National Weather Service United States Department of Commerce

Extreme Heat Watch in Effect from Wednesday through Friday for the Champlain valley and eastern Windsor county in Vermont

Significant heat is expected to build from Wednesday through Friday. Hot temperatures and high humidity will allow heat index values to reach into at least the mid 90s each afternoon from Wednesday through Friday in the Champlain Valley and eastern Windsor county in Vermont. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260630_0000
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 06/30 00Z 0.16 3307  52   9  15 0.00
Tue 06/30 01Z 0.14 3307  48   8  15 0.00
Tue 06/30 02Z 0.07 3405  45   7  15 0.00
Tue 06/30 03Z 0.06 3403  45   8  14 0.00
Tue 06/30 04Z 0.06 3000  44  10  14 0.00
Tue 06/30 05Z 0.16 2502  42  10  14 0.00
Tue 06/30 06Z 0.43 2806  42  10  14 0.00
Tue 06/30 07Z 0.83 2806  51  13  14 0.00
Tue 06/30 08Z 0.70 2706  61  15  14 0.00
Tue 06/30 09Z 0.45 2507  66  24  14 0.00
Tue 06/30 10Z 0.38 2607  67  26  14 0.00
Tue 06/30 11Z 0.38 2607  68  30  14 0.00
Tue 06/30 12Z 0.33 2407  69  41  14 0.00
Tue 06/30 13Z 0.38 2307  67  46  14 0.00
Tue 06/30 14Z 0.60 2307  67  48  14 0.00
Tue 06/30 15Z 1.39 2307  66  50  14 0.00
Tue 06/30 16Z 1.04 2209  63  69  15 0.00
Tue 06/30 17Z 0.87 2211  60  71  15 0.00
Tue 06/30 18Z 1.62 2211  60  83  15 0.00
Tue 06/30 19Z 0.80 2009  59  82  15 0.00
Tue 06/30 20Z 1.00 2010  60  89  16 0.00
Tue 06/30 21Z 0.64 2009  58  87  16 0.00
Tue 06/30 22Z 0.51 2011  59  90  16 0.00
Tue 06/30 23Z 0.49 2014  69  86  16 0.00
Wed 07/01 00Z 0.53 2016  73  94  16 0.00
Wed 07/01 01Z 0.55 2117  79  88  17 0.00
Wed 07/01 02Z 0.60 2218  82  87  17 0.00
Wed 07/01 03Z 0.63 2221  96  90  17 0.03
Wed 07/01 04Z 0.61 2420  97  71  17 0.07
Wed 07/01 05Z 0.59 2518  96  57  17 0.02
Wed 07/01 06Z 0.60 2618  96  50  17 0.01
Wed 07/01 07Z 0.56 2618  97  48  17 0.06
Wed 07/01 08Z 0.48 2515  97  37  18 0.06
Wed 07/01 09Z 0.44 2515  94  29  18 0.02
Wed 07/01 10Z 0.42 2515  93  25  18 0.01
Wed 07/01 11Z 0.47 2517  94  32  18 0.01
Wed 07/01 12Z 0.56 2520  95  15  18 0.02
Wed 07/01 13Z 0.58 2620  96  32  18 0.02
Wed 07/01 14Z 0.59 2719  96  54  18 0.01
Wed 07/01 15Z 0.49 2717  89  50  19 0.00
Wed 07/01 16Z 0.44 2816  78  58  20 0.00
Wed 07/01 17Z 0.41 2814  79  57  20 0.00
Wed 07/01 18Z 0.42 2813  85  54  20 0.00
Wed 07/01 19Z 0.40 2812  86  48  20 0.00
Wed 07/01 20Z 0.35 2811  80  33  21 0.00
Wed 07/01 21Z 0.39 2712  78  25  21 0.00
Wed 07/01 22Z 0.38 2612  72  19  22 0.00
Wed 07/01 23Z 0.38 2612  64  17  23 0.00
Thu 07/02 00Z 0.44 2615  61  20  23 0.00
Thu 07/02 01Z 0.61 2621  64  25  22 0.00
Thu 07/02 02Z 0.77 2624  68  33  22 0.00
Thu 07/02 03Z 0.62 2622  74  42  22 0.00
Thu 07/02 04Z 0.70 2526  86  44  21 0.00
Thu 07/02 05Z 0.67 2725  82  50  22 0.00
Thu 07/02 06Z 0.54 2824  67  51  22 0.00
Thu 07/02 07Z 0.49 2923  68  53  21 0.00
Thu 07/02 08Z 0.41 3021  74  57  20 0.00
Thu 07/02 09Z 0.38 3021  79  45  20 0.00
Thu 07/02 10Z 0.38 2920  75  51  20 0.00
Thu 07/02 11Z 0.37 2920  71  40  21 0.00

Run total areal avg QPF for the Central_Greens is: 0.34 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