National Weather Service United States Department of Commerce

Flood Watch continues for Northern New York and all of Vermont until Noon Sunday.

Multiple rivers are expected to reach minor flood stage with a few potentially climbing to moderate flood stage. Most rivers are expected to crest late this afternoon into this evening, based on anticipated additional rainfall and snow melt. Read More >

Subject: BTV4 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_BTV4_20190420_0600
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 04/20 06Z 0.18 1934  99  97  12 0.00
Sat 04/20 07Z 0.26 1937  98  98  12 0.03
Sat 04/20 08Z 0.41 2037  98  96  12 0.06
Sat 04/20 09Z 0.49 2136  96  89  12 0.03
Sat 04/20 10Z 0.51 2136  96  80  12 0.02
Sat 04/20 11Z 0.45 2132  97  75  11 0.01
Sat 04/20 12Z 0.41 2129  97  75  11 0.01
Sat 04/20 13Z 0.38 2126  97  76  11 0.01
Sat 04/20 14Z 0.34 2023  97  71  11 0.01
Sat 04/20 15Z 0.30 2019  96  64  11 0.01
Sat 04/20 16Z 0.12 1917  96  72  11 0.01
Sat 04/20 17Z 0.06 1815  96  77  11 0.01
Sat 04/20 18Z 0.06 1814  95  80  12 0.01
Sat 04/20 19Z 0.13 1817  95  78  12 0.02
Sat 04/20 20Z 0.13 1821  96  67  12 0.03
Sat 04/20 21Z 0.12 1822  97  55  11 0.04
Sat 04/20 22Z 0.12 1824  96  42  11 0.03
Sat 04/20 23Z 0.13 1827  94  45  12 0.00
Sun 04/21 00Z 0.09 1829  92  60  12 0.00
Sun 04/21 01Z 0.05 1832  90  69  13 0.00
Sun 04/21 02Z 0.03 1735  92  73  12 0.00
Sun 04/21 03Z 0.05 1837  93  70  11 0.01
Sun 04/21 04Z 0.14 1836  89  63  10 0.00
Sun 04/21 05Z 0.21 1934  79  61  11 0.00
Sun 04/21 06Z 0.23 1933  69  66  11 0.00
Sun 04/21 07Z 0.23 1931  63  73  10 0.00
Sun 04/21 08Z 0.20 1928  63  84  10 0.00
Sun 04/21 09Z 0.28 2025  69  92   9 0.00
Sun 04/21 10Z 0.39 2126  74  95   8 0.03
Sun 04/21 11Z 0.27 2021  63  86   9 0.00
Sun 04/21 12Z 0.22 2019  64  66   9 0.00
Sun 04/21 13Z 0.23 2019  68  52   8 0.00
Sun 04/21 14Z 0.27 2018  69  44   8 0.00
Sun 04/21 15Z 0.41 2016  70  42   7 0.00
Sun 04/21 16Z 1.07 2015  68  41   7 0.00
Sun 04/21 17Z 1.99 1915  65  43   8 0.00
Sun 04/21 18Z 2.30 1915  64  48   8 0.00
Sun 04/21 19Z 2.41 1915  66  52   8 0.00
Sun 04/21 20Z 2.45 1914  68  54   8 0.00
Sun 04/21 21Z 1.84 1913  70  51   8 0.00
Sun 04/21 22Z 0.51 1911  73  48   8 0.00
Sun 04/21 23Z 0.26 1909  76  51   7 0.00
Mon 04/22 00Z 0.24 2009  79  56   7 0.00
Mon 04/22 01Z 0.22 2008  81  54   7 0.01
Mon 04/22 02Z 0.24 2107  83  52   7 0.01
Mon 04/22 03Z 0.25 2206  85  46   6 0.00
Mon 04/22 04Z 0.23 2405  87  39   6 0.00
Mon 04/22 05Z 0.20 2504  89  36   6 0.00
Mon 04/22 06Z 0.13 2703  91  36   6 0.00
Mon 04/22 07Z 0.06 3302  91  36   6 0.00
Mon 04/22 08Z 0.06 0103  90  38   6 0.00
Mon 04/22 09Z 0.09 0205  90  41   6 0.00
Mon 04/22 10Z 0.16 0307  89  42   6 0.00
Mon 04/22 11Z 0.24 0309  89  43   6 0.00
Mon 04/22 12Z 0.29 0411  89  46   6 0.00
Mon 04/22 13Z 0.29 0509  88  49   6 0.00
Mon 04/22 14Z 0.26 0408  88  50   6 0.00
Mon 04/22 15Z 0.28 0209  90  51   6 0.00
Mon 04/22 16Z 0.69 0111  91  57   6 0.00
Mon 04/22 17Z 0.44 0112  91  66   6 0.00
Mon 04/22 18Z 0.14 0013  90  75   7 0.00
Mon 04/22 19Z 0.09 0015  90  85   7 0.03
Mon 04/22 20Z 0.12 0017  89  91   7 0.08
Mon 04/22 21Z 0.18 0020  93  90   7 0.08
Mon 04/22 22Z 0.22 0121  96  88   6 0.08
Mon 04/22 23Z 0.16 0122  98  85   6 0.06
Tue 04/23 00Z 0.13 0023  97  90   6 0.02
Tue 04/23 01Z 0.11 0022  96  88   6 0.01
Tue 04/23 02Z 0.09 0021  95  82   6 0.01
Tue 04/23 03Z 0.10 0121  94  73   5 0.01
Tue 04/23 04Z 0.09 0119  94  63   5 0.00
Tue 04/23 05Z 0.05 0017  91  57   5 0.00
Tue 04/23 06Z 0.04 0017  86  58   6 0.00
Tue 04/23 07Z 0.07 3515  86  69   5 0.00
Tue 04/23 08Z 0.11 3415  85  76   5 0.00
Tue 04/23 09Z 0.13 3416  85  83   5 0.00
Tue 04/23 10Z 0.13 3416  84  87   5 0.00
Tue 04/23 11Z 0.13 3315  83  88   5 0.00
Tue 04/23 12Z 0.13 3313  84  89   4 0.00
Tue 04/23 13Z 0.14 3312  84  90   4 0.00
Tue 04/23 14Z 0.15 3210  82  90   4 0.00
Tue 04/23 15Z 0.19 3107  81  92   4 0.00
Tue 04/23 16Z 0.23 2906  80  94   5 0.00
Tue 04/23 17Z 0.33 2605  77  94   5 0.00

Run total areal avg QPF for the greens is: 0.78 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