Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260226_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 02/26 00Z 0.52 2219 85 83 -7 0.00
Thu 02/26 01Z 0.50 2121 84 89 -6 0.00
Thu 02/26 02Z 0.59 2224 88 84 -6 0.02
Thu 02/26 03Z 0.64 2325 93 92 -6 0.03
Thu 02/26 04Z 0.82 2422 95 83 -7 0.02
Thu 02/26 05Z 1.39 2524 94 48 -8 0.01
Thu 02/26 06Z 1.78 2525 88 29 -9 0.01
Thu 02/26 07Z 1.99 2627 86 25 -10 0.00
Thu 02/26 08Z 1.99 2627 85 24 -12 0.00
Thu 02/26 09Z 1.76 2627 82 23 -12 0.00
Thu 02/26 10Z 2.10 2627 85 24 -13 0.00
Thu 02/26 11Z 1.82 2726 80 27 -14 0.00
Thu 02/26 12Z 1.36 2726 77 22 -14 0.00
Thu 02/26 13Z 1.28 2725 75 10 -14 0.00
Thu 02/26 14Z 1.56 2723 74 3 -14 0.00
Thu 02/26 15Z 3.90 2721 75 4 -14 0.00
Thu 02/26 16Z 7.82 2619 79 6 -14 0.00
Thu 02/26 17Z 9.61 2618 83 6 -14 0.00
Thu 02/26 18Z 8.46 2616 83 9 -14 0.00
Thu 02/26 19Z 7.01 2616 82 13 -13 0.00
Thu 02/26 20Z 4.88 2615 81 16 -13 0.00
Thu 02/26 21Z 3.32 2616 80 19 -13 0.00
Thu 02/26 22Z 1.19 2716 79 29 -13 0.00
Thu 02/26 23Z 0.88 2816 77 44 -13 0.00
Fri 02/27 00Z 0.83 2817 78 46 -13 0.00
Fri 02/27 01Z 0.75 2917 77 45 -13 0.00
Fri 02/27 02Z 0.64 2917 74 46 -13 0.00
Fri 02/27 03Z 0.54 2916 71 44 -13 0.00
Fri 02/27 04Z 0.46 2916 68 41 -13 0.00
Fri 02/27 05Z 0.39 2915 67 41 -12 0.00
Fri 02/27 06Z 0.35 2914 67 51 -12 0.00
Fri 02/27 08Z 0.32 2813 66 75 -12 0.00
Fri 02/27 09Z 0.33 2813 67 80 -12 0.00
Fri 02/27 10Z 0.33 2714 65 80 -11 0.00
Fri 02/27 11Z 0.34 2714 67 81 -11 0.00
Fri 02/27 12Z 0.36 2615 70 81 -11 0.00
Fri 02/27 13Z 0.39 2517 75 79 -11 0.00
Fri 02/27 14Z 0.43 2518 79 66 -10 0.00
Fri 02/27 16Z 0.51 2519 73 44 -9 0.00
Fri 02/27 17Z 0.53 2519 80 37 -8 0.00
Fri 02/27 18Z 0.58 2520 83 29 -7 0.00
Fri 02/27 19Z 0.63 2421 84 29 -7 0.00
Fri 02/27 20Z 0.68 2422 84 38 -7 0.00
Fri 02/27 21Z 0.68 2423 84 59 -6 0.00
Fri 02/27 22Z 0.64 2424 81 70 -4 0.00
Fri 02/27 23Z 0.61 2426 79 74 -3 0.00
Sat 02/28 00Z 0.62 2330 76 73 -2 0.00
Sat 02/28 01Z 0.62 2232 70 67 -2 0.00
Sat 02/28 02Z 0.63 2235 65 63 -1 0.00
Sat 02/28 03Z 0.64 2237 64 61 -1 0.00
Sat 02/28 04Z 0.64 2239 61 56 0 0.00
Sat 02/28 05Z 0.69 2242 58 54 0 0.00
Sat 02/28 06Z 0.71 2244 56 44 0 0.00
Sat 02/28 07Z 0.73 2246 52 53 0 0.00
Sat 02/28 08Z 0.76 2248 51 62 1 0.00
Sat 02/28 09Z 0.79 2347 58 62 0 0.00
Sat 02/28 10Z 0.79 2346 65 55 0 0.00
Sat 02/28 11Z 0.77 2344 69 56 0 0.00
Run total areal avg QPF for the greens is: 0.09 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