Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260423_0000
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 04/23 00Z 0.19 2307 89 89 2 0.00
Thu 04/23 01Z 0.24 2509 88 72 2 0.00
Thu 04/23 02Z 0.23 2709 85 49 2 0.00
Thu 04/23 03Z 0.24 2810 84 40 2 0.00
Thu 04/23 04Z 0.24 2911 84 59 2 0.00
Thu 04/23 05Z 0.26 2912 79 66 2 0.00
Thu 04/23 06Z 0.28 2913 73 81 2 0.00
Thu 04/23 07Z 0.34 2915 71 81 2 0.00
Thu 04/23 08Z 0.41 2917 68 77 2 0.00
Thu 04/23 09Z 0.47 3020 72 75 2 0.00
Thu 04/23 10Z 0.41 3122 78 78 1 0.00
Thu 04/23 11Z 0.27 3222 76 58 0 0.00
Thu 04/23 12Z 0.25 3222 75 41 0 0.00
Thu 04/23 13Z 0.32 3223 79 18 -1 0.00
Thu 04/23 14Z 0.54 3324 87 8 -2 0.00
Thu 04/23 15Z 2.63 3224 85 9 -3 0.00
Thu 04/23 16Z 4.14 3223 84 8 -2 0.00
Thu 04/23 17Z 4.62 3221 72 6 -2 0.00
Thu 04/23 18Z 5.02 3221 63 5 -2 0.00
Thu 04/23 19Z 5.02 3220 60 4 -1 0.00
Thu 04/23 20Z 4.53 3220 57 4 -1 0.00
Thu 04/23 21Z 4.26 3221 54 4 -1 0.00
Thu 04/23 22Z 2.77 3322 52 2 -1 0.00
Thu 04/23 23Z 0.91 3323 52 2 -1 0.00
Fri 04/24 00Z 0.56 3325 52 2 -2 0.00
Fri 04/24 02Z 0.42 3326 54 4 -3 0.00
Fri 04/24 03Z 0.29 3423 57 4 -3 0.00
Fri 04/24 05Z 0.11 3516 63 5 -4 0.00
Fri 04/24 06Z 0.10 3414 68 4 -5 0.00
Fri 04/24 07Z 0.07 3413 73 5 -5 0.00
Fri 04/24 08Z 0.08 3414 77 7 -6 0.00
Fri 04/24 09Z 0.12 3315 79 9 -6 0.00
Fri 04/24 13Z 0.03 3417 74 45 -5 0.00
Fri 04/24 16Z 0.60 3413 67 51 -5 0.00
Fri 04/24 19Z 0.84 3414 49 50 -3 0.00
Fri 04/24 20Z 0.53 3412 50 51 -3 0.00
Fri 04/24 21Z 0.32 3412 55 34 -3 0.00
Fri 04/24 22Z 0.49 3511 61 17 -3 0.00
Fri 04/24 23Z 0.56 0011 67 10 -3 0.00
Sat 04/25 00Z 0.41 0111 72 8 -3 0.00
Sat 04/25 01Z 0.61 0312 74 7 -4 0.00
Sat 04/25 02Z 0.70 0415 74 9 -4 0.00
Sat 04/25 03Z 0.58 0515 73 14 -4 0.00
Sat 04/25 04Z 0.44 0514 72 17 -4 0.00
Sat 04/25 05Z 0.32 0510 71 18 -4 0.00
Sat 04/25 06Z 0.23 0508 69 18 -3 0.00
Sat 04/25 07Z 0.16 0606 67 18 -3 0.00
Sat 04/25 08Z 0.13 0605 62 20 -2 0.00
Sat 04/25 09Z 0.13 0705 61 23 -2 0.00
Sat 04/25 10Z 0.11 0704 60 23 -2 0.00
Sat 04/25 11Z 0.12 0904 61 22 -3 0.00
Run total areal avg QPF for the Central_Greens is: 0.00 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