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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260714_0600
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 06Z 0.85 2823 64 76 16 0.00
Tue 07/14 07Z 0.99 2929 68 60 16 0.00
Tue 07/14 08Z 0.88 2929 71 37 16 0.00
Tue 07/14 09Z 0.75 2927 71 31 17 0.00
Tue 07/14 10Z 0.69 2826 69 38 17 0.00
Tue 07/14 11Z 0.66 2826 69 38 18 0.00
Tue 07/14 12Z 0.66 2826 70 32 18 0.00
Tue 07/14 13Z 0.65 2826 68 31 19 0.00
Tue 07/14 14Z 0.66 2826 68 41 19 0.00
Tue 07/14 15Z 0.69 2726 71 41 19 0.00
Tue 07/14 16Z 0.72 2725 75 30 20 0.00
Tue 07/14 17Z 0.76 2725 81 23 20 0.00
Tue 07/14 18Z 0.74 2624 78 21 21 0.00
Tue 07/14 19Z 1.31 2525 80 19 21 0.00
Tue 07/14 20Z 2.96 2526 79 21 21 0.00
Tue 07/14 21Z 4.22 2626 78 18 21 0.00
Tue 07/14 22Z 4.45 2628 80 15 21 0.00
Tue 07/14 23Z 1.76 2628 82 18 20 0.00
Wed 07/15 00Z 1.70 2731 82 32 20 0.00
Wed 07/15 01Z 1.49 2733 84 40 20 0.00
Wed 07/15 02Z 1.26 2834 85 56 19 0.00
Wed 07/15 03Z 1.10 2833 86 58 19 0.00
Wed 07/15 04Z 0.98 2932 89 57 19 0.01
Wed 07/15 05Z 0.90 2932 91 72 18 0.02
Wed 07/15 06Z 0.68 3030 91 76 18 0.02
Wed 07/15 07Z 0.53 3126 96 75 17 0.04
Wed 07/15 08Z 0.45 3224 93 53 16 0.05
Wed 07/15 09Z 0.36 3223 89 49 16 0.02
Wed 07/15 10Z 0.29 3221 89 61 15 0.01
Wed 07/15 11Z 0.34 3218 89 54 15 0.01
Wed 07/15 12Z 0.31 3216 87 49 14 0.01
Wed 07/15 13Z 0.36 3217 83 52 14 0.02
Wed 07/15 14Z 0.52 3117 73 20 14 0.02
Wed 07/15 15Z 1.23 3118 67 17 14 0.00
Wed 07/15 16Z 6.44 3017 76 23 13 0.00
Wed 07/15 17Z 8.18 3021 73 44 13 0.03
Wed 07/15 18Z 7.29 3023 63 44 13 0.04
Wed 07/15 19Z 10.72 3023 58 49 14 0.00
Wed 07/15 20Z 10.45 3024 59 42 14 0.00
Wed 07/15 21Z 11.04 3025 57 43 14 0.00
Wed 07/15 22Z 5.81 3024 56 34 14 0.00
Wed 07/15 23Z 1.96 3024 56 36 14 0.00
Thu 07/16 00Z 1.61 3025 58 42 14 0.00
Thu 07/16 01Z 1.53 3026 60 37 13 0.00
Thu 07/16 02Z 1.17 3027 62 38 13 0.00
Thu 07/16 03Z 0.87 3126 65 50 13 0.00
Thu 07/16 04Z 0.65 3124 68 48 13 0.00
Thu 07/16 05Z 0.55 3123 70 45 13 0.00
Thu 07/16 06Z 0.57 3123 70 46 12 0.00
Thu 07/16 07Z 0.53 3224 72 40 12 0.00
Thu 07/16 08Z 0.38 3223 71 33 11 0.00
Thu 07/16 09Z 0.39 3223 69 33 11 0.00
Thu 07/16 10Z 0.44 3124 65 32 11 0.00
Thu 07/16 11Z 0.44 3123 64 32 11 0.00
Thu 07/16 12Z 0.44 3121 62 33 11 0.00
Thu 07/16 13Z 0.49 3019 61 32 11 0.00
Thu 07/16 14Z 0.63 2918 62 32 11 0.00
Thu 07/16 15Z 0.87 2916 64 30 11 0.00
Thu 07/16 16Z 2.48 2714 68 29 12 0.00
Thu 07/16 17Z 7.58 2615 75 23 12 0.00
Run total areal avg QPF for the Central_Greens is: 0.30 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