Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260913_0600
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)
=== ===== === ==== ==== === === === ====
Sun 09/13 06Z 0.45 2226 95 99 13 0.00
Sun 09/13 07Z 0.49 2228 97 96 14 0.06
Sun 09/13 08Z 0.45 2224 96 89 14 0.09
Sun 09/13 09Z 0.50 2228 98 88 14 0.23
Sun 09/13 10Z 0.49 2227 98 93 14 0.14
Sun 09/13 11Z 0.55 2327 98 93 14 0.17
Sun 09/13 12Z 0.50 2324 97 90 13 0.13
Sun 09/13 13Z 0.46 2323 97 77 13 0.08
Sun 09/13 14Z 0.42 2222 98 73 13 0.06
Sun 09/13 15Z 0.42 2320 98 56 13 0.05
Sun 09/13 16Z 0.38 2316 96 53 14 0.02
Sun 09/13 17Z 0.36 2414 94 53 14 0.01
Sun 09/13 18Z 0.32 2412 91 51 14 0.00
Sun 09/13 19Z 0.34 2411 90 54 14 0.00
Sun 09/13 20Z 0.30 2409 86 52 15 0.00
Sun 09/13 21Z 0.25 2408 84 37 15 0.00
Sun 09/13 22Z 0.38 2511 86 42 15 0.00
Sun 09/13 23Z 0.45 2514 90 53 14 0.01
Mon 09/14 00Z 0.52 2516 94 67 14 0.03
Mon 09/14 01Z 0.59 2517 95 67 14 0.03
Mon 09/14 02Z 0.78 2622 94 68 14 0.12
Mon 09/14 03Z 0.96 2725 94 61 13 0.12
Mon 09/14 04Z 1.18 2826 95 60 12 0.04
Mon 09/14 05Z 1.01 2926 95 63 10 0.03
Mon 09/14 06Z 0.72 3024 90 62 10 0.02
Mon 09/14 07Z 0.74 3024 88 75 9 0.01
Mon 09/14 08Z 0.78 3023 86 83 8 0.01
Mon 09/14 09Z 0.84 2924 92 52 7 0.01
Mon 09/14 10Z 0.87 3026 95 31 6 0.01
Mon 09/14 11Z 0.76 3128 95 21 5 0.02
Mon 09/14 12Z 0.56 3226 92 18 5 0.01
Mon 09/14 13Z 0.46 3224 91 19 5 0.01
Mon 09/14 14Z 0.41 3223 89 17 5 0.02
Mon 09/14 15Z 0.39 3221 87 13 5 0.01
Mon 09/14 16Z 0.39 3220 85 10 5 0.01
Mon 09/14 17Z 0.47 3219 84 6 4 0.00
Mon 09/14 18Z 0.55 3219 84 5 4 0.00
Mon 09/14 19Z 0.92 3219 82 6 4 0.00
Mon 09/14 20Z 1.04 3218 83 10 4 0.00
Mon 09/14 21Z 0.72 3218 80 16 4 0.00
Mon 09/14 22Z 0.58 3220 79 19 4 0.00
Mon 09/14 23Z 0.55 3321 81 20 4 0.00
Tue 09/15 00Z 0.41 3320 82 19 4 0.00
Tue 09/15 01Z 0.28 3420 81 17 4 0.00
Tue 09/15 02Z 0.18 3419 77 15 5 0.00
Tue 09/15 03Z 0.09 3417 71 13 6 0.00
Tue 09/15 04Z 0.04 3514 65 11 7 0.00
Tue 09/15 05Z 0.05 0011 59 9 8 0.00
Tue 09/15 06Z 0.02 3509 60 8 8 0.00
Tue 09/15 07Z 0.04 0106 56 7 8 0.00
Tue 09/15 08Z 0.04 3403 51 6 8 0.00
Tue 09/15 09Z 0.03 3301 47 6 9 0.00
Tue 09/15 10Z 0.03 0201 47 6 8 0.00
Tue 09/15 11Z 0.02 1900 45 5 8 0.00
Tue 09/15 12Z 0.04 1903 44 4 8 0.00
Tue 09/15 13Z 0.04 1904 43 3 8 0.00
Tue 09/15 14Z 0.06 2105 43 3 9 0.00
Tue 09/15 15Z 0.09 2205 46 3 9 0.00
Tue 09/15 16Z 0.08 2105 45 3 10 0.00
Tue 09/15 17Z 0.06 2006 46 3 11 0.00
Run total areal avg QPF for the greens is: 1.56 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