Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260601_1800
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)
=== ===== === ==== ==== === === === ====
Mon 06/01 18Z 0.74 0105 75 67 3 0.00
Mon 06/01 19Z 0.54 0005 75 63 4 0.01
Mon 06/01 20Z 0.36 0005 75 60 4 0.01
Mon 06/01 21Z 0.33 3504 75 60 4 0.01
Mon 06/01 22Z 0.25 3504 75 58 4 0.01
Mon 06/01 23Z 0.21 3404 75 56 4 0.01
Tue 06/02 00Z 0.18 3305 74 53 4 0.00
Tue 06/02 01Z 0.20 3407 73 51 4 0.00
Tue 06/02 02Z 0.28 3409 71 49 4 0.00
Tue 06/02 03Z 0.26 3410 70 45 4 0.00
Tue 06/02 04Z 0.25 3411 69 41 4 0.00
Tue 06/02 05Z 0.27 3311 69 39 4 0.00
Tue 06/02 06Z 0.27 3311 69 37 4 0.00
Tue 06/02 07Z 0.30 3211 67 41 5 0.00
Tue 06/02 08Z 0.33 3211 68 43 5 0.00
Tue 06/02 09Z 0.37 3112 66 45 5 0.00
Tue 06/02 10Z 0.39 3113 64 45 5 0.00
Tue 06/02 11Z 0.38 3215 62 41 5 0.00
Tue 06/02 12Z 0.35 3216 59 28 5 0.00
Tue 06/02 13Z 0.32 3216 55 20 6 0.00
Tue 06/02 14Z 0.36 3317 51 14 6 0.00
Tue 06/02 15Z 0.45 3317 50 10 6 0.00
Tue 06/02 16Z 1.94 3318 50 8 6 0.00
Tue 06/02 17Z 3.57 3318 51 12 6 0.00
Tue 06/02 18Z 4.69 3319 49 22 6 0.00
Tue 06/02 19Z 4.82 3318 52 34 6 0.00
Tue 06/02 20Z 4.41 3318 53 53 6 0.00
Tue 06/02 21Z 3.30 3318 52 67 6 0.00
Tue 06/02 22Z 1.83 3319 54 76 7 0.00
Tue 06/02 23Z 0.64 3421 52 68 7 0.00
Wed 06/03 00Z 0.52 3422 51 56 7 0.00
Wed 06/03 01Z 0.46 3422 49 39 7 0.00
Wed 06/03 02Z 0.23 3520 49 34 7 0.00
Wed 06/03 03Z 0.08 3518 47 27 8 0.00
Wed 06/03 04Z 0.08 3517 45 21 8 0.00
Wed 06/03 05Z 0.12 0015 44 12 8 0.00
Wed 06/03 06Z 0.13 3514 43 13 8 0.00
Wed 06/03 07Z 0.11 3514 44 17 8 0.00
Wed 06/03 08Z 0.09 3514 44 24 8 0.00
Wed 06/03 09Z 0.10 3513 44 34 8 0.00
Wed 06/03 10Z 0.12 3413 44 44 8 0.00
Wed 06/03 11Z 0.10 3512 44 53 8 0.00
Wed 06/03 12Z 0.12 3411 44 54 8 0.00
Wed 06/03 13Z 0.21 3310 45 65 8 0.00
Wed 06/03 14Z 0.34 3210 46 72 8 0.00
Wed 06/03 15Z 0.47 3210 47 76 9 0.00
Wed 06/03 16Z 1.02 3110 48 76 9 0.00
Wed 06/03 17Z 1.66 3111 47 74 9 0.00
Wed 06/03 18Z 1.56 3210 46 71 10 0.00
Wed 06/03 19Z 1.53 3110 48 66 10 0.00
Wed 06/03 20Z 1.46 3010 49 62 10 0.00
Wed 06/03 21Z 0.92 3011 51 59 11 0.00
Wed 06/03 22Z 0.61 3010 52 52 11 0.00
Wed 06/03 23Z 0.58 2911 54 44 11 0.00
Thu 06/04 00Z 0.57 2811 55 41 11 0.00
Thu 06/04 01Z 0.62 2811 56 36 11 0.00
Thu 06/04 02Z 0.67 2812 57 33 11 0.00
Thu 06/04 03Z 0.61 2912 57 34 11 0.00
Thu 06/04 04Z 0.49 3012 58 33 11 0.00
Thu 06/04 05Z 0.40 2911 55 33 11 0.00
Run total areal avg QPF for the greens is: 0.05 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