Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260331_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)
=== ===== === ==== ==== === === === ====
Tue 03/31 18Z 0.72 2422 97 87 7 0.00
Tue 03/31 19Z 0.67 2421 95 90 7 0.02
Tue 03/31 20Z 0.67 2323 98 83 8 0.03
Tue 03/31 21Z 0.70 2423 96 67 8 0.01
Tue 03/31 22Z 0.69 2423 95 55 9 0.01
Tue 03/31 23Z 0.56 2221 97 86 9 0.07
Wed 04/01 00Z 0.46 2024 98 98 9 0.26
Wed 04/01 01Z 0.64 2224 94 93 9 0.48
Wed 04/01 02Z 0.46 2119 94 95 10 0.25
Wed 04/01 03Z 0.47 2320 95 96 10 0.25
Wed 04/01 04Z 0.67 2231 98 89 10 0.17
Wed 04/01 05Z 1.08 2339 98 86 10 0.17
Wed 04/01 06Z 1.35 2438 98 94 9 0.18
Wed 04/01 07Z 1.16 2535 99 84 9 0.06
Wed 04/01 10Z 0.66 2730 99 48 7 0.04
Wed 04/01 11Z 0.47 2827 97 47 6 0.03
Wed 04/01 12Z 0.35 2924 95 36 5 0.03
Wed 04/01 13Z 0.30 3023 91 32 5 0.02
Wed 04/01 14Z 0.23 3122 84 23 5 0.02
Wed 04/01 15Z 0.19 3121 77 20 4 0.01
Wed 04/01 16Z 0.18 3220 73 16 3 0.01
Wed 04/01 17Z 0.18 3219 72 15 2 0.00
Wed 04/01 18Z 0.16 3217 70 14 1 0.00
Wed 04/01 20Z 0.12 3315 67 16 0 0.00
Wed 04/01 21Z 0.06 3413 64 19 0 0.00
Wed 04/01 22Z 0.03 3412 61 22 0 0.00
Wed 04/01 23Z 0.03 3411 59 25 0 0.00
Thu 04/02 00Z 0.02 3510 56 26 0 0.00
Thu 04/02 01Z 0.05 0009 52 26 0 0.00
Thu 04/02 02Z 0.09 0307 46 30 0 0.00
Thu 04/02 03Z 0.09 0505 46 32 0 0.00
Thu 04/02 04Z 0.11 0805 45 35 0 0.00
Thu 04/02 05Z 0.12 1107 46 40 0 0.00
Thu 04/02 06Z 0.09 1409 53 42 0 0.00
Thu 04/02 07Z 0.07 1511 61 45 0 0.00
Thu 04/02 08Z 0.06 1512 69 50 0 0.00
Thu 04/02 09Z 0.05 1610 70 56 0 0.00
Thu 04/02 10Z 0.07 1511 71 85 0 0.00
Thu 04/02 11Z 0.08 1513 69 94 1 0.00
Thu 04/02 12Z 0.08 1513 70 98 1 0.00
Thu 04/02 13Z 0.10 1412 75 99 1 0.00
Thu 04/02 14Z 0.12 1313 80 98 1 0.00
Thu 04/02 15Z 0.13 1314 84 97 1 0.01
Thu 04/02 16Z 0.11 1414 91 99 0 0.01
Thu 04/02 17Z 0.13 1415 95 99 0 0.01
Thu 04/02 18Z 0.13 1415 96 99 0 0.01
Thu 04/02 19Z 0.13 1416 96 98 0 0.02
Thu 04/02 20Z 0.10 1515 96 99 0 0.03
Thu 04/02 21Z 0.07 1516 96 98 1 0.02
Thu 04/02 22Z 0.04 1617 96 98 2 0.02
Thu 04/02 23Z 0.02 1619 96 96 2 0.02
Fri 04/03 00Z 0.05 1721 97 94 3 0.02
Fri 04/03 01Z 0.10 1822 97 81 4 0.02
Fri 04/03 04Z 0.19 2024 97 57 8 0.02
Fri 04/03 05Z 0.21 2025 95 44 9 0.02
Run total areal avg QPF for the Central_Greens is: 2.35 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