National Weather Service United States Department of Commerce

Winter Weather Advisory in Effect Across Southeastern St. Lawrence County Today, then Cold Weather Friday Night and Saturday

Rounds of lake effect snow are expected today into tomorrow in southeastern St. Lawrence County with periods of localized heavy snow. Snowfall rates may exceed 1"/hour at times, and gusty winds 35 mph during falling snow will result in low visibility. Then, cold temperatures and gusty winds will occur Friday night and Saturday across northern New York and Vermont. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260122_0000
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)
=== ===== === ==== ==== === === === ====
Thu 01/22 00Z 0.44 2033  82  87 -11 0.00
Thu 01/22 01Z 0.63 2038  77  80 -11 0.00
Thu 01/22 02Z 0.72 2139  80  90 -10 0.00
Thu 01/22 03Z 0.75 2139  86  93  -9 0.00
Thu 01/22 04Z 0.72 2237  91  95  -8 0.01
Thu 01/22 05Z 0.72 2236  94  96  -8 0.02
Thu 01/22 06Z 0.72 2236  94  95  -7 0.02
Thu 01/22 07Z 0.75 2236  93  94  -7 0.02
Thu 01/22 08Z 0.77 2236  93  80  -6 0.02
Thu 01/22 09Z 0.80 2335  94  48  -6 0.02
Thu 01/22 10Z 0.86 2335  93  78  -6 0.01
Thu 01/22 11Z 0.95 2432  91  91  -7 0.01
Thu 01/22 12Z 1.10 2431  92  88  -9 0.01
Thu 01/22 13Z 1.24 2432  91  73  -9 0.00
Thu 01/22 14Z 1.27 2531  86  60  -9 0.00
Thu 01/22 15Z 1.41 2530  87  71 -10 0.00
Thu 01/22 16Z 1.67 2528  91  85 -10 0.00
Thu 01/22 17Z 3.40 2525  87  68 -11 0.00
Thu 01/22 18Z 4.32 2526  86  53 -11 0.00
Thu 01/22 19Z 7.66 2527  89  25 -11 0.00
Thu 01/22 20Z 10.35 2529  87  13 -11 0.00
Thu 01/22 21Z 9.26 2531  86  24 -12 0.00
Thu 01/22 22Z 5.32 2632  80  26 -13 0.00
Thu 01/22 23Z 4.34 2530  84  29 -13 0.00
Fri 01/23 00Z 6.02 2530  87  30 -14 0.00
Fri 01/23 01Z 2.74 2530  83  32 -14 0.00
Fri 01/23 02Z 1.76 2529  83  28 -14 0.00
Fri 01/23 03Z 1.56 2529  80  28 -14 0.00
Fri 01/23 04Z 1.46 2532  81  26 -14 0.00
Fri 01/23 05Z 1.41 2532  83  25 -15 0.00
Fri 01/23 06Z 1.43 2533  82  25 -15 0.00
Fri 01/23 07Z 1.56 2531  84  27 -16 0.00
Fri 01/23 08Z 1.47 2530  87  23 -17 0.00
Fri 01/23 09Z 1.29 2627  87  25 -17 0.00
Fri 01/23 10Z 1.11 2526  85  28 -17 0.00
Fri 01/23 11Z 1.02 2427  86  28 -16 0.00
Fri 01/23 12Z 1.20 2432  87  38 -16 0.00
Fri 01/23 13Z 1.40 2432  88  31 -17 0.00
Fri 01/23 14Z 1.87 2430  89  34 -17 0.00
Fri 01/23 15Z 6.02 2426  90  26 -17 0.00
Fri 01/23 16Z 6.83 2523  90  22 -17 0.00
Fri 01/23 17Z 12.71 2624  81  26 -18 0.01
Fri 01/23 18Z 14.25 2624  72  31 -18 0.01
Fri 01/23 19Z 13.93 2622  71  43 -19 0.00
Fri 01/23 20Z 13.56 2624  72  59 -19 0.00
Fri 01/23 21Z 13.08 2626  69  66 -20 0.00
Fri 01/23 22Z 6.73 2628  68  68 -20 0.00
Fri 01/23 23Z 3.47 2729  75  69 -21 0.00
Sat 01/24 00Z 3.04 2826  84  69 -21 0.01
Sat 01/24 01Z 2.49 2926  83  63 -22 0.01
Sat 01/24 02Z 4.27 2925  81  55 -23 0.01
Sat 01/24 03Z 3.18 2924  80  40 -24 0.00
Sat 01/24 04Z 3.34 3025  83  31 -25 0.01
Sat 01/24 05Z 2.29 3028  77  23 -26 0.01
Sat 01/24 06Z 3.86 3030  69  23 -27 0.00
Sat 01/24 07Z 1.27 3032  57  26 -28 0.00
Sat 01/24 08Z 1.03 3032  64  27 -28 0.00
Sat 01/24 09Z 0.65 3032  68  26 -28 0.00
Sat 01/24 10Z 0.48 3132  67  22 -27 0.00
Sat 01/24 11Z 0.37 3131  64  18 -26 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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