Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260504_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 05/04 12Z 0.83 2524 72 88 2 0.00
Mon 05/04 13Z 1.03 2526 72 90 2 0.00
Mon 05/04 14Z 1.49 2427 72 89 2 0.00
Mon 05/04 15Z 3.36 2426 74 94 2 0.00
Mon 05/04 16Z 11.84 2422 76 85 2 0.00
Mon 05/04 17Z 15.24 2423 75 93 3 0.00
Mon 05/04 18Z 15.15 2424 73 88 4 0.00
Mon 05/04 19Z 14.59 2423 70 74 5 0.00
Mon 05/04 20Z 13.59 2422 67 65 5 0.00
Mon 05/04 21Z 11.25 2322 68 53 6 0.00
Mon 05/04 22Z 6.37 2322 67 48 6 0.00
Mon 05/04 23Z 2.17 2323 66 70 6 0.00
Tue 05/05 00Z 1.64 2325 67 61 6 0.00
Tue 05/05 01Z 1.17 2325 68 47 7 0.00
Tue 05/05 02Z 1.00 2325 68 18 7 0.00
Tue 05/05 03Z 1.02 2228 70 13 7 0.00
Tue 05/05 04Z 1.21 2233 75 16 6 0.00
Tue 05/05 05Z 1.14 2234 74 27 7 0.00
Tue 05/05 06Z 1.08 2236 71 15 7 0.00
Tue 05/05 07Z 0.94 2235 66 15 8 0.00
Tue 05/05 08Z 0.87 2234 66 9 8 0.00
Tue 05/05 09Z 0.80 2233 72 24 8 0.00
Tue 05/05 10Z 0.87 2232 78 45 8 0.00
Tue 05/05 11Z 0.82 2232 88 62 7 0.00
Tue 05/05 12Z 0.82 2233 90 66 7 0.00
Tue 05/05 13Z 1.06 2331 90 76 7 0.00
Tue 05/05 14Z 1.09 2329 87 76 8 0.00
Tue 05/05 15Z 2.15 2226 86 62 8 0.00
Tue 05/05 16Z 7.72 2227 84 69 8 0.00
Tue 05/05 17Z 10.20 2225 82 75 9 0.00
Tue 05/05 18Z 11.14 2125 79 65 10 0.00
Tue 05/05 19Z 8.13 2126 80 91 10 0.00
Tue 05/05 20Z 5.87 2128 81 84 10 0.02
Tue 05/05 21Z 2.63 2229 85 90 11 0.07
Tue 05/05 22Z 1.57 2328 85 85 11 0.32
Tue 05/05 23Z 0.99 2130 83 93 11 0.02
Wed 05/06 00Z 1.10 2531 95 96 9 0.49
Wed 05/06 01Z 0.95 2628 94 90 9 0.11
Wed 05/06 02Z 1.04 2624 99 94 7 0.13
Wed 05/06 03Z 0.59 2622 95 84 7 0.16
Wed 05/06 04Z 0.56 2622 92 93 6 0.05
Wed 05/06 05Z 0.54 2621 89 93 5 0.03
Wed 05/06 06Z 0.48 2620 83 91 5 0.03
Wed 05/06 07Z 0.42 2618 92 96 4 0.04
Wed 05/06 08Z 0.37 2518 92 90 5 0.04
Wed 05/06 09Z 0.31 2416 87 85 6 0.02
Wed 05/06 10Z 0.30 2415 81 69 6 0.00
Wed 05/06 11Z 0.26 2315 80 88 6 0.00
Wed 05/06 12Z 0.26 2214 85 96 6 0.00
Wed 05/06 13Z 0.18 2114 91 98 6 0.02
Wed 05/06 14Z 0.17 2015 94 83 7 0.02
Wed 05/06 15Z 0.16 1916 97 71 8 0.02
Wed 05/06 16Z 0.14 1918 97 67 8 0.00
Wed 05/06 17Z 0.12 1819 97 79 8 0.01
Wed 05/06 18Z 0.08 1721 97 97 8 0.03
Wed 05/06 19Z 0.11 1724 98 98 8 0.08
Wed 05/06 20Z 0.16 1727 97 99 7 0.13
Wed 05/06 21Z 0.21 1729 97 99 5 0.15
Wed 05/06 22Z 0.12 1730 96 99 5 0.15
Wed 05/06 23Z 0.10 1730 98 98 5 0.12
Run total areal avg QPF for the Central_Greens is: 2.26 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