National Weather Service United States Department of Commerce

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

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

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260312_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)
=== ===== === ==== ==== === === === ====
Thu 03/12 06Z 0.56 2128  89  80   9 0.00
Thu 03/12 07Z 0.70 2233  95  90   9 0.02
Thu 03/12 08Z 0.83 2332  98  92   9 0.07
Thu 03/12 09Z 1.03 2527  98  95   6 0.10
Thu 03/12 10Z 1.15 2631  97  88   2 0.08
Thu 03/12 11Z 1.12 2733  94  82  -1 0.07
Thu 03/12 14Z 1.68 2828  90  53  -9 0.02
Thu 03/12 15Z 1.74 2826  87  33  -9 0.00
Thu 03/12 16Z 1.96 2825  87  21 -10 0.00
Thu 03/12 17Z 3.04 2825  87  24 -11 0.00
Thu 03/12 18Z 3.30 2924  86  34 -11 0.00
Thu 03/12 19Z 3.40 2923  86  28 -12 0.00
Thu 03/12 20Z 2.45 2923  86  38 -12 0.00
Thu 03/12 21Z 2.39 3024  84  39 -13 0.00
Thu 03/12 22Z 1.87 3025  82  20 -13 0.00
Thu 03/12 23Z 1.27 3025  81  25 -13 0.00
Fri 03/13 00Z 1.41 3025  84  32 -13 0.00
Fri 03/13 01Z 1.83 3025  85  40 -14 0.00
Fri 03/13 02Z 2.04 3026  87  46 -14 0.00
Fri 03/13 03Z 1.78 3025  88  47 -14 0.00
Fri 03/13 04Z 1.62 3126  89  50 -14 0.00
Fri 03/13 05Z 1.22 3025  88  49 -14 0.00
Fri 03/13 06Z 0.94 3023  88  50 -14 0.00
Fri 03/13 07Z 0.84 3022  88  52 -13 0.00
Fri 03/13 08Z 0.80 2921  88  53 -13 0.00
Fri 03/13 09Z 0.61 2920  84  46 -12 0.00
Fri 03/13 10Z 0.56 2919  82  38 -12 0.00
Fri 03/13 11Z 0.59 2820  84  33 -12 0.00
Fri 03/13 12Z 0.40 2814  81  14 -12 0.00
Fri 03/13 13Z 0.36 2711  80   8 -12 0.00
Fri 03/13 14Z 0.27 2508  77   5 -11 0.00
Fri 03/13 15Z 0.20 2207  70   4 -11 0.00
Fri 03/13 16Z 0.08 1807  63  10 -10 0.00
Fri 03/13 18Z 0.20 1813  59  67  -9 0.00
Fri 03/13 19Z 0.47 1716  57  87  -9 0.00
Fri 03/13 20Z 0.38 1720  79  88 -10 0.00
Fri 03/13 21Z 0.23 1625  93  89  -9 0.00
Fri 03/13 22Z 0.15 1728  93  90  -9 0.00
Fri 03/13 23Z 0.10 1728  93  89  -9 0.00
Sat 03/14 00Z 0.13 1829  94  91  -8 0.04
Sat 03/14 01Z 0.19 1930  95  90  -8 0.04
Sat 03/14 02Z 0.23 1930  95  86  -7 0.02
Sat 03/14 03Z 0.18 1929  95  92  -5 0.01
Sat 03/14 04Z 0.26 1929  96  89  -6 0.01
Sat 03/14 05Z 0.40 2027  97  84  -6 0.01
Sat 03/14 06Z 0.61 2225  97  85  -6 0.02
Sat 03/14 07Z 0.87 2325  96  86  -7 0.03
Sat 03/14 08Z 1.05 2426  96  85  -7 0.02
Sat 03/14 09Z 1.25 2427  96  85  -8 0.02
Sat 03/14 10Z 1.44 2428  96  83  -9 0.01
Sat 03/14 11Z 1.43 2527  95  82  -9 0.02
Sat 03/14 12Z 1.46 2427  94  85  -9 0.02
Sat 03/14 13Z 1.46 2426  94  85 -10 0.02
Sat 03/14 14Z 1.23 2425  94  81 -10 0.01
Sat 03/14 15Z 1.16 2526  94  84  -9 0.01
Sat 03/14 16Z 1.25 2527  94  84  -9 0.01
Sat 03/14 17Z 1.58 2528  93  81  -8 0.02

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