Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260706_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)
=== ===== === ==== ==== === === === ====
Mon 07/06 00Z 0.08 0004 62 27 14 0.00
Mon 07/06 01Z 0.24 0305 63 18 14 0.00
Mon 07/06 02Z 0.30 0406 64 11 13 0.00
Mon 07/06 03Z 0.37 0608 66 8 13 0.00
Mon 07/06 04Z 0.43 0809 66 7 13 0.00
Mon 07/06 05Z 0.47 0910 66 7 13 0.00
Mon 07/06 06Z 0.47 1011 69 8 13 0.00
Mon 07/06 07Z 0.43 1110 70 10 13 0.00
Mon 07/06 08Z 0.40 1312 72 13 13 0.00
Mon 07/06 09Z 0.34 1312 75 15 13 0.00
Mon 07/06 10Z 0.30 1413 76 18 13 0.00
Mon 07/06 11Z 0.28 1414 77 23 13 0.00
Mon 07/06 12Z 0.31 1415 74 22 13 0.00
Mon 07/06 13Z 0.31 1415 74 28 13 0.00
Mon 07/06 14Z 0.32 1414 73 32 12 0.00
Mon 07/06 15Z 0.39 1314 76 36 12 0.00
Mon 07/06 16Z 0.63 1214 80 41 12 0.00
Mon 07/06 17Z 1.09 1213 78 44 12 0.00
Mon 07/06 18Z 1.28 1213 74 47 12 0.00
Mon 07/06 19Z 1.06 1214 73 52 12 0.00
Mon 07/06 20Z 1.68 1214 71 51 12 0.00
Mon 07/06 21Z 1.47 1314 71 46 12 0.00
Mon 07/06 22Z 0.81 1314 71 39 12 0.00
Mon 07/06 23Z 0.63 1316 71 31 12 0.00
Tue 07/07 00Z 0.56 1318 69 26 12 0.00
Tue 07/07 01Z 0.52 1320 65 25 12 0.00
Tue 07/07 02Z 0.47 1322 61 30 12 0.00
Tue 07/07 03Z 0.48 1223 59 35 13 0.00
Tue 07/07 04Z 0.49 1224 56 39 13 0.00
Tue 07/07 05Z 0.50 1225 57 38 13 0.00
Tue 07/07 06Z 0.50 1225 60 40 12 0.00
Tue 07/07 07Z 0.46 1224 62 43 12 0.00
Tue 07/07 08Z 0.44 1223 63 42 12 0.00
Tue 07/07 09Z 0.43 1222 66 40 12 0.00
Tue 07/07 10Z 0.41 1220 66 41 12 0.00
Tue 07/07 11Z 0.39 1219 66 41 12 0.00
Tue 07/07 12Z 0.39 1118 65 40 12 0.00
Tue 07/07 13Z 0.41 1118 65 35 12 0.00
Tue 07/07 14Z 0.44 1016 65 36 12 0.00
Tue 07/07 15Z 0.48 1014 65 32 12 0.00
Tue 07/07 16Z 0.66 1013 67 32 11 0.00
Tue 07/07 17Z 1.47 1011 68 32 11 0.00
Tue 07/07 18Z 2.46 0909 69 33 11 0.00
Tue 07/07 19Z 2.96 0909 69 33 12 0.00
Tue 07/07 20Z 2.02 1008 67 33 12 0.00
Tue 07/07 21Z 1.02 1007 67 30 12 0.00
Tue 07/07 22Z 0.52 1006 68 28 12 0.00
Tue 07/07 23Z 0.31 1005 70 26 12 0.00
Wed 07/08 00Z 0.25 1005 71 25 12 0.00
Wed 07/08 01Z 0.20 1005 72 23 12 0.00
Wed 07/08 02Z 0.15 0904 72 20 12 0.00
Wed 07/08 03Z 0.13 0802 71 19 12 0.00
Wed 07/08 04Z 0.11 0602 70 16 13 0.00
Wed 07/08 05Z 0.10 0302 71 13 13 0.00
Wed 07/08 06Z 0.10 0102 72 10 13 0.00
Wed 07/08 07Z 0.06 0102 72 9 13 0.00
Wed 07/08 08Z 0.04 3503 72 9 13 0.00
Wed 07/08 09Z 0.06 3404 73 11 12 0.00
Wed 07/08 10Z 0.05 3404 74 12 12 0.00
Wed 07/08 11Z 0.05 0004 73 10 12 0.00
Run total areal avg QPF for the greens is: 0.00 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