Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260831_0600
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 06Z 0.05 3415 88 5 10 0.00
Mon 08/31 07Z 0.03 3514 85 3 9 0.00
Mon 08/31 08Z 0.03 3510 83 2 9 0.00
Mon 08/31 09Z 0.06 3309 80 0 9 0.00
Mon 08/31 10Z 0.10 3208 74 0 10 0.00
Mon 08/31 11Z 0.07 3308 65 0 10 0.00
Mon 08/31 12Z 0.06 3308 62 0 11 0.00
Mon 08/31 13Z 0.07 3307 62 0 10 0.00
Mon 08/31 14Z 0.08 3206 63 0 10 0.00
Mon 08/31 15Z 0.06 3204 62 1 10 0.00
Mon 08/31 16Z 0.08 3103 65 4 10 0.00
Mon 08/31 17Z 0.12 2702 70 12 10 0.00
Mon 08/31 18Z 0.42 2604 71 21 11 0.00
Mon 08/31 19Z 0.54 2504 65 36 11 0.00
Mon 08/31 20Z 0.48 2404 60 53 11 0.00
Mon 08/31 21Z 0.28 2503 60 60 12 0.00
Mon 08/31 22Z 0.16 2303 60 79 12 0.00
Mon 08/31 23Z 0.10 2202 64 86 12 0.00
Tue 09/01 00Z 0.13 2004 69 79 11 0.00
Tue 09/01 01Z 0.13 2004 74 68 11 0.00
Tue 09/01 02Z 0.12 2004 78 60 11 0.00
Tue 09/01 03Z 0.13 2004 83 59 11 0.00
Tue 09/01 04Z 0.10 2004 87 52 11 0.00
Tue 09/01 05Z 0.10 2103 90 52 11 0.00
Tue 09/01 06Z 0.09 2103 92 48 11 0.00
Tue 09/01 07Z 0.08 2103 92 53 11 0.00
Tue 09/01 08Z 0.02 1602 91 43 12 0.00
Tue 09/01 09Z 0.08 1304 91 33 12 0.00
Tue 09/01 10Z 0.10 1406 92 30 12 0.00
Tue 09/01 11Z 0.10 1409 93 29 12 0.00
Tue 09/01 12Z 0.09 1512 95 25 12 0.01
Tue 09/01 13Z 0.11 1514 96 39 12 0.01
Tue 09/01 14Z 0.11 1514 96 60 12 0.01
Tue 09/01 15Z 0.12 1515 96 77 12 0.01
Tue 09/01 16Z 0.10 1515 96 92 12 0.01
Tue 09/01 17Z 0.11 1516 97 97 13 0.04
Tue 09/01 18Z 0.13 1517 98 97 13 0.07
Tue 09/01 19Z 0.13 1518 96 95 13 0.10
Tue 09/01 20Z 0.14 1519 96 86 13 0.07
Tue 09/01 21Z 0.14 1519 97 82 13 0.03
Tue 09/01 22Z 0.11 1519 97 78 13 0.05
Tue 09/01 23Z 0.10 1517 97 64 13 0.03
Wed 09/02 00Z 0.05 1616 97 50 14 0.04
Wed 09/02 01Z 0.05 1714 97 52 14 0.03
Wed 09/02 02Z 0.04 1613 98 42 14 0.03
Wed 09/02 03Z 0.04 1614 98 36 14 0.03
Wed 09/02 04Z 0.04 1617 98 30 13 0.04
Wed 09/02 05Z 0.03 1618 98 24 13 0.02
Wed 09/02 06Z 0.04 1618 98 14 13 0.02
Wed 09/02 07Z 0.03 1618 98 12 12 0.02
Wed 09/02 08Z 0.04 1618 97 11 12 0.02
Wed 09/02 09Z 0.04 1618 98 12 12 0.01
Wed 09/02 10Z 0.03 1617 97 13 12 0.01
Wed 09/02 11Z 0.06 1616 97 13 12 0.01
Wed 09/02 12Z 0.03 1716 96 14 12 0.01
Wed 09/02 13Z 0.04 1614 95 15 12 0.01
Wed 09/02 14Z 0.04 1715 95 15 12 0.01
Wed 09/02 15Z 0.05 1714 96 22 12 0.01
Wed 09/02 16Z 0.03 1713 94 37 12 0.01
Wed 09/02 17Z 0.02 1713 89 47 13 0.00
Run total areal avg QPF for the Central_Greens is: 0.77 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