National Weather Service United States Department of Commerce

Strong Winds Expected Sunday Night into Sunday Morning

A Wind Advisory is in effect for most of northern New York and the northern Champlain Valley of Vermont from 8PM Saturday to 8AM Sunday. South to southwest wind gusts of 40 to 50 mph are expected. Strong winds may break limbs or down trees, resulting in isolated power outages. Travel may be difficult for high profile vehicles. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260403_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)
=== ===== === ==== ==== === === === ====
Fri 04/03 12Z 0.42 2234  85  90  10 0.00
Fri 04/03 13Z 0.49 2236  91  97  11 0.01
Fri 04/03 14Z 0.49 2335  91  95  11 0.01
Fri 04/03 15Z 0.52 2434  90  81  11 0.00
Fri 04/03 16Z 0.55 2433  92  74  11 0.00
Fri 04/03 17Z 0.62 2434  92  85  11 0.00
Fri 04/03 18Z 0.69 2535  93  75  11 0.00
Fri 04/03 19Z 0.72 2534  91  44  11 0.00
Fri 04/03 20Z 0.79 2534  89  49  11 0.00
Fri 04/03 21Z 0.84 2535  87  48  11 0.00
Fri 04/03 22Z 0.98 2537  88  24  11 0.00
Fri 04/03 23Z 1.12 2539  91  21  10 0.00
Sat 04/04 00Z 1.09 2540  95  21  10 0.01
Sat 04/04 01Z 1.26 2542  97  26   9 0.02
Sat 04/04 02Z 1.35 2642  97  19   8 0.03
Sat 04/04 03Z 1.49 2641  97  12   8 0.03
Sat 04/04 04Z 1.52 2739  96  18   6 0.02
Sat 04/04 05Z 1.26 2835  96  17   5 0.02
Sat 04/04 07Z 0.60 3030  92  12   2 0.01
Sat 04/04 09Z 0.25 3227  89  15   1 0.01
Sat 04/04 10Z 0.09 3323  83  16   2 0.01
Sat 04/04 14Z 0.18 0512  59  19   4 0.01
Sat 04/04 15Z 0.19 0711  58  19   4 0.00
Sat 04/04 16Z 0.18 1111  61  21   4 0.00
Sat 04/04 17Z 0.16 1313  64  26   3 0.00
Sat 04/04 18Z 0.18 1314  63  36   3 0.00
Sat 04/04 19Z 0.20 1416  65  60   2 0.00
Sat 04/04 20Z 0.34 1417  69  66   2 0.00
Sat 04/04 21Z 0.57 1420  72  52   2 0.00
Sat 04/04 22Z 0.27 1423  77  35   2 0.00
Sat 04/04 23Z 0.16 1526  75  88   4 0.00
Sun 04/05 00Z 0.10 1528  64  91   6 0.00
Sun 04/05 01Z 0.08 1629  65  81   5 0.00
Sun 04/05 02Z 0.07 1630  72  81   5 0.00
Sun 04/05 03Z 0.05 1631  81  89   6 0.00
Sun 04/05 04Z 0.04 1733  91  94   7 0.00
Sun 04/05 05Z 0.04 1736  96  95   7 0.00
Sun 04/05 06Z 0.07 1739  97  91   7 0.00
Sun 04/05 07Z 0.09 1740  96  63   7 0.00
Sun 04/05 08Z 0.12 1840  97  74   8 0.00
Sun 04/05 09Z 0.15 1841  97  76   8 0.00
Sun 04/05 10Z 0.19 1840  97  88   9 0.03
Sun 04/05 11Z 0.25 1938  98  61   8 0.08
Sun 04/05 12Z 0.34 2036  98  90   7 0.02
Sun 04/05 13Z 0.47 2234  98  97   6 0.02
Sun 04/05 14Z 0.56 2332  96  94   5 0.02
Sun 04/05 15Z 0.58 2430  90  92   5 0.03
Sun 04/05 17Z 0.81 2526  95  17   1 0.05
Sun 04/05 18Z 1.20 2626  97  20   0 0.07
Sun 04/05 19Z 1.71 2626  94  19  -2 0.08
Sun 04/05 21Z 6.94 2627  87  10  -3 0.06
Sun 04/05 22Z 6.86 2627  88   9  -4 0.02
Sun 04/05 23Z 3.57 2629  89   9  -4 0.01

Run total areal avg QPF for the Central_Greens is: 0.68 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