Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260402_0000
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)
=== ===== === ==== ==== === === === ====
Thu 04/02 00Z 0.07 3511 86 18 -3 0.00
Thu 04/02 01Z 0.09 0110 82 16 -3 0.00
Thu 04/02 02Z 0.10 0211 76 18 -3 0.00
Thu 04/02 03Z 0.13 0310 69 20 -2 0.00
Thu 04/02 04Z 0.13 0508 58 22 0 0.00
Thu 04/02 05Z 0.12 0706 51 28 0 0.00
Thu 04/02 06Z 0.11 1005 50 49 0 0.00
Thu 04/02 07Z 0.09 1307 54 49 0 0.00
Thu 04/02 08Z 0.09 1407 63 48 -1 0.01
Thu 04/02 09Z 0.09 1407 68 49 -1 0.01
Thu 04/02 10Z 0.09 1408 72 39 -1 0.01
Thu 04/02 11Z 0.10 1408 74 37 -1 0.00
Thu 04/02 12Z 0.10 1509 77 40 -1 0.00
Thu 04/02 13Z 0.09 1509 81 46 -1 0.00
Thu 04/02 14Z 0.08 1507 84 42 -1 0.00
Thu 04/02 15Z 0.08 1407 86 43 -1 0.00
Thu 04/02 16Z 0.09 1407 86 50 0 0.00
Thu 04/02 17Z 0.11 1307 85 54 0 0.00
Thu 04/02 18Z 0.16 1308 85 56 0 0.00
Thu 04/02 19Z 0.17 1308 83 63 0 0.00
Thu 04/02 20Z 0.20 1410 82 72 0 0.00
Thu 04/02 21Z 0.18 1410 81 81 0 0.00
Thu 04/02 22Z 0.19 1413 82 88 0 0.00
Thu 04/02 23Z 0.19 1516 83 93 1 0.00
Fri 04/03 00Z 0.17 1519 83 80 1 0.00
Fri 04/03 01Z 0.14 1622 82 90 2 0.00
Fri 04/03 02Z 0.09 1624 85 92 3 0.00
Fri 04/03 03Z 0.05 1726 87 91 4 0.00
Fri 04/03 04Z 0.03 1728 90 84 4 0.01
Fri 04/03 05Z 0.04 1831 94 83 5 0.01
Fri 04/03 06Z 0.07 1833 95 83 6 0.01
Fri 04/03 07Z 0.13 1935 96 80 7 0.01
Fri 04/03 08Z 0.18 1936 96 83 8 0.01
Fri 04/03 09Z 0.24 2038 96 84 9 0.01
Fri 04/03 10Z 0.31 2140 96 81 10 0.02
Fri 04/03 11Z 0.36 2142 96 83 11 0.03
Fri 04/03 12Z 0.38 2240 92 84 11 0.02
Fri 04/03 13Z 0.42 2239 94 88 11 0.02
Fri 04/03 14Z 0.47 2338 95 85 11 0.04
Fri 04/03 15Z 0.54 2339 96 74 11 0.02
Fri 04/03 16Z 0.58 2439 95 75 11 0.01
Fri 04/03 17Z 0.62 2438 95 79 11 0.01
Fri 04/03 18Z 0.69 2439 93 85 11 0.01
Fri 04/03 19Z 0.77 2439 93 75 11 0.00
Fri 04/03 20Z 0.87 2439 91 56 10 0.00
Fri 04/03 21Z 1.02 2539 92 28 10 0.00
Fri 04/03 22Z 1.16 2540 93 14 9 0.00
Fri 04/03 23Z 1.25 2540 93 14 9 0.00
Sat 04/04 00Z 1.35 2542 96 17 8 0.01
Sat 04/04 01Z 1.41 2542 97 17 8 0.02
Sat 04/04 02Z 1.46 2640 98 15 7 0.04
Sat 04/04 03Z 1.38 2737 98 14 5 0.04
Sat 04/04 04Z 1.19 2835 96 17 3 0.03
Sat 04/04 05Z 0.94 2830 94 19 2 0.02
Sat 04/04 06Z 0.59 2926 90 19 2 0.01
Sat 04/04 07Z 0.41 3022 87 20 2 0.01
Sat 04/04 08Z 0.29 3019 88 21 3 0.01
Sat 04/04 09Z 0.18 3216 89 23 3 0.01
Sat 04/04 10Z 0.10 3413 89 23 3 0.01
Sat 04/04 11Z 0.07 0010 89 23 2 0.00
Run total areal avg QPF for the greens is: 0.48 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