
Cold Weather Advisory has been issued for St. Lawrence, Franklin, western Clinton, and western Essex counties of New York Thursday 7 PM through Friday 10 AM. Cold temperatures and breezy winds will cause wind chills to fall into the -20F to -30F range. 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_0000
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 00Z 0.47 2812 78 52 -18 0.00
Thu 01/29 01Z 0.54 2913 81 52 -18 0.00
Thu 01/29 02Z 0.58 2914 83 58 -18 0.00
Thu 01/29 03Z 0.60 2914 84 62 -19 0.00
Thu 01/29 04Z 0.64 2914 83 60 -19 0.00
Thu 01/29 05Z 0.66 2915 84 58 -19 0.00
Thu 01/29 06Z 0.54 2915 82 56 -19 0.00
Thu 01/29 07Z 0.53 3015 79 54 -19 0.00
Thu 01/29 08Z 0.56 3016 81 51 -19 0.00
Thu 01/29 09Z 0.56 3017 81 46 -19 0.00
Thu 01/29 10Z 0.50 3015 79 44 -19 0.00
Thu 01/29 11Z 0.45 3014 79 45 -19 0.00
Thu 01/29 12Z 0.45 2914 83 47 -19 0.00
Thu 01/29 13Z 0.43 2914 83 51 -19 0.00
Thu 01/29 14Z 0.40 2913 80 59 -19 0.00
Thu 01/29 15Z 0.41 2913 80 61 -19 0.00
Thu 01/29 16Z 0.46 3013 82 60 -19 0.00
Thu 01/29 17Z 0.63 3014 85 56 -19 0.00
Thu 01/29 18Z 0.88 2914 87 56 -19 0.00
Thu 01/29 19Z 1.13 2915 90 58 -19 0.00
Thu 01/29 20Z 1.14 2916 93 61 -19 0.00
Thu 01/29 21Z 1.11 2918 94 60 -19 0.01
Thu 01/29 22Z 1.25 2921 92 55 -20 0.01
Thu 01/29 23Z 1.68 3024 88 53 -20 0.01
Fri 01/30 00Z 1.32 3026 85 49 -21 0.00
Fri 01/30 01Z 1.10 3027 82 43 -22 0.00
Fri 01/30 02Z 1.02 3027 82 40 -23 0.00
Fri 01/30 03Z 0.87 3028 80 37 -23 0.00
Fri 01/30 04Z 0.78 3028 78 35 -24 0.00
Fri 01/30 05Z 0.69 3028 76 34 -24 0.00
Fri 01/30 06Z 0.62 3029 73 33 -23 0.00
Fri 01/30 07Z 0.57 3030 71 35 -23 0.00
Fri 01/30 08Z 0.52 3030 70 40 -23 0.00
Fri 01/30 09Z 0.49 3029 70 42 -22 0.00
Fri 01/30 10Z 0.46 3029 69 47 -22 0.00
Fri 01/30 11Z 0.44 3029 69 55 -22 0.00
Fri 01/30 12Z 0.40 3028 70 64 -21 0.00
Fri 01/30 13Z 0.37 3027 72 74 -21 0.00
Fri 01/30 14Z 0.35 3026 75 80 -20 0.00
Fri 01/30 15Z 0.33 3024 77 80 -19 0.00
Fri 01/30 16Z 0.32 3022 79 78 -19 0.00
Fri 01/30 17Z 0.31 3021 80 76 -18 0.00
Fri 01/30 18Z 0.32 3020 81 74 -18 0.00
Fri 01/30 19Z 0.33 2919 81 72 -18 0.00
Fri 01/30 20Z 0.36 2920 82 70 -18 0.00
Fri 01/30 21Z 0.37 2920 83 69 -17 0.00
Fri 01/30 22Z 0.36 2920 84 66 -17 0.00
Fri 01/30 23Z 0.34 3021 85 65 -17 0.00
Sat 01/31 00Z 0.30 3021 86 65 -16 0.00
Sat 01/31 01Z 0.25 3120 86 64 -16 0.00
Sat 01/31 02Z 0.22 3119 86 62 -15 0.00
Sat 01/31 03Z 0.20 3119 86 61 -15 0.00
Sat 01/31 04Z 0.18 3117 86 61 -15 0.00
Sat 01/31 05Z 0.17 3117 86 59 -15 0.00
Sat 01/31 06Z 0.17 3116 86 57 -15 0.00
Sat 01/31 07Z 0.18 3116 85 55 -15 0.00
Sat 01/31 08Z 0.19 3116 85 54 -15 0.00
Sat 01/31 09Z 0.20 3117 86 53 -15 0.00
Sat 01/31 10Z 0.20 3117 86 51 -15 0.00
Sat 01/31 11Z 0.19 3117 85 49 -15 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