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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260402_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)
=== ===== === ==== ==== === === === ====
Thu 04/02 18Z 0.08 1409 99 84 0 0.00
Thu 04/02 19Z 0.10 1412 97 91 0 0.00
Thu 04/02 20Z 0.11 1414 96 90 1 0.00
Thu 04/02 21Z 0.10 1416 95 86 1 0.00
Thu 04/02 22Z 0.08 1517 95 97 1 0.00
Thu 04/02 23Z 0.08 1520 95 99 1 0.01
Fri 04/03 00Z 0.05 1623 96 97 2 0.02
Fri 04/03 02Z 0.03 1725 97 88 3 0.02
Fri 04/03 03Z 0.07 1727 97 87 4 0.02
Fri 04/03 04Z 0.10 1828 98 86 4 0.02
Fri 04/03 05Z 0.15 1830 98 88 5 0.03
Fri 04/03 06Z 0.18 1930 97 79 7 0.03
Fri 04/03 07Z 0.24 1932 98 69 7 0.04
Fri 04/03 08Z 0.25 2032 97 73 9 0.03
Fri 04/03 09Z 0.29 2033 98 89 9 0.02
Fri 04/03 10Z 0.36 2136 98 87 10 0.04
Fri 04/03 11Z 0.40 2137 98 90 10 0.04
Fri 04/03 12Z 0.45 2239 98 90 11 0.04
Fri 04/03 13Z 0.47 2237 97 88 11 0.07
Fri 04/03 14Z 0.51 2338 98 88 11 0.05
Fri 04/03 15Z 0.58 2338 98 94 11 0.05
Fri 04/03 16Z 0.64 2438 96 75 11 0.03
Fri 04/03 17Z 0.66 2437 94 76 11 0.02
Fri 04/03 18Z 0.72 2537 95 85 11 0.01
Fri 04/03 19Z 0.76 2537 95 84 11 0.01
Fri 04/03 20Z 0.83 2537 95 51 11 0.02
Fri 04/03 21Z 0.93 2537 94 43 11 0.00
Fri 04/03 22Z 1.05 2538 93 57 10 0.00
Fri 04/03 23Z 1.13 2540 95 34 10 0.00
Sat 04/04 00Z 1.23 2541 96 24 10 0.01
Sat 04/04 01Z 1.30 2544 95 15 9 0.01
Sat 04/04 02Z 1.27 2642 93 12 9 0.01
Sat 04/04 03Z 1.32 2641 92 11 8 0.02
Sat 04/04 04Z 1.23 2739 88 13 7 0.02
Sat 04/04 05Z 0.99 2736 84 25 6 0.02
Sat 04/04 06Z 0.75 2834 81 41 6 0.02
Sat 04/04 07Z 0.56 2830 81 32 5 0.00
Sat 04/04 08Z 0.42 2926 83 18 3 0.00
Sat 04/04 09Z 0.30 3023 86 20 2 0.00
Sat 04/04 10Z 0.19 3120 86 15 2 0.00
Sat 04/04 11Z 0.11 3217 86 20 2 0.00
Sat 04/04 12Z 0.05 3414 86 21 2 0.00
Sat 04/04 13Z 0.05 3510 86 28 2 0.00
Sat 04/04 14Z 0.07 0206 86 33 3 0.00
Sat 04/04 15Z 0.09 0704 87 54 3 0.00
Sat 04/04 16Z 0.10 1106 89 45 2 0.00
Sat 04/04 17Z 0.10 1308 86 46 3 0.00
Sat 04/04 18Z 0.11 1410 85 62 3 0.00
Sat 04/04 19Z 0.13 1513 84 49 3 0.00
Sat 04/04 20Z 0.15 1517 84 31 3 0.00
Sat 04/04 21Z 0.12 1520 84 40 4 0.00
Sat 04/04 22Z 0.05 1621 82 97 5 0.00
Sat 04/04 23Z 0.04 1623 82 97 5 0.00
Sun 04/05 00Z 0.05 1624 85 93 5 0.01
Sun 04/05 01Z 0.05 1626 86 93 6 0.01
Sun 04/05 02Z 0.04 1728 90 94 6 0.00
Sun 04/05 03Z 0.04 1730 93 79 7 0.00
Sun 04/05 04Z 0.07 1732 95 87 7 0.00
Sun 04/05 05Z 0.08 1734 96 94 8 0.01
Run total areal avg QPF for the Central_Greens is: 0.76 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