Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260517_1800
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 05/17 18Z 8.01 2813 76 56 10 0.00
Sun 05/17 19Z 5.81 2913 75 49 10 0.01
Sun 05/17 20Z 3.09 3018 76 41 10 0.04
Sun 05/17 21Z 1.44 3018 75 33 10 0.01
Sun 05/17 22Z 1.14 3117 72 26 10 0.00
Sun 05/17 23Z 0.66 3117 69 24 10 0.00
Mon 05/18 00Z 0.50 3216 66 20 9 0.00
Mon 05/18 01Z 0.39 3214 64 18 9 0.00
Mon 05/18 02Z 0.38 3012 65 17 9 0.00
Mon 05/18 03Z 0.37 2911 66 17 10 0.00
Mon 05/18 04Z 0.33 2810 67 21 10 0.00
Mon 05/18 05Z 0.29 2809 67 31 10 0.00
Mon 05/18 06Z 0.26 2709 65 40 11 0.00
Mon 05/18 07Z 0.26 2709 62 48 11 0.00
Mon 05/18 08Z 0.26 2609 64 43 11 0.00
Mon 05/18 09Z 0.26 2409 68 44 12 0.00
Mon 05/18 10Z 0.21 2209 73 66 12 0.00
Mon 05/18 11Z 0.15 2012 76 85 12 0.00
Mon 05/18 12Z 0.29 2118 86 91 10 0.04
Mon 05/18 13Z 0.15 2018 85 65 12 0.18
Mon 05/18 14Z 0.23 2024 92 60 12 0.01
Mon 05/18 15Z 0.32 2127 96 39 12 0.01
Mon 05/18 16Z 0.41 2126 96 36 12 0.01
Mon 05/18 17Z 0.47 2223 93 36 12 0.01
Mon 05/18 18Z 0.55 2221 90 33 13 0.00
Mon 05/18 19Z 0.60 2222 93 28 13 0.00
Mon 05/18 20Z 0.68 2223 94 21 13 0.01
Mon 05/18 21Z 0.73 2323 94 20 14 0.01
Mon 05/18 22Z 0.75 2323 93 23 14 0.01
Mon 05/18 23Z 0.75 2323 91 27 15 0.01
Tue 05/19 00Z 0.80 2324 91 25 15 0.00
Tue 05/19 01Z 0.84 2326 90 23 15 0.00
Tue 05/19 02Z 0.87 2327 86 21 16 0.00
Tue 05/19 03Z 0.88 2429 81 16 16 0.00
Tue 05/19 04Z 1.03 2433 82 26 16 0.00
Tue 05/19 05Z 1.21 2436 83 33 16 0.00
Tue 05/19 06Z 1.14 2437 78 35 17 0.00
Tue 05/19 07Z 1.28 2539 79 37 17 0.00
Tue 05/19 08Z 1.22 2636 85 47 15 0.02
Tue 05/19 09Z 1.17 2632 86 44 15 0.01
Tue 05/19 10Z 1.22 2632 88 39 14 0.00
Tue 05/19 11Z 0.98 2531 79 47 15 0.00
Tue 05/19 12Z 0.97 2530 85 41 14 0.00
Tue 05/19 13Z 1.03 2530 90 67 14 0.00
Tue 05/19 14Z 1.09 2629 96 81 13 0.02
Tue 05/19 15Z 1.18 2628 97 75 13 0.04
Tue 05/19 16Z 0.99 2724 96 73 13 0.03
Tue 05/19 17Z 0.82 2720 89 54 14 0.01
Tue 05/19 18Z 0.70 2717 82 52 15 0.00
Tue 05/19 19Z 0.74 2616 77 52 15 0.00
Tue 05/19 20Z 0.80 2517 73 51 16 0.00
Tue 05/19 21Z 0.95 2518 74 53 16 0.00
Tue 05/19 22Z 0.96 2420 76 49 16 0.00
Tue 05/19 23Z 1.20 2422 82 51 16 0.00
Wed 05/20 00Z 1.03 2422 82 56 16 0.00
Wed 05/20 01Z 0.96 2327 85 70 16 0.00
Wed 05/20 02Z 0.99 2332 83 79 17 0.00
Wed 05/20 03Z 0.89 2432 70 78 17 0.04
Wed 05/20 04Z 1.23 2439 79 76 17 0.00
Wed 05/20 05Z 1.30 2441 81 76 16 0.00
Run total areal avg QPF for the greens is: 0.53 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