
A Winter Storm Warning and Winter Weather Advisory is in effect from until 7 PM Thursday for most of northern New York. Total snow accumulations between 3 and 9 inches are expected. Precipitation will initially start as rain before changing over to snow with sharply falling temperatures. Travel could be very difficult, including the Thursday commutes. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260114_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)
=== ===== === ==== ==== === === === ====
Wed 01/14 06Z 0.46 2129 79 66 -2 0.00
Wed 01/14 07Z 0.59 2232 77 77 -1 0.00
Wed 01/14 08Z 0.65 2232 76 74 -1 0.00
Wed 01/14 09Z 0.66 2330 78 80 -1 0.00
Wed 01/14 10Z 0.66 2330 78 83 -1 0.00
Wed 01/14 11Z 0.67 2329 78 72 -1 0.00
Wed 01/14 13Z 0.63 2327 80 79 0 0.00
Wed 01/14 14Z 0.62 2327 79 68 0 0.00
Wed 01/14 15Z 0.57 2325 81 61 0 0.00
Wed 01/14 16Z 0.55 2224 81 62 0 0.00
Wed 01/14 17Z 0.56 2223 81 62 0 0.00
Wed 01/14 18Z 0.61 2222 81 65 0 0.00
Wed 01/14 19Z 0.59 2222 82 64 0 0.00
Wed 01/14 20Z 0.62 2221 83 75 -1 0.00
Wed 01/14 22Z 0.45 2118 87 91 -1 0.00
Wed 01/14 23Z 0.37 2117 93 93 -1 0.00
Thu 01/15 00Z 0.32 2117 95 95 -1 0.00
Thu 01/15 01Z 0.26 2116 97 95 -1 0.01
Thu 01/15 02Z 0.16 2014 98 94 -1 0.01
Thu 01/15 03Z 0.08 1813 98 93 -1 0.01
Thu 01/15 04Z 0.07 1712 97 94 -1 0.02
Thu 01/15 05Z 0.07 1713 96 94 -1 0.03
Thu 01/15 07Z 0.06 1715 98 95 -1 0.03
Thu 01/15 08Z 0.05 1715 98 95 -1 0.03
Thu 01/15 09Z 0.05 1715 98 95 -1 0.03
Thu 01/15 10Z 0.04 1816 98 94 -1 0.03
Thu 01/15 11Z 0.07 1815 98 95 -1 0.04
Thu 01/15 12Z 0.11 1915 99 93 -2 0.04
Thu 01/15 13Z 0.23 2016 99 90 -2 0.04
Thu 01/15 14Z 0.35 2116 98 79 -3 0.03
Thu 01/15 15Z 0.44 2216 98 73 -3 0.03
Thu 01/15 16Z 0.40 2316 97 74 -4 0.03
Thu 01/15 17Z 0.37 2317 96 57 -5 0.02
Thu 01/15 18Z 0.42 2418 95 40 -7 0.02
Thu 01/15 19Z 0.79 2519 95 22 -10 0.02
Thu 01/15 20Z 1.61 2519 93 14 -12 0.02
Thu 01/15 21Z 2.65 2521 91 20 -14 0.02
Thu 01/15 22Z 2.88 2521 91 35 -15 0.01
Thu 01/15 23Z 2.94 2522 91 48 -16 0.01
Fri 01/16 00Z 3.97 2521 89 64 -17 0.01
Fri 01/16 01Z 3.13 2522 86 67 -17 0.01
Fri 01/16 02Z 3.75 2522 86 68 -18 0.01
Fri 01/16 03Z 4.43 2522 85 72 -19 0.01
Fri 01/16 04Z 4.84 2622 85 75 -20 0.01
Fri 01/16 05Z 4.21 2621 87 77 -20 0.01
Fri 01/16 06Z 5.33 2722 88 77 -21 0.01
Fri 01/16 08Z 1.53 2824 88 76 -21 0.01
Fri 01/16 09Z 1.01 2825 88 68 -20 0.01
Fri 01/16 10Z 0.91 2826 88 38 -20 0.01
Fri 01/16 11Z 0.71 2825 88 21 -20 0.01
Fri 01/16 12Z 0.53 2924 85 14 -18 0.01
Fri 01/16 13Z 0.42 2923 72 11 -17 0.01
Fri 01/16 14Z 0.34 3023 55 13 -14 0.00
Fri 01/16 15Z 0.30 3021 44 9 -13 0.00
Fri 01/16 16Z 0.27 3018 41 7 -13 0.00
Fri 01/16 17Z 0.27 2916 38 9 -12 0.00
Run total areal avg QPF for the greens is: 0.66 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