Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260806_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)
=== ===== === ==== ==== === === === ====
Thu 08/06 00Z 0.32 2409 80 42 16 0.00
Thu 08/06 01Z 0.38 2410 77 55 16 0.00
Thu 08/06 02Z 0.41 2411 77 62 16 0.00
Thu 08/06 03Z 0.43 2412 77 61 16 0.00
Thu 08/06 04Z 0.41 2312 76 54 16 0.00
Thu 08/06 05Z 0.41 2312 76 48 16 0.00
Thu 08/06 06Z 0.39 2411 76 57 16 0.00
Thu 08/06 07Z 0.37 2411 75 65 16 0.00
Thu 08/06 08Z 0.36 2411 76 72 16 0.00
Thu 08/06 09Z 0.29 2409 73 77 16 0.00
Thu 08/06 10Z 0.25 2408 73 81 16 0.00
Thu 08/06 11Z 0.21 2407 74 80 16 0.00
Thu 08/06 12Z 0.17 2306 75 78 16 0.00
Thu 08/06 13Z 0.16 2106 76 76 16 0.00
Thu 08/06 14Z 0.17 2206 79 78 16 0.00
Thu 08/06 15Z 0.20 2305 82 79 16 0.00
Thu 08/06 16Z 0.24 2205 82 81 16 0.00
Thu 08/06 17Z 0.39 2205 81 82 16 0.00
Thu 08/06 18Z 0.80 2205 81 83 17 0.00
Thu 08/06 19Z 0.85 2205 82 80 17 0.00
Thu 08/06 20Z 0.81 2205 85 80 17 0.00
Thu 08/06 21Z 0.66 2206 88 82 17 0.02
Thu 08/06 22Z 0.43 2205 89 84 17 0.17
Thu 08/06 23Z 0.28 2604 88 79 17 0.25
Fri 08/07 00Z 0.15 3006 88 81 17 0.18
Fri 08/07 01Z 0.20 2705 86 72 17 0.12
Fri 08/07 02Z 0.22 2707 85 77 17 0.00
Fri 08/07 03Z 0.23 2808 84 73 17 0.00
Fri 08/07 04Z 0.22 2908 84 62 17 0.00
Fri 08/07 05Z 0.21 2908 86 51 17 0.00
Fri 08/07 06Z 0.22 2908 89 47 17 0.00
Fri 08/07 07Z 0.21 2908 91 54 17 0.00
Fri 08/07 08Z 0.19 3008 92 60 17 0.00
Fri 08/07 09Z 0.14 3107 92 50 16 0.00
Fri 08/07 10Z 0.15 3006 92 43 16 0.00
Fri 08/07 11Z 0.15 2905 89 33 16 0.00
Fri 08/07 12Z 0.13 2905 86 36 16 0.00
Fri 08/07 13Z 0.13 2905 85 37 16 0.00
Fri 08/07 14Z 0.13 2904 84 34 16 0.00
Fri 08/07 15Z 0.15 2804 83 34 15 0.00
Fri 08/07 16Z 0.15 2603 82 37 16 0.00
Fri 08/07 17Z 0.21 2604 80 43 16 0.00
Fri 08/07 18Z 0.35 2603 76 46 16 0.00
Fri 08/07 19Z 0.60 2704 75 45 16 0.00
Fri 08/07 20Z 0.52 2805 73 46 16 0.00
Fri 08/07 21Z 0.27 2803 72 50 17 0.00
Fri 08/07 22Z 0.19 2703 73 59 17 0.00
Fri 08/07 23Z 0.16 2703 74 54 17 0.00
Sat 08/08 00Z 0.18 2603 76 56 16 0.00
Sat 08/08 01Z 0.19 2404 80 53 16 0.00
Sat 08/08 02Z 0.25 2405 82 72 16 0.00
Sat 08/08 03Z 0.27 2406 85 78 16 0.00
Sat 08/08 04Z 0.31 2407 87 81 16 0.00
Sat 08/08 05Z 0.32 2308 88 79 16 0.00
Sat 08/08 06Z 0.34 2309 87 76 16 0.00
Sat 08/08 07Z 0.36 2311 87 76 16 0.00
Sat 08/08 08Z 0.38 2311 89 79 16 0.00
Sat 08/08 09Z 0.31 2210 88 80 16 0.00
Sat 08/08 10Z 0.32 2211 90 83 16 0.00
Sat 08/08 11Z 0.34 2212 90 82 16 0.00
Run total areal avg QPF for the Central_Greens is: 0.74 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