Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260822_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)
=== ===== === ==== ==== === === === ====
Sat 08/22 18Z 0.74 1309 91 30 10 0.00
Sat 08/22 19Z 0.51 1211 92 31 11 0.00
Sat 08/22 20Z 0.48 1213 91 35 11 0.00
Sat 08/22 21Z 0.50 1214 92 32 11 0.00
Sat 08/22 22Z 0.57 1217 90 32 11 0.00
Sat 08/22 23Z 0.45 1319 84 32 11 0.00
Sun 08/23 00Z 0.36 1320 84 28 12 0.00
Sun 08/23 01Z 0.25 1419 86 25 12 0.00
Sun 08/23 02Z 0.19 1419 88 23 12 0.00
Sun 08/23 03Z 0.17 1519 88 29 12 0.01
Sun 08/23 04Z 0.13 1518 87 43 12 0.00
Sun 08/23 05Z 0.08 1618 88 58 11 0.00
Sun 08/23 06Z 0.04 1617 90 64 11 0.00
Sun 08/23 07Z 0.04 1715 91 61 11 0.00
Sun 08/23 08Z 0.05 1713 92 60 11 0.00
Sun 08/23 09Z 0.04 1712 92 59 11 0.00
Sun 08/23 10Z 0.05 1612 92 61 12 0.00
Sun 08/23 11Z 0.09 1514 94 68 12 0.01
Sun 08/23 12Z 0.12 1515 95 78 11 0.01
Sun 08/23 13Z 0.15 1517 96 72 12 0.01
Sun 08/23 14Z 0.16 1517 96 61 12 0.01
Sun 08/23 15Z 0.13 1517 96 63 12 0.01
Sun 08/23 16Z 0.08 1615 96 62 12 0.01
Sun 08/23 17Z 0.03 1613 96 61 12 0.00
Sun 08/23 18Z 0.08 1513 94 61 13 0.00
Sun 08/23 19Z 0.06 1613 94 64 13 0.00
Sun 08/23 20Z 0.09 1714 97 67 13 0.00
Sun 08/23 21Z 0.11 1813 98 52 13 0.01
Sun 08/23 22Z 0.18 1814 97 38 13 0.01
Sun 08/23 23Z 0.27 1915 97 25 13 0.02
Mon 08/24 00Z 0.38 2016 98 15 12 0.02
Mon 08/24 01Z 0.55 2218 98 44 12 0.03
Mon 08/24 02Z 0.60 2317 94 47 12 0.04
Mon 08/24 03Z 0.70 2418 91 55 11 0.03
Mon 08/24 04Z 0.63 2518 90 49 11 0.00
Mon 08/24 05Z 0.58 2417 87 42 11 0.00
Mon 08/24 06Z 0.50 2416 82 51 11 0.00
Mon 08/24 07Z 0.47 2416 82 25 11 0.00
Mon 08/24 08Z 0.41 2316 78 12 11 0.00
Mon 08/24 09Z 0.40 2316 80 25 11 0.00
Mon 08/24 10Z 0.38 2315 82 34 10 0.00
Mon 08/24 11Z 0.37 2315 84 41 10 0.00
Mon 08/24 12Z 0.36 2215 86 49 10 0.01
Mon 08/24 13Z 0.36 2215 84 55 9 0.00
Mon 08/24 14Z 0.39 2215 84 64 9 0.00
Mon 08/24 15Z 0.41 2215 80 63 9 0.00
Mon 08/24 16Z 0.56 2215 81 71 9 0.00
Mon 08/24 17Z 0.75 2214 82 59 8 0.00
Mon 08/24 18Z 2.62 2212 84 35 8 0.00
Mon 08/24 19Z 4.52 2212 83 20 9 0.00
Mon 08/24 20Z 4.27 2211 81 26 9 0.00
Mon 08/24 21Z 2.48 2111 77 41 9 0.00
Mon 08/24 22Z 1.12 2112 79 49 9 0.00
Mon 08/24 23Z 0.73 2215 80 83 9 0.00
Tue 08/25 00Z 0.65 2218 83 78 9 0.02
Tue 08/25 01Z 0.88 2322 86 86 9 0.01
Tue 08/25 02Z 0.95 2425 95 80 9 0.01
Tue 08/25 03Z 0.81 2524 86 85 8 0.02
Tue 08/25 04Z 0.85 2425 84 86 8 0.00
Tue 08/25 05Z 0.83 2425 91 88 8 0.00
Run total areal avg QPF for the Central_Greens is: 0.30 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