National Weather Service United States Department of Commerce

Dangerous Cold From 7 PM This Evening to 11 AM Friday

An Extreme Cold Warning has been issued for the Adirondacks with wind chills as low as 30 to 40 below zero expected. The Cold Weather Advisory has been expanded to include the Champlain Valley as well as the rest of northern New York and Vermont. The risk of frostbite and hypothermia will be elevated, especially for vulnerable populations. Wear appropriate clothing, a hat, and gloves. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260129_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)
=== ===== === ==== ==== === === === ====
Thu 01/29 18Z 2.70 2911  86  67 -19 0.00
Thu 01/29 19Z 2.01 2914  89  62 -19 0.00
Thu 01/29 20Z 1.32 2816  92  56 -19 0.00
Thu 01/29 21Z 1.10 2818  95  53 -19 0.00
Thu 01/29 22Z 1.27 2920  94  51 -19 0.01
Thu 01/29 23Z 1.45 2924  92  46 -20 0.01
Fri 01/30 00Z 1.23 3026  90  41 -20 0.01
Fri 01/30 01Z 0.85 3026  88  39 -21 0.00
Fri 01/30 02Z 0.81 3026  87  41 -22 0.00
Fri 01/30 03Z 0.83 2927  86  37 -22 0.00
Fri 01/30 04Z 0.80 2928  84  33 -23 0.00
Fri 01/30 05Z 0.72 2928  80  33 -23 0.00
Fri 01/30 06Z 0.65 2929  75  36 -23 0.00
Fri 01/30 07Z 0.58 2929  71  39 -23 0.00
Fri 01/30 10Z 0.48 2929  69  53 -22 0.00
Fri 01/30 11Z 0.46 3029  70  63 -22 0.00
Fri 01/30 12Z 0.43 3028  73  73 -22 0.00
Fri 01/30 13Z 0.40 3028  77  79 -21 0.00
Fri 01/30 14Z 0.38 3027  80  80 -21 0.00
Fri 01/30 15Z 0.37 3025  82  77 -21 0.00
Fri 01/30 16Z 0.36 3023  82  74 -20 0.00
Fri 01/30 17Z 0.35 3022  83  69 -20 0.00
Fri 01/30 18Z 0.37 3021  83  64 -20 0.00
Fri 01/30 19Z 0.40 2921  83  63 -20 0.00
Fri 01/30 20Z 0.42 2921  84  62 -19 0.00
Fri 01/30 21Z 0.42 2921  84  61 -19 0.00
Fri 01/30 22Z 0.39 3022  84  60 -18 0.00
Fri 01/30 23Z 0.33 3022  84  60 -17 0.00
Sat 01/31 00Z 0.28 3122  84  60 -16 0.00
Sat 01/31 01Z 0.23 3122  85  59 -16 0.00
Sat 01/31 02Z 0.21 3221  85  58 -15 0.00
Sat 01/31 03Z 0.19 3220  85  56 -15 0.00
Sat 01/31 04Z 0.18 3219  85  55 -14 0.00
Sat 01/31 05Z 0.18 3219  85  55 -14 0.00
Sat 01/31 06Z 0.19 3219  84  52 -14 0.00
Sat 01/31 07Z 0.19 3119  83  48 -14 0.00
Sat 01/31 08Z 0.20 3119  83  45 -14 0.00
Sat 01/31 09Z 0.21 3119  83  42 -14 0.00
Sat 01/31 10Z 0.21 3119  82  41 -14 0.00
Sat 01/31 11Z 0.20 3119  81  41 -14 0.00
Sat 01/31 12Z 0.19 3119  80  42 -14 0.00
Sat 01/31 13Z 0.18 3118  79  43 -14 0.00
Sat 01/31 14Z 0.17 3116  79  46 -14 0.00
Sat 01/31 15Z 0.16 3114  77  43 -14 0.00
Sat 01/31 16Z 0.16 3113  75  39 -14 0.00
Sat 01/31 17Z 0.16 3113  75  35 -14 0.00
Sat 01/31 18Z 0.16 3112  76  29 -14 0.00
Sat 01/31 19Z 0.16 3112  77  26 -14 0.00
Sat 01/31 20Z 0.15 3111  79  25 -14 0.00
Sat 01/31 21Z 0.14 3111  80  27 -15 0.00
Sat 01/31 22Z 0.15 3112  80  29 -15 0.00
Sat 01/31 23Z 0.14 3213  79  32 -14 0.00
Sun 02/01 00Z 0.11 3313  76  36 -14 0.00
Sun 02/01 01Z 0.07 3312  75  38 -14 0.00
Sun 02/01 02Z 0.04 3411  73  40 -14 0.00
Sun 02/01 03Z 0.02 3510  70  40 -13 0.00
Sun 02/01 04Z 0.02 0011  66  39 -12 0.00
Sun 02/01 05Z 0.02 0011  62  37 -11 0.00

Run total areal avg QPF for the greens is: 0.03 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