Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260429_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 04/29 06Z 0.29 2018 65 75 3 0.00
Wed 04/29 07Z 0.30 2019 65 90 4 0.00
Wed 04/29 08Z 0.28 2018 66 95 4 0.00
Wed 04/29 09Z 0.25 2016 68 86 4 0.00
Wed 04/29 12Z 0.25 2015 78 59 5 0.00
Wed 04/29 13Z 0.17 2012 76 51 6 0.00
Wed 04/29 14Z 0.10 1909 75 47 6 0.00
Wed 04/29 15Z 0.03 1708 74 47 6 0.00
Wed 04/29 16Z 0.24 1510 73 27 6 0.00
Wed 04/29 17Z 0.25 1611 73 39 5 0.00
Wed 04/29 18Z 0.83 1612 72 62 5 0.00
Wed 04/29 19Z 1.87 1514 71 58 5 0.00
Wed 04/29 20Z 2.41 1514 73 51 5 0.00
Wed 04/29 21Z 2.12 1517 75 50 5 0.00
Wed 04/29 22Z 0.48 1517 76 57 5 0.00
Wed 04/29 23Z 0.16 1618 80 67 5 0.00
Thu 04/30 00Z 0.08 1619 87 81 5 0.00
Thu 04/30 01Z 0.05 1621 90 85 6 0.00
Thu 04/30 02Z 0.04 1622 89 91 6 0.00
Thu 04/30 03Z 0.05 1623 85 92 6 0.00
Thu 04/30 04Z 0.06 1625 82 96 6 0.00
Thu 04/30 05Z 0.05 1627 81 96 6 0.00
Thu 04/30 06Z 0.05 1628 88 96 4 0.01
Thu 04/30 07Z 0.06 1628 91 97 4 0.01
Thu 04/30 08Z 0.05 1628 95 99 4 0.03
Thu 04/30 09Z 0.04 1629 96 97 4 0.03
Thu 04/30 10Z 0.04 1728 95 98 3 0.06
Thu 04/30 11Z 0.05 1727 95 98 4 0.11
Thu 04/30 12Z 0.12 1724 98 99 2 0.09
Thu 04/30 13Z 0.14 1821 98 99 2 0.09
Thu 04/30 14Z 0.22 1920 95 99 2 0.07
Thu 04/30 15Z 0.25 1917 97 96 2 0.05
Thu 04/30 16Z 0.26 2012 98 91 1 0.04
Thu 04/30 17Z 0.26 2207 99 88 1 0.02
Thu 04/30 18Z 0.22 2405 99 73 1 0.02
Thu 04/30 19Z 0.25 2705 99 74 1 0.01
Thu 04/30 20Z 0.25 2906 99 85 1 0.01
Thu 04/30 21Z 0.26 3108 99 87 1 0.01
Thu 04/30 22Z 0.24 3211 98 85 1 0.01
Thu 04/30 23Z 0.25 3215 98 83 0 0.01
Fri 05/01 00Z 0.20 3318 97 77 0 0.01
Fri 05/01 01Z 0.30 3219 97 65 0 0.01
Fri 05/01 02Z 0.36 3219 96 64 0 0.01
Fri 05/01 03Z 0.39 3220 96 63 -1 0.01
Fri 05/01 04Z 0.40 3221 94 63 -1 0.01
Fri 05/01 05Z 0.41 3121 93 62 -2 0.01
Fri 05/01 06Z 0.42 3122 95 51 -2 0.01
Fri 05/01 07Z 0.46 3121 96 49 -3 0.01
Fri 05/01 08Z 0.48 3121 95 53 -3 0.01
Fri 05/01 09Z 0.45 3121 90 41 -3 0.01
Fri 05/01 10Z 0.44 3122 89 36 -3 0.01
Fri 05/01 11Z 0.44 3021 88 34 -3 0.01
Fri 05/01 12Z 0.48 3020 88 36 -4 0.00
Fri 05/01 13Z 0.51 3018 88 35 -4 0.00
Fri 05/01 14Z 0.72 3016 87 25 -4 0.00
Fri 05/01 15Z 2.12 2914 91 21 -4 0.00
Fri 05/01 16Z 2.64 2812 92 20 -4 0.00
Fri 05/01 17Z 3.67 2811 91 23 -3 0.00
Run total areal avg QPF for the Central_Greens is: 0.80 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