Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260916_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 09/16 12Z 0.30 2813 86 57 13 0.00
Wed 09/16 13Z 0.30 2813 89 51 13 0.00
Wed 09/16 14Z 0.27 2811 90 51 13 0.00
Wed 09/16 15Z 0.25 2810 91 60 13 0.00
Wed 09/16 16Z 0.25 2809 92 62 13 0.00
Wed 09/16 17Z 0.26 2709 94 63 13 0.00
Wed 09/16 18Z 0.28 2709 95 49 13 0.00
Wed 09/16 19Z 0.30 2708 94 47 13 0.00
Wed 09/16 20Z 0.32 2809 94 44 13 0.00
Wed 09/16 21Z 0.34 2810 94 37 13 0.00
Wed 09/16 22Z 0.33 2810 95 33 13 0.00
Wed 09/16 23Z 0.27 2808 95 29 13 0.00
Thu 09/17 00Z 0.27 2808 97 27 13 0.01
Thu 09/17 01Z 0.28 2809 97 25 13 0.01
Thu 09/17 02Z 0.23 2908 97 26 13 0.00
Thu 09/17 03Z 0.21 2808 97 27 13 0.00
Thu 09/17 04Z 0.16 2806 97 26 13 0.01
Thu 09/17 05Z 0.13 2804 97 23 13 0.01
Thu 09/17 06Z 0.12 2604 97 20 13 0.01
Thu 09/17 07Z 0.11 2403 97 17 13 0.01
Thu 09/17 08Z 0.12 2304 98 18 13 0.01
Thu 09/17 09Z 0.12 2305 99 20 13 0.01
Thu 09/17 10Z 0.14 2206 100 27 13 0.01
Thu 09/17 11Z 0.16 2108 100 27 13 0.01
Thu 09/17 12Z 0.20 2208 100 24 12 0.01
Thu 09/17 13Z 0.23 2209 99 29 12 0.01
Thu 09/17 14Z 0.26 2309 99 34 13 0.01
Thu 09/17 15Z 0.26 2409 99 32 13 0.01
Thu 09/17 16Z 0.27 2409 98 35 13 0.01
Thu 09/17 17Z 0.27 2409 97 41 13 0.00
Thu 09/17 18Z 0.29 2410 99 41 13 0.01
Thu 09/17 19Z 0.28 2409 100 55 13 0.02
Thu 09/17 20Z 0.22 2507 99 61 13 0.03
Thu 09/17 21Z 0.20 2606 99 88 13 0.05
Thu 09/17 22Z 0.17 2806 97 97 13 0.02
Thu 09/17 23Z 0.12 3005 91 95 13 0.03
Fri 09/18 00Z 0.11 2904 87 86 13 0.01
Fri 09/18 01Z 0.10 3005 87 76 13 0.00
Fri 09/18 02Z 0.12 3006 86 74 13 0.00
Fri 09/18 03Z 0.13 3007 82 78 13 0.00
Fri 09/18 04Z 0.14 3110 76 82 12 0.00
Fri 09/18 05Z 0.16 3112 66 84 12 0.00
Fri 09/18 06Z 0.14 3213 54 81 12 0.00
Fri 09/18 07Z 0.13 3215 49 87 12 0.00
Fri 09/18 08Z 0.11 3316 43 81 11 0.00
Fri 09/18 09Z 0.11 3319 49 82 10 0.00
Fri 09/18 10Z 0.12 3320 50 80 10 0.00
Fri 09/18 11Z 0.12 3321 55 55 9 0.00
Fri 09/18 12Z 0.14 3323 66 33 8 0.00
Fri 09/18 13Z 0.14 3323 74 22 7 0.00
Fri 09/18 14Z 0.15 3322 74 15 7 0.00
Fri 09/18 15Z 0.16 3321 74 11 6 0.00
Fri 09/18 16Z 0.35 3320 79 6 5 0.00
Fri 09/18 17Z 0.94 3219 84 2 5 0.00
Fri 09/18 18Z 0.94 3217 86 1 5 0.00
Fri 09/18 19Z 3.07 3218 82 2 5 0.00
Fri 09/18 20Z 3.28 3219 81 3 5 0.00
Fri 09/18 21Z 2.33 3220 78 3 5 0.00
Fri 09/18 22Z 0.80 3223 76 3 4 0.00
Fri 09/18 23Z 0.39 3325 71 3 4 0.00
Run total areal avg QPF for the Central_Greens is: 0.32 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