Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260907_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 09/07 00Z 0.26 3416 79 10 7 0.00
Mon 09/07 01Z 0.36 3317 78 9 7 0.00
Mon 09/07 02Z 0.40 3318 81 12 7 0.00
Mon 09/07 03Z 0.36 3319 84 16 8 0.00
Mon 09/07 04Z 0.37 3320 84 16 8 0.00
Mon 09/07 05Z 0.36 3320 83 17 8 0.00
Mon 09/07 06Z 0.28 3320 79 20 8 0.00
Mon 09/07 07Z 0.21 3419 77 24 8 0.00
Mon 09/07 08Z 0.22 3419 75 28 8 0.00
Mon 09/07 09Z 0.26 3320 74 32 8 0.00
Mon 09/07 10Z 0.30 3321 72 33 8 0.00
Mon 09/07 11Z 0.34 3323 67 30 8 0.00
Mon 09/07 12Z 0.36 3324 65 28 8 0.00
Mon 09/07 13Z 0.38 3325 65 21 8 0.00
Mon 09/07 14Z 0.31 3424 63 17 8 0.00
Mon 09/07 15Z 0.33 3424 64 12 8 0.00
Mon 09/07 16Z 0.60 3421 66 10 9 0.00
Mon 09/07 17Z 1.29 3418 67 8 9 0.00
Mon 09/07 18Z 2.62 3318 67 6 9 0.00
Mon 09/07 19Z 4.09 3318 69 5 9 0.00
Mon 09/07 20Z 2.78 3216 67 4 9 0.00
Mon 09/07 21Z 3.10 3216 70 4 9 0.00
Mon 09/07 22Z 1.78 3116 71 6 9 0.00
Mon 09/07 23Z 1.91 3118 73 9 9 0.00
Tue 09/08 00Z 1.59 3120 76 18 9 0.00
Tue 09/08 01Z 1.39 3121 80 32 9 0.00
Tue 09/08 02Z 1.08 3222 80 45 9 0.00
Tue 09/08 03Z 0.96 3222 80 53 9 0.00
Tue 09/08 04Z 0.90 3223 80 57 9 0.00
Tue 09/08 05Z 0.73 3223 80 57 9 0.00
Tue 09/08 06Z 0.60 3220 81 57 9 0.00
Tue 09/08 07Z 0.53 3219 82 63 10 0.00
Tue 09/08 08Z 0.51 3119 84 69 10 0.00
Tue 09/08 09Z 0.49 3118 86 76 10 0.00
Tue 09/08 10Z 0.51 3119 88 80 10 0.01
Tue 09/08 11Z 0.51 3120 91 78 9 0.02
Tue 09/08 12Z 0.48 3120 92 75 9 0.01
Tue 09/08 13Z 0.42 3119 92 70 9 0.00
Tue 09/08 14Z 0.37 3118 93 64 9 0.01
Tue 09/08 15Z 0.32 3217 89 68 10 0.00
Tue 09/08 16Z 0.30 3216 87 59 10 0.00
Tue 09/08 17Z 0.30 3215 84 64 10 0.00
Tue 09/08 18Z 0.28 3213 81 69 10 0.00
Tue 09/08 19Z 0.24 3212 75 64 10 0.00
Tue 09/08 20Z 0.21 3211 71 56 10 0.00
Tue 09/08 21Z 0.20 3209 68 69 10 0.00
Tue 09/08 22Z 0.21 3108 68 81 11 0.00
Tue 09/08 23Z 0.21 3007 69 73 11 0.00
Wed 09/09 00Z 0.24 2907 71 76 11 0.00
Wed 09/09 01Z 0.26 2807 75 73 11 0.00
Wed 09/09 02Z 0.26 2707 79 73 11 0.00
Wed 09/09 03Z 0.27 2607 85 65 11 0.00
Wed 09/09 04Z 0.25 2407 91 67 11 0.00
Wed 09/09 05Z 0.23 2308 94 70 11 0.00
Wed 09/09 06Z 0.23 2209 95 75 11 0.00
Wed 09/09 07Z 0.24 2211 95 75 11 0.00
Wed 09/09 08Z 0.29 2113 95 74 11 0.00
Wed 09/09 09Z 0.32 2116 94 70 11 0.00
Wed 09/09 10Z 0.44 2219 93 65 11 0.00
Wed 09/09 11Z 0.41 2219 86 60 11 0.00
Run total areal avg QPF for the greens is: 0.05 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