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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260714_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 07/14 12Z 0.53 2822 70 35 18 0.00
Tue 07/14 13Z 0.64 2825 69 31 18 0.00
Tue 07/14 14Z 0.66 2726 67 35 19 0.00
Tue 07/14 15Z 0.62 2724 69 32 19 0.00
Tue 07/14 16Z 0.63 2725 70 29 20 0.00
Tue 07/14 17Z 0.70 2725 75 23 20 0.00
Tue 07/14 18Z 0.80 2626 75 18 21 0.00
Tue 07/14 19Z 1.01 2625 76 14 21 0.00
Tue 07/14 20Z 2.96 2526 77 15 20 0.00
Tue 07/14 21Z 4.04 2527 78 15 20 0.00
Tue 07/14 22Z 4.31 2628 82 16 20 0.00
Tue 07/14 23Z 2.34 2630 83 25 20 0.00
Wed 07/15 00Z 1.77 2731 83 34 20 0.00
Wed 07/15 01Z 1.50 2733 86 42 19 0.00
Wed 07/15 02Z 1.22 2733 87 39 20 0.00
Wed 07/15 03Z 1.04 2834 89 40 20 0.00
Wed 07/15 04Z 0.92 2833 89 50 20 0.00
Wed 07/15 05Z 0.88 2933 93 62 19 0.00
Wed 07/15 06Z 0.72 2930 94 55 19 0.01
Wed 07/15 07Z 0.68 3028 94 75 18 0.02
Wed 07/15 08Z 0.59 3025 95 83 17 0.02
Wed 07/15 09Z 0.46 3122 96 92 16 0.05
Wed 07/15 10Z 0.23 3323 92 91 16 0.12
Wed 07/15 11Z 0.07 3420 84 70 15 0.01
Wed 07/15 12Z 0.21 3319 75 36 14 0.00
Wed 07/15 13Z 0.38 3220 64 16 14 0.00
Wed 07/15 14Z 0.56 3120 54 18 14 0.00
Wed 07/15 15Z 1.14 3119 56 20 14 0.00
Wed 07/15 16Z 3.55 3017 67 24 13 0.00
Wed 07/15 17Z 6.67 2920 72 44 13 0.00
Wed 07/15 18Z 8.47 3022 61 47 13 0.00
Wed 07/15 19Z 11.97 3023 58 44 13 0.00
Wed 07/15 20Z 9.49 2923 64 66 13 0.01
Wed 07/15 21Z 3.91 3027 67 61 13 0.02
Wed 07/15 22Z 0.93 3126 75 56 13 0.00
Wed 07/15 23Z 0.93 3125 72 51 13 0.00
Thu 07/16 00Z 1.07 3125 68 48 12 0.00
Thu 07/16 01Z 0.99 3126 64 39 13 0.00
Thu 07/16 02Z 1.08 3127 65 39 12 0.00
Thu 07/16 03Z 0.89 3127 67 29 12 0.00
Thu 07/16 04Z 0.67 3225 65 26 12 0.00
Thu 07/16 05Z 0.63 3223 64 24 12 0.00
Thu 07/16 06Z 0.66 3121 66 25 12 0.00
Thu 07/16 07Z 0.70 3120 68 30 11 0.00
Thu 07/16 08Z 0.69 3120 70 30 11 0.00
Thu 07/16 09Z 0.63 3120 70 35 11 0.00
Thu 07/16 10Z 0.62 3120 71 36 11 0.00
Thu 07/16 11Z 0.60 3020 68 42 11 0.00
Thu 07/16 12Z 0.65 3020 69 40 11 0.00
Thu 07/16 13Z 0.77 2921 69 38 11 0.00
Thu 07/16 14Z 1.13 2821 71 32 12 0.00
Thu 07/16 15Z 2.60 2721 74 32 12 0.00
Thu 07/16 16Z 11.57 2621 75 28 12 0.00
Thu 07/16 17Z 13.65 2622 74 25 13 0.00
Thu 07/16 18Z 11.69 2623 71 37 13 0.00
Thu 07/16 19Z 11.70 2624 69 46 13 0.00
Thu 07/16 20Z 12.06 2627 69 42 13 0.00
Thu 07/16 21Z 10.16 2631 62 44 14 0.00
Thu 07/16 22Z 3.41 2924 73 62 14 0.02
Thu 07/16 23Z 0.75 3224 81 74 12 0.11
Run total areal avg QPF for the Central_Greens is: 0.39 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