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 greens

Model run: BTV_GRID_D2D_NAM3_20260403_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)
=== ===== === ==== ==== === === === ====
Fri 04/03 18Z 0.58 2530  79  92  10 0.00
Fri 04/03 19Z 0.64 2532  83  91  11 0.00
Fri 04/03 20Z 0.74 2433  88  85  11 0.00
Fri 04/03 21Z 0.84 2435  91  68  10 0.00
Fri 04/03 22Z 0.89 2435  92  39  10 0.00
Fri 04/03 23Z 1.06 2441  96  38  10 0.01
Sat 04/04 00Z 1.16 2543  96  39  10 0.01
Sat 04/04 01Z 1.18 2541  97  41   9 0.04
Sat 04/04 02Z 1.35 2640  98  22   8 0.05
Sat 04/04 03Z 1.57 2738  96  23   6 0.04
Sat 04/04 04Z 1.40 2738  95  27   5 0.02
Sat 04/04 05Z 1.23 2837  94  25   3 0.02
Sat 04/04 06Z 0.95 2933  93  20   2 0.01
Sat 04/04 07Z 0.66 3029  93  16   1 0.01
Sat 04/04 08Z 0.43 3126  92  15   0 0.01
Sat 04/04 09Z 0.27 3224  88  15   1 0.01
Sat 04/04 10Z 0.15 3420  83  14   1 0.01
Sat 04/04 11Z 0.10 3517  80  14   2 0.00
Sat 04/04 12Z 0.11 0215  73  13   2 0.00
Sat 04/04 13Z 0.14 0314  66  16   3 0.00
Sat 04/04 14Z 0.20 0515  58  19   4 0.00
Sat 04/04 15Z 0.23 0713  56  20   3 0.00
Sat 04/04 16Z 0.22 1012  57  26   3 0.00
Sat 04/04 17Z 0.20 1213  58  37   3 0.00
Sat 04/04 18Z 0.22 1314  62  55   3 0.00
Sat 04/04 19Z 0.25 1417  64  69   3 0.00
Sat 04/04 20Z 0.40 1419  67  53   2 0.00
Sat 04/04 21Z 0.61 1422  70  59   2 0.00
Sat 04/04 22Z 0.47 1526  72  89   2 0.00
Sat 04/04 23Z 0.28 1529  71  91   3 0.00
Sun 04/05 00Z 0.20 1532  69  92   5 0.00
Sun 04/05 01Z 0.15 1633  77  89   4 0.01
Sun 04/05 02Z 0.11 1634  82  81   5 0.01
Sun 04/05 03Z 0.08 1735  85  74   6 0.00
Sun 04/05 04Z 0.06 1737  91  72   7 0.01
Sun 04/05 05Z 0.05 1740  95  83   8 0.01
Sun 04/05 06Z 0.04 1743  95  91   8 0.03
Sun 04/05 07Z 0.05 1845  96  75   9 0.04
Sun 04/05 08Z 0.05 1845  96  88   9 0.02
Sun 04/05 09Z 0.09 1844  96  89  10 0.03
Sun 04/05 10Z 0.14 1944  97  76  10 0.03
Sun 04/05 11Z 0.20 1942  98  87   8 0.08
Sun 04/05 12Z 0.31 2038  98  96   6 0.13
Sun 04/05 13Z 0.45 2232  98  98   4 0.13
Sun 04/05 14Z 0.53 2329  98  95   4 0.08
Sun 04/05 15Z 0.60 2428  93  81   3 0.04
Sun 04/05 16Z 0.71 2528  91  52   2 0.01
Sun 04/05 17Z 0.87 2526  93  29   0 0.00
Sun 04/05 18Z 1.08 2526  94  21   0 0.01
Sun 04/05 19Z 1.88 2525  94  26  -1 0.01
Sun 04/05 20Z 7.32 2525  89  23  -2 0.01
Sun 04/05 21Z 8.20 2628  87  23  -3 0.00
Sun 04/05 22Z 7.89 2629  86  27  -3 0.00
Sun 04/05 23Z 4.41 2631  86  28  -4 0.00
Mon 04/06 00Z 2.44 2632  88  28  -5 0.00
Mon 04/06 01Z 1.69 2632  87  33  -5 0.01
Mon 04/06 02Z 2.17 2631  91  33  -6 0.01
Mon 04/06 03Z 1.70 2731  91  38  -7 0.00
Mon 04/06 04Z 1.81 2730  95  42  -8 0.00
Mon 04/06 05Z 1.60 2730  95  47  -8 0.00

Run total areal avg QPF for the greens is: 0.95 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