Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260425_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)
=== ===== === ==== ==== === === === ====
Sat 04/25 06Z 0.26 1008 72 21 -2 0.00
Sat 04/25 07Z 0.18 1309 73 21 -3 0.00
Sat 04/25 08Z 0.12 1409 75 21 -3 0.00
Sat 04/25 09Z 0.05 1608 75 21 -2 0.00
Sat 04/25 10Z 0.03 1607 73 21 -2 0.00
Sat 04/25 11Z 0.04 1506 73 20 -2 0.00
Sat 04/25 12Z 0.04 1506 73 19 -2 0.00
Sat 04/25 13Z 0.04 1605 74 19 -2 0.00
Sat 04/25 14Z 0.31 1405 73 18 -2 0.00
Sat 04/25 15Z 0.90 1405 73 18 -2 0.00
Sat 04/25 16Z 0.61 1505 71 18 -2 0.00
Sat 04/25 17Z 0.55 1503 69 19 -1 0.00
Sat 04/25 18Z 0.43 1503 69 19 0 0.00
Sat 04/25 19Z 0.80 1403 69 19 0 0.00
Sat 04/25 20Z 0.49 1302 70 19 0 0.00
Sat 04/25 21Z 0.54 1202 70 20 0 0.00
Sat 04/25 22Z 0.39 1002 70 23 0 0.00
Sat 04/25 23Z 0.42 0904 70 31 0 0.00
Sun 04/26 00Z 0.40 0906 67 42 0 0.00
Sun 04/26 01Z 0.38 1007 67 47 0 0.00
Sun 04/26 02Z 0.33 1106 69 49 0 0.00
Sun 04/26 03Z 0.26 1105 69 51 0 0.00
Sun 04/26 04Z 0.23 1105 68 51 0 0.00
Sun 04/26 05Z 0.22 1005 67 44 0 0.00
Sun 04/26 06Z 0.23 0905 67 38 0 0.00
Sun 04/26 07Z 0.23 0804 68 34 0 0.00
Sun 04/26 08Z 0.19 0604 69 31 0 0.00
Sun 04/26 09Z 0.25 0605 69 28 0 0.00
Sun 04/26 10Z 0.36 0607 68 28 0 0.00
Sun 04/26 11Z 0.46 0709 68 27 0 0.00
Sun 04/26 12Z 0.48 0709 67 22 0 0.00
Sun 04/26 13Z 0.95 0808 67 19 0 0.00
Sun 04/26 14Z 3.10 0907 69 16 0 0.00
Sun 04/26 15Z 3.58 0805 69 14 0 0.00
Sun 04/26 16Z 2.68 0504 68 12 0 0.00
Sun 04/26 17Z 2.10 0304 67 12 1 0.00
Sun 04/26 18Z 2.03 0305 65 11 1 0.00
Sun 04/26 19Z 1.84 0304 65 10 2 0.00
Sun 04/26 20Z 1.67 0304 65 11 2 0.00
Sun 04/26 21Z 1.73 0405 65 13 2 0.00
Sun 04/26 22Z 1.79 0506 66 27 3 0.00
Sun 04/26 23Z 1.00 0507 66 43 3 0.00
Mon 04/27 00Z 0.66 0608 65 50 2 0.00
Mon 04/27 01Z 0.56 0608 66 63 2 0.00
Mon 04/27 02Z 0.52 0608 67 68 2 0.00
Mon 04/27 03Z 0.46 0608 66 61 2 0.00
Mon 04/27 04Z 0.48 0609 66 55 2 0.00
Mon 04/27 05Z 0.54 0610 67 50 2 0.00
Mon 04/27 06Z 0.60 0711 68 48 2 0.00
Mon 04/27 07Z 0.65 0713 71 50 2 0.00
Mon 04/27 08Z 0.62 0714 70 56 2 0.00
Mon 04/27 09Z 0.59 0815 66 59 3 0.00
Mon 04/27 10Z 0.57 0816 61 58 3 0.00
Mon 04/27 11Z 0.56 0918 54 53 2 0.00
Mon 04/27 12Z 0.56 1018 59 48 2 0.00
Mon 04/27 13Z 0.50 1015 65 49 2 0.00
Mon 04/27 14Z 0.54 1012 65 50 2 0.00
Mon 04/27 15Z 1.21 1010 65 49 2 0.00
Mon 04/27 16Z 3.79 1007 64 47 2 0.00
Mon 04/27 17Z 4.31 0906 64 46 3 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