Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260817_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)
=== ===== === ==== ==== === === === ====
Mon 08/17 18Z 0.27 2606 96 81 14 0.00
Mon 08/17 19Z 0.14 2603 93 75 15 0.00
Mon 08/17 20Z 0.10 2502 92 77 16 0.00
Mon 08/17 21Z 0.13 2702 93 79 15 0.02
Mon 08/17 22Z 0.16 3003 94 83 15 0.05
Mon 08/17 23Z 0.13 3304 95 84 15 0.10
Tue 08/18 00Z 0.15 0104 96 87 14 0.01
Tue 08/18 01Z 0.12 0104 93 88 15 0.04
Tue 08/18 02Z 0.15 0204 93 94 15 0.20
Tue 08/18 03Z 0.14 0404 93 95 15 0.11
Tue 08/18 04Z 0.12 0703 94 88 15 0.01
Tue 08/18 05Z 0.08 0401 95 81 14 0.01
Tue 08/18 06Z 0.05 0002 96 66 14 0.01
Tue 08/18 07Z 0.04 3504 96 53 14 0.01
Tue 08/18 08Z 0.03 3505 94 42 14 0.01
Tue 08/18 09Z 0.02 3506 93 31 14 0.01
Tue 08/18 10Z 0.02 3506 90 26 14 0.00
Tue 08/18 11Z 0.02 3406 88 17 14 0.00
Tue 08/18 12Z 0.02 3505 88 14 13 0.00
Tue 08/18 13Z 0.02 3505 89 8 13 0.00
Tue 08/18 14Z 0.03 3503 90 6 13 0.00
Tue 08/18 15Z 0.03 3502 91 5 13 0.00
Tue 08/18 16Z 0.04 3302 92 4 13 0.01
Tue 08/18 17Z 0.06 3102 91 3 13 0.01
Tue 08/18 18Z 0.11 3004 91 3 13 0.01
Tue 08/18 19Z 0.11 3004 88 3 13 0.00
Tue 08/18 20Z 0.16 2905 86 3 13 0.00
Tue 08/18 21Z 0.22 2907 84 4 13 0.00
Tue 08/18 22Z 0.12 3004 80 3 13 0.00
Tue 08/18 23Z 0.10 2903 80 3 13 0.00
Wed 08/19 00Z 0.15 2804 82 9 13 0.00
Wed 08/19 01Z 0.13 2804 82 8 12 0.00
Wed 08/19 02Z 0.16 2804 83 15 12 0.00
Wed 08/19 03Z 0.13 2804 84 11 12 0.00
Wed 08/19 04Z 0.14 2704 87 6 12 0.00
Wed 08/19 05Z 0.20 2806 91 6 11 0.00
Wed 08/19 06Z 0.14 2804 90 12 11 0.00
Wed 08/19 07Z 0.15 2804 90 15 11 0.00
Wed 08/19 08Z 0.15 2805 90 11 11 0.00
Wed 08/19 09Z 0.13 2804 88 15 11 0.00
Wed 08/19 10Z 0.17 2706 87 12 11 0.00
Wed 08/19 11Z 0.18 2706 82 10 12 0.00
Wed 08/19 12Z 0.17 2607 75 25 12 0.00
Wed 08/19 13Z 0.21 2608 70 47 13 0.00
Wed 08/19 14Z 0.22 2509 67 59 13 0.00
Wed 08/19 15Z 0.24 2509 65 69 13 0.00
Wed 08/19 16Z 0.26 2409 60 65 13 0.00
Wed 08/19 17Z 0.34 2411 57 61 13 0.00
Wed 08/19 18Z 0.45 2414 52 51 14 0.00
Wed 08/19 19Z 0.55 2416 54 45 15 0.00
Wed 08/19 20Z 0.62 2516 71 48 14 0.00
Wed 08/19 21Z 0.83 2517 84 38 14 0.00
Wed 08/19 22Z 0.75 2518 91 29 13 0.00
Wed 08/19 23Z 0.69 2518 92 29 13 0.01
Thu 08/20 00Z 0.79 2520 91 32 13 0.01
Thu 08/20 01Z 0.79 2520 92 28 13 0.01
Thu 08/20 02Z 0.65 2618 90 31 14 0.01
Thu 08/20 03Z 0.57 2618 87 34 14 0.02
Thu 08/20 04Z 0.50 2617 84 29 14 0.01
Thu 08/20 05Z 0.41 2715 80 25 14 0.01
Run total areal avg QPF for the Central_Greens is: 0.70 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