Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260511_0600
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 06Z 0.60 3015 76 66 -1 0.00
Mon 05/11 07Z 0.60 2915 80 58 -1 0.00
Mon 05/11 08Z 0.59 2916 84 36 -1 0.00
Mon 05/11 09Z 0.56 3016 82 31 -2 0.00
Mon 05/11 10Z 0.55 3017 77 34 -2 0.00
Mon 05/11 11Z 0.58 3017 75 36 -2 0.00
Mon 05/11 12Z 0.60 3016 73 40 -2 0.00
Mon 05/11 13Z 0.71 3014 70 42 -2 0.00
Mon 05/11 14Z 2.86 3012 69 57 -2 0.00
Mon 05/11 15Z 4.38 3011 68 65 -2 0.00
Mon 05/11 16Z 5.21 2910 70 75 -2 0.00
Mon 05/11 17Z 5.02 2811 79 83 -1 0.00
Mon 05/11 18Z 4.77 2811 78 77 -1 0.01
Mon 05/11 19Z 4.98 2812 74 73 -1 0.01
Mon 05/11 20Z 4.07 2911 76 65 -1 0.00
Mon 05/11 21Z 3.01 3011 74 58 -1 0.01
Mon 05/11 22Z 2.68 3110 71 51 -1 0.00
Mon 05/11 23Z 1.78 3211 70 56 -1 0.00
Tue 05/12 00Z 1.36 3213 69 51 -2 0.00
Tue 05/12 01Z 0.94 3316 69 55 -2 0.00
Tue 05/12 02Z 0.72 3317 70 56 -2 0.00
Tue 05/12 03Z 0.64 3318 70 54 -2 0.00
Tue 05/12 04Z 0.62 3318 72 49 -3 0.00
Tue 05/12 05Z 0.45 3418 72 47 -3 0.00
Tue 05/12 06Z 0.32 3418 69 34 -3 0.00
Tue 05/12 07Z 0.21 3417 67 25 -3 0.00
Tue 05/12 08Z 0.16 3515 65 27 -4 0.00
Tue 05/12 09Z 0.15 3514 65 31 -4 0.00
Tue 05/12 10Z 0.25 3413 66 37 -4 0.00
Tue 05/12 11Z 0.36 3312 67 39 -4 0.00
Tue 05/12 12Z 1.12 3212 68 38 -5 0.00
Tue 05/12 13Z 2.97 3211 69 34 -5 0.00
Tue 05/12 14Z 4.50 3111 69 28 -4 0.00
Tue 05/12 15Z 4.94 3111 66 31 -4 0.00
Tue 05/12 16Z 5.95 3112 65 34 -3 0.00
Tue 05/12 17Z 7.17 3012 69 40 -3 0.00
Tue 05/12 18Z 6.23 3011 69 42 -2 0.00
Tue 05/12 19Z 6.11 3011 67 42 -2 0.00
Tue 05/12 20Z 5.02 3009 65 39 -1 0.00
Tue 05/12 21Z 4.10 3009 63 36 -1 0.00
Tue 05/12 22Z 2.44 3007 62 33 0 0.00
Tue 05/12 23Z 0.92 2907 62 32 0 0.00
Wed 05/13 00Z 0.46 2806 61 31 0 0.00
Wed 05/13 01Z 0.37 2706 60 30 0 0.00
Wed 05/13 02Z 0.30 2505 61 29 0 0.00
Wed 05/13 03Z 0.29 2306 63 24 0 0.00
Wed 05/13 04Z 0.35 2307 64 19 0 0.00
Wed 05/13 05Z 0.39 2309 64 16 0 0.00
Wed 05/13 06Z 0.38 2209 64 14 0 0.00
Wed 05/13 07Z 0.36 2210 65 27 0 0.00
Wed 05/13 08Z 0.32 2111 67 54 0 0.00
Wed 05/13 09Z 0.29 2011 69 76 0 0.00
Wed 05/13 10Z 0.20 1912 72 92 0 0.00
Wed 05/13 11Z 0.07 1813 78 96 0 0.00
Wed 05/13 12Z 0.07 1715 85 96 0 0.01
Wed 05/13 13Z 0.12 1619 88 97 0 0.01
Wed 05/13 14Z 0.14 1622 90 97 1 0.01
Wed 05/13 15Z 0.16 1625 93 97 2 0.02
Wed 05/13 16Z 0.15 1725 94 97 2 0.03
Wed 05/13 17Z 0.13 1626 95 96 3 0.03
Run total areal avg QPF for the greens is: 0.14 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