
Wildfires and poor air quality continue for the Pacific Northwest, Rockies and extended into the Plains. Severe thunderstorms possible for the northern Plains and upper Midwest on Monday along a frontal boundary. Another boundary will focus showers and thunderstorms for the eastern seaboard with localized heavy rainfall possible. For Alaska, a strong Bering Sea storm will bring winds and rainfall. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260803_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 08/03 00Z 0.15 1823 84 52 15 0.00
Mon 08/03 01Z 0.17 1825 82 59 15 0.00
Mon 08/03 02Z 0.16 1828 80 66 15 0.00
Mon 08/03 03Z 0.17 1928 76 75 15 0.00
Mon 08/03 04Z 0.17 1925 75 83 16 0.00
Mon 08/03 05Z 0.15 1925 74 81 16 0.00
Mon 08/03 06Z 0.11 1824 77 87 16 0.01
Mon 08/03 07Z 0.05 1824 88 96 15 0.03
Mon 08/03 08Z 0.10 1726 94 94 15 0.11
Mon 08/03 09Z 0.14 1728 95 92 16 0.18
Mon 08/03 10Z 0.22 1828 97 88 16 0.30
Mon 08/03 11Z 0.18 1927 97 85 16 0.11
Mon 08/03 12Z 0.22 1926 97 83 16 0.04
Mon 08/03 13Z 0.35 2025 97 84 16 0.01
Mon 08/03 14Z 0.40 2024 97 78 16 0.01
Mon 08/03 15Z 0.45 2023 98 80 16 0.01
Mon 08/03 16Z 0.44 2022 96 79 16 0.01
Mon 08/03 17Z 0.46 2022 92 76 16 0.01
Mon 08/03 18Z 0.63 2021 90 79 16 0.00
Mon 08/03 19Z 1.49 2020 92 82 16 0.01
Mon 08/03 20Z 0.59 2219 95 90 16 0.29
Mon 08/03 21Z 0.75 2424 90 56 15 0.38
Mon 08/03 22Z 0.83 2422 95 48 14 0.02
Mon 08/03 23Z 0.87 2524 97 41 13 0.04
Tue 08/04 00Z 0.77 2723 98 49 12 0.06
Tue 08/04 01Z 0.75 2926 98 74 12 0.07
Tue 08/04 02Z 0.69 3129 99 86 11 0.11
Tue 08/04 03Z 0.55 3231 98 91 11 0.10
Tue 08/04 04Z 0.55 3232 92 67 11 0.02
Tue 08/04 05Z 0.67 3232 90 28 10 0.01
Tue 08/04 06Z 0.83 3129 84 8 10 0.00
Tue 08/04 07Z 0.73 3228 79 6 10 0.00
Tue 08/04 08Z 0.57 3224 74 4 11 0.00
Tue 08/04 09Z 0.51 3222 71 4 11 0.00
Tue 08/04 10Z 0.47 3220 70 4 11 0.00
Tue 08/04 11Z 0.46 3119 67 3 11 0.00
Tue 08/04 12Z 0.43 3119 63 2 12 0.00
Tue 08/04 13Z 0.40 3118 60 3 12 0.00
Tue 08/04 14Z 0.37 3117 57 2 12 0.00
Tue 08/04 15Z 0.41 3115 60 2 12 0.00
Tue 08/04 16Z 0.46 3013 61 2 12 0.00
Tue 08/04 17Z 0.59 3011 62 2 12 0.00
Tue 08/04 18Z 0.58 2910 60 1 13 0.00
Tue 08/04 19Z 0.43 2808 56 1 14 0.00
Tue 08/04 20Z 0.29 2807 50 1 15 0.00
Tue 08/04 21Z 0.24 2706 45 2 15 0.00
Tue 08/04 22Z 0.21 2606 41 2 16 0.00
Tue 08/04 23Z 0.19 2506 38 3 16 0.00
Wed 08/05 00Z 0.21 2407 39 3 16 0.00
Wed 08/05 01Z 0.22 2308 39 2 16 0.00
Wed 08/05 02Z 0.24 2308 42 1 16 0.00
Wed 08/05 03Z 0.29 2310 50 1 16 0.00
Wed 08/05 04Z 0.34 2311 55 1 15 0.00
Wed 08/05 05Z 0.32 2410 54 1 15 0.00
Wed 08/05 06Z 0.29 2310 49 1 15 0.00
Wed 08/05 07Z 0.25 2310 49 1 15 0.00
Wed 08/05 08Z 0.27 2310 51 1 15 0.00
Wed 08/05 09Z 0.27 2310 54 1 15 0.00
Wed 08/05 10Z 0.30 2411 57 1 15 0.00
Wed 08/05 11Z 0.31 2410 62 1 14 0.00
Run total areal avg QPF for the greens is: 1.94 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