Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260829_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 08/29 12Z 0.08 3413 65 5 6 0.00
Sat 08/29 13Z 0.12 3310 65 7 7 0.00
Sat 08/29 14Z 0.21 3209 68 7 7 0.00
Sat 08/29 15Z 0.43 3107 70 7 7 0.00
Sat 08/29 16Z 0.95 3007 70 7 7 0.00
Sat 08/29 17Z 1.43 2905 69 6 8 0.00
Sat 08/29 18Z 1.71 2706 69 7 8 0.00
Sat 08/29 19Z 1.79 2507 72 6 8 0.00
Sat 08/29 20Z 2.16 2509 80 5 8 0.00
Sat 08/29 21Z 0.94 2410 79 5 9 0.00
Sat 08/29 22Z 0.57 2412 75 6 9 0.00
Sat 08/29 23Z 0.57 2414 76 7 10 0.00
Sun 08/30 00Z 0.72 2518 74 9 10 0.00
Sun 08/30 01Z 0.87 2521 72 9 10 0.00
Sun 08/30 02Z 0.84 2622 69 16 11 0.00
Sun 08/30 03Z 0.86 2724 68 28 11 0.00
Sun 08/30 04Z 0.90 2725 68 39 11 0.00
Sun 08/30 05Z 0.98 2727 70 48 11 0.00
Sun 08/30 06Z 1.12 2730 73 55 11 0.00
Sun 08/30 07Z 1.21 2730 71 53 11 0.00
Sun 08/30 08Z 1.11 2728 69 44 12 0.00
Sun 08/30 09Z 1.07 2727 70 52 12 0.00
Sun 08/30 10Z 0.99 2726 70 50 12 0.00
Sun 08/30 11Z 1.01 2726 70 48 11 0.00
Sun 08/30 12Z 0.95 2726 73 54 11 0.00
Sun 08/30 13Z 0.89 2724 72 42 12 0.00
Sun 08/30 14Z 0.88 2723 73 46 12 0.00
Sun 08/30 15Z 0.93 2621 74 45 12 0.00
Sun 08/30 16Z 0.96 2619 73 47 12 0.00
Sun 08/30 17Z 1.11 2519 74 52 12 0.00
Sun 08/30 18Z 1.27 2519 78 56 12 0.00
Sun 08/30 19Z 1.25 2520 83 79 12 0.01
Sun 08/30 20Z 1.03 2517 74 85 12 0.00
Sun 08/30 21Z 1.17 2518 86 92 12 0.01
Sun 08/30 22Z 1.15 2520 89 96 11 0.02
Sun 08/30 23Z 0.85 2620 82 95 11 0.03
Mon 08/31 00Z 0.86 2620 89 98 11 0.03
Mon 08/31 01Z 0.67 2719 94 98 11 0.06
Mon 08/31 02Z 0.58 2819 94 92 11 0.06
Mon 08/31 03Z 0.47 3019 96 84 10 0.02
Mon 08/31 04Z 0.31 3218 93 80 10 0.01
Mon 08/31 05Z 0.28 3116 91 74 10 0.01
Mon 08/31 06Z 0.18 3317 92 66 10 0.01
Mon 08/31 07Z 0.06 3416 87 33 11 0.01
Mon 08/31 08Z 0.05 3514 83 9 10 0.00
Mon 08/31 09Z 0.05 3513 75 4 11 0.00
Mon 08/31 10Z 0.03 3511 69 4 10 0.00
Mon 08/31 11Z 0.03 3511 63 5 10 0.00
Mon 08/31 12Z 0.02 3510 58 6 10 0.00
Mon 08/31 13Z 0.02 3509 54 7 11 0.00
Mon 08/31 14Z 0.01 3407 53 8 11 0.00
Mon 08/31 15Z 0.02 3406 54 10 11 0.00
Mon 08/31 16Z 0.03 3304 56 13 11 0.00
Mon 08/31 17Z 0.07 3204 59 14 11 0.00
Mon 08/31 18Z 0.08 3103 59 14 11 0.00
Mon 08/31 19Z 0.13 3003 59 14 11 0.00
Mon 08/31 20Z 0.16 2904 56 14 11 0.00
Mon 08/31 21Z 0.10 2902 51 13 11 0.00
Mon 08/31 22Z 0.09 2802 47 13 11 0.00
Mon 08/31 23Z 0.07 3002 45 14 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.28 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