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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260427_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 04/27 12Z 0.18 0803 69 41 4 0.00
Mon 04/27 13Z 0.20 0903 70 37 4 0.00
Mon 04/27 14Z 0.35 0903 71 32 4 0.00
Mon 04/27 15Z 0.71 0903 71 30 4 0.00
Mon 04/27 16Z 0.99 1002 71 30 4 0.00
Mon 04/27 17Z 1.12 1102 70 30 5 0.00
Mon 04/27 18Z 0.80 1401 69 30 5 0.00
Mon 04/27 19Z 0.72 1700 70 32 5 0.00
Mon 04/27 20Z 0.48 2600 71 37 6 0.00
Mon 04/27 21Z 0.38 0700 72 37 6 0.01
Mon 04/27 22Z 0.60 1003 69 26 6 0.00
Mon 04/27 23Z 0.46 1304 66 23 6 0.00
Tue 04/28 00Z 0.37 1406 65 20 6 0.00
Tue 04/28 01Z 0.32 1508 66 16 6 0.00
Tue 04/28 02Z 0.23 1610 64 14 5 0.00
Tue 04/28 03Z 0.06 1711 63 14 5 0.00
Tue 04/28 04Z 0.07 1710 60 11 6 0.00
Tue 04/28 05Z 0.07 1710 58 11 6 0.00
Tue 04/28 06Z 0.10 1712 58 10 5 0.00
Tue 04/28 07Z 0.23 1613 55 10 5 0.00
Tue 04/28 08Z 0.07 1713 54 10 5 0.00
Tue 04/28 09Z 0.09 1813 54 9 5 0.00
Tue 04/28 10Z 0.18 1614 54 8 5 0.00
Tue 04/28 11Z 0.19 1617 55 8 5 0.00
Tue 04/28 12Z 0.30 1519 57 8 4 0.00
Tue 04/28 13Z 0.28 1521 61 7 4 0.00
Tue 04/28 14Z 0.34 1521 64 7 4 0.00
Tue 04/28 15Z 0.38 1620 67 6 4 0.00
Tue 04/28 16Z 0.99 1619 67 6 3 0.00
Tue 04/28 17Z 1.47 1618 66 6 4 0.00
Tue 04/28 18Z 2.23 1617 63 6 4 0.00
Tue 04/28 19Z 2.29 1618 62 7 4 0.00
Tue 04/28 20Z 1.32 1617 64 8 4 0.00
Tue 04/28 21Z 0.83 1617 66 11 4 0.00
Tue 04/28 22Z 0.54 1619 69 47 4 0.00
Tue 04/28 23Z 0.37 1622 71 74 4 0.00
Wed 04/29 00Z 0.19 1623 70 89 4 0.00
Wed 04/29 01Z 0.07 1723 69 94 4 0.00
Wed 04/29 02Z 0.05 1823 70 94 4 0.00
Wed 04/29 03Z 0.11 1923 72 94 4 0.00
Wed 04/29 04Z 0.12 1922 75 92 4 0.00
Wed 04/29 05Z 0.15 1921 73 89 4 0.00
Wed 04/29 06Z 0.22 2022 71 85 4 0.00
Wed 04/29 07Z 0.32 2123 77 87 4 0.00
Wed 04/29 08Z 0.28 2120 88 80 5 0.00
Wed 04/29 09Z 0.17 2114 90 62 7 0.00
Wed 04/29 10Z 0.15 2112 91 50 7 0.00
Wed 04/29 11Z 0.15 2211 92 44 7 0.00
Wed 04/29 12Z 0.10 2108 91 35 7 0.00
Wed 04/29 13Z 0.04 1907 89 32 7 0.00
Wed 04/29 14Z 0.03 1808 89 29 7 0.00
Wed 04/29 15Z 0.02 1709 89 27 6 0.00
Wed 04/29 16Z 0.03 1710 87 30 6 0.00
Wed 04/29 17Z 0.04 1711 85 34 6 0.00
Wed 04/29 18Z 0.15 1712 83 34 6 0.00
Wed 04/29 19Z 0.45 1613 82 35 6 0.00
Wed 04/29 20Z 0.53 1615 83 37 6 0.00
Wed 04/29 21Z 0.30 1617 84 36 6 0.00
Wed 04/29 22Z 0.26 1621 86 33 6 0.00
Wed 04/29 23Z 0.28 1624 86 35 6 0.00
Run total areal avg QPF for the greens is: 0.01 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