Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260307_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)
=== ===== === ==== ==== === === === ====
Sat 03/07 12Z 0.36 2131 82 79 8 0.00
Sat 03/07 13Z 0.42 2233 88 87 9 0.00
Sat 03/07 14Z 0.48 2335 93 86 9 0.02
Sat 03/07 15Z 0.50 2434 93 65 10 0.00
Sat 03/07 16Z 0.47 2431 89 76 11 0.00
Sat 03/07 17Z 0.48 2430 90 78 11 0.01
Sat 03/07 18Z 0.49 2331 86 73 12 0.00
Sat 03/07 19Z 0.52 2333 88 73 12 0.00
Sat 03/07 20Z 0.59 2336 88 84 12 0.00
Sat 03/07 21Z 0.64 2338 88 83 12 0.00
Sat 03/07 22Z 0.71 2342 87 67 12 0.00
Sat 03/07 23Z 0.71 2343 85 47 13 0.00
Sun 03/08 00Z 0.76 2347 85 77 13 0.00
Sun 03/08 01Z 0.85 2349 87 88 12 0.00
Sun 03/08 02Z 0.83 2445 90 82 11 0.00
Sun 03/08 03Z 0.76 2441 96 80 11 0.01
Sun 03/08 04Z 0.74 2440 97 81 10 0.02
Sun 03/08 05Z 0.75 2441 98 85 10 0.03
Sun 03/08 06Z 0.78 2442 97 93 11 0.07
Sun 03/08 07Z 0.77 2537 97 92 9 0.15
Sun 03/08 08Z 0.74 2634 91 88 8 0.07
Sun 03/08 09Z 0.79 2634 93 60 7 0.04
Sun 03/08 10Z 0.90 2637 92 30 7 0.01
Sun 03/08 11Z 1.11 2637 92 32 5 0.01
Sun 03/08 12Z 1.06 2636 87 9 4 0.01
Sun 03/08 13Z 1.05 2635 89 10 3 0.02
Sun 03/08 14Z 0.99 2633 89 8 2 0.01
Sun 03/08 15Z 0.94 2631 90 6 1 0.01
Sun 03/08 16Z 0.88 2629 89 4 1 0.01
Sun 03/08 17Z 0.85 2626 90 5 0 0.01
Sun 03/08 18Z 0.82 2623 89 7 0 0.01
Sun 03/08 19Z 0.78 2623 86 6 0 0.00
Sun 03/08 20Z 0.84 2625 84 8 0 0.00
Sun 03/08 21Z 0.87 2627 83 14 0 0.00
Sun 03/08 22Z 0.81 2629 80 21 0 0.00
Sun 03/08 23Z 0.75 2631 76 65 0 0.00
Mon 03/09 00Z 0.73 2633 66 73 0 0.01
Mon 03/09 01Z 0.87 2639 68 41 0 0.01
Mon 03/09 02Z 1.18 2640 82 22 -2 0.01
Mon 03/09 03Z 1.48 2639 92 9 -2 0.00
Mon 03/09 04Z 1.33 2737 92 6 -2 0.00
Mon 03/09 05Z 1.12 2737 89 11 -1 0.00
Mon 03/09 07Z 0.88 2736 70 25 0 0.00
Mon 03/09 08Z 0.78 2735 61 31 1 0.00
Mon 03/09 09Z 0.72 2733 55 44 1 0.00
Mon 03/09 10Z 0.67 2732 49 61 2 0.00
Mon 03/09 11Z 0.69 2632 50 81 3 0.00
Mon 03/09 12Z 0.65 2631 56 74 3 0.00
Mon 03/09 13Z 0.65 2532 61 61 4 0.00
Mon 03/09 14Z 0.68 2434 60 43 5 0.00
Mon 03/09 15Z 0.73 2438 42 42 6 0.00
Mon 03/09 16Z 0.79 2438 50 60 7 0.00
Mon 03/09 17Z 0.87 2438 49 56 7 0.00
Mon 03/09 18Z 0.87 2436 52 63 7 0.00
Mon 03/09 19Z 0.90 2435 54 63 7 0.00
Mon 03/09 20Z 0.98 2435 57 57 7 0.00
Mon 03/09 21Z 1.07 2436 60 48 7 0.00
Mon 03/09 22Z 1.15 2437 60 40 7 0.00
Mon 03/09 23Z 1.20 2538 55 31 7 0.00
Run total areal avg QPF for the Central_Greens is: 0.55 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