Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260720_1800
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 07/20 18Z 3.18 2504 73 53 11 0.00
Mon 07/20 19Z 3.34 2306 73 50 11 0.00
Mon 07/20 20Z 3.58 2307 74 46 11 0.00
Mon 07/20 21Z 3.50 2208 76 42 11 0.00
Mon 07/20 22Z 2.18 2210 76 36 11 0.00
Mon 07/20 23Z 1.00 2113 73 29 11 0.00
Tue 07/21 00Z 0.71 2114 68 24 12 0.00
Tue 07/21 01Z 0.69 2116 67 21 12 0.00
Tue 07/21 02Z 0.68 2119 67 20 12 0.00
Tue 07/21 03Z 0.65 2120 68 21 12 0.00
Tue 07/21 04Z 0.70 2121 69 17 12 0.00
Tue 07/21 05Z 0.81 2223 72 17 12 0.00
Tue 07/21 06Z 0.80 2225 73 16 12 0.00
Tue 07/21 07Z 0.75 2225 73 15 12 0.00
Tue 07/21 08Z 0.75 2225 74 14 12 0.00
Tue 07/21 09Z 0.65 2123 79 14 12 0.00
Tue 07/21 10Z 0.48 2023 80 14 12 0.00
Tue 07/21 11Z 0.50 2025 84 13 12 0.00
Tue 07/21 12Z 0.48 2024 87 10 12 0.01
Tue 07/21 13Z 0.39 1923 89 21 12 0.01
Tue 07/21 14Z 0.39 1925 91 55 12 0.01
Tue 07/21 15Z 0.33 1926 93 83 12 0.01
Tue 07/21 16Z 0.25 1827 95 75 13 0.01
Tue 07/21 17Z 0.22 1828 96 84 13 0.02
Tue 07/21 18Z 0.19 1830 96 73 13 0.02
Tue 07/21 19Z 0.17 1830 97 83 13 0.04
Tue 07/21 20Z 0.10 1731 95 66 13 0.06
Tue 07/21 21Z 0.04 1632 94 64 14 0.01
Tue 07/21 22Z 0.06 1732 94 65 15 0.01
Tue 07/21 23Z 0.05 1631 97 78 14 0.02
Wed 07/22 00Z 0.05 1626 98 89 15 0.03
Wed 07/22 01Z 0.03 1724 96 87 15 0.02
Wed 07/22 02Z 0.16 1827 97 91 15 0.04
Wed 07/22 03Z 0.43 2027 93 90 15 0.02
Wed 07/22 04Z 0.54 2129 88 79 16 0.00
Wed 07/22 05Z 0.60 2227 82 78 16 0.00
Wed 07/22 06Z 0.60 2224 92 77 15 0.00
Wed 07/22 07Z 0.62 2224 96 73 15 0.07
Wed 07/22 08Z 0.65 2223 98 78 15 0.11
Wed 07/22 09Z 0.60 2221 97 63 15 0.09
Wed 07/22 10Z 0.66 2322 94 60 15 0.01
Wed 07/22 11Z 0.65 2222 97 69 14 0.02
Wed 07/22 12Z 0.69 2322 98 73 14 0.02
Wed 07/22 13Z 0.71 2320 98 78 14 0.03
Wed 07/22 14Z 0.70 2418 96 85 14 0.03
Wed 07/22 15Z 0.80 2518 94 86 13 0.02
Wed 07/22 16Z 1.10 2519 95 69 13 0.00
Wed 07/22 17Z 1.57 2421 95 51 13 0.04
Wed 07/22 18Z 1.69 2520 88 39 13 0.01
Wed 07/22 19Z 5.99 2520 78 17 12 0.00
Wed 07/22 20Z 9.44 2621 79 2 11 0.00
Wed 07/22 21Z 12.14 2622 81 5 10 0.00
Wed 07/22 22Z 7.15 2621 83 17 9 0.00
Wed 07/22 23Z 3.29 2622 86 29 8 0.00
Thu 07/23 00Z 1.52 2625 91 36 7 0.00
Thu 07/23 01Z 1.22 2725 91 39 7 0.00
Thu 07/23 02Z 0.89 2823 94 44 7 0.00
Thu 07/23 03Z 0.77 2922 95 38 6 0.01
Thu 07/23 04Z 0.55 3022 91 37 6 0.00
Thu 07/23 05Z 0.34 3223 83 37 7 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