Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260709_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)
=== ===== === ==== ==== === === === ====
Thu 07/09 12Z 0.38 2913 86 27 15 0.00
Thu 07/09 13Z 0.34 2911 80 18 15 0.00
Thu 07/09 14Z 0.36 2809 80 21 15 0.00
Thu 07/09 15Z 0.54 2806 79 21 15 0.00
Thu 07/09 16Z 0.82 2604 77 14 15 0.00
Thu 07/09 17Z 1.62 2305 75 12 16 0.00
Thu 07/09 18Z 2.38 2206 74 13 16 0.00
Thu 07/09 19Z 3.60 2109 76 32 16 0.00
Thu 07/09 20Z 3.77 2211 75 36 16 0.00
Thu 07/09 21Z 3.20 2313 77 28 16 0.00
Thu 07/09 22Z 1.02 2313 85 33 16 0.00
Thu 07/09 23Z 0.58 2413 86 51 16 0.01
Fri 07/10 00Z 0.65 2414 89 49 16 0.03
Fri 07/10 01Z 0.52 2413 91 53 16 0.01
Fri 07/10 02Z 0.50 2413 92 57 16 0.03
Fri 07/10 03Z 0.46 2514 94 57 16 0.04
Fri 07/10 04Z 0.41 2613 94 74 16 0.02
Fri 07/10 05Z 0.41 2713 92 70 16 0.01
Fri 07/10 06Z 0.42 2814 93 66 15 0.01
Fri 07/10 07Z 0.44 2816 92 70 15 0.01
Fri 07/10 08Z 0.43 2917 93 67 14 0.01
Fri 07/10 09Z 0.35 3017 96 68 14 0.01
Fri 07/10 10Z 0.26 3217 98 70 13 0.01
Fri 07/10 11Z 0.15 3316 97 70 13 0.01
Fri 07/10 12Z 0.11 3315 95 74 13 0.01
Fri 07/10 13Z 0.05 3414 90 71 13 0.00
Fri 07/10 14Z 0.06 3412 87 73 13 0.00
Fri 07/10 15Z 0.06 3411 86 79 13 0.00
Fri 07/10 16Z 0.05 3510 86 84 13 0.00
Fri 07/10 17Z 0.06 3509 87 79 13 0.00
Fri 07/10 18Z 0.11 3507 88 64 13 0.00
Fri 07/10 19Z 0.07 3407 88 65 13 0.00
Fri 07/10 20Z 0.15 3408 86 52 13 0.01
Fri 07/10 21Z 0.08 3409 81 58 13 0.01
Fri 07/10 22Z 0.14 3509 78 54 13 0.00
Fri 07/10 23Z 0.14 0009 74 51 13 0.00
Sat 07/11 00Z 0.16 0010 66 49 13 0.00
Sat 07/11 01Z 0.16 0011 61 47 13 0.00
Sat 07/11 02Z 0.19 0012 61 39 13 0.00
Sat 07/11 03Z 0.19 0111 66 37 12 0.00
Sat 07/11 04Z 0.16 0010 73 42 12 0.00
Sat 07/11 05Z 0.13 0010 76 45 12 0.00
Sat 07/11 06Z 0.11 0011 77 51 11 0.00
Sat 07/11 07Z 0.09 0010 77 53 11 0.00
Sat 07/11 08Z 0.14 0009 77 57 11 0.00
Sat 07/11 09Z 0.15 0107 76 54 11 0.00
Sat 07/11 10Z 0.14 0206 75 49 11 0.00
Sat 07/11 11Z 0.15 0206 75 46 11 0.00
Sat 07/11 12Z 0.13 0205 74 55 11 0.00
Sat 07/11 13Z 0.09 0104 75 56 11 0.00
Sat 07/11 14Z 0.12 0003 80 53 10 0.00
Sat 07/11 15Z 0.51 0004 81 35 10 0.00
Sat 07/11 16Z 0.43 0003 83 30 11 0.00
Sat 07/11 17Z 0.28 3505 84 35 11 0.01
Sat 07/11 18Z 0.26 3506 82 28 11 0.01
Sat 07/11 19Z 0.50 0006 80 15 11 0.00
Sat 07/11 20Z 0.66 0007 78 14 11 0.00
Sat 07/11 21Z 0.65 0007 77 13 11 0.00
Sat 07/11 22Z 0.56 0008 77 13 11 0.00
Sat 07/11 23Z 0.37 0008 76 11 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.26 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