Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260704_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)
=== ===== === ==== ==== === === === ====
Sat 07/04 12Z 0.52 3016 90 61 15 0.00
Sat 07/04 13Z 0.50 3016 90 54 15 0.00
Sat 07/04 14Z 0.60 3017 95 60 15 0.01
Sat 07/04 15Z 0.56 3016 93 68 15 0.01
Sat 07/04 16Z 0.54 3115 93 71 15 0.09
Sat 07/04 17Z 0.45 3116 93 69 14 0.12
Sat 07/04 18Z 0.44 3115 90 68 14 0.05
Sat 07/04 19Z 0.53 3014 88 73 14 0.01
Sat 07/04 20Z 0.58 3114 85 69 14 0.01
Sat 07/04 21Z 0.52 3215 83 67 14 0.02
Sat 07/04 22Z 0.48 3115 83 57 14 0.04
Sat 07/04 23Z 0.53 3215 80 49 14 0.00
Sun 07/05 00Z 0.35 3317 77 38 13 0.00
Sun 07/05 01Z 0.30 3316 73 30 13 0.00
Sun 07/05 02Z 0.34 3316 69 25 13 0.00
Sun 07/05 03Z 0.23 3415 67 25 12 0.00
Sun 07/05 04Z 0.10 3515 64 21 12 0.00
Sun 07/05 05Z 0.05 3514 62 16 12 0.00
Sun 07/05 06Z 0.05 3511 61 15 12 0.00
Sun 07/05 07Z 0.08 0009 60 15 12 0.00
Sun 07/05 08Z 0.05 0008 59 16 12 0.00
Sun 07/05 09Z 0.04 0007 59 16 12 0.00
Sun 07/05 10Z 0.04 0006 58 15 11 0.00
Sun 07/05 11Z 0.05 0007 58 17 11 0.00
Sun 07/05 12Z 0.06 0007 59 11 11 0.00
Sun 07/05 13Z 0.06 0106 61 8 11 0.00
Sun 07/05 14Z 0.15 0104 66 8 11 0.00
Sun 07/05 15Z 0.26 0102 70 7 11 0.00
Sun 07/05 16Z 0.29 0001 73 6 11 0.00
Sun 07/05 17Z 0.23 3401 76 7 11 0.00
Sun 07/05 18Z 0.22 3502 77 6 11 0.00
Sun 07/05 19Z 0.21 3502 77 6 12 0.00
Sun 07/05 20Z 0.23 0002 77 4 12 0.00
Sun 07/05 21Z 0.18 0002 77 4 12 0.00
Sun 07/05 22Z 0.20 0103 78 4 12 0.00
Sun 07/05 23Z 0.25 0304 77 4 12 0.00
Mon 07/06 00Z 0.32 0504 76 4 12 0.00
Mon 07/06 01Z 0.43 0605 75 4 11 0.00
Mon 07/06 02Z 0.68 0607 73 5 11 0.00
Mon 07/06 03Z 0.75 0709 71 5 11 0.00
Mon 07/06 04Z 0.68 0910 71 6 11 0.00
Mon 07/06 05Z 0.61 1110 72 6 11 0.00
Mon 07/06 06Z 0.49 1211 73 6 11 0.00
Mon 07/06 07Z 0.35 1412 74 6 11 0.00
Mon 07/06 08Z 0.29 1513 77 6 11 0.00
Mon 07/06 09Z 0.23 1615 78 6 11 0.00
Mon 07/06 10Z 0.12 1715 78 5 11 0.00
Mon 07/06 11Z 0.14 1714 77 6 11 0.00
Mon 07/06 12Z 0.16 1613 77 7 11 0.00
Mon 07/06 13Z 0.19 1612 77 7 11 0.00
Mon 07/06 14Z 0.21 1512 79 8 10 0.00
Mon 07/06 15Z 0.27 1512 78 8 10 0.00
Mon 07/06 16Z 0.48 1412 78 7 10 0.00
Mon 07/06 17Z 0.71 1412 77 9 10 0.00
Mon 07/06 18Z 0.84 1412 77 10 11 0.00
Mon 07/06 19Z 0.80 1513 77 11 11 0.00
Mon 07/06 20Z 0.48 1513 78 15 11 0.00
Mon 07/06 21Z 0.33 1514 80 20 11 0.00
Mon 07/06 22Z 0.26 1514 82 25 11 0.00
Mon 07/06 23Z 0.28 1515 80 33 10 0.00
Run total areal avg QPF for the greens is: 0.36 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