Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260503_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)
=== ===== === ==== ==== === === === ====
Sun 05/03 12Z 0.29 3316 87 71 -5 0.00
Sun 05/03 13Z 1.43 3317 86 72 -4 0.00
Sun 05/03 14Z 3.69 3217 83 71 -4 0.00
Sun 05/03 15Z 4.90 3217 73 62 -4 0.00
Sun 05/03 16Z 6.15 3117 69 57 -3 0.00
Sun 05/03 17Z 5.64 3117 78 63 -3 0.00
Sun 05/03 18Z 6.32 3116 73 61 -3 0.00
Sun 05/03 19Z 7.60 3016 69 64 -2 0.00
Sun 05/03 20Z 8.88 2917 68 55 -2 0.00
Sun 05/03 21Z 9.95 2919 65 50 -2 0.00
Sun 05/03 22Z 8.66 2919 62 36 -1 0.00
Sun 05/03 23Z 4.18 2920 57 21 -1 0.00
Mon 05/04 00Z 2.02 2922 53 9 -1 0.00
Mon 05/04 01Z 1.63 2823 48 3 -1 0.00
Mon 05/04 02Z 1.01 2823 45 5 0 0.00
Mon 05/04 03Z 1.00 2724 60 23 0 0.00
Mon 05/04 04Z 1.14 2624 71 73 0 0.00
Mon 05/04 05Z 0.92 2624 83 91 0 0.00
Mon 05/04 06Z 0.72 2725 93 91 0 0.02
Mon 05/04 07Z 0.77 2727 95 93 0 0.02
Mon 05/04 08Z 0.73 2727 96 85 1 0.02
Mon 05/04 09Z 0.82 2629 97 89 1 0.03
Mon 05/04 10Z 0.90 2630 94 82 1 0.04
Mon 05/04 11Z 0.88 2630 88 79 1 0.01
Mon 05/04 12Z 0.96 2631 85 66 1 0.00
Mon 05/04 13Z 1.05 2530 83 67 1 0.00
Mon 05/04 14Z 1.23 2530 84 78 2 0.00
Mon 05/04 15Z 2.29 2429 89 79 1 0.00
Mon 05/04 16Z 1.38 2428 90 72 2 0.01
Mon 05/04 17Z 2.95 2426 89 69 2 0.00
Mon 05/04 18Z 4.65 2424 87 55 3 0.00
Mon 05/04 19Z 10.94 2422 85 42 3 0.00
Mon 05/04 20Z 11.87 2421 83 41 4 0.00
Mon 05/04 21Z 8.81 2421 82 30 4 0.00
Mon 05/04 22Z 5.12 2421 79 25 5 0.00
Mon 05/04 23Z 1.86 2322 78 26 5 0.00
Tue 05/05 00Z 1.63 2324 77 21 6 0.00
Tue 05/05 01Z 1.41 2326 79 16 6 0.00
Tue 05/05 02Z 1.25 2327 79 14 6 0.00
Tue 05/05 03Z 1.24 2330 80 11 6 0.00
Tue 05/05 04Z 1.24 2331 81 27 6 0.00
Tue 05/05 05Z 1.23 2333 83 12 6 0.00
Tue 05/05 06Z 1.14 2334 86 9 6 0.00
Tue 05/05 07Z 0.97 2332 86 4 7 0.01
Tue 05/05 08Z 0.79 2331 85 1 8 0.01
Tue 05/05 09Z 0.83 2333 89 7 8 0.01
Tue 05/05 10Z 0.90 2336 88 73 8 0.01
Tue 05/05 11Z 0.84 2434 88 87 9 0.01
Tue 05/05 12Z 0.87 2333 86 59 9 0.00
Tue 05/05 13Z 0.95 2333 85 68 9 0.00
Tue 05/05 14Z 1.13 2332 83 80 9 0.00
Tue 05/05 15Z 1.32 2328 78 81 10 0.00
Tue 05/05 16Z 6.38 2226 76 82 10 0.00
Tue 05/05 17Z 10.51 2225 75 85 10 0.00
Tue 05/05 18Z 12.15 2125 72 87 11 0.00
Tue 05/05 19Z 12.00 2125 73 76 11 0.00
Tue 05/05 20Z 10.05 2028 73 40 12 0.00
Tue 05/05 21Z 9.26 2031 72 28 12 0.00
Tue 05/05 22Z 5.25 2034 71 29 11 0.00
Tue 05/05 23Z 2.57 2134 69 52 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.20 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