Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260608_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 06/08 12Z 0.16 0404 73 6 7 0.00
Mon 06/08 13Z 0.17 0305 75 7 7 0.00
Mon 06/08 14Z 0.17 0204 78 8 7 0.00
Mon 06/08 15Z 0.30 0203 80 8 8 0.00
Mon 06/08 16Z 0.22 3502 82 8 8 0.00
Mon 06/08 17Z 0.19 3101 83 7 8 0.00
Mon 06/08 18Z 0.38 2903 84 6 9 0.00
Mon 06/08 19Z 0.49 2903 82 6 9 0.00
Mon 06/08 20Z 0.61 2903 78 5 10 0.00
Mon 06/08 21Z 0.60 2804 73 5 10 0.00
Mon 06/08 22Z 0.39 2803 66 5 10 0.00
Mon 06/08 23Z 0.28 2705 59 4 11 0.00
Tue 06/09 00Z 0.35 2708 59 4 11 0.00
Tue 06/09 01Z 0.49 2610 65 3 11 0.00
Tue 06/09 02Z 0.45 2710 65 3 11 0.00
Tue 06/09 03Z 0.42 2709 66 2 11 0.00
Tue 06/09 04Z 0.36 2709 69 2 11 0.00
Tue 06/09 05Z 0.47 2611 67 3 11 0.00
Tue 06/09 06Z 0.55 2613 67 2 11 0.00
Tue 06/09 07Z 0.58 2615 70 2 11 0.00
Tue 06/09 08Z 0.66 2617 75 2 10 0.00
Tue 06/09 09Z 0.60 2618 78 2 10 0.00
Tue 06/09 10Z 0.50 2617 81 2 10 0.00
Tue 06/09 11Z 0.36 2714 78 2 11 0.01
Tue 06/09 12Z 0.30 2712 78 2 11 0.01
Tue 06/09 13Z 0.24 2609 75 2 11 0.01
Tue 06/09 14Z 0.25 2509 74 2 11 0.00
Tue 06/09 15Z 0.24 2508 70 2 11 0.00
Tue 06/09 16Z 0.28 2608 72 2 11 0.00
Tue 06/09 17Z 0.36 2608 75 2 11 0.00
Tue 06/09 18Z 0.40 2607 74 2 12 0.00
Tue 06/09 19Z 0.48 2609 74 2 13 0.00
Tue 06/09 20Z 0.50 2610 73 2 13 0.00
Tue 06/09 21Z 0.55 2611 72 3 13 0.00
Tue 06/09 22Z 0.57 2513 72 2 13 0.00
Tue 06/09 23Z 0.53 2513 77 2 14 0.00
Wed 06/10 00Z 0.62 2516 80 2 13 0.00
Wed 06/10 01Z 0.59 2616 83 1 14 0.00
Wed 06/10 02Z 0.55 2616 81 1 14 0.00
Wed 06/10 03Z 0.45 2715 74 1 15 0.00
Wed 06/10 04Z 0.45 2615 74 1 15 0.00
Wed 06/10 05Z 0.46 2615 74 1 14 0.00
Wed 06/10 06Z 0.38 2713 73 2 15 0.00
Wed 06/10 07Z 0.32 2611 71 8 15 0.00
Wed 06/10 08Z 0.29 2510 72 36 15 0.00
Wed 06/10 09Z 0.25 2409 73 57 15 0.00
Wed 06/10 10Z 0.22 2408 75 58 15 0.00
Wed 06/10 11Z 0.22 2308 75 79 15 0.00
Wed 06/10 12Z 0.18 2208 75 76 15 0.00
Wed 06/10 13Z 0.19 2209 75 72 15 0.00
Wed 06/10 14Z 0.20 2110 76 79 15 0.00
Wed 06/10 15Z 0.23 2110 81 79 15 0.00
Wed 06/10 16Z 0.30 2110 86 73 15 0.00
Wed 06/10 17Z 0.44 2010 87 78 15 0.00
Wed 06/10 18Z 0.46 2010 86 78 15 0.00
Wed 06/10 19Z 0.35 2011 86 83 15 0.00
Wed 06/10 20Z 0.33 2010 86 87 15 0.00
Wed 06/10 21Z 0.38 2010 88 80 15 0.00
Wed 06/10 22Z 0.43 2112 91 84 15 0.00
Wed 06/10 23Z 0.31 2012 91 94 15 0.01
Run total areal avg QPF for the Central_Greens is: 0.04 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