Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260415_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)
=== ===== === ==== ==== === === === ====
Wed 04/15 18Z 0.30 2013 83 94 11 0.00
Wed 04/15 19Z 0.65 2217 85 95 11 0.00
Wed 04/15 20Z 1.37 2320 86 85 12 0.00
Wed 04/15 21Z 0.94 2519 83 75 12 0.00
Wed 04/15 22Z 0.71 2615 84 69 12 0.00
Wed 04/15 23Z 0.76 2615 93 84 11 0.00
Thu 04/16 00Z 0.75 2617 94 82 11 0.01
Thu 04/16 01Z 0.69 2617 93 89 11 0.00
Thu 04/16 02Z 0.47 2714 87 87 11 0.00
Thu 04/16 03Z 0.40 2613 86 90 12 0.00
Thu 04/16 04Z 0.38 2512 86 94 12 0.00
Thu 04/16 05Z 0.44 2613 89 95 11 0.02
Thu 04/16 06Z 0.43 2613 93 94 11 0.17
Thu 04/16 07Z 0.30 2610 89 95 11 0.07
Thu 04/16 08Z 0.23 2408 89 96 11 0.05
Thu 04/16 09Z 0.26 2509 91 98 11 0.03
Thu 04/16 10Z 0.21 2407 90 93 11 0.02
Thu 04/16 11Z 0.23 2408 91 93 11 0.01
Thu 04/16 12Z 0.21 2308 92 83 11 0.01
Thu 04/16 13Z 0.27 2709 94 83 11 0.01
Thu 04/16 14Z 0.23 2707 94 75 11 0.00
Thu 04/16 15Z 0.22 2607 93 55 11 0.00
Thu 04/16 16Z 0.27 2608 92 53 11 0.00
Thu 04/16 17Z 0.29 2509 87 66 12 0.00
Thu 04/16 18Z 0.34 2510 86 69 12 0.00
Thu 04/16 19Z 0.37 2310 87 73 12 0.00
Thu 04/16 20Z 0.41 2211 83 60 12 0.00
Thu 04/16 21Z 0.36 2111 80 40 13 0.00
Thu 04/16 22Z 0.43 2015 78 32 13 0.00
Thu 04/16 23Z 0.59 2019 82 29 12 0.00
Fri 04/17 00Z 0.59 2024 87 26 13 0.00
Fri 04/17 01Z 0.60 2123 93 90 13 0.06
Fri 04/17 02Z 0.88 2625 92 93 11 0.61
Fri 04/17 03Z 0.80 2626 86 84 11 0.10
Fri 04/17 04Z 0.92 2628 93 81 10 0.02
Fri 04/17 05Z 0.80 2625 91 67 11 0.01
Fri 04/17 06Z 0.72 2623 92 49 11 0.01
Fri 04/17 07Z 0.68 2722 93 40 10 0.01
Fri 04/17 08Z 0.69 2721 95 33 10 0.02
Fri 04/17 09Z 0.65 2821 97 37 9 0.03
Fri 04/17 10Z 0.51 2920 97 39 9 0.03
Fri 04/17 11Z 0.34 3121 97 53 8 0.02
Fri 04/17 12Z 0.12 3423 96 68 7 0.02
Fri 04/17 13Z 0.05 3523 94 73 7 0.01
Fri 04/17 14Z 0.04 3522 92 71 7 0.00
Fri 04/17 15Z 0.06 3520 90 66 7 0.00
Fri 04/17 16Z 0.06 3518 89 69 7 0.00
Fri 04/17 17Z 0.07 3517 88 61 7 0.00
Fri 04/17 18Z 0.07 3516 88 51 8 0.00
Fri 04/17 19Z 0.06 3516 86 42 8 0.00
Fri 04/17 20Z 0.05 3516 84 26 8 0.00
Fri 04/17 21Z 0.08 3516 80 17 8 0.00
Fri 04/17 22Z 0.11 0015 77 10 8 0.00
Fri 04/17 23Z 0.14 0014 73 8 8 0.00
Sat 04/18 00Z 0.18 0213 69 7 9 0.00
Sat 04/18 01Z 0.19 0311 66 5 9 0.00
Sat 04/18 02Z 0.19 0410 65 5 9 0.00
Sat 04/18 03Z 0.18 0508 63 5 9 0.00
Sat 04/18 04Z 0.18 0607 65 5 9 0.00
Sat 04/18 05Z 0.17 1008 68 4 9 0.00
Run total areal avg QPF for the Central_Greens is: 1.35 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