Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260726_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)
=== ===== === ==== ==== === === === ====
Sun 07/26 06Z 0.15 2005 75 14 13 0.00
Sun 07/26 07Z 0.19 2105 76 13 13 0.00
Sun 07/26 08Z 0.21 2205 77 13 13 0.00
Sun 07/26 09Z 0.19 2304 78 12 12 0.00
Sun 07/26 10Z 0.14 2402 78 13 12 0.00
Sun 07/26 11Z 0.07 2500 78 12 12 0.00
Sun 07/26 12Z 0.07 1201 77 12 12 0.00
Sun 07/26 13Z 0.08 1101 77 11 12 0.00
Sun 07/26 14Z 0.24 1202 78 10 12 0.00
Sun 07/26 15Z 0.92 1104 80 8 13 0.00
Sun 07/26 16Z 1.33 1204 79 8 13 0.00
Sun 07/26 17Z 1.46 1305 79 13 13 0.00
Sun 07/26 18Z 1.78 1306 76 22 13 0.02
Sun 07/26 19Z 1.51 1407 75 26 13 0.01
Sun 07/26 20Z 1.06 1508 75 28 13 0.00
Sun 07/26 21Z 0.51 1607 75 30 13 0.00
Sun 07/26 22Z 0.18 1607 75 29 13 0.00
Sun 07/26 23Z 0.10 1607 74 25 13 0.00
Mon 07/27 00Z 0.08 1707 72 22 13 0.00
Mon 07/27 01Z 0.12 1807 72 20 13 0.00
Mon 07/27 02Z 0.16 1808 71 18 13 0.00
Mon 07/27 03Z 0.14 1808 71 17 13 0.00
Mon 07/27 04Z 0.12 1907 72 16 13 0.00
Mon 07/27 05Z 0.10 1906 74 14 13 0.00
Mon 07/27 06Z 0.27 2206 78 17 13 0.00
Mon 07/27 07Z 0.38 2307 80 30 12 0.00
Mon 07/27 08Z 0.40 2309 84 50 12 0.01
Mon 07/27 09Z 0.31 2307 84 62 12 0.01
Mon 07/27 10Z 0.18 2106 82 65 12 0.00
Mon 07/27 11Z 0.16 2006 82 69 12 0.00
Mon 07/27 12Z 0.16 2007 83 69 12 0.00
Mon 07/27 13Z 0.16 2006 88 74 12 0.00
Mon 07/27 14Z 0.14 2006 90 72 12 0.00
Mon 07/27 15Z 0.17 1906 90 69 12 0.00
Mon 07/27 16Z 0.22 2005 90 66 13 0.00
Mon 07/27 17Z 0.40 2005 90 66 13 0.00
Mon 07/27 18Z 0.47 2005 89 66 13 0.00
Mon 07/27 19Z 0.49 2005 88 63 13 0.00
Mon 07/27 20Z 0.29 1804 88 65 14 0.00
Mon 07/27 21Z 0.26 1806 88 64 14 0.01
Mon 07/27 22Z 0.13 1706 89 64 14 0.01
Mon 07/27 23Z 0.08 1708 90 65 14 0.02
Tue 07/28 00Z 0.12 1809 89 61 14 0.02
Tue 07/28 01Z 0.11 1812 89 58 14 0.01
Tue 07/28 02Z 0.13 1812 90 63 14 0.01
Tue 07/28 03Z 0.10 1811 90 65 13 0.02
Tue 07/28 04Z 0.13 1910 92 72 13 0.02
Tue 07/28 05Z 0.18 2010 95 77 13 0.01
Tue 07/28 06Z 0.25 2111 96 76 13 0.03
Tue 07/28 07Z 0.24 2111 96 73 13 0.04
Tue 07/28 08Z 0.19 2010 95 72 13 0.02
Tue 07/28 09Z 0.17 2009 93 76 14 0.01
Tue 07/28 10Z 0.10 1909 92 81 14 0.00
Tue 07/28 11Z 0.07 1809 92 81 14 0.00
Tue 07/28 12Z 0.04 1709 94 79 13 0.00
Tue 07/28 13Z 0.02 1708 96 77 13 0.00
Tue 07/28 14Z 0.03 1610 97 76 13 0.01
Tue 07/28 16Z 0.05 1710 98 77 13 0.01
Tue 07/28 17Z 0.05 1610 98 75 13 0.01
Run total areal avg QPF for the Central_Greens is: 0.31 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