National Weather Service United States Department of Commerce

Extreme Heat Warnings and Heat Advisories remain in effect through Friday

Dangerous heat will build today and continue through Friday. Extreme Heat Warnings are in effect for the entire Champlain Valley & eastern Windsor County in Vermont. Heat Advisories in effect for the remainder of our region. Heat index values will peak around 105 degrees in warning areas with locally higher values possible. Advisory areas will see heat index values up to 100 degrees. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260701_1800
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 18Z 0.77 2606  85  44  19 0.00
Wed 07/01 19Z 0.55 2507  83  38  20 0.00
Wed 07/01 20Z 0.40 2307  80  34  20 0.00
Wed 07/01 21Z 0.47 2309  81  32  20 0.00
Wed 07/01 22Z 0.62 2313  87  42  20 0.00
Wed 07/01 23Z 0.65 2418  89  51  20 0.00
Thu 07/02 00Z 0.73 2522  81  55  20 0.09
Thu 07/02 01Z 0.81 2523  86  56  20 0.02
Thu 07/02 02Z 0.80 2623  90  61  20 0.05
Thu 07/02 03Z 0.69 2623  82  49  20 0.05
Thu 07/02 04Z 0.56 2720  68  49  22 0.00
Thu 07/02 05Z 0.67 2625  61  56  21 0.00
Thu 07/02 06Z 0.72 2727  66  57  21 0.00
Thu 07/02 07Z 0.69 2827  70  52  20 0.00
Thu 07/02 08Z 0.59 2925  69  49  20 0.00
Thu 07/02 09Z 0.52 2923  66  49  20 0.00
Thu 07/02 10Z 0.51 2923  66  37  20 0.00
Thu 07/02 11Z 0.51 2924  61  44  20 0.00
Thu 07/02 12Z 0.52 2923  63  55  19 0.00
Thu 07/02 13Z 0.54 2923  79  57  19 0.00
Thu 07/02 14Z 0.55 2922  84  56  18 0.01
Thu 07/02 15Z 0.50 2920  83  57  19 0.01
Thu 07/02 16Z 0.48 2917  80  59  19 0.00
Thu 07/02 17Z 0.51 2815  79  64  20 0.00
Thu 07/02 18Z 0.58 2715  80  67  20 0.00
Thu 07/02 19Z 0.66 2616  81  66  20 0.00
Thu 07/02 20Z 0.83 2517  88  52  20 0.00
Thu 07/02 21Z 1.04 2519  90  40  19 0.00
Thu 07/02 22Z 1.20 2520  87  40  19 0.01
Thu 07/02 23Z 1.46 2625  83  51  20 0.02
Fri 07/03 00Z 1.18 2626  87  64  19 0.01
Fri 07/03 01Z 1.08 2627  84  56  20 0.01
Fri 07/03 02Z 1.07 2729  86  64  19 0.01
Fri 07/03 03Z 1.00 2729  85  61  19 0.00
Fri 07/03 04Z 0.95 2828  87  56  19 0.00
Fri 07/03 05Z 0.87 2928  81  54  19 0.01
Fri 07/03 06Z 0.78 2927  79  42  18 0.01
Fri 07/03 07Z 0.71 2927  81  43  18 0.01
Fri 07/03 08Z 0.60 3025  81  38  18 0.02
Fri 07/03 09Z 0.54 3024  79  36  18 0.02
Fri 07/03 10Z 0.49 3022  80  27  18 0.01
Fri 07/03 11Z 0.45 3020  77  23  18 0.01
Fri 07/03 12Z 0.41 2918  76  21  18 0.01
Fri 07/03 13Z 0.42 2917  74  17  18 0.01
Fri 07/03 14Z 0.48 2918  73  17  18 0.01
Fri 07/03 15Z 0.58 2819  75  15  18 0.00
Fri 07/03 16Z 0.69 2820  74  14  17 0.00
Fri 07/03 17Z 0.88 2821  75  14  17 0.00
Fri 07/03 18Z 2.24 2821  78  17  17 0.00
Fri 07/03 19Z 7.93 2821  75  21  17 0.00
Fri 07/03 20Z 9.79 2822  64  18  17 0.00
Fri 07/03 21Z 8.55 2822  62  22  17 0.00
Fri 07/03 22Z 4.09 2823  64  24  17 0.00
Fri 07/03 23Z 2.36 2823  66  25  17 0.00
Sat 07/04 00Z 1.77 2824  67  26  17 0.00
Sat 07/04 01Z 2.06 2926  71  22  16 0.01
Sat 07/04 02Z 1.45 2926  81  24  16 0.00
Sat 07/04 03Z 1.19 2925  83  24  16 0.01
Sat 07/04 04Z 1.04 3025  83  24  15 0.00
Sat 07/04 05Z 0.91 3023  81  23  15 0.00

Run total areal avg QPF for the greens is: 0.43 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