National Weather Service United States Department of Commerce

Winter Weather Advisory in Effect for the southern Green Mountains and northern Adirondacks this Afternoon into Saturday

A Winter Weather Advisory in effect from 2 PM Today to 2 PM Saturday for 2 to 6 inches of snow for parts of the Adirondack Mountains in New York and Eastern Rutland and Western Windsor Counties in Vermont. The snow could impact the evening commute today. Plan on slippery road conditions. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260313_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 03/13 18Z 1.26 2010  74   3  -9 0.00
Fri 03/13 19Z 0.94 1912  66  20  -9 0.00
Fri 03/13 20Z 0.19 1813  58  72  -8 0.00
Fri 03/13 21Z 0.82 1818  54  83  -8 0.00
Fri 03/13 22Z 0.16 1820  64  88  -8 0.00
Fri 03/13 23Z 0.18 1722  81  90  -8 0.01
Sat 03/14 00Z 0.13 1724  88  92  -8 0.01
Sat 03/14 01Z 0.11 1727  90  91  -8 0.01
Sat 03/14 02Z 0.12 1729  91  77  -8 0.01
Sat 03/14 03Z 0.13 1729  94  87  -7 0.02
Sat 03/14 04Z 0.10 1729  95  91  -7 0.05
Sat 03/14 05Z 0.12 1827  95  81  -7 0.05
Sat 03/14 06Z 0.23 1926  96  80  -6 0.02
Sat 03/14 07Z 0.38 2022  97  85  -6 0.02
Sat 03/14 08Z 0.61 2223  97  87  -6 0.02
Sat 03/14 09Z 0.78 2224  97  86  -6 0.02
Sat 03/14 10Z 0.93 2326  96  85  -7 0.02
Sat 03/14 11Z 1.07 2426  96  84  -7 0.03
Sat 03/14 12Z 1.20 2426  95  82  -8 0.02
Sat 03/14 13Z 1.42 2526  95  80  -8 0.03
Sat 03/14 14Z 2.68 2525  94  77  -9 0.02
Sat 03/14 15Z 5.35 2524  93  75  -9 0.01
Sat 03/14 16Z 7.38 2623  90  75  -9 0.01
Sat 03/14 17Z 4.86 2622  91  75  -8 0.01
Sat 03/14 18Z 1.84 2622  93  79  -8 0.01
Sat 03/14 19Z 1.01 2621  95  83  -7 0.02
Sat 03/14 20Z 0.89 2622  96  85  -7 0.03
Sat 03/14 21Z 0.96 2625  97  82  -6 0.04
Sat 03/14 22Z 1.86 2831  94  81  -8 0.05
Sat 03/14 23Z 1.61 2832  94  79  -9 0.03
Sun 03/15 00Z 1.54 2934  94  79  -9 0.03
Sun 03/15 01Z 1.49 2935  95  76 -10 0.03
Sun 03/15 02Z 1.26 3034  95  63 -10 0.02
Sun 03/15 03Z 1.15 3032  95  46 -10 0.01
Sun 03/15 04Z 1.12 3031  96  21 -11 0.02
Sun 03/15 05Z 1.03 3029  95   9 -11 0.01
Sun 03/15 06Z 0.72 3127  90   5 -11 0.01
Sun 03/15 07Z 0.51 3124  80   6 -11 0.00
Sun 03/15 08Z 0.38 3122  67   8 -10 0.00
Sun 03/15 09Z 0.32 3119  58  10  -9 0.00
Sun 03/15 10Z 0.27 3117  48   7  -9 0.00
Sun 03/15 11Z 0.19 3214  37  13  -8 0.00
Sun 03/15 12Z 0.14 3210  31  40  -8 0.00
Sun 03/15 13Z 0.10 3106  27  68  -7 0.00
Sun 03/15 14Z 0.06 2702  26  85  -7 0.00
Sun 03/15 15Z 0.03 1904  27  93  -7 0.00
Sun 03/15 16Z 0.03 1708  29  97  -7 0.00
Sun 03/15 17Z 0.06 1713  36  96  -7 0.00
Sun 03/15 18Z 0.07 1716  51  97  -6 0.00
Sun 03/15 19Z 0.07 1720  55  82  -6 0.00
Sun 03/15 20Z 0.10 1724  53  76  -5 0.00
Sun 03/15 21Z 0.11 1730  43  52  -4 0.00
Sun 03/15 22Z 0.10 1733  41  35  -3 0.00
Sun 03/15 23Z 0.07 1737  41  32  -2 0.00
Mon 03/16 00Z 0.12 1840  42  33  -1 0.00
Mon 03/16 01Z 0.18 1942  37  35   0 0.00
Mon 03/16 02Z 0.22 1945  32  37   1 0.00
Mon 03/16 03Z 0.24 1947  37  36   2 0.00
Mon 03/16 04Z 0.24 1948  43  37   3 0.00
Mon 03/16 05Z 0.22 1949  52  38   4 0.00

Run total areal avg QPF for the greens is: 0.70 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