Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260921_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 09/21 06Z 0.11 0111 92 14 6 0.00
Mon 09/21 07Z 0.17 0113 90 7 6 0.00
Mon 09/21 08Z 0.20 0114 89 4 5 0.00
Mon 09/21 09Z 0.20 0116 87 2 5 0.00
Mon 09/21 10Z 0.20 0117 84 1 5 0.00
Mon 09/21 11Z 0.18 0117 84 1 5 0.00
Mon 09/21 12Z 0.17 0117 86 0 5 0.00
Mon 09/21 13Z 0.17 0116 88 1 4 0.00
Mon 09/21 14Z 0.16 0115 88 2 4 0.00
Mon 09/21 15Z 0.17 0114 88 2 4 0.00
Mon 09/21 16Z 0.17 0113 87 2 4 0.00
Mon 09/21 17Z 0.18 0112 84 2 4 0.00
Mon 09/21 18Z 0.18 0111 80 2 4 0.00
Mon 09/21 19Z 0.18 0210 77 2 4 0.00
Mon 09/21 20Z 0.14 0109 73 2 4 0.00
Mon 09/21 21Z 0.15 0210 68 2 5 0.00
Mon 09/21 22Z 0.14 0210 62 2 5 0.00
Mon 09/21 23Z 0.14 0210 56 2 5 0.00
Tue 09/22 00Z 0.15 0211 53 2 5 0.00
Tue 09/22 01Z 0.17 0311 49 2 5 0.00
Tue 09/22 02Z 0.15 0309 47 2 6 0.00
Tue 09/22 03Z 0.17 0409 45 2 5 0.00
Tue 09/22 04Z 0.18 0509 43 2 5 0.00
Tue 09/22 05Z 0.18 0608 43 2 5 0.00
Tue 09/22 06Z 0.17 0707 49 2 4 0.00
Tue 09/22 07Z 0.15 0806 55 2 4 0.00
Tue 09/22 08Z 0.13 1005 61 2 3 0.00
Tue 09/22 09Z 0.14 1106 62 2 3 0.00
Tue 09/22 10Z 0.13 1106 65 2 3 0.00
Tue 09/22 11Z 0.13 1206 69 2 2 0.00
Tue 09/22 12Z 0.13 1105 71 3 2 0.00
Tue 09/22 13Z 0.16 0906 71 3 2 0.00
Tue 09/22 14Z 0.17 0806 71 3 2 0.00
Tue 09/22 15Z 0.20 0606 70 3 2 0.00
Tue 09/22 16Z 0.28 0607 72 3 2 0.00
Tue 09/22 17Z 0.56 0606 74 3 2 0.00
Tue 09/22 18Z 1.19 0605 74 3 2 0.00
Tue 09/22 19Z 1.34 0505 76 3 2 0.00
Tue 09/22 20Z 1.43 0505 76 4 2 0.00
Tue 09/22 21Z 1.11 0606 77 4 2 0.00
Tue 09/22 22Z 0.73 0607 78 6 2 0.00
Tue 09/22 23Z 0.57 0608 77 10 2 0.00
Wed 09/23 00Z 0.58 0610 76 16 2 0.00
Wed 09/23 01Z 0.58 0611 73 22 2 0.00
Wed 09/23 02Z 0.58 0713 70 27 3 0.00
Wed 09/23 03Z 0.61 0814 65 29 3 0.00
Wed 09/23 04Z 0.54 0914 60 28 3 0.00
Wed 09/23 05Z 0.53 0916 57 22 3 0.00
Wed 09/23 06Z 0.48 0916 56 17 3 0.00
Wed 09/23 07Z 0.46 0917 50 11 4 0.00
Wed 09/23 08Z 0.43 0817 48 6 4 0.00
Wed 09/23 09Z 0.42 0816 45 5 4 0.00
Wed 09/23 10Z 0.42 0717 44 5 4 0.00
Wed 09/23 11Z 0.42 0816 46 6 4 0.00
Wed 09/23 12Z 0.43 0817 46 7 4 0.00
Wed 09/23 13Z 0.44 0818 48 7 4 0.00
Wed 09/23 14Z 0.43 0917 49 6 4 0.00
Wed 09/23 15Z 0.44 0916 50 6 4 0.00
Wed 09/23 16Z 0.42 0913 54 5 3 0.00
Wed 09/23 17Z 0.43 0911 54 4 3 0.00
Run total areal avg QPF for the Central_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