Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260831_0000
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 00Z 0.67 2819 91 93 11 0.00
Mon 08/31 01Z 0.69 2921 93 83 10 0.00
Mon 08/31 02Z 0.51 3120 97 77 10 0.01
Mon 08/31 03Z 0.33 3219 92 58 10 0.00
Mon 08/31 04Z 0.21 3318 87 25 10 0.00
Mon 08/31 05Z 0.13 3316 83 7 10 0.00
Mon 08/31 06Z 0.09 3314 80 6 10 0.00
Mon 08/31 07Z 0.07 3412 78 2 10 0.00
Mon 08/31 08Z 0.06 3410 78 1 10 0.00
Mon 08/31 09Z 0.06 3410 80 1 10 0.00
Mon 08/31 10Z 0.05 3309 80 1 10 0.00
Mon 08/31 11Z 0.06 3308 77 1 10 0.00
Mon 08/31 12Z 0.08 3308 74 1 10 0.00
Mon 08/31 13Z 0.08 3207 72 2 10 0.00
Mon 08/31 14Z 0.09 3206 70 2 10 0.00
Mon 08/31 15Z 0.09 3104 70 3 10 0.00
Mon 08/31 16Z 0.13 2803 73 7 10 0.00
Mon 08/31 17Z 0.34 2503 75 12 10 0.00
Mon 08/31 18Z 0.59 2504 73 19 10 0.00
Mon 08/31 19Z 0.92 2505 72 29 11 0.00
Mon 08/31 20Z 0.50 2504 72 34 11 0.00
Mon 08/31 21Z 0.37 2404 73 34 11 0.00
Mon 08/31 22Z 0.26 2404 76 40 11 0.00
Mon 08/31 23Z 0.20 2304 76 40 11 0.00
Tue 09/01 00Z 0.24 2305 79 45 11 0.00
Tue 09/01 01Z 0.21 2304 82 50 11 0.00
Tue 09/01 02Z 0.19 2204 84 49 11 0.00
Tue 09/01 03Z 0.17 2304 87 50 11 0.00
Tue 09/01 04Z 0.12 2203 89 52 11 0.00
Tue 09/01 05Z 0.09 2103 91 55 11 0.00
Tue 09/01 06Z 0.03 1703 93 67 11 0.00
Tue 09/01 07Z 0.05 1504 95 83 11 0.00
Tue 09/01 08Z 0.08 1406 96 88 11 0.02
Tue 09/01 09Z 0.09 1406 97 83 11 0.01
Tue 09/01 10Z 0.09 1408 97 74 11 0.01
Tue 09/01 11Z 0.07 1509 98 74 12 0.01
Tue 09/01 12Z 0.10 1511 98 75 12 0.02
Tue 09/01 13Z 0.11 1412 98 80 12 0.01
Tue 09/01 14Z 0.10 1512 97 85 12 0.01
Tue 09/01 15Z 0.09 1513 97 92 12 0.01
Tue 09/01 16Z 0.11 1514 97 95 12 0.01
Tue 09/01 17Z 0.14 1413 96 97 12 0.01
Tue 09/01 18Z 0.17 1413 95 97 12 0.01
Tue 09/01 19Z 0.18 1314 95 95 12 0.01
Tue 09/01 20Z 0.15 1413 95 97 12 0.01
Tue 09/01 21Z 0.13 1413 95 99 12 0.01
Tue 09/01 22Z 0.14 1414 97 99 12 0.01
Tue 09/01 23Z 0.14 1414 97 97 12 0.01
Wed 09/02 00Z 0.12 1515 96 91 12 0.01
Wed 09/02 01Z 0.12 1516 96 80 12 0.01
Wed 09/02 02Z 0.10 1517 96 69 12 0.01
Wed 09/02 03Z 0.11 1517 96 47 12 0.01
Wed 09/02 04Z 0.08 1619 97 54 12 0.01
Wed 09/02 05Z 0.05 1620 97 54 13 0.02
Wed 09/02 06Z 0.05 1620 97 39 13 0.02
Wed 09/02 07Z 0.04 1619 97 38 13 0.02
Wed 09/02 08Z 0.05 1719 97 45 13 0.01
Wed 09/02 09Z 0.04 1719 97 31 13 0.02
Wed 09/02 10Z 0.05 1719 97 18 13 0.02
Wed 09/02 11Z 0.10 1818 98 33 12 0.01
Run total areal avg QPF for the Central_Greens is: 0.36 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