Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260602_0600
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)
=== ===== === ==== ==== === === === ====
Tue 06/02 06Z 0.22 3313 64 67 5 0.00
Tue 06/02 07Z 0.30 3314 65 68 6 0.00
Tue 06/02 08Z 0.33 3215 66 66 6 0.00
Tue 06/02 09Z 0.33 3216 64 65 6 0.00
Tue 06/02 10Z 0.31 3217 62 65 6 0.00
Tue 06/02 11Z 0.27 3317 58 62 6 0.00
Tue 06/02 12Z 0.28 3317 54 56 6 0.00
Tue 06/02 13Z 0.27 3318 48 47 6 0.00
Tue 06/02 14Z 0.26 3318 44 34 6 0.00
Tue 06/02 15Z 0.29 3318 44 27 6 0.00
Tue 06/02 16Z 1.16 3318 46 22 6 0.00
Tue 06/02 17Z 2.51 3318 46 17 6 0.00
Tue 06/02 18Z 3.84 3318 47 17 6 0.00
Tue 06/02 19Z 4.07 3318 48 26 6 0.00
Tue 06/02 20Z 3.76 3319 48 42 6 0.00
Tue 06/02 21Z 2.84 3420 50 54 6 0.00
Tue 06/02 22Z 1.60 3420 52 65 6 0.00
Tue 06/02 23Z 0.40 3521 53 68 6 0.00
Wed 06/03 00Z 0.18 3522 50 64 7 0.00
Wed 06/03 01Z 0.09 3523 48 58 7 0.00
Wed 06/03 02Z 0.17 0023 46 47 7 0.00
Wed 06/03 03Z 0.26 0121 44 37 7 0.00
Wed 06/03 04Z 0.27 0119 46 25 7 0.00
Wed 06/03 05Z 0.26 0017 47 15 7 0.00
Wed 06/03 06Z 0.19 0016 47 12 7 0.00
Wed 06/03 07Z 0.13 0015 47 22 7 0.00
Wed 06/03 08Z 0.13 0014 48 37 7 0.00
Wed 06/03 09Z 0.12 0013 48 54 8 0.00
Wed 06/03 10Z 0.07 0011 48 72 8 0.00
Wed 06/03 11Z 0.11 3510 48 83 8 0.00
Wed 06/03 12Z 0.22 3411 48 88 8 0.00
Wed 06/03 13Z 0.23 3311 48 88 8 0.00
Wed 06/03 14Z 0.33 3312 49 87 8 0.00
Wed 06/03 15Z 0.53 3212 50 84 8 0.00
Wed 06/03 16Z 0.66 3211 50 79 9 0.00
Wed 06/03 17Z 1.29 3110 52 72 9 0.00
Wed 06/03 18Z 1.64 3110 52 64 9 0.00
Wed 06/03 19Z 1.87 3010 53 60 10 0.00
Wed 06/03 20Z 1.64 3012 53 59 10 0.00
Wed 06/03 21Z 1.10 3012 54 59 11 0.00
Wed 06/03 22Z 0.68 3012 54 53 11 0.00
Wed 06/03 23Z 0.61 3012 54 47 11 0.00
Thu 06/04 00Z 0.66 2914 56 40 11 0.00
Thu 06/04 01Z 0.68 2913 56 38 11 0.00
Thu 06/04 02Z 0.71 2913 56 33 11 0.00
Thu 06/04 03Z 0.62 3013 57 33 11 0.00
Thu 06/04 04Z 0.48 3013 57 33 11 0.00
Thu 06/04 05Z 0.46 3012 54 33 11 0.00
Thu 06/04 06Z 0.47 2912 52 34 11 0.00
Thu 06/04 07Z 0.49 2912 50 37 11 0.00
Thu 06/04 08Z 0.52 2911 49 41 11 0.00
Thu 06/04 09Z 0.66 2912 52 40 11 0.00
Thu 06/04 10Z 0.68 2912 54 35 11 0.00
Thu 06/04 11Z 0.60 2912 53 31 11 0.00
Thu 06/04 12Z 0.53 2812 53 26 11 0.00
Thu 06/04 13Z 0.54 2713 55 21 11 0.00
Thu 06/04 14Z 0.66 2714 54 20 11 0.00
Thu 06/04 15Z 0.71 2715 43 20 11 0.00
Thu 06/04 16Z 0.82 2715 41 20 12 0.00
Thu 06/04 17Z 1.02 2716 51 23 11 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