National Weather Service United States Department of Commerce

Flood Watch Continues for Northern New York and Most of Vermont until 2 PM Thursday

Additional river rises are expected with minor and localized ice jam flooding possible late tonight into Thursday. Also, minor open water flooding is forecasted on the Ausable River and Otter Creek, with Action Stage possible on the Lamoille, Winooski and Missisquoi Rivers on Thursday. The threat for flooding ends by Thursday night. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260311_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)
=== ===== === ==== ==== === === === ====
Wed 03/11 12Z 0.06 1625  84  86   9 0.00
Wed 03/11 13Z 0.06 1629  87  85  10 0.00
Wed 03/11 14Z 0.03 1730  83  78  11 0.00
Wed 03/11 15Z 0.06 1733  82  94  11 0.01
Wed 03/11 16Z 0.11 1834  82  93  11 0.02
Wed 03/11 17Z 0.17 1833  82  90  11 0.01
Wed 03/11 18Z 0.22 1935  80  79  11 0.00
Wed 03/11 19Z 0.26 1935  79  55  12 0.00
Wed 03/11 20Z 0.27 1934  79  74  12 0.00
Wed 03/11 21Z 0.32 1938  81  93  12 0.00
Wed 03/11 22Z 0.41 2039  91  86  11 0.01
Wed 03/11 23Z 0.50 2040  93  80  11 0.00
Thu 03/12 00Z 0.56 2041  93  85  12 0.01
Thu 03/12 02Z 0.62 2140  92  93  12 0.01
Thu 03/12 03Z 0.83 2238  96  94  10 0.01
Thu 03/12 04Z 1.03 2333  95  93   9 0.13
Thu 03/12 05Z 0.70 2325  87  86  10 0.14
Thu 03/12 06Z 0.76 2325  93  81   9 0.15
Thu 03/12 07Z 0.91 2328  97  64   8 0.01
Thu 03/12 08Z 0.92 2328  98  84   8 0.03
Thu 03/12 09Z 1.70 2631  98  88   4 0.04
Thu 03/12 10Z 0.92 2633  95  54   0 0.12
Thu 03/12 11Z 0.77 2731  89  56  -2 0.06
Thu 03/12 12Z 0.85 2731  89  41  -5 0.01
Thu 03/12 14Z 0.92 2829  89   6  -8 0.00
Thu 03/12 15Z 0.98 2827  89  12  -8 0.00
Thu 03/12 16Z 1.69 2727  92   4 -10 0.00
Thu 03/12 17Z 4.05 2826  91   3 -10 0.00
Thu 03/12 18Z 5.03 2826  89  11 -11 0.00
Thu 03/12 19Z 3.61 2923  87  26 -11 0.00
Thu 03/12 20Z 3.09 2921  87  16 -11 0.00
Thu 03/12 21Z 2.30 2920  87  27 -12 0.00
Thu 03/12 22Z 1.01 2919  87  37 -12 0.00
Thu 03/12 23Z 0.87 3020  87  42 -12 0.00
Fri 03/13 00Z 1.02 2922  88  52 -12 0.00
Fri 03/13 01Z 1.22 2923  90  56 -12 0.00
Fri 03/13 02Z 1.25 2924  91  57 -13 0.00
Fri 03/13 03Z 1.13 2923  92  55 -13 0.00
Fri 03/13 04Z 1.05 2922  94  53 -13 0.00
Fri 03/13 05Z 1.12 2923  95  54 -13 0.00
Fri 03/13 06Z 1.07 2921  95  49 -13 0.00
Fri 03/13 07Z 0.92 2919  95  35 -13 0.00
Fri 03/13 08Z 0.83 2816  96  25 -13 0.00
Fri 03/13 09Z 0.63 2814  94   7 -12 0.00
Fri 03/13 10Z 0.64 2714  93   3 -12 0.00
Fri 03/13 11Z 0.41 2612  87   2 -11 0.00
Fri 03/13 12Z 0.27 2509  77   4 -10 0.00
Fri 03/13 13Z 0.16 2108  66   8 -10 0.00
Fri 03/13 14Z 0.19 2011  56  12  -9 0.00
Fri 03/13 15Z 0.15 1814  45  22  -8 0.00
Fri 03/13 16Z 0.21 1915  44  60  -8 0.00
Fri 03/13 17Z 0.43 1918  48  87  -8 0.00
Fri 03/13 18Z 1.76 1821  59  90  -9 0.00
Fri 03/13 19Z 0.14 1726  93  88  -9 0.01
Fri 03/13 21Z 0.48 1932  94  87  -8 0.01
Fri 03/13 22Z 0.52 1931  91  73  -8 0.02
Fri 03/13 23Z 0.55 1931  90  90  -7 0.06

Run total areal avg QPF for the Central_Greens is: 0.87 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