Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260521_1800
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 05/21 18Z 1.75 3210 69 6 0 0.00
Thu 05/21 19Z 1.53 3212 64 6 1 0.00
Thu 05/21 20Z 1.05 3212 62 5 1 0.00
Thu 05/21 21Z 0.84 3312 61 5 1 0.00
Thu 05/21 22Z 0.63 3313 63 4 1 0.00
Thu 05/21 23Z 0.28 3312 63 3 1 0.00
Fri 05/22 00Z 0.21 3413 63 3 1 0.00
Fri 05/22 01Z 0.19 3414 64 2 0 0.00
Fri 05/22 02Z 0.19 3414 65 2 0 0.00
Fri 05/22 03Z 0.24 3414 65 2 0 0.00
Fri 05/22 04Z 0.25 3514 64 2 0 0.00
Fri 05/22 05Z 0.12 3513 64 2 0 0.00
Fri 05/22 06Z 0.05 0011 61 2 0 0.00
Fri 05/22 07Z 0.07 0011 59 2 0 0.00
Fri 05/22 08Z 0.10 0111 59 2 0 0.00
Fri 05/22 09Z 0.14 0111 58 3 0 0.00
Fri 05/22 10Z 0.18 0212 53 4 0 0.00
Fri 05/22 11Z 0.19 0212 48 5 0 0.00
Fri 05/22 12Z 0.22 0312 46 6 0 0.00
Fri 05/22 13Z 0.22 0310 45 6 0 0.00
Fri 05/22 14Z 0.30 0308 45 8 0 0.00
Fri 05/22 15Z 0.37 0205 46 11 0 0.00
Fri 05/22 16Z 0.56 0203 47 15 0 0.00
Fri 05/22 17Z 0.42 0102 47 16 1 0.00
Fri 05/22 18Z 0.36 3502 47 20 2 0.00
Fri 05/22 19Z 0.37 0002 47 19 3 0.00
Fri 05/22 20Z 0.32 3503 48 19 3 0.00
Fri 05/22 21Z 0.24 0003 50 17 3 0.00
Fri 05/22 22Z 0.16 0103 50 18 3 0.00
Fri 05/22 23Z 0.10 0202 49 19 4 0.00
Sat 05/23 00Z 0.12 0303 45 20 4 0.00
Sat 05/23 01Z 0.13 0304 42 20 4 0.00
Sat 05/23 02Z 0.22 0505 42 19 4 0.00
Sat 05/23 03Z 0.23 0505 43 18 4 0.00
Sat 05/23 04Z 0.29 0506 45 14 4 0.00
Sat 05/23 05Z 0.34 0607 46 11 3 0.00
Sat 05/23 06Z 0.42 0608 46 8 3 0.00
Sat 05/23 07Z 0.42 0609 46 6 3 0.00
Sat 05/23 08Z 0.44 0609 46 4 3 0.00
Sat 05/23 09Z 0.49 0810 46 4 3 0.00
Sat 05/23 10Z 0.54 0812 46 5 3 0.00
Sat 05/23 11Z 0.56 0913 46 6 3 0.00
Sat 05/23 12Z 0.55 1013 46 6 3 0.00
Sat 05/23 13Z 0.56 1014 47 5 3 0.00
Sat 05/23 14Z 0.55 1012 50 5 3 0.00
Sat 05/23 15Z 0.83 1011 54 4 3 0.00
Sat 05/23 16Z 1.28 1110 57 4 3 0.00
Sat 05/23 17Z 2.12 1209 58 4 4 0.00
Sat 05/23 18Z 2.42 1308 59 4 4 0.00
Sat 05/23 19Z 2.58 1309 61 3 4 0.00
Sat 05/23 20Z 1.83 1309 63 3 4 0.00
Sat 05/23 21Z 2.14 1311 66 3 4 0.00
Sat 05/23 22Z 1.39 1412 69 3 4 0.00
Sat 05/23 23Z 0.84 1414 69 2 4 0.00
Sun 05/24 00Z 0.55 1317 67 2 4 0.00
Sun 05/24 01Z 0.42 1318 61 3 5 0.00
Sun 05/24 02Z 0.40 1320 49 3 5 0.00
Sun 05/24 03Z 0.39 1323 36 3 6 0.00
Sun 05/24 04Z 0.38 1425 30 3 7 0.00
Sun 05/24 05Z 0.38 1427 27 3 7 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