Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260412_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)
=== ===== === ==== ==== === === === ====
Sun 04/12 18Z 0.19 1906 51 54 -1 0.00
Sun 04/12 19Z 0.22 1808 47 67 0 0.00
Sun 04/12 20Z 0.22 1811 47 79 0 0.00
Sun 04/12 21Z 0.07 1615 43 96 0 0.00
Sun 04/12 22Z 0.80 1817 50 89 0 0.00
Sun 04/12 23Z 0.58 1922 63 98 0 0.02
Mon 04/13 00Z 0.44 1925 85 98 -1 0.03
Mon 04/13 01Z 0.41 2026 89 99 0 0.05
Mon 04/13 02Z 0.42 2028 85 99 2 0.04
Mon 04/13 03Z 0.46 2131 84 98 3 0.05
Mon 04/13 04Z 0.45 2133 83 97 5 0.05
Mon 04/13 05Z 0.45 2134 87 97 7 0.04
Mon 04/13 06Z 0.51 2237 87 97 7 0.04
Mon 04/13 07Z 0.54 2239 87 80 10 0.01
Mon 04/13 08Z 0.62 2343 90 89 10 0.02
Mon 04/13 09Z 0.70 2443 93 87 10 0.02
Mon 04/13 10Z 0.74 2543 90 85 11 0.00
Mon 04/13 11Z 0.75 2542 87 80 11 0.01
Mon 04/13 12Z 0.73 2540 85 73 11 0.00
Mon 04/13 13Z 0.72 2538 84 62 11 0.00
Mon 04/13 14Z 0.69 2534 79 44 11 0.00
Mon 04/13 15Z 0.66 2432 78 50 11 0.00
Mon 04/13 16Z 0.79 2334 71 21 11 0.00
Mon 04/13 17Z 1.32 2336 85 90 9 0.02
Mon 04/13 18Z 1.38 2340 92 95 9 0.06
Mon 04/13 19Z 1.34 2342 97 96 9 0.05
Mon 04/13 20Z 1.30 2541 98 93 9 0.09
Mon 04/13 21Z 1.19 2639 98 80 10 0.04
Mon 04/13 22Z 1.26 2639 98 67 10 0.03
Mon 04/13 23Z 1.26 2738 97 66 10 0.03
Tue 04/14 00Z 1.30 2737 97 62 9 0.01
Tue 04/14 01Z 1.32 2737 98 60 9 0.02
Tue 04/14 02Z 1.25 2835 98 54 8 0.03
Tue 04/14 03Z 1.10 2831 97 53 8 0.02
Tue 04/14 04Z 0.85 2928 97 39 8 0.02
Tue 04/14 05Z 0.66 3025 97 33 7 0.02
Tue 04/14 06Z 0.51 3023 95 34 7 0.01
Tue 04/14 07Z 0.41 3021 92 35 8 0.01
Tue 04/14 08Z 0.36 3020 87 36 8 0.01
Tue 04/14 09Z 0.31 2918 80 30 9 0.01
Tue 04/14 10Z 0.30 2917 75 28 9 0.01
Tue 04/14 11Z 0.23 2913 69 21 10 0.00
Tue 04/14 12Z 0.24 2812 72 25 9 0.00
Tue 04/14 13Z 0.23 2611 69 25 10 0.00
Tue 04/14 14Z 0.22 2411 66 31 10 0.00
Tue 04/14 15Z 0.26 2314 67 43 11 0.00
Tue 04/14 16Z 0.35 2317 73 51 11 0.00
Tue 04/14 17Z 0.52 2420 85 68 10 0.00
Tue 04/14 18Z 0.38 2120 73 69 12 0.00
Tue 04/14 19Z 0.37 2022 76 69 13 0.00
Tue 04/14 20Z 0.50 2122 79 69 13 0.00
Tue 04/14 21Z 1.01 2223 85 71 12 0.05
Tue 04/14 22Z 1.08 2224 86 79 12 0.04
Tue 04/14 23Z 0.70 2323 94 85 12 0.22
Wed 04/15 00Z 0.99 2527 94 88 11 0.24
Wed 04/15 01Z 0.84 2726 94 87 12 0.09
Wed 04/15 02Z 0.82 2826 93 78 11 0.10
Wed 04/15 03Z 0.79 2724 93 68 11 0.02
Wed 04/15 04Z 0.79 2726 97 53 11 0.03
Wed 04/15 05Z 0.64 2823 96 36 11 0.02
Run total areal avg QPF for the Central_Greens is: 1.68 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