Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260730_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)
=== ===== === ==== ==== === === === ====
Thu 07/30 12Z 0.25 0409 93 93 11 0.00
Thu 07/30 13Z 0.23 0310 89 92 11 0.01
Thu 07/30 14Z 0.21 0309 88 87 11 0.02
Thu 07/30 15Z 0.26 0309 90 84 11 0.02
Thu 07/30 16Z 0.19 0109 91 85 11 0.01
Thu 07/30 17Z 0.10 0009 92 83 12 0.02
Thu 07/30 18Z 0.33 3410 93 78 12 0.05
Thu 07/30 19Z 0.14 3513 91 81 12 0.09
Thu 07/30 20Z 0.09 3514 89 83 12 0.04
Thu 07/30 21Z 0.10 0014 90 80 12 0.04
Thu 07/30 22Z 0.12 0113 91 79 12 0.06
Thu 07/30 23Z 0.10 0111 93 81 12 0.04
Fri 07/31 00Z 0.10 0110 91 81 12 0.03
Fri 07/31 01Z 0.08 0110 87 79 12 0.03
Fri 07/31 02Z 0.07 0110 85 79 12 0.00
Fri 07/31 03Z 0.04 0010 85 79 12 0.00
Fri 07/31 04Z 0.04 0009 84 80 12 0.00
Fri 07/31 05Z 0.04 0008 83 82 12 0.00
Fri 07/31 06Z 0.05 3508 83 84 12 0.00
Fri 07/31 07Z 0.08 3408 84 84 12 0.00
Fri 07/31 08Z 0.08 3409 84 84 12 0.00
Fri 07/31 09Z 0.10 3409 85 81 12 0.00
Fri 07/31 10Z 0.12 3309 86 78 12 0.00
Fri 07/31 11Z 0.12 3309 87 76 12 0.00
Fri 07/31 12Z 0.16 3310 89 73 12 0.00
Fri 07/31 13Z 0.21 3210 91 72 11 0.01
Fri 07/31 14Z 0.25 3111 92 67 11 0.02
Fri 07/31 15Z 0.28 3110 92 59 11 0.01
Fri 07/31 16Z 0.29 3110 92 55 11 0.01
Fri 07/31 17Z 0.33 3110 90 48 12 0.01
Fri 07/31 18Z 0.37 3110 90 45 12 0.00
Fri 07/31 19Z 0.51 3110 90 51 12 0.00
Fri 07/31 20Z 0.46 3111 90 61 12 0.00
Fri 07/31 21Z 0.40 3111 88 61 12 0.01
Fri 07/31 22Z 0.34 3110 86 56 13 0.00
Fri 07/31 23Z 0.32 3109 88 55 13 0.00
Sat 08/01 00Z 0.38 3011 89 56 13 0.00
Sat 08/01 01Z 0.29 3109 90 52 13 0.01
Sat 08/01 02Z 0.25 3108 91 47 13 0.00
Sat 08/01 03Z 0.24 3007 91 45 13 0.00
Sat 08/01 04Z 0.25 2906 91 46 12 0.00
Sat 08/01 05Z 0.24 2906 88 44 13 0.00
Sat 08/01 06Z 0.25 2806 86 40 13 0.00
Sat 08/01 07Z 0.24 2906 84 32 13 0.00
Sat 08/01 08Z 0.17 2905 82 28 13 0.00
Sat 08/01 09Z 0.22 2805 82 24 13 0.00
Sat 08/01 10Z 0.19 2705 81 19 13 0.00
Sat 08/01 11Z 0.18 2704 78 16 13 0.00
Sat 08/01 12Z 0.16 2504 76 13 13 0.00
Sat 08/01 13Z 0.17 2505 75 14 13 0.00
Sat 08/01 14Z 0.13 2304 74 13 14 0.00
Sat 08/01 15Z 0.14 2203 75 14 14 0.00
Sat 08/01 16Z 0.18 2103 76 14 14 0.00
Sat 08/01 17Z 0.28 2003 76 16 14 0.00
Sat 08/01 18Z 0.28 2003 74 19 14 0.00
Sat 08/01 19Z 0.20 1904 74 25 15 0.00
Sat 08/01 20Z 0.18 1805 77 30 15 0.00
Sat 08/01 21Z 0.08 1706 79 32 15 0.00
Sat 08/01 22Z 0.09 1808 83 40 15 0.00
Sat 08/01 23Z 0.06 1810 85 54 15 0.00
Run total areal avg QPF for the greens is: 0.54 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