Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260302_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 03/02 18Z 0.67 2610 55 19 -17 0.00
Mon 03/02 19Z 0.60 2712 50 17 -16 0.00
Mon 03/02 20Z 0.49 2610 51 24 -16 0.00
Mon 03/02 21Z 0.46 2610 55 35 -15 0.00
Mon 03/02 22Z 0.41 2610 59 44 -15 0.00
Mon 03/02 23Z 0.43 2512 61 46 -14 0.00
Tue 03/03 00Z 0.41 2613 59 37 -14 0.00
Tue 03/03 01Z 0.39 2613 54 30 -12 0.00
Tue 03/03 02Z 0.35 2614 48 27 -11 0.00
Tue 03/03 03Z 0.35 2515 41 33 -10 0.00
Tue 03/03 04Z 0.36 2516 35 41 -9 0.00
Tue 03/03 05Z 0.36 2517 31 46 -8 0.00
Tue 03/03 06Z 0.36 2418 30 43 -7 0.00
Tue 03/03 07Z 0.40 2420 31 42 -7 0.00
Tue 03/03 08Z 0.42 2421 33 45 -6 0.00
Tue 03/03 09Z 0.40 2420 36 46 -6 0.00
Tue 03/03 10Z 0.38 2419 35 47 -5 0.00
Tue 03/03 11Z 0.35 2318 33 46 -5 0.00
Tue 03/03 12Z 0.33 2318 31 46 -4 0.00
Tue 03/03 13Z 0.31 2218 31 43 -4 0.00
Tue 03/03 14Z 0.31 2219 35 40 -4 0.00
Tue 03/03 15Z 0.33 2220 59 38 -4 0.00
Tue 03/03 16Z 0.35 2221 77 36 -4 0.00
Tue 03/03 17Z 0.38 2222 86 29 -4 0.00
Tue 03/03 18Z 0.42 2222 94 38 -5 0.01
Tue 03/03 19Z 0.38 2220 96 63 -4 0.01
Tue 03/03 20Z 0.36 2221 97 85 -3 0.02
Tue 03/03 21Z 0.36 2222 98 97 -3 0.03
Tue 03/03 22Z 0.38 2125 98 96 -3 0.03
Tue 03/03 23Z 0.38 2026 98 97 -2 0.03
Wed 03/04 00Z 0.41 2127 98 94 -2 0.05
Wed 03/04 01Z 0.47 2127 98 95 -2 0.07
Wed 03/04 02Z 0.52 2226 98 95 -2 0.07
Wed 03/04 03Z 0.55 2325 98 92 -2 0.05
Wed 03/04 04Z 0.56 2523 98 92 -2 0.04
Wed 03/04 05Z 0.50 2621 98 90 -2 0.04
Wed 03/04 06Z 0.43 2820 97 78 -3 0.03
Wed 03/04 07Z 0.38 3021 96 59 -3 0.02
Wed 03/04 08Z 0.27 3120 83 41 -1 0.01
Wed 03/04 09Z 0.21 3119 64 46 0 0.00
Wed 03/04 10Z 0.23 3018 53 24 0 0.00
Wed 03/04 11Z 0.21 3117 47 13 0 0.00
Wed 03/04 12Z 0.26 3018 49 6 0 0.00
Wed 03/04 13Z 0.31 3019 52 4 0 0.00
Wed 03/04 14Z 0.34 3020 52 3 0 0.00
Wed 03/04 16Z 0.27 3015 45 3 0 0.00
Wed 03/04 17Z 0.27 2813 44 5 0 0.00
Wed 03/04 18Z 0.29 2712 42 6 0 0.00
Wed 03/04 19Z 0.34 2613 40 7 0 0.00
Wed 03/04 20Z 0.41 2515 37 8 0 0.00
Wed 03/04 21Z 0.44 2616 37 11 0 0.00
Wed 03/04 22Z 0.43 2616 36 12 1 0.00
Wed 03/04 23Z 0.40 2615 34 12 2 0.00
Thu 03/05 00Z 0.42 2616 34 14 2 0.00
Thu 03/05 01Z 0.43 2517 33 16 2 0.00
Thu 03/05 02Z 0.45 2518 31 16 3 0.00
Thu 03/05 03Z 0.48 2519 30 17 3 0.00
Thu 03/05 04Z 0.50 2620 28 20 3 0.00
Thu 03/05 05Z 0.52 2620 29 18 3 0.00
Run total areal avg QPF for the Central_Greens is: 0.51 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