Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260401_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)
=== ===== === ==== ==== === === === ====
Wed 04/01 06Z 0.74 2329 97 98 9 0.00
Wed 04/01 07Z 0.79 2430 98 94 9 0.09
Wed 04/01 08Z 0.74 2629 98 96 8 0.12
Wed 04/01 09Z 0.66 2728 98 85 8 0.05
Wed 04/01 10Z 0.55 2826 98 88 7 0.02
Wed 04/01 11Z 0.44 2924 97 68 7 0.01
Wed 04/01 12Z 0.38 2923 95 70 7 0.01
Wed 04/01 13Z 0.33 2921 95 74 6 0.00
Wed 04/01 14Z 0.28 3020 97 63 5 0.01
Wed 04/01 15Z 0.25 3020 95 41 4 0.01
Wed 04/01 16Z 0.23 3018 89 34 3 0.00
Wed 04/01 17Z 0.23 3016 82 28 3 0.00
Wed 04/01 18Z 0.22 3015 74 20 2 0.00
Wed 04/01 19Z 0.19 3114 69 17 1 0.00
Wed 04/01 20Z 0.16 3112 64 17 0 0.00
Wed 04/01 21Z 0.12 3211 59 18 0 0.00
Wed 04/01 22Z 0.09 3211 55 19 1 0.00
Wed 04/01 23Z 0.05 3310 53 30 1 0.00
Thu 04/02 00Z 0.04 3507 52 30 1 0.00
Thu 04/02 01Z 0.04 3505 53 29 1 0.00
Thu 04/02 02Z 0.04 0104 50 31 1 0.00
Thu 04/02 03Z 0.05 0402 48 31 1 0.00
Thu 04/02 04Z 0.07 1003 48 37 1 0.00
Thu 04/02 05Z 0.09 1106 50 48 1 0.00
Thu 04/02 06Z 0.09 1308 59 51 0 0.00
Thu 04/02 07Z 0.11 1412 71 52 0 0.00
Thu 04/02 08Z 0.10 1412 81 46 0 0.01
Thu 04/02 09Z 0.09 1411 85 44 1 0.00
Thu 04/02 10Z 0.12 1312 89 44 1 0.01
Thu 04/02 11Z 0.13 1313 92 46 1 0.01
Thu 04/02 12Z 0.14 1313 94 49 1 0.01
Thu 04/02 13Z 0.13 1313 95 54 0 0.01
Thu 04/02 14Z 0.12 1313 96 41 0 0.01
Thu 04/02 15Z 0.09 1411 96 57 0 0.00
Thu 04/02 16Z 0.08 1410 96 63 0 0.00
Thu 04/02 17Z 0.10 1310 96 56 0 0.00
Thu 04/02 18Z 0.08 1409 95 52 1 0.00
Thu 04/02 19Z 0.08 1308 94 56 1 0.00
Thu 04/02 20Z 0.09 1310 93 70 1 0.00
Thu 04/02 21Z 0.09 1410 92 84 2 0.00
Thu 04/02 22Z 0.10 1412 90 90 2 0.00
Thu 04/02 23Z 0.10 1415 90 96 2 0.00
Fri 04/03 00Z 0.09 1518 93 98 2 0.00
Fri 04/03 01Z 0.06 1621 94 96 3 0.01
Fri 04/03 02Z 0.03 1623 94 92 4 0.01
Fri 04/03 03Z 0.04 1724 96 88 4 0.01
Fri 04/03 04Z 0.08 1826 97 70 5 0.01
Fri 04/03 05Z 0.12 1827 97 59 6 0.01
Fri 04/03 06Z 0.17 1928 97 50 7 0.01
Fri 04/03 07Z 0.21 1929 97 57 7 0.01
Fri 04/03 08Z 0.25 2031 97 55 8 0.02
Fri 04/03 09Z 0.31 2033 98 68 9 0.02
Fri 04/03 10Z 0.38 2135 98 62 9 0.02
Fri 04/03 11Z 0.44 2237 97 70 11 0.01
Fri 04/03 12Z 0.49 2239 96 76 11 0.01
Fri 04/03 13Z 0.56 2340 93 72 11 0.03
Fri 04/03 14Z 0.58 2439 93 60 12 0.01
Fri 04/03 15Z 0.63 2439 95 70 11 0.01
Fri 04/03 16Z 0.67 2438 95 74 10 0.01
Fri 04/03 17Z 0.72 2539 92 73 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.59 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