Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260831_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 08/31 12Z 0.04 3305 80 2 10 0.00
Mon 08/31 13Z 0.06 3204 78 3 10 0.00
Mon 08/31 14Z 0.06 3103 76 3 10 0.00
Mon 08/31 15Z 0.07 3002 75 1 10 0.00
Mon 08/31 16Z 0.09 2702 76 0 10 0.00
Mon 08/31 17Z 0.19 2602 75 0 10 0.00
Mon 08/31 18Z 0.31 2503 72 0 11 0.00
Mon 08/31 19Z 0.53 2503 69 9 11 0.00
Mon 08/31 20Z 0.43 2503 66 25 11 0.00
Mon 08/31 21Z 0.36 2504 66 35 11 0.00
Mon 08/31 22Z 0.28 2405 68 51 12 0.00
Mon 08/31 23Z 0.19 2404 69 80 12 0.00
Tue 09/01 00Z 0.13 2303 68 94 12 0.00
Tue 09/01 01Z 0.11 2203 71 96 12 0.00
Tue 09/01 02Z 0.10 2004 75 97 12 0.00
Tue 09/01 03Z 0.08 1904 79 97 12 0.00
Tue 09/01 04Z 0.07 1904 82 96 12 0.00
Tue 09/01 05Z 0.04 1804 84 96 12 0.00
Tue 09/01 06Z 0.03 1704 86 96 12 0.00
Tue 09/01 07Z 0.05 1505 88 96 12 0.01
Tue 09/01 08Z 0.10 1406 92 97 12 0.01
Tue 09/01 09Z 0.17 1309 94 97 12 0.01
Tue 09/01 10Z 0.17 1411 96 95 12 0.01
Tue 09/01 11Z 0.17 1412 95 88 12 0.01
Tue 09/01 12Z 0.19 1414 95 93 12 0.01
Tue 09/01 13Z 0.18 1417 96 97 13 0.02
Tue 09/01 14Z 0.15 1520 98 99 13 0.06
Tue 09/01 15Z 0.12 1519 98 97 13 0.14
Tue 09/01 16Z 0.16 1419 98 90 13 0.06
Tue 09/01 17Z 0.23 1420 98 99 13 0.10
Tue 09/01 18Z 0.37 1222 98 99 12 0.27
Tue 09/01 19Z 0.48 1124 97 97 11 0.30
Tue 09/01 20Z 0.59 1025 96 98 10 0.38
Tue 09/01 21Z 0.57 1125 94 95 10 0.12
Tue 09/01 22Z 0.52 1127 94 91 11 0.03
Tue 09/01 23Z 0.51 1231 93 89 11 0.01
Wed 09/02 00Z 0.49 1231 92 81 11 0.01
Wed 09/02 01Z 0.49 1231 93 74 10 0.01
Wed 09/02 02Z 0.47 1230 93 73 10 0.01
Wed 09/02 03Z 0.44 1329 92 72 10 0.01
Wed 09/02 04Z 0.42 1328 91 71 10 0.01
Wed 09/02 05Z 0.37 1326 89 68 10 0.01
Wed 09/02 06Z 0.32 1323 86 67 10 0.01
Wed 09/02 07Z 0.30 1322 84 68 10 0.01
Wed 09/02 08Z 0.29 1322 79 67 10 0.01
Wed 09/02 09Z 0.26 1321 76 69 10 0.00
Wed 09/02 10Z 0.23 1319 75 67 10 0.00
Wed 09/02 11Z 0.25 1319 73 59 10 0.00
Wed 09/02 12Z 0.23 1319 74 55 10 0.00
Wed 09/02 13Z 0.19 1418 74 55 10 0.00
Wed 09/02 14Z 0.14 1518 77 50 10 0.00
Wed 09/02 15Z 0.10 1517 77 42 10 0.00
Wed 09/02 16Z 0.05 1615 78 33 10 0.00
Wed 09/02 17Z 0.04 1613 81 26 10 0.00
Wed 09/02 18Z 0.05 1612 84 27 10 0.00
Wed 09/02 19Z 0.02 1611 87 46 9 0.00
Wed 09/02 20Z 0.06 1711 90 44 9 0.00
Wed 09/02 21Z 0.07 1611 90 51 10 0.00
Wed 09/02 22Z 0.06 1613 90 63 11 0.00
Wed 09/02 23Z 0.03 1615 90 78 12 0.00
Run total areal avg QPF for the Central_Greens is: 1.64 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