Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260522_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)
=== ===== === ==== ==== === === === ====
Fri 05/22 12Z 0.11 0208 58 4 0 0.00
Fri 05/22 13Z 0.14 0208 57 5 0 0.00
Fri 05/22 14Z 0.22 0306 57 6 0 0.00
Fri 05/22 15Z 0.80 0305 58 7 0 0.00
Fri 05/22 16Z 1.04 0303 57 10 1 0.00
Fri 05/22 17Z 0.67 0201 56 13 2 0.00
Fri 05/22 18Z 0.44 0001 56 16 2 0.00
Fri 05/22 19Z 0.37 3501 58 19 3 0.00
Fri 05/22 20Z 0.32 3502 59 22 3 0.00
Fri 05/22 21Z 0.24 0002 60 24 3 0.00
Fri 05/22 22Z 0.18 3502 60 25 4 0.00
Fri 05/22 23Z 0.11 0103 58 25 4 0.00
Sat 05/23 00Z 0.14 0203 55 25 4 0.00
Sat 05/23 01Z 0.18 0403 52 25 4 0.00
Sat 05/23 02Z 0.19 0404 49 24 4 0.00
Sat 05/23 03Z 0.19 0504 48 23 4 0.00
Sat 05/23 04Z 0.24 0605 48 21 4 0.00
Sat 05/23 05Z 0.29 0706 49 20 4 0.00
Sat 05/23 06Z 0.35 0707 49 17 4 0.00
Sat 05/23 07Z 0.45 0708 46 14 4 0.00
Sat 05/23 08Z 0.51 0809 44 12 3 0.00
Sat 05/23 09Z 0.58 0910 47 9 3 0.00
Sat 05/23 10Z 0.57 1012 49 6 3 0.00
Sat 05/23 11Z 0.57 1113 48 5 3 0.00
Sat 05/23 12Z 0.55 1214 48 5 3 0.00
Sat 05/23 13Z 0.52 1214 49 4 3 0.00
Sat 05/23 14Z 0.56 1214 52 4 3 0.00
Sat 05/23 15Z 0.90 1213 54 4 3 0.00
Sat 05/23 16Z 0.83 1212 57 4 3 0.00
Sat 05/23 17Z 0.70 1312 58 4 4 0.00
Sat 05/23 18Z 0.71 1312 59 3 4 0.00
Sat 05/23 19Z 0.55 1412 61 3 4 0.00
Sat 05/23 20Z 0.43 1413 63 3 4 0.00
Sat 05/23 21Z 0.39 1414 64 3 4 0.00
Sat 05/23 22Z 0.36 1415 64 2 4 0.00
Sat 05/23 23Z 0.39 1418 61 3 4 0.00
Sun 05/24 00Z 0.40 1420 57 4 4 0.00
Sun 05/24 01Z 0.42 1422 54 6 4 0.00
Sun 05/24 02Z 0.41 1423 51 13 4 0.00
Sun 05/24 03Z 0.39 1424 51 25 4 0.00
Sun 05/24 04Z 0.38 1426 49 39 5 0.00
Sun 05/24 05Z 0.37 1528 48 59 5 0.00
Sun 05/24 06Z 0.34 1529 49 67 5 0.00
Sun 05/24 07Z 0.34 1530 55 73 5 0.01
Sun 05/24 08Z 0.38 1432 61 80 5 0.02
Sun 05/24 09Z 0.40 1434 66 92 5 0.02
Sun 05/24 10Z 0.40 1435 74 98 5 0.03
Sun 05/24 11Z 0.40 1437 81 99 5 0.06
Sun 05/24 12Z 0.39 1439 83 99 5 0.07
Sun 05/24 13Z 0.37 1540 86 99 5 0.08
Sun 05/24 14Z 0.32 1541 88 98 5 0.08
Sun 05/24 15Z 0.27 1541 92 97 5 0.10
Sun 05/24 16Z 0.22 1640 94 98 5 0.11
Sun 05/24 17Z 0.18 1639 96 98 5 0.11
Sun 05/24 18Z 0.15 1638 96 98 5 0.09
Sun 05/24 19Z 0.11 1737 96 96 5 0.05
Sun 05/24 20Z 0.08 1737 97 88 6 0.03
Sun 05/24 21Z 0.08 1737 97 81 6 0.03
Sun 05/24 22Z 0.08 1737 97 78 7 0.02
Sun 05/24 23Z 0.07 1736 97 63 8 0.03
Run total areal avg QPF for the greens is: 0.94 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