Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260602_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)
=== ===== === ==== ==== === === === ====
Tue 06/02 18Z 3.90 3313 48 34 7 0.00
Tue 06/02 19Z 4.66 3216 48 30 8 0.00
Tue 06/02 20Z 3.66 3317 46 29 8 0.00
Tue 06/02 21Z 2.40 3318 46 32 8 0.00
Tue 06/02 22Z 1.53 3419 49 36 8 0.00
Tue 06/02 23Z 0.60 3420 50 43 8 0.00
Wed 06/03 00Z 0.40 3421 49 46 8 0.00
Wed 06/03 01Z 0.31 3421 47 45 8 0.00
Wed 06/03 02Z 0.22 3520 46 40 9 0.00
Wed 06/03 03Z 0.16 3518 46 38 9 0.00
Wed 06/03 04Z 0.10 0017 46 35 9 0.00
Wed 06/03 05Z 0.15 0014 45 30 9 0.00
Wed 06/03 06Z 0.18 0112 44 26 9 0.00
Wed 06/03 07Z 0.14 0110 44 20 9 0.00
Wed 06/03 08Z 0.10 0108 43 15 9 0.00
Wed 06/03 09Z 0.04 3506 43 11 9 0.00
Wed 06/03 10Z 0.14 3306 44 12 9 0.00
Wed 06/03 11Z 0.20 3307 43 14 9 0.00
Wed 06/03 12Z 0.30 3109 44 15 9 0.00
Wed 06/03 13Z 0.38 3111 45 19 9 0.00
Wed 06/03 14Z 0.50 3113 46 25 9 0.00
Wed 06/03 15Z 1.00 3112 47 31 9 0.00
Wed 06/03 16Z 1.80 3212 48 36 9 0.00
Wed 06/03 17Z 2.29 3211 49 40 10 0.00
Wed 06/03 18Z 1.96 3209 50 42 10 0.00
Wed 06/03 19Z 1.75 3108 51 44 11 0.00
Wed 06/03 20Z 1.71 3008 51 45 11 0.00
Wed 06/03 21Z 1.30 2908 52 45 11 0.00
Wed 06/03 22Z 0.96 2809 55 48 11 0.00
Wed 06/03 23Z 0.73 2810 57 53 11 0.00
Thu 06/04 00Z 0.74 2712 59 55 12 0.00
Thu 06/04 01Z 0.80 2713 61 54 12 0.00
Thu 06/04 02Z 0.80 2813 59 50 11 0.00
Thu 06/04 03Z 0.74 3013 58 46 11 0.00
Thu 06/04 04Z 0.54 3012 61 41 11 0.00
Thu 06/04 05Z 0.46 3012 59 40 11 0.00
Thu 06/04 06Z 0.47 2911 57 37 12 0.00
Thu 06/04 07Z 0.47 2911 54 31 12 0.00
Thu 06/04 08Z 0.47 2910 52 28 12 0.00
Thu 06/04 09Z 0.45 2911 50 27 12 0.00
Thu 06/04 10Z 0.43 2910 49 28 12 0.00
Thu 06/04 11Z 0.51 2911 49 31 12 0.00
Thu 06/04 12Z 0.52 2911 51 32 12 0.00
Thu 06/04 13Z 0.53 2811 53 31 11 0.00
Thu 06/04 14Z 0.59 2810 56 31 12 0.00
Thu 06/04 15Z 0.96 2710 57 31 12 0.00
Thu 06/04 16Z 1.71 2611 56 30 12 0.00
Thu 06/04 17Z 3.12 2612 52 29 12 0.00
Thu 06/04 18Z 4.40 2613 55 27 12 0.00
Thu 06/04 19Z 6.69 2613 58 26 13 0.00
Thu 06/04 20Z 6.83 2714 55 29 13 0.00
Thu 06/04 21Z 3.49 2714 54 35 13 0.00
Thu 06/04 22Z 2.27 2715 57 30 13 0.00
Thu 06/04 23Z 2.00 2717 58 32 13 0.00
Fri 06/05 00Z 2.13 2719 60 29 13 0.00
Fri 06/05 01Z 1.68 2821 63 29 12 0.00
Fri 06/05 02Z 1.15 2922 65 31 12 0.00
Fri 06/05 03Z 0.96 2923 67 25 12 0.00
Fri 06/05 04Z 0.98 2924 71 26 11 0.00
Fri 06/05 05Z 0.95 3024 74 28 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