Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260307_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)
=== ===== === ==== ==== === === === ====
Sat 03/07 18Z 0.40 2229 81 89 10 0.00
Sat 03/07 19Z 0.46 2233 83 85 11 0.00
Sat 03/07 20Z 0.51 2235 85 73 12 0.00
Sat 03/07 21Z 0.52 2238 88 66 12 0.00
Sat 03/07 22Z 0.59 2342 87 36 13 0.00
Sat 03/07 23Z 0.60 2342 76 51 13 0.00
Sun 03/08 01Z 0.68 2346 84 66 13 0.00
Sun 03/08 02Z 0.73 2347 89 77 12 0.01
Sun 03/08 03Z 0.77 2445 92 88 11 0.02
Sun 03/08 04Z 0.79 2444 95 88 10 0.07
Sun 03/08 05Z 0.80 2542 96 81 9 0.08
Sun 03/08 06Z 0.76 2538 95 82 9 0.08
Sun 03/08 07Z 0.72 2536 94 46 9 0.04
Sun 03/08 08Z 0.75 2536 93 67 8 0.02
Sun 03/08 09Z 0.80 2536 94 60 8 0.02
Sun 03/08 10Z 0.85 2535 92 36 7 0.02
Sun 03/08 11Z 1.01 2636 95 27 5 0.03
Sun 03/08 12Z 1.12 2635 94 9 4 0.01
Sun 03/08 13Z 1.18 2634 93 6 2 0.02
Sun 03/08 15Z 1.05 2730 91 8 0 0.02
Sun 03/08 16Z 1.04 2728 92 5 0 0.02
Sun 03/08 17Z 1.02 2726 93 4 -1 0.01
Sun 03/08 18Z 1.00 2624 93 10 -1 0.01
Sun 03/08 19Z 0.89 2624 92 9 -2 0.01
Sun 03/08 20Z 0.77 2624 88 13 -1 0.01
Sun 03/08 21Z 0.81 2628 85 15 -1 0.01
Sun 03/08 22Z 0.79 2629 80 28 -1 0.01
Sun 03/08 23Z 0.72 2531 72 64 0 0.00
Mon 03/09 00Z 0.73 2534 67 78 0 0.00
Mon 03/09 01Z 0.91 2538 72 40 0 0.00
Mon 03/09 02Z 1.20 2540 86 25 -2 0.00
Mon 03/09 03Z 1.25 2640 89 22 -2 0.00
Mon 03/09 04Z 1.12 2738 86 18 -1 0.00
Mon 03/09 05Z 1.03 2738 82 20 0 0.01
Mon 03/09 06Z 0.98 2738 79 28 0 0.00
Mon 03/09 07Z 0.90 2737 71 34 0 0.00
Mon 03/09 08Z 0.87 2736 66 34 1 0.00
Mon 03/09 09Z 0.78 2733 62 26 1 0.00
Mon 03/09 10Z 0.72 2631 60 22 2 0.00
Mon 03/09 11Z 0.70 2631 59 32 2 0.00
Mon 03/09 12Z 0.71 2532 58 57 3 0.00
Mon 03/09 13Z 0.69 2533 53 64 4 0.00
Mon 03/09 14Z 0.71 2535 55 82 5 0.00
Mon 03/09 15Z 0.71 2437 55 73 7 0.00
Mon 03/09 16Z 0.74 2439 41 56 8 0.00
Mon 03/09 17Z 0.81 2439 42 54 7 0.00
Mon 03/09 18Z 0.85 2439 43 49 7 0.00
Mon 03/09 19Z 0.89 2437 47 49 7 0.00
Mon 03/09 20Z 0.98 2437 51 46 7 0.00
Mon 03/09 21Z 1.03 2437 50 45 7 0.00
Mon 03/09 22Z 1.07 2438 49 50 7 0.00
Mon 03/09 23Z 1.08 2439 46 56 7 0.00
Tue 03/10 00Z 1.12 2440 44 59 7 0.00
Tue 03/10 01Z 1.14 2440 41 56 7 0.00
Tue 03/10 02Z 1.11 2439 38 52 7 0.00
Tue 03/10 03Z 1.06 2537 36 54 7 0.00
Tue 03/10 04Z 1.01 2535 37 55 7 0.00
Tue 03/10 05Z 0.98 2533 39 53 6 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