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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260629_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)
=== ===== === ==== ==== === === === ====
Mon 06/29 12Z 0.06 3511 73 34 13 0.00
Mon 06/29 13Z 0.13 0011 74 36 13 0.00
Mon 06/29 14Z 0.22 0009 76 39 13 0.00
Mon 06/29 15Z 0.51 0008 76 44 13 0.00
Mon 06/29 16Z 0.79 0006 73 47 13 0.02
Mon 06/29 17Z 0.68 0006 71 55 13 0.03
Mon 06/29 18Z 0.35 3506 69 59 13 0.03
Mon 06/29 19Z 0.20 3506 67 52 14 0.01
Mon 06/29 20Z 0.36 3306 66 41 14 0.00
Mon 06/29 21Z 0.36 3306 66 34 14 0.00
Mon 06/29 22Z 0.15 3305 63 38 14 0.00
Mon 06/29 23Z 0.09 3305 59 36 14 0.00
Tue 06/30 00Z 0.06 3405 54 20 14 0.00
Tue 06/30 01Z 0.04 3504 52 9 14 0.00
Tue 06/30 02Z 0.07 3401 53 5 14 0.00
Tue 06/30 03Z 0.21 2702 54 6 14 0.00
Tue 06/30 04Z 0.61 2704 55 9 14 0.00
Tue 06/30 05Z 0.77 2705 57 10 14 0.00
Tue 06/30 06Z 0.69 2706 58 13 14 0.00
Tue 06/30 07Z 0.60 2706 58 12 14 0.00
Tue 06/30 08Z 0.53 2706 59 15 14 0.00
Tue 06/30 09Z 0.59 2508 59 20 13 0.00
Tue 06/30 10Z 0.59 2608 60 28 13 0.00
Tue 06/30 11Z 0.60 2508 61 34 13 0.00
Tue 06/30 12Z 0.48 2407 61 38 13 0.00
Tue 06/30 13Z 0.61 2407 65 52 13 0.00
Tue 06/30 14Z 1.17 2309 71 56 13 0.00
Tue 06/30 15Z 2.00 2208 77 54 14 0.00
Tue 06/30 16Z 2.39 2210 78 65 14 0.00
Tue 06/30 17Z 1.38 2208 76 57 14 0.00
Tue 06/30 18Z 0.62 2106 73 73 15 0.00
Tue 06/30 19Z 0.30 1907 72 84 15 0.00
Tue 06/30 20Z 0.37 1910 70 89 15 0.00
Tue 06/30 21Z 0.33 1914 73 78 15 0.00
Tue 06/30 22Z 0.46 2015 80 74 15 0.00
Tue 06/30 23Z 0.50 2018 80 84 16 0.00
Wed 07/01 00Z 0.62 2121 87 85 16 0.00
Wed 07/01 01Z 0.72 2224 91 71 17 0.00
Wed 07/01 02Z 0.81 2328 95 55 17 0.01
Wed 07/01 03Z 0.88 2331 98 43 17 0.02
Wed 07/01 04Z 0.99 2434 98 38 17 0.04
Wed 07/01 05Z 0.96 2533 96 45 18 0.06
Wed 07/01 06Z 0.90 2631 95 62 18 0.14
Wed 07/01 07Z 0.77 2628 94 60 18 0.18
Wed 07/01 08Z 0.83 2630 95 32 18 0.11
Wed 07/01 09Z 0.58 2826 79 19 19 0.02
Wed 07/01 10Z 0.59 2826 91 15 19 0.00
Wed 07/01 11Z 0.54 2823 93 17 19 0.01
Wed 07/01 12Z 0.49 2822 90 17 20 0.01
Wed 07/01 13Z 0.43 2820 89 26 21 0.01
Wed 07/01 14Z 0.40 2819 86 28 21 0.01
Wed 07/01 15Z 0.38 2817 83 27 21 0.00
Wed 07/01 16Z 0.38 2917 77 21 22 0.00
Wed 07/01 17Z 0.38 2817 75 17 22 0.00
Wed 07/01 18Z 0.37 2916 72 17 23 0.00
Wed 07/01 19Z 0.37 2915 71 16 23 0.00
Wed 07/01 20Z 0.39 2814 74 31 23 0.00
Wed 07/01 21Z 0.39 2814 75 51 23 0.00
Wed 07/01 22Z 0.40 2713 77 36 23 0.00
Wed 07/01 23Z 0.44 2614 81 26 22 0.00
Run total areal avg QPF for the Central_Greens is: 0.71 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