National Weather Service United States Department of Commerce

Strong Winds Expected Tonight into Sunday Morning

A Wind Advisory is in effect for most of northern New York and northwestern Vermont from 8 PM this evening to 8 AM Sunday. South to southeast wind gusts up to 50 mph are expected, with locally higher gusts possible. 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_20260404_1200
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)
=== ===== === ==== ==== === === === ====
Sat 04/04 12Z 0.08 0112  78  10   4 0.00
Sat 04/04 13Z 0.11 0312  71   8   4 0.00
Sat 04/04 14Z 0.14 0511  65   7   5 0.00
Sat 04/04 15Z 0.16 0710  60   9   5 0.00
Sat 04/04 16Z 0.17 1010  61  16   5 0.00
Sat 04/04 17Z 0.18 1211  68  28   4 0.00
Sat 04/04 18Z 0.20 1415  78  41   3 0.00
Sat 04/04 19Z 0.27 1417  84  57   2 0.00
Sat 04/04 20Z 0.33 1520  87  76   2 0.00
Sat 04/04 21Z 0.35 1524  87  85   3 0.01
Sat 04/04 22Z 0.33 1526  79  94   4 0.00
Sat 04/04 23Z 0.24 1529  74  97   4 0.00
Sun 04/05 00Z 0.17 1632  83  93   4 0.01
Sun 04/05 01Z 0.11 1634  86  93   5 0.02
Sun 04/05 02Z 0.07 1735  90  82   7 0.02
Sun 04/05 03Z 0.06 1736  92  83   8 0.01
Sun 04/05 04Z 0.06 1739  94  89   8 0.01
Sun 04/05 05Z 0.06 1743  95  87   8 0.02
Sun 04/05 06Z 0.05 1746  96  82   9 0.02
Sun 04/05 07Z 0.05 1846  96  81   9 0.02
Sun 04/05 08Z 0.06 1845  96  80  10 0.02
Sun 04/05 09Z 0.11 1944  97  74  10 0.02
Sun 04/05 10Z 0.17 1943  97  71  10 0.03
Sun 04/05 11Z 0.29 2041  98  80   7 0.08
Sun 04/05 12Z 0.41 2234  98  94   6 0.13
Sun 04/05 13Z 0.40 2329  97  98   7 0.09
Sun 04/05 14Z 0.51 2329  97  86   6 0.08
Sun 04/05 15Z 0.59 2427  94  70   4 0.02
Sun 04/05 16Z 0.66 2526  96  56   2 0.01
Sun 04/05 17Z 0.78 2525  95  30   1 0.01
Sun 04/05 18Z 0.87 2524  93  23   0 0.01
Sun 04/05 19Z 1.23 2524  95  22  -1 0.01
Sun 04/05 20Z 1.66 2623  92  25  -1 0.01
Sun 04/05 21Z 2.35 2623  91  23  -2 0.01
Sun 04/05 22Z 2.64 2624  89  24  -3 0.00
Sun 04/05 23Z 2.42 2626  91  23  -4 0.00
Mon 04/06 00Z 2.08 2628  92  25  -5 0.00
Mon 04/06 01Z 1.82 2629  92  30  -5 0.00
Mon 04/06 02Z 1.74 2729  94  37  -6 0.00
Mon 04/06 03Z 1.56 2729  95  43  -6 0.00
Mon 04/06 04Z 1.62 2731  96  47  -7 0.01
Mon 04/06 05Z 1.70 2732  97  56  -8 0.01
Mon 04/06 06Z 1.50 2832  96  63  -8 0.01
Mon 04/06 07Z 1.39 2832  97  67  -8 0.01
Mon 04/06 08Z 1.43 2832  97  58  -8 0.01
Mon 04/06 09Z 1.67 2931  97  49  -9 0.01
Mon 04/06 10Z 1.66 2930  97  46  -9 0.01
Mon 04/06 11Z 1.52 2929  97  50 -10 0.00
Mon 04/06 12Z 1.61 2927  97  55 -10 0.01
Mon 04/06 13Z 1.67 2825  96  61 -10 0.00
Mon 04/06 14Z 1.78 2823  94  70 -10 0.00
Mon 04/06 15Z 3.69 2822  92  75 -10 0.00
Mon 04/06 16Z 6.24 2821  90  76 -10 0.00
Mon 04/06 17Z 10.03 2720  84  76  -9 0.00
Mon 04/06 18Z 12.64 2820  78  75  -9 0.00
Mon 04/06 19Z 10.42 2820  80  79  -8 0.00
Mon 04/06 20Z 7.15 2819  84  81  -8 0.00
Mon 04/06 21Z 6.22 2819  84  81  -8 0.00
Mon 04/06 22Z 3.62 2819  85  79  -8 0.00
Mon 04/06 23Z 2.09 2819  88  79  -9 0.00

Run total areal avg QPF for the greens is: 0.75 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