Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260819_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)
=== ===== === ==== ==== === === === ====
Wed 08/19 18Z 4.65 2509 83 62 12 0.00
Wed 08/19 19Z 2.95 2511 82 73 12 0.00
Wed 08/19 20Z 1.37 2413 84 85 13 0.00
Wed 08/19 21Z 1.35 2414 87 86 13 0.00
Wed 08/19 22Z 1.10 2514 83 83 13 0.00
Wed 08/19 23Z 1.20 2515 82 84 13 0.00
Thu 08/20 00Z 1.21 2517 84 77 13 0.00
Thu 08/20 01Z 1.13 2518 86 72 12 0.00
Thu 08/20 02Z 0.88 2617 88 62 12 0.00
Thu 08/20 03Z 0.62 2716 89 54 12 0.00
Thu 08/20 04Z 0.45 2814 84 44 13 0.00
Thu 08/20 05Z 0.40 2814 82 52 13 0.00
Thu 08/20 06Z 0.35 2914 79 53 13 0.00
Thu 08/20 07Z 0.25 3012 72 49 13 0.00
Thu 08/20 08Z 0.20 3010 70 51 13 0.00
Thu 08/20 09Z 0.18 3009 68 48 13 0.00
Thu 08/20 10Z 0.19 3010 68 50 13 0.00
Thu 08/20 11Z 0.17 3008 64 64 12 0.00
Thu 08/20 12Z 0.16 3108 65 68 12 0.00
Thu 08/20 13Z 0.15 3107 66 54 11 0.00
Thu 08/20 14Z 0.14 3106 67 24 11 0.00
Thu 08/20 15Z 0.20 3005 70 24 11 0.00
Thu 08/20 16Z 0.28 3002 73 18 10 0.00
Thu 08/20 17Z 0.50 3003 72 14 11 0.00
Thu 08/20 18Z 0.80 2904 69 14 11 0.00
Thu 08/20 19Z 0.27 2703 67 14 11 0.00
Thu 08/20 20Z 0.18 2803 66 18 11 0.00
Thu 08/20 21Z 0.16 2803 66 18 11 0.00
Thu 08/20 22Z 0.13 2903 67 15 11 0.00
Thu 08/20 23Z 0.13 3104 68 14 11 0.00
Fri 08/21 00Z 0.10 3204 68 13 10 0.00
Fri 08/21 01Z 0.09 3305 70 10 10 0.00
Fri 08/21 02Z 0.06 3506 73 12 10 0.00
Fri 08/21 03Z 0.05 0006 75 18 10 0.00
Fri 08/21 04Z 0.11 0007 77 19 9 0.00
Fri 08/21 05Z 0.18 0108 75 23 9 0.00
Fri 08/21 06Z 0.18 0208 73 22 9 0.00
Fri 08/21 07Z 0.21 0209 71 22 9 0.00
Fri 08/21 08Z 0.21 0208 71 23 9 0.00
Fri 08/21 09Z 0.26 0308 72 22 9 0.00
Fri 08/21 10Z 0.27 0408 72 19 9 0.00
Fri 08/21 11Z 0.27 0408 72 14 9 0.00
Fri 08/21 12Z 0.27 0408 72 12 9 0.00
Fri 08/21 13Z 0.28 0508 74 12 9 0.00
Fri 08/21 14Z 0.32 0607 78 12 8 0.00
Fri 08/21 15Z 0.49 0606 80 8 8 0.00
Fri 08/21 16Z 1.45 0704 81 7 8 0.00
Fri 08/21 17Z 1.09 0602 81 6 9 0.00
Fri 08/21 18Z 0.81 0601 81 6 9 0.00
Fri 08/21 19Z 0.40 0600 83 7 10 0.00
Fri 08/21 20Z 0.60 0702 84 7 10 0.00
Fri 08/21 21Z 0.64 0702 82 6 10 0.00
Fri 08/21 22Z 0.59 0703 82 6 10 0.00
Fri 08/21 23Z 0.47 0904 82 6 10 0.00
Sat 08/22 00Z 0.47 0905 83 6 10 0.00
Sat 08/22 01Z 0.49 1106 84 6 9 0.00
Sat 08/22 02Z 0.46 1207 86 6 9 0.00
Sat 08/22 03Z 0.36 1308 88 6 9 0.00
Sat 08/22 04Z 0.29 1408 86 6 9 0.00
Sat 08/22 05Z 0.26 1308 84 5 9 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