Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260904_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 09/04 18Z 0.63 3209 89 72 12 0.00
Fri 09/04 19Z 0.67 3212 88 77 12 0.03
Fri 09/04 20Z 0.66 3212 86 74 12 0.02
Fri 09/04 21Z 0.47 3212 86 74 12 0.00
Fri 09/04 22Z 0.28 3211 92 84 11 0.01
Fri 09/04 23Z 0.21 3213 90 75 11 0.02
Sat 09/05 00Z 0.20 3314 88 66 11 0.00
Sat 09/05 01Z 0.17 3313 90 73 11 0.00
Sat 09/05 02Z 0.25 3111 94 81 11 0.02
Sat 09/05 03Z 0.26 3214 94 81 10 0.03
Sat 09/05 04Z 0.20 3214 93 76 10 0.01
Sat 09/05 05Z 0.17 3214 93 55 10 0.01
Sat 09/05 06Z 0.15 3314 94 55 10 0.01
Sat 09/05 07Z 0.10 3315 96 60 10 0.02
Sat 09/05 08Z 0.07 3415 97 58 10 0.01
Sat 09/05 09Z 0.05 3515 96 58 10 0.01
Sat 09/05 10Z 0.03 3515 92 54 10 0.01
Sat 09/05 11Z 0.03 3416 91 58 10 0.01
Sat 09/05 12Z 0.04 3516 93 59 9 0.01
Sat 09/05 13Z 0.11 0016 96 62 9 0.01
Sat 09/05 14Z 0.20 0115 96 64 9 0.01
Sat 09/05 15Z 0.24 0113 94 69 9 0.00
Sat 09/05 16Z 0.26 0112 94 70 9 0.00
Sat 09/05 17Z 0.32 0111 94 67 9 0.00
Sat 09/05 18Z 0.29 0111 94 66 9 0.00
Sat 09/05 19Z 0.22 0011 95 64 9 0.00
Sat 09/05 20Z 0.16 0012 95 67 9 0.00
Sat 09/05 21Z 0.18 0014 96 69 9 0.01
Sat 09/05 22Z 0.29 0114 94 70 9 0.00
Sat 09/05 23Z 0.34 0215 96 74 9 0.00
Sun 09/06 00Z 0.45 0317 98 77 8 0.01
Sun 09/06 01Z 0.55 0318 97 78 8 0.01
Sun 09/06 02Z 0.68 0518 95 80 7 0.01
Sun 09/06 03Z 0.77 0516 89 81 7 0.00
Sun 09/06 04Z 0.71 0615 88 74 7 0.00
Sun 09/06 05Z 0.57 0613 86 68 7 0.00
Sun 09/06 06Z 0.42 0512 78 60 7 0.00
Sun 09/06 07Z 0.28 0410 75 57 7 0.00
Sun 09/06 08Z 0.24 0310 72 57 7 0.00
Sun 09/06 09Z 0.25 0212 71 53 7 0.00
Sun 09/06 10Z 0.23 0214 74 53 7 0.00
Sun 09/06 11Z 0.22 0115 76 57 7 0.00
Sun 09/06 12Z 0.17 0115 73 62 7 0.00
Sun 09/06 13Z 0.15 0016 72 62 7 0.00
Sun 09/06 14Z 0.14 0016 74 61 7 0.00
Sun 09/06 15Z 0.11 0015 77 57 7 0.00
Sun 09/06 16Z 0.07 3514 80 53 7 0.00
Sun 09/06 17Z 0.12 3514 81 48 7 0.00
Sun 09/06 18Z 0.23 3513 82 43 7 0.00
Sun 09/06 19Z 0.26 3414 84 31 7 0.00
Sun 09/06 20Z 0.24 3414 85 25 7 0.00
Sun 09/06 21Z 0.16 3414 86 28 7 0.00
Sun 09/06 22Z 0.11 3416 86 32 7 0.00
Sun 09/06 23Z 0.06 3419 84 27 7 0.00
Mon 09/07 00Z 0.06 3520 84 21 7 0.00
Mon 09/07 01Z 0.08 3520 86 39 6 0.00
Mon 09/07 02Z 0.05 3520 84 71 7 0.00
Mon 09/07 03Z 0.04 3418 85 83 7 0.00
Mon 09/07 04Z 0.04 3418 84 81 7 0.00
Mon 09/07 05Z 0.04 3517 86 60 7 0.00
Run total areal avg QPF for the Central_Greens is: 0.29 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