Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260730_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)
=== ===== === ==== ==== === === === ====
Thu 07/30 00Z 0.65 1129 90 93 13 0.00
Thu 07/30 01Z 0.68 1130 91 92 13 0.03
Thu 07/30 02Z 0.67 1128 92 91 12 0.04
Thu 07/30 03Z 0.64 1226 92 91 12 0.01
Thu 07/30 04Z 0.60 1223 92 90 12 0.01
Thu 07/30 05Z 0.55 1120 91 89 12 0.01
Thu 07/30 06Z 0.50 1118 92 91 12 0.01
Thu 07/30 07Z 0.46 1016 91 91 12 0.01
Thu 07/30 08Z 0.41 0914 93 91 12 0.01
Thu 07/30 09Z 0.39 0813 93 91 12 0.01
Thu 07/30 10Z 0.39 0713 93 89 12 0.02
Thu 07/30 11Z 0.37 0612 91 88 12 0.02
Thu 07/30 12Z 0.24 0411 88 84 12 0.01
Thu 07/30 13Z 0.20 0212 84 80 12 0.00
Thu 07/30 14Z 0.21 0212 85 81 12 0.00
Thu 07/30 15Z 0.29 0213 86 83 11 0.00
Thu 07/30 16Z 0.33 0212 88 82 11 0.00
Thu 07/30 17Z 0.19 0110 86 78 12 0.00
Thu 07/30 18Z 0.12 0010 86 73 12 0.01
Thu 07/30 19Z 0.15 0109 83 64 13 0.05
Thu 07/30 20Z 0.12 3509 85 59 13 0.02
Thu 07/30 21Z 0.13 3411 87 58 13 0.00
Thu 07/30 22Z 0.07 3512 89 54 13 0.00
Thu 07/30 23Z 0.05 3514 91 57 13 0.01
Fri 07/31 00Z 0.05 0013 90 62 13 0.02
Fri 07/31 01Z 0.03 0014 89 66 13 0.01
Fri 07/31 02Z 0.03 0014 89 73 13 0.00
Fri 07/31 03Z 0.05 0014 89 78 13 0.00
Fri 07/31 04Z 0.04 0012 89 77 13 0.00
Fri 07/31 05Z 0.07 3512 89 79 13 0.00
Fri 07/31 06Z 0.06 3512 87 78 13 0.00
Fri 07/31 07Z 0.07 3412 85 78 13 0.00
Fri 07/31 08Z 0.07 3412 82 74 13 0.00
Fri 07/31 09Z 0.03 3511 80 69 13 0.00
Fri 07/31 10Z 0.07 3412 80 68 12 0.00
Fri 07/31 11Z 0.08 3412 81 68 12 0.00
Fri 07/31 12Z 0.11 3412 86 61 12 0.00
Fri 07/31 13Z 0.11 3411 90 58 12 0.00
Fri 07/31 14Z 0.10 3410 91 54 12 0.00
Fri 07/31 15Z 0.17 3310 93 54 12 0.01
Fri 07/31 16Z 0.23 3311 91 58 11 0.01
Fri 07/31 17Z 0.35 3312 89 55 12 0.00
Fri 07/31 18Z 0.67 3210 87 44 12 0.00
Fri 07/31 19Z 0.83 3109 87 33 12 0.00
Fri 07/31 20Z 0.71 3109 87 38 13 0.00
Fri 07/31 21Z 0.53 3109 86 43 13 0.01
Fri 07/31 22Z 0.37 3008 89 50 13 0.01
Fri 07/31 23Z 0.28 3108 87 54 13 0.02
Sat 08/01 00Z 0.27 3109 85 50 13 0.01
Sat 08/01 01Z 0.24 3108 83 40 13 0.00
Sat 08/01 02Z 0.23 3107 83 36 13 0.01
Sat 08/01 03Z 0.28 3007 86 27 13 0.00
Sat 08/01 04Z 0.28 2906 87 24 13 0.00
Sat 08/01 05Z 0.23 2906 84 20 13 0.00
Sat 08/01 06Z 0.20 2805 82 18 13 0.00
Sat 08/01 07Z 0.17 2704 79 22 13 0.00
Sat 08/01 08Z 0.17 2504 78 19 13 0.00
Sat 08/01 09Z 0.18 2404 78 20 13 0.00
Sat 08/01 10Z 0.19 2305 78 23 13 0.00
Sat 08/01 11Z 0.22 2306 79 25 13 0.00
Run total areal avg QPF for the greens is: 0.39 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