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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260701_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)
=== ===== === ==== ==== === === === ====
Wed 07/01 06Z 0.70 2524 83 89 17 0.00
Wed 07/01 07Z 0.68 2623 91 91 17 0.03
Wed 07/01 08Z 0.68 2623 94 89 17 0.04
Wed 07/01 09Z 0.74 2725 96 73 17 0.03
Wed 07/01 10Z 0.67 2925 95 64 17 0.13
Wed 07/01 11Z 0.58 3023 94 64 17 0.05
Wed 07/01 12Z 0.46 3018 93 66 18 0.01
Wed 07/01 13Z 0.44 2916 93 65 18 0.01
Wed 07/01 14Z 0.41 2915 91 67 18 0.01
Wed 07/01 15Z 0.42 2913 89 59 18 0.00
Wed 07/01 17Z 0.53 2710 89 65 18 0.00
Wed 07/01 18Z 0.69 2711 90 69 18 0.00
Wed 07/01 19Z 0.55 2611 93 70 18 0.00
Wed 07/01 20Z 0.70 2615 93 72 19 0.00
Wed 07/01 21Z 0.47 2414 87 63 19 0.01
Wed 07/01 22Z 0.55 2518 83 61 20 0.00
Wed 07/01 23Z 0.64 2619 81 56 20 0.00
Thu 07/02 00Z 0.64 2521 90 50 20 0.00
Thu 07/02 01Z 0.67 2622 89 43 20 0.00
Thu 07/02 02Z 0.65 2722 88 46 20 0.00
Thu 07/02 03Z 0.59 2721 87 46 20 0.00
Thu 07/02 04Z 0.62 2722 87 45 20 0.00
Thu 07/02 05Z 0.60 2823 82 47 20 0.00
Thu 07/02 06Z 0.58 2923 78 51 20 0.00
Thu 07/02 07Z 0.55 2923 82 51 20 0.00
Thu 07/02 08Z 0.52 2922 86 55 19 0.00
Thu 07/02 09Z 0.49 2922 87 54 19 0.00
Thu 07/02 10Z 0.44 2920 83 44 19 0.01
Thu 07/02 11Z 0.43 2920 73 28 20 0.01
Thu 07/02 12Z 0.43 2820 62 34 20 0.01
Thu 07/02 13Z 0.46 2820 65 41 20 0.00
Thu 07/02 14Z 0.51 2820 72 51 19 0.00
Thu 07/02 15Z 0.54 2820 72 56 20 0.00
Thu 07/02 16Z 0.54 2818 72 55 20 0.00
Thu 07/02 17Z 0.55 2818 71 48 20 0.00
Thu 07/02 18Z 0.57 2716 73 35 20 0.00
Thu 07/02 19Z 0.66 2616 78 37 20 0.00
Thu 07/02 20Z 0.84 2517 84 47 20 0.00
Thu 07/02 21Z 1.11 2420 86 51 20 0.00
Thu 07/02 22Z 1.35 2424 87 58 20 0.00
Thu 07/02 23Z 2.10 2528 86 57 20 0.00
Fri 07/03 00Z 1.55 2631 88 62 19 0.03
Fri 07/03 01Z 1.30 2732 79 51 20 0.07
Fri 07/03 02Z 1.10 2732 77 51 19 0.01
Fri 07/03 03Z 1.04 2832 82 52 19 0.00
Fri 07/03 04Z 0.98 2831 86 37 19 0.03
Fri 07/03 05Z 0.97 2831 88 36 18 0.02
Fri 07/03 06Z 0.92 2930 88 46 18 0.00
Fri 07/03 07Z 0.84 2829 87 46 18 0.00
Fri 07/03 08Z 0.74 2928 82 48 18 0.00
Fri 07/03 09Z 0.65 2925 76 41 18 0.01
Fri 07/03 10Z 0.51 2922 63 36 19 0.01
Fri 07/03 11Z 0.47 2921 58 37 19 0.01
Fri 07/03 12Z 0.48 2920 60 25 18 0.01
Fri 07/03 13Z 0.52 2821 63 16 18 0.01
Fri 07/03 14Z 0.58 2822 64 17 18 0.01
Fri 07/03 15Z 0.64 2822 65 19 18 0.01
Fri 07/03 16Z 0.83 2823 70 15 17 0.00
Fri 07/03 17Z 1.66 2822 77 17 16 0.00
Run total areal avg QPF for the greens is: 0.58 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