Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260827_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)
=== ===== === ==== ==== === === === ====
Thu 08/27 06Z 0.20 1911 80 18 11 0.00
Thu 08/27 07Z 0.31 2013 76 18 12 0.00
Thu 08/27 08Z 0.44 2017 73 20 12 0.00
Thu 08/27 09Z 0.53 2020 70 18 12 0.00
Thu 08/27 10Z 0.53 2022 68 22 12 0.00
Thu 08/27 11Z 0.54 2022 60 32 13 0.00
Thu 08/27 12Z 0.59 2123 56 31 13 0.00
Thu 08/27 13Z 0.61 2124 58 38 13 0.00
Thu 08/27 14Z 0.64 2123 69 44 13 0.00
Thu 08/27 15Z 0.71 2022 72 44 13 0.00
Thu 08/27 16Z 2.07 2021 80 38 13 0.00
Thu 08/27 17Z 1.82 2021 85 63 13 0.00
Thu 08/27 18Z 0.76 2021 92 86 13 0.01
Thu 08/27 19Z 0.56 2021 93 89 13 0.02
Thu 08/27 20Z 0.52 1920 94 86 14 0.01
Thu 08/27 21Z 0.48 1922 96 81 14 0.05
Thu 08/27 22Z 0.36 1924 95 80 14 0.06
Thu 08/27 23Z 0.50 2024 90 79 14 0.40
Fri 08/28 00Z 0.56 2026 91 81 13 0.27
Fri 08/28 01Z 0.58 2127 92 78 14 0.02
Fri 08/28 02Z 0.58 2126 82 71 14 0.05
Fri 08/28 03Z 0.64 2226 85 74 14 0.03
Fri 08/28 04Z 0.66 2326 87 67 14 0.02
Fri 08/28 05Z 0.64 2424 87 66 14 0.01
Fri 08/28 06Z 0.62 2522 92 58 14 0.01
Fri 08/28 07Z 0.56 2519 93 56 13 0.01
Fri 08/28 08Z 0.48 2616 91 61 13 0.01
Fri 08/28 09Z 0.39 2614 88 54 13 0.01
Fri 08/28 10Z 0.34 2612 88 63 13 0.00
Fri 08/28 11Z 0.29 2610 87 52 12 0.00
Fri 08/28 12Z 0.30 2611 88 42 12 0.00
Fri 08/28 13Z 0.30 2610 89 53 12 0.00
Fri 08/28 14Z 0.27 2609 90 50 12 0.00
Fri 08/28 15Z 0.26 2608 91 45 12 0.00
Fri 08/28 16Z 0.27 2608 91 28 12 0.00
Fri 08/28 17Z 0.31 2608 91 19 12 0.00
Fri 08/28 18Z 0.36 2608 90 9 12 0.00
Fri 08/28 19Z 0.38 2709 92 4 11 0.00
Fri 08/28 20Z 0.33 2809 93 5 11 0.01
Fri 08/28 21Z 0.27 2808 91 8 12 0.00
Fri 08/28 22Z 0.26 2908 93 9 11 0.01
Fri 08/28 23Z 0.25 2909 92 11 11 0.01
Sat 08/29 00Z 0.25 3010 92 15 11 0.00
Sat 08/29 01Z 0.23 3011 92 19 10 0.00
Sat 08/29 02Z 0.19 3110 91 21 10 0.00
Sat 08/29 03Z 0.17 3110 87 22 10 0.00
Sat 08/29 04Z 0.17 3111 81 26 10 0.00
Sat 08/29 05Z 0.16 3111 74 26 10 0.00
Sat 08/29 06Z 0.17 3111 67 20 10 0.00
Sat 08/29 07Z 0.16 3112 58 17 10 0.00
Sat 08/29 08Z 0.15 3112 51 14 9 0.00
Sat 08/29 09Z 0.14 3212 48 15 9 0.00
Sat 08/29 10Z 0.12 3212 46 12 9 0.00
Sat 08/29 11Z 0.10 3211 45 10 9 0.00
Sat 08/29 12Z 0.09 3210 45 6 9 0.00
Sat 08/29 13Z 0.09 3210 47 5 8 0.00
Sat 08/29 14Z 0.12 3209 51 5 8 0.00
Sat 08/29 15Z 0.15 3108 54 5 8 0.00
Sat 08/29 16Z 0.16 3006 58 5 8 0.00
Sat 08/29 17Z 0.28 2906 58 4 8 0.00
Run total areal avg QPF for the Central_Greens is: 1.02 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