Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260503_1800
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 18Z 6.25 3113 74 68 -3 0.00
Sun 05/03 19Z 6.80 3014 72 66 -2 0.00
Sun 05/03 20Z 7.02 2915 74 79 -2 0.00
Sun 05/03 21Z 5.13 2917 69 73 -2 0.00
Sun 05/03 22Z 5.90 2918 60 48 -1 0.00
Sun 05/03 23Z 3.60 2919 57 26 -1 0.00
Mon 05/04 00Z 1.74 2921 56 13 -1 0.00
Mon 05/04 01Z 1.67 2824 53 8 -1 0.00
Mon 05/04 02Z 1.13 2927 49 5 -1 0.00
Mon 05/04 03Z 1.01 2827 58 19 0 0.00
Mon 05/04 04Z 0.97 2727 70 66 0 0.00
Mon 05/04 05Z 0.84 2628 87 91 0 0.02
Mon 05/04 06Z 0.88 2632 91 92 0 0.04
Mon 05/04 07Z 0.86 2631 94 91 0 0.04
Mon 05/04 08Z 0.86 2630 94 84 0 0.02
Mon 05/04 09Z 0.90 2630 95 77 0 0.02
Mon 05/04 10Z 0.86 2630 92 71 1 0.02
Mon 05/04 11Z 0.88 2632 88 74 2 0.01
Mon 05/04 12Z 0.94 2633 79 84 2 0.00
Mon 05/04 13Z 1.07 2533 80 85 2 0.00
Mon 05/04 14Z 1.15 2531 81 83 2 0.00
Mon 05/04 15Z 1.57 2529 83 79 2 0.00
Mon 05/04 16Z 7.51 2527 82 78 2 0.01
Mon 05/04 17Z 13.22 2425 78 85 3 0.00
Mon 05/04 18Z 13.32 2424 76 81 4 0.00
Mon 05/04 19Z 14.28 2423 76 70 4 0.00
Mon 05/04 20Z 14.29 2421 73 59 5 0.00
Mon 05/04 21Z 11.48 2420 72 55 5 0.00
Mon 05/04 22Z 6.67 2322 73 51 6 0.00
Mon 05/04 23Z 1.58 2423 70 37 6 0.00
Tue 05/05 00Z 1.34 2324 72 26 6 0.00
Tue 05/05 01Z 1.35 2326 73 47 6 0.00
Tue 05/05 02Z 1.40 2327 74 19 6 0.00
Tue 05/05 03Z 1.43 2329 77 15 6 0.00
Tue 05/05 04Z 1.47 2332 79 10 5 0.00
Tue 05/05 05Z 1.35 2333 80 9 6 0.00
Tue 05/05 06Z 1.09 2332 76 9 6 0.00
Tue 05/05 07Z 0.96 2332 71 9 7 0.00
Tue 05/05 08Z 0.90 2333 70 10 7 0.00
Tue 05/05 09Z 0.85 2332 66 8 8 0.00
Tue 05/05 10Z 0.75 2231 74 14 8 0.00
Tue 05/05 11Z 0.76 2232 89 77 8 0.01
Tue 05/05 12Z 0.78 2235 90 66 8 0.00
Tue 05/05 13Z 0.86 2335 83 73 9 0.00
Tue 05/05 14Z 1.12 2334 82 73 9 0.00
Tue 05/05 15Z 1.17 2230 78 62 10 0.00
Tue 05/05 16Z 8.23 2227 79 47 9 0.00
Tue 05/05 17Z 10.20 2227 75 64 10 0.00
Tue 05/05 18Z 14.86 2129 71 64 11 0.00
Tue 05/05 19Z 10.70 2128 72 61 11 0.00
Tue 05/05 20Z 11.76 2030 72 63 11 0.00
Tue 05/05 21Z 6.51 2232 81 74 11 0.19
Tue 05/05 22Z 3.40 2132 82 78 11 0.03
Tue 05/05 23Z 1.34 2134 79 52 11 0.02
Wed 05/06 00Z 1.23 2036 71 36 11 0.00
Wed 05/06 01Z 1.32 2138 72 66 11 0.05
Wed 05/06 02Z 1.21 2331 82 59 10 0.12
Wed 05/06 03Z 0.97 2427 86 78 9 0.03
Wed 05/06 04Z 0.83 2423 91 90 9 0.12
Wed 05/06 05Z 0.65 2323 94 83 8 0.07
Run total areal avg QPF for the Central_Greens is: 0.82 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