Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260522_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)
=== ===== === ==== ==== === === === ====
Fri 05/22 00Z 0.19 3412 65 3 1 0.00
Fri 05/22 01Z 0.18 3414 65 2 1 0.00
Fri 05/22 02Z 0.19 3415 62 2 1 0.00
Fri 05/22 03Z 0.16 3415 59 3 0 0.00
Fri 05/22 04Z 0.10 3514 59 2 0 0.00
Fri 05/22 05Z 0.06 0013 58 2 0 0.00
Fri 05/22 06Z 0.09 0111 56 2 0 0.00
Fri 05/22 07Z 0.11 0110 54 2 0 0.00
Fri 05/22 08Z 0.13 0111 54 3 0 0.00
Fri 05/22 09Z 0.19 0212 51 4 0 0.00
Fri 05/22 10Z 0.23 0213 46 5 0 0.00
Fri 05/22 11Z 0.27 0313 43 6 0 0.00
Fri 05/22 12Z 0.27 0311 40 6 0 0.00
Fri 05/22 13Z 0.28 0310 39 6 0 0.00
Fri 05/22 14Z 0.43 0307 39 7 0 0.00
Fri 05/22 15Z 0.80 0305 41 9 0 0.00
Fri 05/22 16Z 0.88 0303 42 12 0 0.00
Fri 05/22 17Z 0.60 0102 43 14 1 0.00
Fri 05/22 18Z 0.42 0201 45 13 2 0.00
Fri 05/22 19Z 0.27 3501 47 13 3 0.00
Fri 05/22 20Z 0.27 3301 49 14 3 0.00
Fri 05/22 21Z 0.23 3301 51 15 3 0.00
Fri 05/22 22Z 0.14 3202 52 15 4 0.00
Fri 05/22 23Z 0.07 0001 50 19 4 0.00
Sat 05/23 00Z 0.04 0002 47 20 4 0.00
Sat 05/23 01Z 0.07 0202 44 19 4 0.00
Sat 05/23 02Z 0.12 0304 42 19 4 0.00
Sat 05/23 03Z 0.23 0505 41 17 4 0.00
Sat 05/23 04Z 0.21 0504 40 16 4 0.00
Sat 05/23 05Z 0.29 0506 40 14 4 0.00
Sat 05/23 06Z 0.35 0607 42 10 4 0.00
Sat 05/23 07Z 0.44 0808 44 7 4 0.00
Sat 05/23 08Z 0.46 0808 44 6 3 0.00
Sat 05/23 09Z 0.48 0909 44 5 3 0.00
Sat 05/23 10Z 0.43 1009 44 4 3 0.00
Sat 05/23 11Z 0.43 1110 44 4 3 0.00
Sat 05/23 12Z 0.50 1212 43 4 3 0.00
Sat 05/23 13Z 0.50 1213 45 4 3 0.00
Sat 05/23 14Z 0.54 1213 48 5 3 0.00
Sat 05/23 15Z 0.78 1212 51 5 3 0.00
Sat 05/23 16Z 1.83 1212 54 4 4 0.00
Sat 05/23 17Z 3.12 1311 57 5 4 0.00
Sat 05/23 18Z 2.69 1411 58 5 4 0.00
Sat 05/23 19Z 2.16 1411 59 5 4 0.00
Sat 05/23 20Z 1.59 1412 62 4 4 0.00
Sat 05/23 21Z 1.14 1413 65 3 4 0.00
Sat 05/23 22Z 0.77 1415 64 3 4 0.00
Sat 05/23 23Z 0.50 1417 63 3 4 0.00
Sun 05/24 00Z 0.42 1418 62 4 4 0.00
Sun 05/24 01Z 0.40 1420 57 4 4 0.00
Sun 05/24 02Z 0.40 1422 52 6 4 0.00
Sun 05/24 03Z 0.40 1423 49 11 4 0.00
Sun 05/24 04Z 0.42 1424 46 19 4 0.00
Sun 05/24 05Z 0.42 1425 46 32 4 0.00
Sun 05/24 06Z 0.42 1426 44 39 4 0.00
Sun 05/24 07Z 0.41 1428 43 50 5 0.00
Sun 05/24 08Z 0.42 1430 43 63 5 0.00
Sun 05/24 09Z 0.44 1433 48 74 5 0.00
Sun 05/24 10Z 0.42 1435 57 86 6 0.01
Sun 05/24 11Z 0.40 1437 64 81 7 0.02
Run total areal avg QPF for the greens is: 0.03 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