Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260511_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)
=== ===== === ==== ==== === === === ====
Mon 05/11 12Z 0.57 2911 79 50 -2 0.00
Mon 05/11 13Z 0.87 2909 77 53 -2 0.00
Mon 05/11 14Z 2.31 2809 73 64 -2 0.00
Mon 05/11 15Z 4.91 2810 69 63 -1 0.00
Mon 05/11 16Z 7.11 2811 70 68 -1 0.00
Mon 05/11 17Z 6.71 2713 75 66 -1 0.00
Mon 05/11 18Z 7.33 2813 73 75 -1 0.00
Mon 05/11 19Z 4.58 2813 75 70 -1 0.00
Mon 05/11 20Z 5.55 2813 74 62 0 0.00
Mon 05/11 21Z 4.24 2913 77 71 -1 0.01
Mon 05/11 22Z 2.74 3014 77 74 -1 0.01
Mon 05/11 23Z 0.81 3115 80 70 -1 0.01
Tue 05/12 00Z 0.55 3216 78 51 -2 0.00
Tue 05/12 01Z 0.47 3317 77 60 -2 0.00
Tue 05/12 02Z 0.40 3317 76 70 -2 0.00
Tue 05/12 03Z 0.39 3318 79 64 -3 0.00
Tue 05/12 04Z 0.37 3319 83 54 -3 0.00
Tue 05/12 05Z 0.41 3419 78 47 -3 0.00
Tue 05/12 06Z 0.33 3419 76 39 -3 0.00
Tue 05/12 07Z 0.27 3419 74 34 -3 0.00
Tue 05/12 08Z 0.23 3417 72 26 -4 0.00
Tue 05/12 09Z 0.21 3416 71 25 -4 0.00
Tue 05/12 10Z 0.22 3415 70 29 -4 0.00
Tue 05/12 11Z 0.29 3414 71 35 -5 0.00
Tue 05/12 12Z 0.76 3313 73 37 -5 0.00
Tue 05/12 13Z 2.72 3213 77 33 -5 0.00
Tue 05/12 14Z 3.75 3212 78 26 -5 0.00
Tue 05/12 15Z 4.05 3211 74 25 -4 0.00
Tue 05/12 16Z 5.29 3112 72 25 -4 0.00
Tue 05/12 17Z 6.52 3013 72 31 -3 0.00
Tue 05/12 18Z 6.56 3013 72 34 -3 0.00
Tue 05/12 19Z 6.24 3012 71 34 -2 0.00
Tue 05/12 20Z 5.45 3011 68 28 -1 0.00
Tue 05/12 21Z 4.03 3109 66 23 -1 0.00
Tue 05/12 22Z 2.52 3108 64 21 -1 0.00
Tue 05/12 23Z 0.83 3107 63 21 0 0.00
Wed 05/13 00Z 0.42 3007 63 21 0 0.00
Wed 05/13 01Z 0.43 2807 63 24 0 0.00
Wed 05/13 02Z 0.35 2706 63 25 0 0.00
Wed 05/13 03Z 0.26 2605 63 26 0 0.00
Wed 05/13 04Z 0.24 2405 63 27 0 0.00
Wed 05/13 05Z 0.29 2307 63 23 0 0.00
Wed 05/13 06Z 0.29 2208 63 19 0 0.00
Wed 05/13 07Z 0.32 2110 61 18 0 0.00
Wed 05/13 08Z 0.36 2211 61 38 0 0.00
Wed 05/13 09Z 0.35 2112 62 72 0 0.00
Wed 05/13 10Z 0.36 2113 66 89 0 0.00
Wed 05/13 11Z 0.23 2013 66 95 0 0.00
Wed 05/13 12Z 0.16 1914 66 97 0 0.00
Wed 05/13 13Z 0.05 1816 71 98 1 0.00
Wed 05/13 14Z 0.08 1719 77 98 1 0.00
Wed 05/13 15Z 0.32 1622 83 97 1 0.01
Wed 05/13 16Z 0.19 1625 88 97 2 0.02
Wed 05/13 17Z 0.18 1627 93 97 3 0.03
Wed 05/13 18Z 0.13 1728 95 97 3 0.05
Wed 05/13 19Z 0.16 1730 96 96 3 0.06
Wed 05/13 20Z 0.15 1731 96 97 4 0.06
Wed 05/13 21Z 0.15 1830 96 97 4 0.06
Wed 05/13 22Z 0.15 1929 97 95 4 0.05
Wed 05/13 23Z 0.19 1930 97 95 4 0.07
Run total areal avg QPF for the greens is: 0.44 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