Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260706_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)
=== ===== === ==== ==== === === === ====
Mon 07/06 12Z 0.15 1407 83 22 13 0.00
Mon 07/06 13Z 0.21 1410 79 18 13 0.00
Mon 07/06 14Z 0.23 1411 76 18 13 0.00
Mon 07/06 15Z 0.29 1311 75 19 13 0.00
Mon 07/06 16Z 0.38 1311 76 20 13 0.00
Mon 07/06 17Z 0.89 1311 79 25 12 0.00
Mon 07/06 18Z 1.82 1411 77 26 12 0.00
Mon 07/06 19Z 1.74 1412 75 25 12 0.00
Mon 07/06 20Z 2.21 1412 76 26 12 0.00
Mon 07/06 21Z 1.35 1412 77 28 12 0.00
Mon 07/06 22Z 1.00 1412 76 30 12 0.01
Mon 07/06 23Z 0.54 1314 74 41 12 0.00
Tue 07/07 00Z 0.42 1317 71 46 13 0.00
Tue 07/07 01Z 0.44 1320 64 45 13 0.00
Tue 07/07 02Z 0.40 1321 60 46 13 0.00
Tue 07/07 03Z 0.38 1422 58 45 13 0.00
Tue 07/07 04Z 0.34 1421 59 44 14 0.00
Tue 07/07 05Z 0.30 1420 62 46 13 0.00
Tue 07/07 06Z 0.28 1419 65 45 13 0.00
Tue 07/07 07Z 0.29 1318 69 38 13 0.00
Tue 07/07 08Z 0.30 1317 73 39 13 0.00
Tue 07/07 09Z 0.33 1217 76 47 13 0.00
Tue 07/07 10Z 0.36 1218 76 56 13 0.01
Tue 07/07 11Z 0.37 1218 74 60 13 0.01
Tue 07/07 12Z 0.43 1119 74 60 13 0.02
Tue 07/07 13Z 0.44 1020 75 60 13 0.01
Tue 07/07 14Z 0.46 1021 77 70 12 0.01
Tue 07/07 15Z 0.49 1021 78 74 12 0.01
Tue 07/07 16Z 0.48 1020 78 72 12 0.02
Tue 07/07 17Z 0.50 0919 81 67 12 0.01
Tue 07/07 18Z 0.53 0918 82 61 12 0.01
Tue 07/07 19Z 0.65 0817 81 56 12 0.00
Tue 07/07 20Z 0.80 0817 83 50 11 0.00
Tue 07/07 21Z 0.77 0817 82 46 11 0.00
Tue 07/07 22Z 0.58 0818 82 45 12 0.00
Tue 07/07 23Z 0.49 0917 82 46 12 0.00
Wed 07/08 00Z 0.41 0916 81 41 12 0.00
Wed 07/08 01Z 0.35 0914 79 33 12 0.00
Wed 07/08 02Z 0.31 0813 78 23 12 0.00
Wed 07/08 03Z 0.30 0712 75 15 12 0.00
Wed 07/08 04Z 0.27 0711 72 14 12 0.00
Wed 07/08 05Z 0.22 0510 68 13 12 0.00
Wed 07/08 06Z 0.19 0410 65 11 13 0.00
Wed 07/08 07Z 0.14 0308 64 10 12 0.00
Wed 07/08 08Z 0.10 0208 63 12 12 0.00
Wed 07/08 09Z 0.12 0209 62 10 12 0.00
Wed 07/08 10Z 0.11 0209 61 10 12 0.00
Wed 07/08 11Z 0.15 0209 59 8 12 0.00
Wed 07/08 12Z 0.17 0309 60 5 12 0.00
Wed 07/08 13Z 0.12 0307 61 4 12 0.00
Wed 07/08 14Z 0.06 0006 65 4 12 0.00
Wed 07/08 15Z 0.07 3406 67 6 13 0.00
Wed 07/08 16Z 0.10 3405 67 4 13 0.00
Wed 07/08 17Z 0.50 3104 69 3 13 0.00
Wed 07/08 18Z 0.73 3006 68 2 13 0.00
Wed 07/08 19Z 0.62 3007 64 3 14 0.00
Wed 07/08 20Z 0.59 3009 62 5 14 0.00
Wed 07/08 21Z 0.57 2911 69 6 14 0.00
Wed 07/08 22Z 0.55 2912 80 5 14 0.00
Wed 07/08 23Z 0.54 2812 85 9 14 0.00
Run total areal avg QPF for the greens is: 0.12 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