Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260424_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)
=== ===== === ==== ==== === === === ====
Fri 04/24 18Z 2.80 3310 62 13 -3 0.00
Fri 04/24 19Z 2.57 3311 60 13 -2 0.00
Fri 04/24 20Z 1.52 3411 60 18 -2 0.00
Fri 04/24 21Z 0.70 3510 60 21 -2 0.00
Fri 04/24 22Z 0.44 0011 62 21 -2 0.00
Fri 04/24 23Z 0.77 0111 65 17 -2 0.00
Sat 04/25 00Z 0.85 0212 68 15 -2 0.00
Sat 04/25 01Z 0.93 0315 69 14 -3 0.00
Sat 04/25 02Z 0.85 0417 69 14 -3 0.00
Sat 04/25 03Z 0.78 0418 64 14 -3 0.00
Sat 04/25 04Z 0.68 0419 63 13 -3 0.00
Sat 04/25 05Z 0.52 0517 60 12 -3 0.00
Sat 04/25 06Z 0.44 0613 58 11 -3 0.00
Sat 04/25 07Z 0.38 0711 60 10 -3 0.00
Sat 04/25 08Z 0.31 0910 61 9 -3 0.00
Sat 04/25 09Z 0.26 1009 60 8 -2 0.00
Sat 04/25 10Z 0.20 1108 60 8 -2 0.00
Sat 04/25 11Z 0.16 1207 60 8 -2 0.00
Sat 04/25 12Z 0.15 1206 58 9 -2 0.00
Sat 04/25 13Z 0.17 1105 58 9 -2 0.00
Sat 04/25 14Z 0.25 1105 58 9 -2 0.00
Sat 04/25 15Z 1.11 1006 58 10 -2 0.00
Sat 04/25 16Z 1.87 1106 58 11 -2 0.00
Sat 04/25 17Z 2.09 1104 57 12 -1 0.00
Sat 04/25 18Z 1.70 1103 56 12 0 0.00
Sat 04/25 19Z 1.32 1103 56 13 0 0.00
Sat 04/25 20Z 1.09 1103 56 13 0 0.00
Sat 04/25 21Z 0.96 1103 56 13 0 0.00
Sat 04/25 22Z 0.42 1103 55 13 0 0.00
Sat 04/25 23Z 0.31 1004 54 13 0 0.00
Sun 04/26 00Z 0.34 1005 53 13 0 0.00
Sun 04/26 01Z 0.39 0907 54 13 0 0.00
Sun 04/26 02Z 0.42 0808 57 13 0 0.00
Sun 04/26 03Z 0.45 0808 59 14 0 0.00
Sun 04/26 04Z 0.44 0909 59 15 0 0.00
Sun 04/26 05Z 0.40 1008 59 18 0 0.00
Sun 04/26 06Z 0.37 1008 58 18 0 0.00
Sun 04/26 07Z 0.33 1007 57 19 0 0.00
Sun 04/26 08Z 0.31 1107 57 15 0 0.00
Sun 04/26 09Z 0.28 1206 58 18 0 0.00
Sun 04/26 10Z 0.30 1106 59 27 0 0.00
Sun 04/26 11Z 0.31 1106 61 33 0 0.00
Sun 04/26 12Z 0.31 1006 63 28 0 0.00
Sun 04/26 13Z 0.41 0906 64 26 0 0.00
Sun 04/26 14Z 0.72 0807 65 33 0 0.00
Sun 04/26 15Z 1.00 0806 66 47 0 0.00
Sun 04/26 16Z 1.74 0706 67 55 0 0.00
Sun 04/26 17Z 2.93 0606 68 59 0 0.00
Sun 04/26 18Z 2.51 0606 69 69 1 0.00
Sun 04/26 19Z 1.80 0606 70 81 1 0.00
Sun 04/26 20Z 1.18 0506 71 75 2 0.00
Sun 04/26 21Z 0.75 0406 71 69 2 0.00
Sun 04/26 22Z 0.38 0307 72 63 2 0.00
Sun 04/26 23Z 0.35 0308 72 59 3 0.00
Mon 04/27 00Z 0.49 0410 73 53 3 0.00
Mon 04/27 01Z 0.61 0512 75 47 3 0.00
Mon 04/27 02Z 0.72 0613 76 48 3 0.00
Mon 04/27 03Z 0.77 0714 76 55 3 0.00
Mon 04/27 04Z 0.66 0913 76 54 2 0.00
Mon 04/27 05Z 0.64 0915 76 60 2 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