Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260712_0600
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 07/12 06Z 0.29 0310 75 26 11 0.00
Sun 07/12 07Z 0.31 0210 77 25 11 0.00
Sun 07/12 08Z 0.28 0308 77 29 11 0.00
Sun 07/12 09Z 0.24 0207 77 39 11 0.01
Sun 07/12 10Z 0.21 0207 78 48 11 0.01
Sun 07/12 11Z 0.19 0207 77 39 11 0.00
Sun 07/12 12Z 0.17 0206 76 31 11 0.00
Sun 07/12 13Z 0.16 0205 76 25 11 0.00
Sun 07/12 14Z 0.20 0203 78 18 11 0.00
Sun 07/12 15Z 0.39 0301 81 14 11 0.00
Sun 07/12 16Z 0.31 0001 82 14 11 0.00
Sun 07/12 17Z 0.24 3202 82 23 11 0.02
Sun 07/12 18Z 0.25 3202 78 25 12 0.02
Sun 07/12 19Z 0.30 3102 76 20 12 0.00
Sun 07/12 20Z 0.52 3002 72 15 12 0.00
Sun 07/12 21Z 0.46 2904 70 17 12 0.00
Sun 07/12 22Z 0.29 2904 67 36 13 0.00
Sun 07/12 23Z 0.21 2803 66 34 13 0.00
Mon 07/13 00Z 0.22 2703 68 31 12 0.00
Mon 07/13 01Z 0.27 2504 71 13 12 0.00
Mon 07/13 02Z 0.35 2305 74 14 12 0.00
Mon 07/13 03Z 0.52 2307 74 13 12 0.00
Mon 07/13 04Z 0.68 2310 77 14 12 0.00
Mon 07/13 05Z 0.91 2413 78 17 12 0.00
Mon 07/13 06Z 0.92 2415 82 21 12 0.00
Mon 07/13 07Z 0.84 2516 82 19 12 0.00
Mon 07/13 08Z 0.88 2617 80 24 12 0.00
Mon 07/13 09Z 0.82 2616 76 32 12 0.00
Mon 07/13 10Z 0.75 2616 71 42 12 0.00
Mon 07/13 11Z 0.65 2616 66 57 12 0.00
Mon 07/13 12Z 0.54 2714 65 70 13 0.00
Mon 07/13 13Z 0.44 2712 64 72 13 0.00
Mon 07/13 14Z 0.37 2710 62 71 14 0.00
Mon 07/13 15Z 0.37 2709 60 69 14 0.00
Mon 07/13 16Z 0.65 2608 63 66 14 0.00
Mon 07/13 17Z 0.97 2507 62 65 14 0.00
Mon 07/13 18Z 1.19 2408 61 66 15 0.00
Mon 07/13 19Z 1.48 2409 63 69 15 0.00
Mon 07/13 20Z 1.77 2310 72 69 15 0.00
Mon 07/13 21Z 1.06 2413 82 68 15 0.00
Mon 07/13 22Z 0.87 2415 86 69 15 0.00
Mon 07/13 23Z 0.93 2518 86 73 15 0.00
Tue 07/14 00Z 0.76 2618 86 76 15 0.00
Tue 07/14 01Z 0.77 2620 85 70 15 0.00
Tue 07/14 02Z 0.74 2620 83 67 16 0.00
Tue 07/14 03Z 0.59 2619 74 60 16 0.00
Tue 07/14 04Z 0.53 2619 67 55 17 0.00
Tue 07/14 05Z 0.57 2720 60 61 16 0.00
Tue 07/14 06Z 0.66 2823 62 62 16 0.00
Tue 07/14 07Z 0.61 2822 66 51 16 0.00
Tue 07/14 08Z 0.59 2822 70 37 16 0.00
Tue 07/14 09Z 0.59 2821 77 32 16 0.00
Tue 07/14 10Z 0.56 2820 79 22 16 0.00
Tue 07/14 11Z 0.59 2721 79 23 16 0.00
Tue 07/14 12Z 0.74 2726 78 27 16 0.00
Tue 07/14 13Z 0.71 2726 73 28 17 0.00
Tue 07/14 14Z 0.66 2726 71 31 18 0.00
Tue 07/14 15Z 0.65 2726 70 37 19 0.00
Tue 07/14 16Z 0.64 2725 70 41 19 0.00
Tue 07/14 17Z 0.68 2625 73 38 20 0.00
Run total areal avg QPF for the Central_Greens is: 0.06 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