Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260413_1200
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 04/13 12Z 0.61 2434 70 79 11 0.00
Mon 04/13 13Z 0.60 2432 71 77 11 0.00
Mon 04/13 14Z 0.60 2431 71 82 11 0.00
Mon 04/13 15Z 0.69 2334 68 58 11 0.00
Mon 04/13 16Z 0.79 2334 67 62 11 0.00
Mon 04/13 17Z 1.10 2436 76 90 10 0.00
Mon 04/13 18Z 1.96 2436 79 82 9 0.00
Mon 04/13 19Z 5.37 2435 83 91 9 0.00
Mon 04/13 20Z 2.29 2435 90 98 9 0.02
Mon 04/13 21Z 1.39 2639 96 95 9 0.07
Mon 04/13 22Z 1.42 2738 96 93 9 0.04
Mon 04/13 23Z 1.34 2736 96 88 9 0.02
Tue 04/14 00Z 1.24 2736 97 89 9 0.04
Tue 04/14 01Z 1.13 2834 97 78 8 0.02
Tue 04/14 02Z 1.03 2833 97 61 8 0.01
Tue 04/14 03Z 0.91 2931 97 55 8 0.01
Tue 04/14 04Z 0.75 2928 95 50 7 0.01
Tue 04/14 05Z 0.62 3025 94 46 7 0.01
Tue 04/14 06Z 0.52 2922 93 33 8 0.01
Tue 04/14 07Z 0.46 2921 91 28 8 0.01
Tue 04/14 08Z 0.41 2919 89 28 8 0.01
Tue 04/14 09Z 0.41 2819 88 27 8 0.01
Tue 04/14 10Z 0.37 2817 88 25 8 0.01
Tue 04/14 11Z 0.35 2817 86 21 9 0.01
Tue 04/14 12Z 0.27 2814 82 21 10 0.00
Tue 04/14 13Z 0.23 2711 78 20 10 0.00
Tue 04/14 14Z 0.21 2410 76 20 11 0.00
Tue 04/14 15Z 0.24 2213 74 20 12 0.00
Tue 04/14 16Z 0.32 2117 78 23 11 0.00
Tue 04/14 17Z 0.40 2120 83 44 11 0.00
Tue 04/14 18Z 0.50 2121 90 43 11 0.00
Tue 04/14 19Z 0.66 2021 83 64 12 0.00
Tue 04/14 20Z 1.48 1924 79 47 13 0.00
Tue 04/14 21Z 0.99 2123 90 90 12 0.11
Tue 04/14 22Z 1.04 2429 93 83 12 0.26
Tue 04/14 23Z 1.19 2630 97 71 11 0.01
Wed 04/15 00Z 1.31 2630 98 58 11 0.02
Wed 04/15 01Z 1.20 2729 98 40 10 0.02
Wed 04/15 02Z 1.05 2728 98 35 10 0.03
Wed 04/15 03Z 0.84 2726 98 29 10 0.03
Wed 04/15 04Z 0.74 2825 98 20 9 0.03
Wed 04/15 05Z 0.63 2924 98 16 9 0.03
Wed 04/15 06Z 0.45 2922 97 13 8 0.02
Wed 04/15 07Z 0.33 2918 93 10 9 0.01
Wed 04/15 08Z 0.28 2916 87 10 10 0.01
Wed 04/15 09Z 0.26 2814 81 10 11 0.01
Wed 04/15 10Z 0.23 2813 77 9 11 0.01
Wed 04/15 11Z 0.20 2710 73 8 11 0.00
Wed 04/15 12Z 0.21 2510 69 9 12 0.00
Wed 04/15 13Z 0.27 2513 70 12 11 0.00
Wed 04/15 14Z 0.29 2413 77 26 11 0.00
Wed 04/15 15Z 0.32 2314 87 50 11 0.00
Wed 04/15 16Z 0.33 2117 97 83 10 0.09
Wed 04/15 17Z 0.21 2111 96 95 9 0.04
Wed 04/15 18Z 0.25 2017 98 92 10 0.05
Wed 04/15 19Z 0.45 2122 98 87 11 0.03
Wed 04/15 20Z 0.84 2323 97 88 11 0.02
Wed 04/15 21Z 1.19 2523 96 90 11 0.04
Wed 04/15 22Z 0.72 2722 97 82 10 0.05
Wed 04/15 23Z 0.57 2820 97 76 10 0.02
Run total areal avg QPF for the Central_Greens is: 1.25 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