Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260425_1800
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)
=== ===== === ==== ==== === === === ====
Sat 04/25 18Z 0.46 0900 62 33 0 0.00
Sat 04/25 19Z 0.68 0801 61 32 0 0.00
Sat 04/25 20Z 0.72 1101 62 31 0 0.00
Sat 04/25 21Z 0.50 1101 63 30 1 0.00
Sat 04/25 22Z 0.33 0802 64 29 1 0.00
Sat 04/25 23Z 0.26 0802 65 30 0 0.00
Sun 04/26 00Z 0.21 0902 66 32 0 0.00
Sun 04/26 01Z 0.17 1102 66 33 0 0.00
Sun 04/26 02Z 0.16 0802 67 33 0 0.00
Sun 04/26 03Z 0.17 0702 67 32 0 0.00
Sun 04/26 04Z 0.18 0703 69 32 0 0.00
Sun 04/26 05Z 0.15 0602 69 34 0 0.00
Sun 04/26 06Z 0.09 0302 68 37 0 0.00
Sun 04/26 07Z 0.05 3502 68 37 0 0.00
Sun 04/26 08Z 0.07 0203 67 35 0 0.00
Sun 04/26 09Z 0.19 0405 65 31 0 0.00
Sun 04/26 10Z 0.15 0305 66 29 0 0.00
Sun 04/26 11Z 0.15 0305 65 30 0 0.00
Sun 04/26 12Z 0.17 0306 66 31 0 0.00
Sun 04/26 13Z 0.36 0306 67 30 0 0.00
Sun 04/26 14Z 1.27 0406 69 26 0 0.00
Sun 04/26 15Z 1.80 0305 71 24 0 0.00
Sun 04/26 16Z 0.87 0104 72 23 0 0.00
Sun 04/26 17Z 0.65 0005 72 21 1 0.00
Sun 04/26 18Z 0.45 0005 73 20 1 0.00
Sun 04/26 19Z 0.39 0005 74 16 1 0.00
Sun 04/26 20Z 0.50 0005 74 13 2 0.00
Sun 04/26 21Z 0.57 0105 73 12 2 0.00
Sun 04/26 22Z 0.47 0105 74 11 2 0.00
Sun 04/26 23Z 0.47 0305 73 10 2 0.00
Mon 04/27 00Z 0.38 0306 73 10 2 0.00
Mon 04/27 01Z 0.48 0306 72 11 2 0.00
Mon 04/27 02Z 0.55 0506 71 12 2 0.00
Mon 04/27 03Z 0.55 0506 71 13 2 0.00
Mon 04/27 04Z 0.57 0607 71 15 2 0.00
Mon 04/27 05Z 0.48 0706 71 17 2 0.00
Mon 04/27 06Z 0.36 0705 70 19 2 0.00
Mon 04/27 07Z 0.27 0704 69 22 2 0.00
Mon 04/27 08Z 0.17 0502 69 28 2 0.00
Mon 04/27 09Z 0.14 0303 70 35 2 0.00
Mon 04/27 10Z 0.21 0404 70 36 2 0.00
Mon 04/27 11Z 0.35 0606 70 36 2 0.00
Mon 04/27 12Z 0.34 0705 70 40 2 0.00
Mon 04/27 13Z 0.45 0705 70 40 2 0.00
Mon 04/27 14Z 1.02 0803 71 40 2 0.00
Mon 04/27 15Z 2.02 0904 71 38 2 0.00
Mon 04/27 16Z 1.73 1103 69 39 3 0.00
Mon 04/27 17Z 1.65 1203 66 38 4 0.00
Mon 04/27 18Z 2.61 1204 64 33 4 0.00
Mon 04/27 19Z 2.17 1304 61 31 5 0.00
Mon 04/27 20Z 1.81 1404 61 29 5 0.00
Mon 04/27 21Z 1.08 1504 61 28 5 0.00
Mon 04/27 22Z 0.45 1704 64 30 5 0.00
Mon 04/27 23Z 0.22 1605 64 27 5 0.00
Tue 04/28 00Z 0.08 1708 64 24 5 0.00
Tue 04/28 01Z 0.17 1910 64 23 5 0.00
Tue 04/28 02Z 0.11 1810 63 16 5 0.00
Tue 04/28 03Z 0.10 1810 61 12 5 0.00
Tue 04/28 04Z 0.06 1710 60 11 5 0.00
Tue 04/28 05Z 0.15 1612 56 10 5 0.00
Run total areal avg QPF for the 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