 0817 96 96 3 0.13
Fri 05/15 04Z 0.72 0923 97 97 3 0.10
Fri 05/15 05Z 0.82 1029 97 95 4 0.07
Fri 05/15 06Z 0.84 1030 94 94 3 0.05
Fri 05/15 07Z 0.84 1031 96 89 3 0.04
Fri 05/15 08Z 0.83 1029 95 92 3 0.03
Fri 05/15 09Z 0.82 1028 96 94 3 0.02
Fri 05/15 10Z 0.80 1026 94 96 2 0.02
Fri 05/15 11Z 0.80 0924 93 96 2 0.03
Fri 05/15 12Z 0.78 0923 91 95 2 0.01
Fri 05/15 13Z 0.83 0822 89 94 2 0.01
Fri 05/15 14Z 0.87 0822 88 92 2 0.01
Fri 05/15 15Z 0.89 0919 91 88 2 0.00
Fri 05/15 16Z 1.02 0815 95 86 2 0.00
Fri 05/15 17Z 0.89 0812 95 87 2 0.01
Fri 05/15 18Z 0.91 0911 95 87 3 0.01
Fri 05/15 19Z 0.67 0909 93 89 3 0.01
Fri 05/15 20Z 0.54 0908 90 90 3 0.00
Fri 05/15 21Z 0.34 1006 88 90 3 0.00
Fri 05/15 22Z 0.21 1104 87 92 3 0.00
Fri 05/15 23Z 0.18 1102 86 88 4 0.00
Sat 05/16 00Z 0.13 1201 84 80 4 0.00
Sat 05/16 01Z 0.11 3000 80 72 4 0.00
Sat 05/16 02Z 0.11 2901 76 60 4 0.00
Sat 05/16 03Z 0.10 2501 73 54 5 0.00
Sat 05/16 04Z 0.18 2306 79 51 4 0.00
Sat 05/16 05Z 0.25 2408 81 47 4 0.00
Sat 05/16 06Z 0.27 2508 80 42 4 0.00
Sat 05/16 07Z 0.33 2510 85 40 4 0.00
Sat 05/16 08Z 0.37 2512 87 37 4 0.00
Sat 05/16 09Z 0.37 2513 85 34 4 0.00
Sat 05/16 10Z 0.46 2516 85 38 4 0.00
Sat 05/16 11Z 0.50 2517 83 37 4 0.00
Run total areal avg QPF for the Central_Greens is: 2.52 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