Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260812_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 08/12 12Z 0.22 3213 81 72 11 0.00
Wed 08/12 13Z 0.20 3313 80 73 11 0.00
Wed 08/12 14Z 0.28 3210 80 76 11 0.00
Wed 08/12 15Z 1.08 3107 79 76 11 0.00
Wed 08/12 16Z 1.66 3006 76 77 12 0.00
Wed 08/12 17Z 1.57 2904 72 81 12 0.00
Wed 08/12 18Z 1.23 2603 70 86 13 0.00
Wed 08/12 19Z 0.92 2506 78 93 12 0.07
Wed 08/12 20Z 0.43 2410 88 95 12 0.16
Wed 08/12 21Z 0.35 2508 83 87 12 0.06
Wed 08/12 22Z 0.33 2709 87 81 12 0.04
Wed 08/12 23Z 0.36 2710 83 78 12 0.00
Thu 08/13 00Z 0.36 2810 83 87 12 0.02
Thu 08/13 01Z 0.37 2911 87 87 12 0.03
Thu 08/13 02Z 0.24 3008 82 85 12 0.00
Thu 08/13 03Z 0.28 2706 82 89 12 0.00
Thu 08/13 04Z 0.24 2405 83 88 12 0.00
Thu 08/13 05Z 0.36 2408 85 95 12 0.00
Thu 08/13 06Z 0.43 2411 90 96 11 0.03
Thu 08/13 07Z 0.52 2513 94 89 11 0.07
Thu 08/13 08Z 0.56 2515 97 88 11 0.04
Thu 08/13 09Z 0.59 2616 96 68 11 0.05
Thu 08/13 10Z 0.57 2616 97 55 11 0.01
Thu 08/13 11Z 0.57 2716 97 57 11 0.02
Thu 08/13 12Z 0.47 2915 96 56 11 0.01
Thu 08/13 13Z 0.39 3015 95 54 11 0.00
Thu 08/13 14Z 0.38 3013 95 57 11 0.00
Thu 08/13 15Z 0.37 3113 96 60 11 0.00
Thu 08/13 16Z 0.44 3014 94 63 11 0.00
Thu 08/13 17Z 0.53 3013 94 63 11 0.01
Thu 08/13 18Z 0.58 3014 93 65 11 0.02
Thu 08/13 19Z 1.02 3015 91 61 11 0.04
Thu 08/13 20Z 1.20 3015 91 55 11 0.01
Thu 08/13 21Z 2.03 3018 89 45 11 0.01
Thu 08/13 22Z 2.34 3020 87 33 11 0.00
Thu 08/13 23Z 1.12 3021 87 38 11 0.00
Fri 08/14 00Z 0.78 3122 84 44 11 0.00
Fri 08/14 01Z 0.59 3224 85 38 10 0.03
Fri 08/14 02Z 0.44 3225 88 37 10 0.00
Fri 08/14 03Z 0.41 3226 87 24 9 0.01
Fri 08/14 04Z 0.35 3226 85 24 9 0.00
Fri 08/14 05Z 0.30 3224 86 19 9 0.00
Fri 08/14 06Z 0.26 3223 83 17 8 0.00
Fri 08/14 07Z 0.25 3222 79 16 8 0.00
Fri 08/14 08Z 0.29 3222 78 16 8 0.00
Fri 08/14 09Z 0.32 3224 77 15 8 0.00
Fri 08/14 10Z 0.32 3225 69 15 8 0.00
Fri 08/14 11Z 0.32 3226 67 14 8 0.00
Fri 08/14 12Z 0.29 3225 65 13 8 0.00
Fri 08/14 13Z 0.27 3224 65 15 9 0.00
Fri 08/14 14Z 0.21 3222 63 18 9 0.00
Fri 08/14 15Z 0.22 3221 63 20 9 0.00
Fri 08/14 16Z 0.22 3221 61 23 9 0.00
Fri 08/14 17Z 0.27 3222 63 25 9 0.00
Fri 08/14 18Z 0.33 3221 64 27 9 0.00
Fri 08/14 19Z 0.48 3121 65 31 8 0.00
Fri 08/14 20Z 0.70 3120 64 36 8 0.00
Fri 08/14 21Z 0.66 3118 63 35 9 0.00
Fri 08/14 22Z 0.66 3119 62 32 9 0.00
Fri 08/14 23Z 0.59 3119 60 26 9 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