Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260819_0000
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 00Z 0.13 3105 79 37 13 0.00
Wed 08/19 01Z 0.14 3104 75 39 13 0.00
Wed 08/19 02Z 0.13 3205 71 37 13 0.00
Wed 08/19 03Z 0.10 3204 72 41 13 0.00
Wed 08/19 04Z 0.06 3303 76 39 12 0.00
Wed 08/19 05Z 0.07 3204 78 36 12 0.00
Wed 08/19 06Z 0.08 3204 80 18 12 0.00
Wed 08/19 07Z 0.06 3202 80 5 12 0.00
Wed 08/19 08Z 0.12 2903 79 4 12 0.00
Wed 08/19 09Z 0.13 2703 79 7 12 0.00
Wed 08/19 10Z 0.18 2504 79 11 11 0.00
Wed 08/19 11Z 0.23 2505 80 13 11 0.00
Wed 08/19 12Z 0.26 2406 82 19 11 0.00
Wed 08/19 13Z 0.29 2307 83 31 11 0.00
Wed 08/19 14Z 0.32 2308 82 51 11 0.00
Wed 08/19 15Z 0.33 2209 74 47 12 0.00
Wed 08/19 16Z 0.51 2311 68 49 12 0.00
Wed 08/19 17Z 0.54 2312 68 60 13 0.00
Wed 08/19 18Z 0.74 2413 67 78 13 0.00
Wed 08/19 19Z 1.11 2414 70 90 13 0.00
Wed 08/19 20Z 0.80 2315 79 86 13 0.00
Wed 08/19 21Z 0.98 2316 83 78 13 0.00
Wed 08/19 22Z 1.06 2317 84 73 13 0.00
Wed 08/19 23Z 0.99 2421 89 49 13 0.03
Thu 08/20 00Z 1.12 2622 89 48 13 0.02
Thu 08/20 01Z 0.92 2620 91 39 13 0.00
Thu 08/20 02Z 0.72 2619 87 17 13 0.00
Thu 08/20 03Z 0.55 2717 79 20 13 0.00
Thu 08/20 04Z 0.53 2718 77 16 13 0.01
Thu 08/20 05Z 0.51 2817 79 16 12 0.01
Thu 08/20 06Z 0.46 2817 88 16 12 0.01
Thu 08/20 07Z 0.41 2915 86 23 11 0.01
Thu 08/20 08Z 0.36 2915 86 16 11 0.00
Thu 08/20 09Z 0.32 3014 80 11 11 0.00
Thu 08/20 10Z 0.31 3014 79 9 11 0.00
Thu 08/20 11Z 0.28 3013 76 8 10 0.00
Thu 08/20 12Z 0.27 3012 72 9 10 0.00
Thu 08/20 13Z 0.21 3010 68 14 10 0.00
Thu 08/20 14Z 0.21 3008 67 34 10 0.00
Thu 08/20 15Z 0.25 2905 68 22 10 0.00
Thu 08/20 16Z 0.50 2704 63 54 10 0.00
Thu 08/20 17Z 0.57 2705 56 30 11 0.00
Thu 08/20 18Z 0.36 2705 53 40 11 0.00
Thu 08/20 19Z 0.39 2706 54 29 11 0.00
Thu 08/20 20Z 0.34 2607 58 31 11 0.00
Thu 08/20 21Z 0.30 2606 60 46 11 0.00
Thu 08/20 22Z 0.24 2605 61 41 11 0.00
Thu 08/20 23Z 0.29 2506 65 49 11 0.00
Fri 08/21 00Z 0.27 2606 70 31 11 0.00
Fri 08/21 01Z 0.19 2604 72 28 11 0.00
Fri 08/21 02Z 0.14 2803 73 28 10 0.00
Fri 08/21 03Z 0.07 3002 73 29 10 0.00
Fri 08/21 04Z 0.03 3402 74 31 10 0.00
Fri 08/21 05Z 0.03 0002 77 31 10 0.00
Fri 08/21 06Z 0.06 0202 79 31 10 0.00
Fri 08/21 07Z 0.07 0302 82 31 10 0.00
Fri 08/21 08Z 0.06 0203 82 26 10 0.00
Fri 08/21 09Z 0.06 0103 80 20 10 0.00
Fri 08/21 10Z 0.07 0203 78 16 10 0.00
Fri 08/21 11Z 0.11 0304 78 20 10 0.00
Run total areal avg QPF for the Central_Greens is: 0.09 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