Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260427_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 04/27 06Z 0.20 0605 61 49 4 0.00
Mon 04/27 07Z 0.18 0504 61 47 4 0.00
Mon 04/27 08Z 0.16 0404 62 45 4 0.00
Mon 04/27 09Z 0.13 0304 62 46 4 0.00
Mon 04/27 10Z 0.14 0205 64 48 4 0.00
Mon 04/27 11Z 0.19 0306 65 47 4 0.00
Mon 04/27 12Z 0.22 0406 66 42 4 0.00
Mon 04/27 13Z 0.23 0505 66 36 4 0.00
Mon 04/27 14Z 0.43 0605 66 31 4 0.00
Mon 04/27 15Z 1.30 0705 66 27 4 0.00
Mon 04/27 16Z 2.47 0804 64 25 4 0.00
Mon 04/27 17Z 1.81 1003 62 24 5 0.00
Mon 04/27 18Z 0.52 1501 62 25 5 0.00
Mon 04/27 19Z 0.46 0400 64 26 5 0.00
Mon 04/27 20Z 0.30 0500 64 26 6 0.00
Mon 04/27 21Z 0.71 0901 64 24 6 0.00
Mon 04/27 22Z 0.52 1303 62 21 6 0.00
Mon 04/27 23Z 0.07 1603 62 22 6 0.00
Tue 04/28 00Z 0.12 1504 62 17 6 0.00
Tue 04/28 01Z 0.09 1606 60 13 6 0.00
Tue 04/28 02Z 0.08 1708 61 12 6 0.00
Tue 04/28 03Z 0.10 1709 61 12 5 0.00
Tue 04/28 04Z 0.06 1707 60 11 5 0.00
Tue 04/28 05Z 0.05 1608 58 10 6 0.00
Tue 04/28 06Z 0.10 1609 57 10 5 0.00
Tue 04/28 07Z 0.13 1511 58 10 5 0.00
Tue 04/28 08Z 0.16 1810 60 9 5 0.00
Tue 04/28 09Z 0.13 1810 60 9 5 0.00
Tue 04/28 10Z 0.09 1612 56 9 5 0.00
Tue 04/28 11Z 0.08 1614 54 8 5 0.00
Tue 04/28 12Z 0.15 1517 53 8 5 0.00
Tue 04/28 13Z 0.18 1519 55 8 4 0.00
Tue 04/28 14Z 0.46 1618 59 8 4 0.00
Tue 04/28 15Z 0.63 1617 60 8 4 0.00
Tue 04/28 16Z 0.95 1615 60 8 5 0.00
Tue 04/28 17Z 1.04 1615 59 7 5 0.00
Tue 04/28 18Z 0.98 1614 59 7 5 0.00
Tue 04/28 19Z 1.76 1614 61 7 6 0.00
Tue 04/28 20Z 0.87 1615 63 7 6 0.00
Tue 04/28 21Z 1.93 1516 65 7 5 0.00
Tue 04/28 22Z 0.54 1716 67 10 5 0.00
Tue 04/28 23Z 0.25 1717 70 14 5 0.00
Wed 04/29 00Z 0.19 1718 75 62 4 0.00
Wed 04/29 01Z 0.07 1718 77 88 4 0.00
Wed 04/29 02Z 0.10 1818 77 98 4 0.00
Wed 04/29 03Z 0.12 1817 79 97 4 0.00
Wed 04/29 04Z 0.18 1917 79 95 4 0.00
Wed 04/29 05Z 0.21 1917 79 91 3 0.00
Wed 04/29 06Z 0.22 1916 69 82 3 0.00
Wed 04/29 07Z 0.18 1915 62 77 4 0.00
Wed 04/29 08Z 0.22 2015 58 79 4 0.00
Wed 04/29 09Z 0.33 2018 60 85 4 0.00
Wed 04/29 10Z 0.40 2120 67 88 4 0.00
Wed 04/29 11Z 0.18 1916 64 80 6 0.00
Wed 04/29 12Z 0.15 1914 66 73 6 0.00
Wed 04/29 13Z 0.09 1813 67 50 6 0.00
Wed 04/29 14Z 0.07 1813 68 40 6 0.00
Wed 04/29 15Z 0.07 1812 68 39 6 0.00
Wed 04/29 16Z 0.17 1712 66 42 5 0.00
Wed 04/29 17Z 0.26 1611 65 38 5 0.00
Run total areal avg QPF for the Central_Greens is: 0.00 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