Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260827_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 08/27 12Z 0.46 2120 88 50 13 0.00
Thu 08/27 13Z 0.51 2121 92 53 13 0.00
Thu 08/27 14Z 0.56 2121 95 67 12 0.00
Thu 08/27 15Z 0.57 2119 92 92 13 0.00
Thu 08/27 16Z 0.50 2018 93 76 13 0.01
Thu 08/27 17Z 0.42 1917 93 71 13 0.02
Thu 08/27 18Z 0.56 1919 95 65 13 0.05
Thu 08/27 19Z 0.53 1919 94 64 13 0.02
Thu 08/27 20Z 0.49 1920 94 76 14 0.00
Thu 08/27 21Z 0.54 1923 93 78 14 0.01
Thu 08/27 22Z 0.62 2026 93 70 14 0.01
Thu 08/27 23Z 0.65 2029 93 72 14 0.01
Fri 08/28 00Z 0.62 2129 87 65 14 0.00
Fri 08/28 01Z 0.63 2127 88 59 14 0.00
Fri 08/28 02Z 0.65 2227 93 70 14 0.00
Fri 08/28 03Z 0.64 2224 94 72 14 0.01
Fri 08/28 04Z 0.61 2321 95 76 13 0.01
Fri 08/28 05Z 0.58 2319 97 76 13 0.02
Fri 08/28 06Z 0.53 2317 97 78 13 0.01
Fri 08/28 07Z 0.51 2315 97 69 13 0.02
Fri 08/28 08Z 0.48 2315 97 68 13 0.02
Fri 08/28 09Z 0.47 2315 95 72 13 0.03
Fri 08/28 10Z 0.43 2414 94 64 13 0.02
Fri 08/28 11Z 0.37 2511 93 66 13 0.01
Fri 08/28 12Z 0.34 2511 93 75 13 0.01
Fri 08/28 13Z 0.32 2510 93 81 13 0.00
Fri 08/28 14Z 0.30 2509 91 88 13 0.00
Fri 08/28 15Z 0.31 2509 90 94 13 0.00
Fri 08/28 16Z 0.37 2509 91 86 12 0.00
Fri 08/28 17Z 0.51 2510 91 62 12 0.00
Fri 08/28 18Z 0.60 2610 93 35 12 0.00
Fri 08/28 19Z 0.59 2710 95 17 12 0.00
Fri 08/28 20Z 0.46 2810 96 7 12 0.01
Fri 08/28 21Z 0.34 2911 95 7 12 0.01
Fri 08/28 22Z 0.27 3011 92 14 12 0.01
Fri 08/28 23Z 0.25 3112 95 17 11 0.01
Sat 08/29 00Z 0.23 3114 94 21 11 0.01
Sat 08/29 01Z 0.21 3113 90 21 10 0.00
Sat 08/29 02Z 0.18 3112 84 22 10 0.00
Sat 08/29 03Z 0.15 3212 76 17 10 0.00
Sat 08/29 04Z 0.13 3213 66 13 10 0.00
Sat 08/29 05Z 0.13 3213 59 10 10 0.00
Sat 08/29 06Z 0.12 3213 54 8 10 0.00
Sat 08/29 07Z 0.11 3214 51 6 10 0.00
Sat 08/29 08Z 0.08 3314 51 6 9 0.00
Sat 08/29 09Z 0.06 3314 51 5 9 0.00
Sat 08/29 10Z 0.05 3313 50 5 9 0.00
Sat 08/29 11Z 0.03 3412 49 5 9 0.00
Sat 08/29 12Z 0.02 3411 47 5 9 0.00
Sat 08/29 13Z 0.03 3409 47 5 9 0.00
Sat 08/29 14Z 0.06 3206 50 6 9 0.00
Sat 08/29 15Z 0.11 3106 53 7 9 0.00
Sat 08/29 16Z 0.10 3105 55 7 9 0.00
Sat 08/29 17Z 0.20 3005 56 6 9 0.00
Sat 08/29 18Z 0.30 3006 54 6 9 0.00
Sat 08/29 19Z 0.32 3006 48 6 9 0.00
Sat 08/29 20Z 0.22 3006 45 6 9 0.00
Sat 08/29 21Z 0.21 3007 46 5 9 0.00
Sat 08/29 22Z 0.19 2906 50 4 10 0.00
Sat 08/29 23Z 0.20 2806 54 3 10 0.00
Run total areal avg QPF for the Central_Greens is: 0.34 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