Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260412_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)
=== ===== === ==== ==== === === === ====
Sun 04/12 12Z 0.03 0005 64 19 -3 0.00
Sun 04/12 13Z 0.02 3301 62 22 -3 0.00
Sun 04/12 14Z 0.05 2002 59 24 -2 0.00
Sun 04/12 15Z 0.09 1904 58 26 -2 0.00
Sun 04/12 16Z 0.26 1906 59 27 -2 0.00
Sun 04/12 17Z 0.80 1907 60 29 -2 0.00
Sun 04/12 18Z 1.01 2009 57 77 -1 0.00
Sun 04/12 19Z 0.33 1911 51 88 0 0.00
Sun 04/12 20Z 0.20 1813 48 97 0 0.00
Sun 04/12 21Z 0.13 1713 57 95 -1 0.00
Sun 04/12 22Z 0.14 1716 59 87 0 0.00
Sun 04/12 23Z 0.37 1920 67 99 -1 0.00
Mon 04/13 00Z 0.34 1922 87 98 0 0.02
Mon 04/13 01Z 0.37 2024 88 99 0 0.02
Mon 04/13 02Z 0.42 2027 88 99 1 0.02
Mon 04/13 03Z 0.44 2129 93 99 3 0.04
Mon 04/13 04Z 0.44 2230 95 95 5 0.03
Mon 04/13 05Z 0.47 2233 92 96 7 0.04
Mon 04/13 06Z 0.47 2232 90 96 8 0.03
Mon 04/13 07Z 0.51 2234 90 83 9 0.02
Mon 04/13 08Z 0.54 2335 89 31 10 0.00
Mon 04/13 09Z 0.59 2335 89 64 9 0.01
Mon 04/13 10Z 0.65 2438 93 86 9 0.03
Mon 04/13 11Z 0.70 2438 90 85 10 0.01
Mon 04/13 12Z 0.71 2438 91 68 10 0.01
Mon 04/13 13Z 0.76 2439 88 79 10 0.01
Mon 04/13 14Z 0.78 2438 92 85 9 0.03
Mon 04/13 15Z 0.89 2343 86 93 9 0.01
Mon 04/13 16Z 1.00 2246 97 96 8 0.09
Mon 04/13 17Z 1.12 2346 98 96 8 0.11
Mon 04/13 18Z 1.20 2445 98 95 8 0.11
Mon 04/13 19Z 1.19 2643 98 62 9 0.05
Mon 04/13 20Z 1.11 2639 97 53 9 0.02
Mon 04/13 21Z 1.14 2638 97 53 10 0.02
Mon 04/13 22Z 1.24 2637 98 54 9 0.02
Mon 04/13 23Z 1.37 2638 97 53 9 0.03
Tue 04/14 00Z 1.37 2638 98 42 9 0.03
Tue 04/14 01Z 1.49 2738 98 28 8 0.04
Tue 04/14 02Z 1.24 2835 97 27 8 0.02
Tue 04/14 03Z 0.97 2932 97 34 7 0.02
Tue 04/14 04Z 0.80 3028 96 36 7 0.01
Tue 04/14 05Z 0.59 3025 94 41 7 0.01
Tue 04/14 07Z 0.33 3020 83 46 8 0.01
Tue 04/14 08Z 0.26 3017 75 44 9 0.01
Tue 04/14 09Z 0.23 3014 70 42 10 0.01
Tue 04/14 10Z 0.23 2812 66 32 10 0.01
Tue 04/14 11Z 0.24 2612 62 36 10 0.00
Tue 04/14 12Z 0.25 2512 59 38 10 0.01
Tue 04/14 13Z 0.26 2513 57 50 10 0.00
Tue 04/14 14Z 0.27 2314 58 50 10 0.00
Tue 04/14 15Z 0.38 2318 63 56 11 0.00
Tue 04/14 16Z 0.47 2320 82 61 11 0.00
Tue 04/14 17Z 0.52 2322 85 51 11 0.00
Tue 04/14 18Z 0.62 2322 89 81 11 0.00
Tue 04/14 19Z 0.73 2327 87 82 11 0.00
Tue 04/14 20Z 0.76 2231 79 72 12 0.01
Tue 04/14 21Z 0.73 2330 70 61 13 0.02
Tue 04/14 22Z 0.71 2327 75 65 13 0.01
Tue 04/14 23Z 0.79 2230 83 65 13 0.00
Run total areal avg QPF for the Central_Greens is: 1.00 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