Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260423_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 04/23 00Z 0.17 2306 87 76 1 0.00
Thu 04/23 01Z 0.23 2508 87 62 2 0.00
Thu 04/23 02Z 0.24 2609 84 57 2 0.00
Thu 04/23 03Z 0.28 2810 82 52 2 0.00
Thu 04/23 04Z 0.31 2911 80 64 2 0.00
Thu 04/23 05Z 0.36 2912 76 69 2 0.00
Thu 04/23 06Z 0.41 2914 71 83 2 0.00
Thu 04/23 07Z 0.48 2916 72 85 2 0.00
Thu 04/23 08Z 0.53 2917 72 84 2 0.00
Thu 04/23 09Z 0.52 3019 76 83 1 0.00
Thu 04/23 10Z 0.47 3121 80 84 0 0.00
Thu 04/23 11Z 0.37 3221 78 64 0 0.00
Thu 04/23 12Z 0.34 3321 77 42 -1 0.00
Thu 04/23 13Z 0.46 3222 82 24 -2 0.00
Thu 04/23 14Z 1.00 3223 87 17 -3 0.00
Thu 04/23 15Z 3.68 3223 84 14 -3 0.00
Thu 04/23 16Z 5.82 3222 81 11 -3 0.00
Thu 04/23 17Z 6.49 3220 72 7 -3 0.00
Thu 04/23 18Z 7.41 3220 64 5 -2 0.00
Thu 04/23 19Z 7.60 3220 61 5 -2 0.00
Thu 04/23 20Z 7.46 3220 61 7 -2 0.00
Thu 04/23 21Z 7.25 3221 57 6 -1 0.00
Thu 04/23 22Z 5.79 3221 54 5 -2 0.00
Thu 04/23 23Z 2.78 3322 54 5 -2 0.00
Fri 04/24 00Z 1.08 3324 53 7 -2 0.00
Fri 04/24 02Z 0.53 3423 57 7 -3 0.00
Fri 04/24 03Z 0.38 3421 61 8 -4 0.00
Fri 04/24 05Z 0.13 3516 68 8 -5 0.00
Fri 04/24 06Z 0.12 3514 72 8 -5 0.00
Fri 04/24 07Z 0.14 3413 76 9 -6 0.00
Fri 04/24 08Z 0.16 3414 80 8 -6 0.00
Fri 04/24 09Z 0.19 3416 83 8 -7 0.00
Fri 04/24 13Z 0.15 3417 81 55 -6 0.00
Fri 04/24 16Z 1.16 3314 75 46 -5 0.00
Fri 04/24 19Z 2.04 3413 59 39 -4 0.00
Fri 04/24 20Z 1.38 3412 59 36 -3 0.00
Fri 04/24 21Z 0.80 3512 63 25 -3 0.00
Fri 04/24 22Z 0.34 3511 67 14 -3 0.00
Fri 04/24 23Z 0.30 0011 70 9 -3 0.00
Sat 04/25 00Z 0.31 0211 73 9 -4 0.00
Sat 04/25 01Z 0.54 0313 74 9 -4 0.00
Sat 04/25 02Z 0.74 0416 74 11 -4 0.00
Sat 04/25 03Z 0.69 0517 73 14 -4 0.00
Sat 04/25 04Z 0.53 0516 73 16 -4 0.00
Sat 04/25 05Z 0.37 0513 72 16 -4 0.00
Sat 04/25 06Z 0.26 0610 69 17 -3 0.00
Sat 04/25 07Z 0.19 0708 66 18 -3 0.00
Sat 04/25 08Z 0.16 0607 62 19 -2 0.00
Sat 04/25 09Z 0.16 0707 60 21 -2 0.00
Sat 04/25 10Z 0.15 0707 58 25 -2 0.00
Sat 04/25 11Z 0.17 0807 58 28 -2 0.00
Run total areal avg QPF for the 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