Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260518_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 05/18 00Z 0.35 3212 65 20 11 0.00
Mon 05/18 01Z 0.26 3313 63 20 11 0.00
Mon 05/18 02Z 0.21 3312 62 23 11 0.00
Mon 05/18 03Z 0.18 3210 62 30 11 0.00
Mon 05/18 04Z 0.14 3207 62 31 11 0.00
Mon 05/18 05Z 0.15 2905 62 34 11 0.00
Mon 05/18 06Z 0.18 2706 62 38 12 0.00
Mon 05/18 07Z 0.19 2607 61 41 12 0.00
Mon 05/18 08Z 0.18 2407 63 50 13 0.00
Mon 05/18 09Z 0.19 2308 65 60 12 0.00
Mon 05/18 10Z 0.17 2110 69 64 12 0.00
Mon 05/18 11Z 0.18 2013 74 67 12 0.00
Mon 05/18 12Z 0.16 2016 80 74 12 0.00
Mon 05/18 13Z 0.15 1921 84 52 13 0.00
Mon 05/18 14Z 0.23 1926 87 49 13 0.00
Mon 05/18 15Z 0.37 2127 90 41 13 0.06
Mon 05/18 16Z 0.46 2225 87 27 13 0.02
Mon 05/18 17Z 0.56 2223 81 22 13 0.00
Mon 05/18 18Z 1.01 2222 82 29 13 0.00
Mon 05/18 19Z 2.87 2221 84 29 14 0.00
Mon 05/18 20Z 2.88 2221 84 23 14 0.00
Mon 05/18 21Z 2.62 2321 85 20 14 0.01
Mon 05/18 22Z 1.52 2321 85 22 14 0.01
Mon 05/18 23Z 1.18 2322 84 19 15 0.00
Tue 05/19 00Z 1.17 2423 86 20 15 0.01
Tue 05/19 01Z 1.14 2425 87 29 15 0.01
Tue 05/19 02Z 1.11 2427 83 25 15 0.00
Tue 05/19 03Z 0.92 2428 73 29 17 0.00
Tue 05/19 04Z 0.99 2530 68 15 17 0.00
Tue 05/19 05Z 1.05 2432 70 15 17 0.00
Tue 05/19 06Z 1.22 2436 79 44 16 0.00
Tue 05/19 07Z 1.22 2635 84 51 16 0.05
Tue 05/19 08Z 1.00 2633 76 51 16 0.03
Tue 05/19 09Z 1.11 2633 74 58 15 0.00
Tue 05/19 10Z 1.10 2730 73 56 15 0.00
Tue 05/19 11Z 1.01 2628 75 52 15 0.00
Tue 05/19 12Z 1.00 2627 79 41 14 0.00
Tue 05/19 13Z 0.89 2623 81 47 14 0.00
Tue 05/19 14Z 0.88 2522 81 64 15 0.00
Tue 05/19 15Z 1.03 2423 82 73 15 0.00
Tue 05/19 16Z 1.62 2423 86 62 15 0.00
Tue 05/19 17Z 3.23 2424 90 80 15 0.00
Tue 05/19 18Z 2.89 2424 91 84 15 0.01
Tue 05/19 19Z 3.61 2427 84 87 15 0.06
Tue 05/19 20Z 3.83 2525 84 79 15 0.00
Tue 05/19 21Z 2.47 2525 81 73 15 0.00
Tue 05/19 22Z 3.87 2526 84 62 15 0.00
Tue 05/19 23Z 1.79 2527 82 55 15 0.00
Wed 05/20 00Z 1.43 2429 86 56 15 0.00
Wed 05/20 01Z 1.01 2530 80 46 16 0.02
Wed 05/20 02Z 1.14 2534 78 49 16 0.00
Wed 05/20 03Z 1.40 2439 85 72 16 0.00
Wed 05/20 04Z 1.45 2441 88 73 16 0.00
Wed 05/20 05Z 1.34 2540 90 73 16 0.02
Wed 05/20 06Z 1.27 2539 90 78 15 0.03
Wed 05/20 07Z 1.22 2538 90 74 15 0.06
Wed 05/20 08Z 1.15 2535 91 54 15 0.02
Wed 05/20 09Z 1.24 2535 93 51 14 0.01
Wed 05/20 10Z 1.25 2635 96 61 13 0.02
Wed 05/20 11Z 1.29 2634 97 58 12 0.03
Run total areal avg QPF for the greens is: 0.48 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