Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260408_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)
=== ===== === ==== ==== === === === ====
Wed 04/08 12Z 0.19 3211 78 16 -10 0.00
Wed 04/08 13Z 0.16 3108 73 14 -9 0.00
Wed 04/08 14Z 0.14 3006 69 13 -9 0.00
Wed 04/08 15Z 0.13 2904 64 8 -9 0.00
Wed 04/08 16Z 0.16 2703 60 6 -8 0.00
Wed 04/08 17Z 0.28 2604 54 4 -7 0.00
Wed 04/08 18Z 0.38 2505 46 3 -6 0.00
Wed 04/08 19Z 0.34 2305 39 3 -5 0.00
Wed 04/08 20Z 0.34 2305 34 3 -5 0.00
Wed 04/08 21Z 0.27 2406 30 4 -4 0.00
Wed 04/08 22Z 0.22 2308 28 5 -3 0.00
Wed 04/08 23Z 0.24 2309 28 6 -3 0.00
Thu 04/09 00Z 0.25 2310 27 8 -2 0.00
Thu 04/09 01Z 0.23 2212 24 13 -1 0.00
Thu 04/09 02Z 0.25 2214 21 20 -1 0.00
Thu 04/09 03Z 0.30 2216 20 26 0 0.00
Thu 04/09 04Z 0.31 2217 21 32 0 0.00
Thu 04/09 05Z 0.30 2218 20 35 0 0.00
Thu 04/09 06Z 0.26 2218 19 38 1 0.00
Thu 04/09 07Z 0.25 2119 20 38 2 0.00
Thu 04/09 08Z 0.23 2119 19 36 2 0.00
Thu 04/09 09Z 0.24 2121 17 38 2 0.00
Thu 04/09 10Z 0.27 2123 16 36 2 0.00
Thu 04/09 11Z 0.30 2124 14 37 3 0.00
Thu 04/09 12Z 0.30 2124 12 46 3 0.00
Thu 04/09 13Z 0.29 2124 10 58 3 0.00
Thu 04/09 14Z 0.28 2125 10 62 4 0.00
Thu 04/09 15Z 0.27 2125 11 52 4 0.00
Thu 04/09 16Z 0.27 2026 13 38 4 0.00
Thu 04/09 17Z 0.30 2026 15 32 3 0.00
Thu 04/09 18Z 0.36 2027 17 33 3 0.00
Thu 04/09 19Z 0.40 2028 19 32 3 0.00
Thu 04/09 20Z 0.38 2028 20 32 4 0.00
Thu 04/09 21Z 0.37 2028 21 34 5 0.00
Thu 04/09 22Z 0.34 2028 24 36 5 0.00
Thu 04/09 23Z 0.32 2029 33 41 6 0.00
Fri 04/10 00Z 0.35 2130 40 44 6 0.00
Fri 04/10 01Z 0.41 2131 46 45 6 0.00
Fri 04/10 02Z 0.49 2232 53 51 6 0.00
Fri 04/10 03Z 0.54 2332 59 56 6 0.00
Fri 04/10 04Z 0.57 2332 61 76 6 0.00
Fri 04/10 05Z 0.61 2432 65 77 6 0.00
Fri 04/10 06Z 0.66 2434 69 76 5 0.00
Fri 04/10 07Z 0.67 2532 76 70 5 0.00
Fri 04/10 08Z 0.64 2529 79 64 4 0.00
Fri 04/10 09Z 0.59 2526 81 43 4 0.00
Fri 04/10 10Z 0.54 2623 81 32 3 0.00
Fri 04/10 11Z 0.53 2622 80 22 3 0.00
Fri 04/10 12Z 0.49 2621 76 20 3 0.00
Fri 04/10 13Z 0.49 2520 78 21 3 0.00
Fri 04/10 14Z 0.51 2520 80 17 3 0.00
Fri 04/10 15Z 0.54 2519 79 67 3 0.00
Fri 04/10 16Z 0.57 2517 77 94 2 0.00
Fri 04/10 17Z 0.51 2415 74 90 2 0.01
Fri 04/10 18Z 0.49 2315 76 89 2 0.01
Fri 04/10 19Z 0.46 2316 82 86 3 0.01
Fri 04/10 20Z 0.38 2217 85 52 4 0.01
Fri 04/10 21Z 0.44 2219 88 73 5 0.00
Fri 04/10 22Z 0.43 2219 91 96 5 0.03
Fri 04/10 23Z 0.32 2118 91 90 5 0.04
Run total areal avg QPF for the greens is: 0.11 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