Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260429_0000
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 00Z 0.16 1514 58 45 7 0.00
Wed 04/29 01Z 0.09 1618 63 29 6 0.00
Wed 04/29 02Z 0.04 1618 61 34 6 0.00
Wed 04/29 03Z 0.05 1718 57 50 5 0.00
Wed 04/29 04Z 0.08 1718 56 67 5 0.00
Wed 04/29 05Z 0.18 1819 57 82 5 0.00
Wed 04/29 06Z 0.35 2021 57 92 4 0.00
Wed 04/29 07Z 0.36 2020 63 90 4 0.00
Wed 04/29 08Z 0.26 2016 62 70 4 0.00
Wed 04/29 09Z 0.26 2015 63 59 4 0.00
Wed 04/29 10Z 0.32 2117 67 52 4 0.00
Wed 04/29 11Z 0.26 2115 70 39 5 0.00
Wed 04/29 12Z 0.24 2114 74 38 5 0.00
Wed 04/29 13Z 0.18 2111 76 32 6 0.00
Wed 04/29 14Z 0.13 2008 77 24 6 0.00
Wed 04/29 15Z 0.07 1808 76 16 6 0.00
Wed 04/29 16Z 0.18 1608 74 12 6 0.00
Wed 04/29 17Z 0.31 1609 73 15 6 0.00
Wed 04/29 18Z 0.85 1509 73 20 6 0.00
Wed 04/29 19Z 1.58 1511 74 26 6 0.00
Wed 04/29 20Z 1.51 1513 75 41 6 0.00
Wed 04/29 21Z 1.37 1515 77 48 6 0.00
Wed 04/29 22Z 0.79 1516 80 60 6 0.00
Wed 04/29 23Z 0.51 1519 82 74 5 0.00
Thu 04/30 00Z 0.18 1621 85 75 5 0.00
Thu 04/30 01Z 0.11 1621 89 61 6 0.00
Thu 04/30 02Z 0.05 1621 87 63 6 0.00
Thu 04/30 03Z 0.05 1623 83 71 7 0.00
Thu 04/30 04Z 0.07 1625 78 64 7 0.00
Thu 04/30 05Z 0.09 1625 74 61 7 0.01
Thu 04/30 06Z 0.05 1725 73 81 6 0.01
Thu 04/30 07Z 0.10 1823 79 87 4 0.01
Thu 04/30 08Z 0.07 1722 83 92 4 0.01
Thu 04/30 09Z 0.09 1722 79 96 4 0.02
Thu 04/30 10Z 0.06 1621 88 96 4 0.05
Thu 04/30 11Z 0.03 1620 91 98 3 0.03
Thu 04/30 12Z 0.06 1717 92 99 2 0.01
Thu 04/30 13Z 0.06 1714 96 99 1 0.02
Thu 04/30 14Z 0.16 1913 98 99 1 0.03
Thu 04/30 15Z 0.25 2011 99 99 0 0.04
Thu 04/30 16Z 0.28 2209 99 89 0 0.03
Thu 04/30 17Z 0.34 2308 99 83 0 0.01
Thu 04/30 18Z 0.38 2607 98 85 0 0.00
Thu 04/30 19Z 0.43 3007 95 78 0 0.00
Thu 04/30 20Z 0.63 3108 94 69 0 0.00
Thu 04/30 21Z 0.28 3108 97 69 1 0.01
Thu 04/30 22Z 0.32 3113 98 64 0 0.03
Thu 04/30 23Z 0.31 3216 97 57 0 0.01
Fri 05/01 00Z 0.31 3217 96 59 0 0.01
Fri 05/01 01Z 0.34 3218 95 66 -1 0.01
Fri 05/01 02Z 0.36 3219 95 67 -1 0.00
Fri 05/01 03Z 0.37 3219 95 65 -2 0.00
Fri 05/01 04Z 0.36 3220 94 66 -2 0.01
Fri 05/01 05Z 0.40 3221 93 65 -2 0.01
Fri 05/01 06Z 0.39 3120 93 66 -3 0.00
Fri 05/01 07Z 0.38 3120 92 66 -3 0.00
Fri 05/01 08Z 0.38 3120 92 53 -3 0.00
Fri 05/01 09Z 0.39 3119 90 42 -3 0.00
Fri 05/01 10Z 0.37 3120 88 36 -3 0.00
Fri 05/01 11Z 0.36 3119 85 35 -3 0.00
Run total areal avg QPF for the Central_Greens is: 0.37 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