National Weather Service United States Department of Commerce

Extreme Heat Warnings and Heat Advisories remain in effect through Friday

Dangerous heat will 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_20260702_0600
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)
=== ===== === ==== ==== === === === ====
Thu 07/02 06Z 0.61 2722  74  72  20 0.00
Thu 07/02 07Z 0.72 2826  77  66  20 0.00
Thu 07/02 08Z 0.73 2826  77  59  19 0.00
Thu 07/02 09Z 0.67 2926  74  55  19 0.00
Thu 07/02 10Z 0.64 2928  69  51  20 0.00
Thu 07/02 11Z 0.59 2927  63  48  20 0.00
Thu 07/02 12Z 0.56 2925  63  56  20 0.00
Thu 07/02 13Z 0.54 2924  64  60  20 0.00
Thu 07/02 14Z 0.53 3022  63  58  20 0.00
Thu 07/02 15Z 0.56 2919  65  53  19 0.00
Thu 07/02 16Z 0.65 2818  71  54  19 0.00
Thu 07/02 17Z 0.76 2816  78  54  19 0.00
Thu 07/02 18Z 1.28 2715  87  55  19 0.00
Thu 07/02 19Z 2.11 2716  87  55  18 0.00
Thu 07/02 20Z 2.58 2715  84  58  19 0.00
Thu 07/02 21Z 1.56 2714  83  69  19 0.02
Thu 07/02 22Z 0.92 2616  85  64  19 0.07
Thu 07/02 23Z 0.88 2620  83  62  19 0.01
Fri 07/03 00Z 0.88 2620  86  56  19 0.03
Fri 07/03 01Z 1.04 2623  87  57  19 0.01
Fri 07/03 02Z 0.97 2623  85  58  19 0.03
Fri 07/03 03Z 0.88 2725  85  62  18 0.10
Fri 07/03 04Z 0.92 2826  86  67  18 0.04
Fri 07/03 05Z 0.90 2826  88  71  18 0.01
Fri 07/03 06Z 0.89 2826  92  70  17 0.00
Fri 07/03 07Z 0.82 2926  93  57  17 0.00
Fri 07/03 08Z 0.71 2924  92  35  17 0.01
Fri 07/03 09Z 0.63 2923  89  25  17 0.01
Fri 07/03 10Z 0.57 2923  87  19  17 0.01
Fri 07/03 11Z 0.50 3022  83  14  18 0.01
Fri 07/03 12Z 0.41 3020  79  12  18 0.01
Fri 07/03 13Z 0.39 3018  77  15  18 0.01
Fri 07/03 14Z 0.42 3017  78  17  18 0.01
Fri 07/03 15Z 0.43 2916  77  16  18 0.00
Fri 07/03 16Z 0.45 2916  74  25  18 0.00
Fri 07/03 17Z 0.55 2817  73  27  18 0.00
Fri 07/03 18Z 0.63 2816  73  35  18 0.00
Fri 07/03 19Z 0.63 2715  69  32  19 0.00
Fri 07/03 20Z 0.83 2715  70  36  18 0.00
Fri 07/03 21Z 1.36 2616  74  53  18 0.00
Fri 07/03 22Z 1.72 2617  81  59  18 0.00
Fri 07/03 23Z 1.82 2619  80  69  17 0.00
Sat 07/04 00Z 1.54 2719  77  76  17 0.00
Sat 07/04 01Z 1.59 2621  83  87  17 0.00
Sat 07/04 02Z 0.95 2623  93  83  17 0.03
Sat 07/04 03Z 0.87 2723  91  78  17 0.08
Sat 07/04 04Z 0.73 2824  94  72  17 0.06
Sat 07/04 05Z 0.74 2926  94  70  16 0.05
Sat 07/04 06Z 0.59 3023  93  54  16 0.02
Sat 07/04 07Z 0.55 3022  89  44  15 0.01
Sat 07/04 08Z 0.58 3022  89  51  15 0.01
Sat 07/04 09Z 0.57 3022  89  50  14 0.01
Sat 07/04 10Z 0.59 3023  90  51  14 0.01
Sat 07/04 11Z 0.54 3022  89  48  14 0.01
Sat 07/04 12Z 0.50 3123  85  45  13 0.01
Sat 07/04 13Z 0.49 3122  82  39  13 0.00
Sat 07/04 14Z 0.54 3121  79  35  13 0.01
Sat 07/04 15Z 0.56 3020  80  30  12 0.01
Sat 07/04 16Z 0.58 3019  82  22  12 0.01
Sat 07/04 17Z 0.62 3018  83  23  12 0.01

Run total areal avg QPF for the greens is: 0.73 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