Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260226_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 02/26 12Z 1.22 2722 79 45 -12 0.00
Thu 02/26 13Z 1.49 2724 79 23 -12 0.00
Thu 02/26 14Z 5.50 2621 80 15 -13 0.00
Thu 02/26 15Z 10.59 2619 81 7 -13 0.00
Thu 02/26 16Z 12.86 2619 84 4 -13 0.00
Thu 02/26 17Z 10.59 2618 85 5 -13 0.00
Thu 02/26 18Z 8.86 2616 83 9 -13 0.00
Thu 02/26 19Z 8.03 2616 82 13 -13 0.00
Thu 02/26 20Z 6.68 2616 81 20 -13 0.00
Thu 02/26 21Z 3.84 2716 81 28 -13 0.00
Thu 02/26 22Z 1.34 2716 80 36 -13 0.00
Thu 02/26 23Z 1.00 2817 78 39 -13 0.00
Fri 02/27 00Z 0.76 2818 76 40 -13 0.00
Fri 02/27 01Z 0.65 2918 74 46 -13 0.00
Fri 02/27 02Z 0.53 2917 73 44 -13 0.00
Fri 02/27 03Z 0.44 2915 71 42 -13 0.00
Fri 02/27 04Z 0.38 2915 69 47 -12 0.00
Fri 02/27 05Z 0.34 2914 68 57 -12 0.00
Fri 02/27 06Z 0.33 2814 67 59 -11 0.00
Fri 02/27 07Z 0.31 2813 66 61 -11 0.00
Fri 02/27 08Z 0.30 2813 63 60 -10 0.00
Fri 02/27 09Z 0.31 2714 61 63 -10 0.00
Fri 02/27 10Z 0.33 2715 60 63 -10 0.00
Fri 02/27 11Z 0.35 2716 62 66 -10 0.00
Fri 02/27 12Z 0.36 2617 62 73 -9 0.00
Fri 02/27 13Z 0.37 2617 64 79 -8 0.00
Fri 02/27 14Z 0.34 2517 59 84 -8 0.00
Fri 02/27 15Z 0.36 2417 55 85 -7 0.00
Fri 02/27 16Z 0.42 2419 51 86 -7 0.00
Fri 02/27 17Z 0.48 2420 49 82 -7 0.00
Fri 02/27 18Z 0.53 2421 46 78 -6 0.00
Fri 02/27 19Z 0.59 2421 47 70 -6 0.00
Fri 02/27 20Z 0.61 2420 55 53 -6 0.00
Fri 02/27 21Z 0.66 2420 63 35 -6 0.00
Fri 02/27 22Z 0.72 2421 70 32 -6 0.00
Fri 02/27 23Z 0.72 2421 73 35 -5 0.00
Sat 02/28 00Z 0.68 2422 76 32 -5 0.00
Sat 02/28 01Z 0.63 2323 76 30 -4 0.00
Sat 02/28 02Z 0.56 2324 73 33 -3 0.00
Sat 02/28 03Z 0.51 2226 66 34 -2 0.00
Sat 02/28 04Z 0.52 2230 63 26 -2 0.00
Sat 02/28 05Z 0.54 2134 62 22 -1 0.00
Sat 02/28 06Z 0.55 2136 60 20 -1 0.00
Sat 02/28 07Z 0.59 2138 61 19 -1 0.00
Sat 02/28 08Z 0.62 2140 60 25 0 0.00
Sat 02/28 09Z 0.65 2241 59 36 0 0.00
Sat 02/28 10Z 0.68 2241 56 60 0 0.00
Sat 02/28 11Z 0.73 2341 63 76 0 0.00
Sat 02/28 12Z 0.74 2340 69 82 0 0.00
Sat 02/28 13Z 0.71 2339 74 84 0 0.00
Sat 02/28 15Z 0.71 2337 81 92 0 0.00
Sat 02/28 16Z 0.75 2335 84 90 0 0.00
Sat 02/28 17Z 0.79 2433 87 92 0 0.00
Sat 02/28 18Z 0.87 2431 88 85 -1 0.00
Sat 02/28 19Z 0.82 2529 82 76 -1 0.01
Sat 02/28 20Z 0.79 2527 75 61 -1 0.01
Sat 02/28 21Z 0.80 2525 70 50 -2 0.00
Sat 02/28 22Z 0.78 2623 66 43 -2 0.00
Run total areal avg QPF for the greens is: 0.02 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