Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260510_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 05/10 18Z 4.22 2411 91 20 3 0.00
Sun 05/10 19Z 4.06 2513 88 29 3 0.00
Sun 05/10 20Z 3.17 2513 86 35 3 0.00
Sun 05/10 21Z 2.63 2515 83 31 3 0.01
Sun 05/10 23Z 4.17 2719 62 21 3 0.01
Mon 05/11 00Z 2.36 2822 59 18 2 0.00
Mon 05/11 01Z 1.71 2822 54 20 1 0.00
Mon 05/11 02Z 1.38 2921 50 24 0 0.00
Mon 05/11 03Z 1.09 2921 64 22 0 0.00
Mon 05/11 04Z 0.78 3020 74 17 -1 0.00
Mon 05/11 05Z 0.70 3119 75 18 -1 0.00
Mon 05/11 06Z 0.55 3116 76 18 -2 0.00
Mon 05/11 07Z 0.47 3115 78 18 -2 0.00
Mon 05/11 08Z 0.42 3114 79 16 -2 0.00
Mon 05/11 09Z 0.38 3114 78 16 -2 0.00
Mon 05/11 10Z 0.37 3115 76 16 -2 0.00
Mon 05/11 11Z 0.39 3114 73 20 -2 0.00
Mon 05/11 12Z 0.47 3114 74 26 -2 0.00
Mon 05/11 13Z 1.27 3013 74 33 -3 0.00
Mon 05/11 14Z 3.99 3011 68 36 -3 0.00
Mon 05/11 15Z 4.47 3010 63 40 -2 0.00
Mon 05/11 16Z 5.11 3010 63 37 -1 0.00
Mon 05/11 17Z 5.36 2909 63 38 -1 0.00
Mon 05/11 18Z 5.07 2808 64 57 0 0.00
Mon 05/11 19Z 5.01 2808 64 65 0 0.00
Mon 05/11 20Z 4.72 2909 63 73 0 0.00
Mon 05/11 21Z 4.21 2909 63 76 0 0.00
Mon 05/11 22Z 2.50 3009 63 70 0 0.00
Mon 05/11 23Z 1.06 3109 65 68 0 0.00
Tue 05/12 00Z 0.38 3210 69 67 -1 0.00
Tue 05/12 01Z 0.19 3311 73 68 -1 0.00
Tue 05/12 02Z 0.09 3412 74 70 -1 0.00
Tue 05/12 03Z 0.11 3414 78 68 -2 0.00
Tue 05/12 04Z 0.12 3416 78 68 -2 0.00
Tue 05/12 05Z 0.12 3418 76 71 -2 0.00
Tue 05/12 06Z 0.09 3419 72 71 -2 0.00
Tue 05/12 07Z 0.04 3419 67 57 -2 0.00
Tue 05/12 08Z 0.05 3419 65 46 -3 0.00
Tue 05/12 09Z 0.06 3418 66 31 -3 0.00
Tue 05/12 10Z 0.06 3417 66 24 -3 0.00
Tue 05/12 11Z 0.09 3415 67 33 -3 0.00
Tue 05/12 12Z 0.26 3313 68 47 -4 0.00
Tue 05/12 13Z 1.10 3311 70 56 -4 0.00
Tue 05/12 14Z 1.73 3211 70 49 -4 0.00
Tue 05/12 15Z 2.41 3211 68 33 -3 0.00
Tue 05/12 16Z 3.07 3211 64 25 -3 0.00
Tue 05/12 17Z 3.76 3112 62 25 -2 0.00
Tue 05/12 18Z 4.28 3111 64 31 -2 0.00
Tue 05/12 19Z 3.57 3110 64 38 -1 0.00
Tue 05/12 20Z 3.59 3110 65 44 -1 0.00
Tue 05/12 21Z 3.32 3110 66 45 -1 0.00
Tue 05/12 22Z 2.34 3109 67 43 -1 0.00
Tue 05/12 23Z 0.34 3207 66 33 0 0.00
Wed 05/13 00Z 0.21 3207 65 30 0 0.00
Wed 05/13 01Z 0.23 3107 65 29 0 0.00
Wed 05/13 02Z 0.10 3205 65 26 0 0.00
Wed 05/13 03Z 0.08 3102 65 27 0 0.00
Wed 05/13 04Z 0.12 2502 66 29 0 0.00
Wed 05/13 05Z 0.16 2303 66 32 0 0.00
Run total areal avg QPF for the Central_Greens is: 0.02 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