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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260701_1800
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)
=== ===== === ==== ==== === === === ====
Wed 07/01 18Z 0.91 2706 82 44 19 0.00
Wed 07/01 19Z 0.62 2507 81 34 20 0.00
Wed 07/01 20Z 0.52 2407 80 26 20 0.00
Wed 07/01 21Z 0.53 2408 81 20 20 0.00
Wed 07/01 22Z 0.72 2413 87 24 20 0.00
Wed 07/01 23Z 0.69 2418 87 36 20 0.01
Thu 07/02 00Z 0.76 2522 82 51 20 0.01
Thu 07/02 01Z 0.85 2623 86 50 20 0.00
Thu 07/02 02Z 0.85 2625 90 56 20 0.01
Thu 07/02 03Z 0.75 2625 83 48 21 0.00
Thu 07/02 04Z 0.53 2720 68 48 22 0.00
Thu 07/02 05Z 0.60 2623 64 54 21 0.00
Thu 07/02 06Z 0.65 2726 68 53 21 0.00
Thu 07/02 07Z 0.63 2827 67 48 21 0.00
Thu 07/02 08Z 0.53 2925 63 48 21 0.00
Thu 07/02 09Z 0.48 2924 58 47 21 0.00
Thu 07/02 10Z 0.45 2924 55 28 21 0.00
Thu 07/02 11Z 0.46 3025 55 37 20 0.00
Thu 07/02 12Z 0.48 2925 62 53 19 0.00
Thu 07/02 13Z 0.51 2924 75 55 19 0.00
Thu 07/02 14Z 0.53 2924 82 51 19 0.00
Thu 07/02 15Z 0.48 3021 82 52 19 0.00
Thu 07/02 16Z 0.48 2918 80 54 19 0.00
Thu 07/02 17Z 0.51 2816 80 60 20 0.00
Thu 07/02 18Z 0.61 2715 82 69 20 0.00
Thu 07/02 19Z 0.70 2616 83 65 20 0.00
Thu 07/02 20Z 0.84 2517 87 44 20 0.00
Thu 07/02 21Z 1.08 2519 89 32 20 0.00
Thu 07/02 22Z 1.25 2620 86 40 20 0.01
Thu 07/02 23Z 1.70 2625 82 51 20 0.02
Fri 07/03 00Z 1.29 2626 89 62 19 0.01
Fri 07/03 01Z 1.08 2627 82 49 20 0.01
Fri 07/03 02Z 1.08 2729 87 64 20 0.01
Fri 07/03 03Z 0.93 2729 84 62 20 0.00
Fri 07/03 04Z 0.85 2828 86 64 19 0.00
Fri 07/03 05Z 0.71 2927 77 60 19 0.00
Fri 07/03 06Z 0.64 2927 73 52 19 0.00
Fri 07/03 07Z 0.59 2926 74 51 19 0.00
Fri 07/03 08Z 0.53 3026 76 44 18 0.00
Fri 07/03 09Z 0.48 3025 74 43 18 0.00
Fri 07/03 10Z 0.45 3024 77 33 18 0.00
Fri 07/03 11Z 0.40 3021 74 27 18 0.00
Fri 07/03 12Z 0.36 3018 72 23 18 0.00
Fri 07/03 13Z 0.35 2917 69 16 18 0.00
Fri 07/03 14Z 0.41 2918 68 17 18 0.00
Fri 07/03 15Z 0.47 2919 69 15 18 0.00
Fri 07/03 16Z 0.57 2919 68 15 18 0.00
Fri 07/03 17Z 0.74 2819 71 13 18 0.00
Fri 07/03 18Z 2.53 2820 76 17 17 0.00
Fri 07/03 19Z 9.35 2820 74 22 17 0.00
Fri 07/03 20Z 10.80 2821 64 18 18 0.00
Fri 07/03 21Z 8.33 2822 59 21 18 0.00
Fri 07/03 22Z 3.46 2821 59 24 18 0.00
Fri 07/03 23Z 1.95 2822 60 24 18 0.00
Sat 07/04 00Z 1.72 2823 58 27 18 0.00
Sat 07/04 01Z 2.07 2825 66 24 17 0.00
Sat 07/04 02Z 1.23 2925 79 23 16 0.00
Sat 07/04 03Z 0.92 2925 82 25 16 0.00
Sat 07/04 04Z 0.82 3025 81 24 16 0.00
Sat 07/04 05Z 0.68 3024 79 23 16 0.00
Run total areal avg QPF for the Central_Greens is: 0.09 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