Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260528_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)
=== ===== === ==== ==== === === === ====
Thu 05/28 12Z 0.05 3514 88 80 5 0.00
Thu 05/28 13Z 0.08 3414 91 77 4 0.00
Thu 05/28 14Z 0.14 3415 92 79 4 0.00
Thu 05/28 15Z 0.16 3416 91 76 4 0.00
Thu 05/28 16Z 0.34 3416 87 72 4 0.00
Thu 05/28 17Z 1.51 3317 82 68 4 0.00
Thu 05/28 18Z 1.78 3319 76 61 4 0.00
Thu 05/28 19Z 1.66 3420 77 59 4 0.00
Thu 05/28 20Z 0.91 3420 83 58 4 0.00
Thu 05/28 21Z 0.72 3319 83 55 4 0.00
Thu 05/28 22Z 0.80 3320 85 58 5 0.00
Thu 05/28 23Z 0.31 3323 91 78 4 0.03
Fri 05/29 00Z 0.07 3427 90 58 4 0.02
Fri 05/29 01Z 0.09 3526 92 47 4 0.00
Fri 05/29 02Z 0.12 3524 93 44 3 0.00
Fri 05/29 03Z 0.03 3524 92 44 3 0.00
Fri 05/29 04Z 0.03 3422 93 35 2 0.00
Fri 05/29 05Z 0.10 3422 94 33 2 0.00
Fri 05/29 06Z 0.13 3421 93 37 2 0.00
Fri 05/29 07Z 0.24 3321 92 45 3 0.00
Fri 05/29 08Z 0.34 3222 90 77 3 0.00
Fri 05/29 09Z 0.37 3223 83 86 3 0.00
Fri 05/29 10Z 0.37 3223 74 78 2 0.00
Fri 05/29 11Z 0.39 3224 72 80 2 0.00
Fri 05/29 12Z 0.36 3222 70 82 2 0.00
Fri 05/29 13Z 0.45 3219 74 81 2 0.00
Fri 05/29 14Z 1.08 3116 75 75 2 0.00
Fri 05/29 15Z 4.50 3014 75 73 3 0.00
Fri 05/29 16Z 5.51 2911 76 78 4 0.00
Fri 05/29 17Z 5.66 2709 76 69 5 0.00
Fri 05/29 18Z 6.02 2511 73 84 5 0.00
Fri 05/29 19Z 6.81 2514 66 96 6 0.00
Fri 05/29 20Z 4.13 2618 66 86 6 0.00
Fri 05/29 21Z 6.55 2616 63 86 6 0.00
Fri 05/29 22Z 0.78 2520 83 70 5 0.03
Fri 05/29 23Z 1.23 2425 86 82 5 0.01
Sat 05/30 00Z 1.26 2425 87 91 5 0.02
Sat 05/30 01Z 0.82 2522 98 94 5 0.09
Sat 05/30 02Z 0.76 2818 98 98 3 0.12
Sat 05/30 03Z 0.55 3119 92 93 1 0.06
Sat 05/30 04Z 0.43 3119 87 75 0 0.02
Sat 05/30 05Z 0.26 3216 93 64 0 0.01
Sat 05/30 06Z 0.14 3315 90 40 0 0.01
Sat 05/30 07Z 0.12 3513 90 31 0 0.00
Sat 05/30 08Z 0.24 0214 95 66 0 0.02
Sat 05/30 09Z 0.56 0522 97 86 -1 0.09
Sat 05/30 10Z 0.95 0729 98 75 -1 0.05
Sat 05/30 11Z 0.89 0730 98 83 -1 0.06
Sat 05/30 12Z 0.69 0526 98 91 0 0.06
Sat 05/30 13Z 0.65 0524 94 93 -1 0.06
Sat 05/30 14Z 0.70 0420 89 92 -1 0.04
Sat 05/30 15Z 2.01 0316 90 78 -1 0.00
Sat 05/30 16Z 2.68 0114 89 63 -1 0.00
Sat 05/30 17Z 2.88 0114 87 49 0 0.00
Sat 05/30 18Z 3.23 0214 86 42 0 0.00
Sat 05/30 19Z 2.36 0215 87 50 0 0.00
Sat 05/30 20Z 2.03 0116 87 67 0 0.00
Sat 05/30 21Z 2.20 0117 84 77 0 0.00
Sat 05/30 22Z 2.07 0117 80 80 0 0.00
Sat 05/30 23Z 0.82 0117 80 79 0 0.00
Run total areal avg QPF for the Central_Greens is: 0.80 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