Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260819_1200
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 12Z 0.20 2405 85 24 11 0.00
Wed 08/19 13Z 0.23 2306 83 27 12 0.00
Wed 08/19 14Z 0.30 2207 81 32 12 0.00
Wed 08/19 15Z 0.54 2308 76 40 12 0.00
Wed 08/19 16Z 1.19 2409 71 46 12 0.00
Wed 08/19 17Z 1.22 2411 68 59 12 0.00
Wed 08/19 18Z 1.25 2513 67 69 13 0.00
Wed 08/19 19Z 0.99 2415 70 77 13 0.00
Wed 08/19 20Z 1.12 2518 82 89 12 0.00
Wed 08/19 21Z 1.17 2516 84 85 13 0.00
Wed 08/19 22Z 1.37 2516 89 87 13 0.01
Wed 08/19 23Z 0.82 2516 89 79 12 0.02
Thu 08/20 00Z 0.90 2618 87 67 13 0.00
Thu 08/20 01Z 0.82 2618 87 45 12 0.00
Thu 08/20 02Z 0.62 2616 85 23 13 0.00
Thu 08/20 03Z 0.52 2616 83 21 13 0.00
Thu 08/20 04Z 0.44 2715 75 28 13 0.00
Thu 08/20 05Z 0.41 2815 73 37 13 0.00
Thu 08/20 06Z 0.38 2916 73 31 13 0.00
Thu 08/20 07Z 0.37 2916 74 24 12 0.00
Thu 08/20 08Z 0.28 3014 76 25 12 0.00
Thu 08/20 09Z 0.25 3113 75 33 12 0.00
Thu 08/20 10Z 0.23 3112 74 16 11 0.00
Thu 08/20 11Z 0.23 3111 74 12 11 0.00
Thu 08/20 12Z 0.22 3110 73 13 10 0.00
Thu 08/20 13Z 0.19 3109 70 12 10 0.00
Thu 08/20 14Z 0.22 3007 70 13 10 0.00
Thu 08/20 16Z 0.51 3003 69 9 10 0.00
Thu 08/20 17Z 1.04 2804 63 19 10 0.00
Thu 08/20 18Z 0.65 2903 58 9 11 0.00
Thu 08/20 19Z 0.84 2804 58 11 11 0.00
Thu 08/20 20Z 0.58 2805 58 19 11 0.00
Thu 08/20 21Z 0.33 2704 61 14 11 0.00
Thu 08/20 22Z 0.30 2705 66 10 11 0.00
Thu 08/20 23Z 0.25 2804 71 12 11 0.00
Fri 08/21 00Z 0.23 2804 75 12 11 0.00
Fri 08/21 01Z 0.20 2904 78 14 10 0.00
Fri 08/21 02Z 0.19 2803 80 18 10 0.00
Fri 08/21 03Z 0.14 2802 82 16 10 0.00
Fri 08/21 04Z 0.12 2902 84 17 10 0.00
Fri 08/21 05Z 0.10 2902 84 18 10 0.00
Fri 08/21 06Z 0.06 2801 85 18 10 0.00
Fri 08/21 07Z 0.06 2501 85 18 9 0.00
Fri 08/21 08Z 0.06 1800 85 18 9 0.00
Fri 08/21 10Z 0.08 1501 86 19 9 0.00
Fri 08/21 11Z 0.10 1302 87 19 9 0.00
Fri 08/21 13Z 0.14 1407 88 21 9 0.00
Fri 08/21 14Z 0.17 1409 87 21 9 0.00
Fri 08/21 15Z 0.17 1408 86 22 9 0.00
Fri 08/21 16Z 0.49 1407 85 22 9 0.00
Fri 08/21 17Z 0.98 1407 84 24 9 0.00
Fri 08/21 18Z 0.83 1406 85 27 10 0.00
Fri 08/21 20Z 0.12 1505 88 30 10 0.00
Fri 08/21 21Z 0.08 1504 90 34 10 0.00
Fri 08/21 22Z 0.11 1405 90 39 11 0.00
Fri 08/21 23Z 0.08 1406 90 42 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.03 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