Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260724_0600
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)
=== ===== === ==== ==== === === === ====
Fri 07/24 06Z 0.29 2905 70 8 10 0.00
Fri 07/24 07Z 0.35 2905 68 9 10 0.00
Fri 07/24 08Z 0.38 2905 66 9 10 0.00
Fri 07/24 09Z 0.39 2805 66 9 9 0.00
Fri 07/24 10Z 0.35 2704 66 11 9 0.00
Fri 07/24 11Z 0.30 2504 67 13 9 0.00
Fri 07/24 12Z 0.23 2204 69 14 9 0.00
Fri 07/24 13Z 0.22 2106 71 15 9 0.00
Fri 07/24 14Z 0.48 2106 72 17 9 0.00
Fri 07/24 15Z 1.37 2206 74 22 9 0.00
Fri 07/24 16Z 1.69 2306 73 27 10 0.00
Fri 07/24 17Z 1.90 2306 70 34 10 0.00
Fri 07/24 18Z 1.97 2405 66 41 11 0.00
Fri 07/24 19Z 1.45 2504 62 45 11 0.00
Fri 07/24 20Z 0.86 2503 61 46 11 0.00
Fri 07/24 21Z 0.40 2602 60 47 12 0.00
Fri 07/24 22Z 0.14 2101 60 48 12 0.00
Fri 07/24 23Z 0.09 1902 61 49 12 0.00
Sat 07/25 00Z 0.09 2003 61 49 12 0.00
Sat 07/25 01Z 0.08 2002 60 46 12 0.00
Sat 07/25 02Z 0.07 2002 61 47 12 0.00
Sat 07/25 03Z 0.07 1903 61 46 12 0.00
Sat 07/25 04Z 0.11 2104 62 48 12 0.00
Sat 07/25 05Z 0.09 2003 63 49 12 0.00
Sat 07/25 06Z 0.06 2002 62 49 12 0.00
Sat 07/25 07Z 0.04 1802 61 47 12 0.00
Sat 07/25 08Z 0.03 1802 59 46 12 0.00
Sat 07/25 09Z 0.04 1602 58 42 12 0.00
Sat 07/25 10Z 0.03 1803 59 42 12 0.00
Sat 07/25 11Z 0.04 1803 60 41 12 0.00
Sat 07/25 12Z 0.03 1804 62 40 11 0.00
Sat 07/25 13Z 0.03 1803 64 40 11 0.00
Sat 07/25 14Z 0.07 1603 67 38 11 0.00
Sat 07/25 15Z 0.25 1602 71 34 11 0.00
Sat 07/25 16Z 0.62 1503 73 31 11 0.00
Sat 07/25 17Z 1.02 1404 74 27 12 0.00
Sat 07/25 18Z 1.10 1505 73 23 12 0.00
Sat 07/25 19Z 1.30 1506 72 19 13 0.00
Sat 07/25 20Z 1.13 1506 72 16 13 0.00
Sat 07/25 21Z 0.73 1606 73 14 13 0.00
Sat 07/25 22Z 0.56 1606 74 11 13 0.00
Sat 07/25 23Z 0.30 1607 77 9 12 0.00
Sun 07/26 00Z 0.20 1609 80 7 12 0.00
Sun 07/26 01Z 0.11 1710 83 6 12 0.00
Sun 07/26 02Z 0.08 1810 85 6 12 0.00
Sun 07/26 03Z 0.12 1910 85 5 12 0.00
Sun 07/26 04Z 0.17 2009 84 5 12 0.00
Sun 07/26 05Z 0.23 2107 83 5 12 0.00
Sun 07/26 06Z 0.25 2206 83 5 11 0.00
Sun 07/26 07Z 0.25 2405 84 5 11 0.00
Sun 07/26 08Z 0.28 2605 85 6 11 0.00
Sun 07/26 09Z 0.22 2704 85 6 11 0.00
Sun 07/26 10Z 0.16 2803 85 6 11 0.00
Sun 07/26 11Z 0.07 3201 84 6 11 0.00
Sun 07/26 12Z 0.08 0301 83 6 11 0.00
Sun 07/26 13Z 0.12 0901 85 6 11 0.00
Sun 07/26 14Z 0.19 1102 86 6 11 0.00
Sun 07/26 15Z 0.21 1302 88 6 11 0.00
Sun 07/26 16Z 0.22 1302 87 7 11 0.00
Sun 07/26 17Z 0.26 1401 86 7 12 0.00
Run total areal avg QPF for the greens is: 0.00 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