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 greens

Model run: BTV_GRID_D2D_NAM3_20260311_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)
=== ===== === ==== ==== === === === ====
Wed 03/11 18Z 0.09 1834  76  83  10 0.00
Wed 03/11 19Z 0.11 1936  78  80  11 0.00
Wed 03/11 20Z 0.14 1937  78  90  12 0.00
Wed 03/11 21Z 0.16 1938  82  87  11 0.00
Wed 03/11 22Z 0.15 1940  92  91  11 0.02
Wed 03/11 23Z 0.24 1942  96  89  11 0.04
Thu 03/12 00Z 0.41 2043  98  96  11 0.08
Thu 03/12 01Z 0.65 2242  98  95  11 0.10
Thu 03/12 02Z 0.80 2240  97  92  11 0.08
Thu 03/12 03Z 0.81 2237  96  91  11 0.07
Thu 03/12 04Z 0.70 2232  97  83  11 0.08
Thu 03/12 05Z 0.92 2332  97  79  10 0.07
Thu 03/12 06Z 0.77 2327  96  72  10 0.04
Thu 03/12 07Z 0.83 2329  95  92   9 0.04
Thu 03/12 08Z 0.80 2329  97  88   9 0.08
Thu 03/12 09Z 1.25 2634  96  84   5 0.09
Thu 03/12 10Z 1.05 2633  93  60   0 0.05
Thu 03/12 11Z 1.10 2633  91  53  -3 0.01
Thu 03/12 12Z 0.98 2730  92  38  -5 0.00
Thu 03/12 13Z 1.20 2730  94  23  -7 0.00
Thu 03/12 14Z 1.33 2728  93  15  -9 0.00
Thu 03/12 15Z 1.57 2828  92  22 -10 0.00
Thu 03/12 16Z 2.20 2827  92  13 -11 0.00
Thu 03/12 17Z 2.81 2825  92   8 -11 0.00
Thu 03/12 18Z 2.52 2823  90  12 -12 0.00
Thu 03/12 19Z 2.26 2823  90  15 -12 0.00
Thu 03/12 20Z 2.34 2921  90  25 -12 0.00
Thu 03/12 21Z 2.04 2921  89  26 -12 0.00
Thu 03/12 22Z 2.00 2922  90  36 -13 0.00
Thu 03/12 23Z 1.48 2923  90  41 -13 0.00
Fri 03/13 00Z 1.47 2925  91  48 -13 0.00
Fri 03/13 01Z 1.66 2927  92  52 -13 0.00
Fri 03/13 02Z 1.51 2927  93  60 -13 0.00
Fri 03/13 03Z 1.36 2926  94  62 -13 0.00
Fri 03/13 04Z 1.46 2924  95  64 -13 0.00
Fri 03/13 05Z 1.36 3022  95  60 -13 0.00
Fri 03/13 06Z 1.26 2922  95  60 -13 0.00
Fri 03/13 07Z 1.09 2922  94  56 -13 0.00
Fri 03/13 08Z 1.02 2922  93  52 -13 0.00
Fri 03/13 09Z 0.74 2819  90  40 -12 0.00
Fri 03/13 10Z 0.52 2815  89  19 -12 0.00
Fri 03/13 11Z 0.57 2717  89  13 -12 0.00
Fri 03/13 12Z 0.31 2710  82   5 -11 0.00
Fri 03/13 13Z 0.25 2409  76   4 -10 0.00
Fri 03/13 14Z 0.09 2008  63  10  -9 0.00
Fri 03/13 15Z 0.04 1813  56  30  -8 0.00
Fri 03/13 16Z 0.11 1817  55  81  -8 0.00
Fri 03/13 17Z 0.22 1920  53  86  -8 0.00
Fri 03/13 18Z 0.59 1823  68  89 -10 0.00
Fri 03/13 19Z 0.13 1729  91  88  -9 0.03
Fri 03/13 20Z 0.11 1733  92  92  -9 0.05
Fri 03/13 21Z 0.15 1833  93  88  -9 0.03
Fri 03/13 22Z 0.25 1933  94  90  -8 0.01
Fri 03/13 23Z 0.32 1934  93  88  -7 0.01
Sat 03/14 00Z 0.33 1934  92  81  -6 0.00
Sat 03/14 01Z 0.27 1934  90  89  -5 0.00
Sat 03/14 02Z 0.38 2034  93  82  -5 0.01
Sat 03/14 03Z 0.61 2134  95  54  -5 0.02
Sat 03/14 04Z 0.88 2233  97  34  -6 0.02
Sat 03/14 05Z 1.44 2332  97  28  -8 0.02

Run total areal avg QPF for the greens is: 1.05 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