Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260428_1800
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)
=== ===== === ==== ==== === === === ====
Tue 04/28 18Z 2.00 1512 55 11 7 0.00
Tue 04/28 19Z 1.89 1514 56 12 7 0.00
Tue 04/28 20Z 0.75 1614 57 17 7 0.00
Tue 04/28 21Z 0.51 1614 61 16 7 0.00
Tue 04/28 22Z 0.62 1516 64 6 6 0.00
Tue 04/28 23Z 0.44 1519 68 3 5 0.00
Wed 04/29 00Z 0.28 1522 72 20 5 0.00
Wed 04/29 01Z 0.11 1623 71 58 5 0.00
Wed 04/29 02Z 0.05 1621 66 78 5 0.00
Wed 04/29 03Z 0.09 1721 64 87 5 0.00
Wed 04/29 04Z 0.20 1821 68 84 4 0.00
Wed 04/29 05Z 0.23 1919 73 77 4 0.00
Wed 04/29 06Z 0.25 1918 70 78 4 0.00
Wed 04/29 07Z 0.25 2017 69 78 4 0.00
Wed 04/29 08Z 0.25 2017 67 65 4 0.00
Wed 04/29 09Z 0.17 2014 64 51 6 0.00
Wed 04/29 10Z 0.18 2014 67 48 6 0.00
Wed 04/29 11Z 0.23 2114 72 47 6 0.00
Wed 04/29 12Z 0.20 2112 78 40 6 0.00
Wed 04/29 13Z 0.11 2008 79 31 7 0.00
Wed 04/29 14Z 0.07 1907 79 31 7 0.00
Wed 04/29 15Z 0.10 1908 81 36 6 0.00
Wed 04/29 16Z 0.10 1607 81 32 6 0.00
Wed 04/29 17Z 0.19 1608 80 38 6 0.00
Wed 04/29 18Z 0.76 1509 77 39 6 0.00
Wed 04/29 19Z 1.66 1511 76 42 6 0.00
Wed 04/29 20Z 1.81 1511 75 51 6 0.00
Wed 04/29 21Z 1.86 1512 75 52 6 0.00
Wed 04/29 22Z 2.19 1414 77 45 6 0.00
Wed 04/29 23Z 0.36 1515 80 42 6 0.00
Thu 04/30 00Z 0.16 1517 87 39 7 0.00
Thu 04/30 01Z 0.11 1519 83 40 7 0.00
Thu 04/30 02Z 0.09 1520 77 43 7 0.00
Thu 04/30 03Z 0.07 1622 73 47 7 0.00
Thu 04/30 04Z 0.08 1623 72 49 7 0.00
Thu 04/30 05Z 0.09 1525 81 57 7 0.01
Thu 04/30 06Z 0.09 1525 91 68 7 0.01
Thu 04/30 07Z 0.11 1526 94 73 7 0.01
Thu 04/30 08Z 0.16 1527 95 55 7 0.01
Thu 04/30 09Z 0.13 1527 96 74 7 0.02
Thu 04/30 10Z 0.09 1526 98 89 6 0.04
Thu 04/30 11Z 0.03 1623 98 95 5 0.07
Thu 04/30 12Z 0.04 1717 98 93 5 0.07
Thu 04/30 13Z 0.04 1614 98 97 3 0.09
Thu 04/30 14Z 0.04 1612 98 99 3 0.05
Thu 04/30 15Z 0.04 1708 99 96 2 0.03
Thu 04/30 16Z 0.06 1805 99 96 1 0.02
Thu 04/30 17Z 0.12 2105 99 99 1 0.04
Thu 04/30 18Z 0.24 2506 99 98 1 0.03
Thu 04/30 19Z 0.33 2708 99 97 0 0.03
Thu 04/30 20Z 0.45 2912 99 97 0 0.03
Thu 04/30 21Z 0.43 3015 98 95 0 0.02
Thu 04/30 22Z 0.40 3117 97 93 0 0.01
Thu 04/30 23Z 0.46 3017 97 94 -1 0.02
Fri 05/01 00Z 0.46 3018 97 90 -2 0.01
Fri 05/01 01Z 0.51 3020 97 79 -2 0.01
Fri 05/01 02Z 0.56 3020 96 63 -3 0.01
Fri 05/01 03Z 0.59 3021 96 48 -3 0.01
Fri 05/01 04Z 0.60 3021 95 44 -4 0.00
Fri 05/01 05Z 0.55 3021 95 43 -4 0.00
Run total areal avg QPF for the Central_Greens is: 0.65 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