
A Winter Weather Advisory is in effect from 1 PM today to 5 AM Tuesday for lake effect snow in southern St. Lawrence County. Total snow accumulations between 2 and 5 inches are expected. Plan on slippery road conditions. Strong winds will cause blowing snow and further reduce visibilities. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260119_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)
=== ===== === ==== ==== === === === ====
Mon 01/19 18Z 4.34 2212 88 74 -14 0.00
Mon 01/19 19Z 4.01 2214 88 72 -14 0.00
Mon 01/19 20Z 3.50 2318 90 83 -14 0.00
Mon 01/19 21Z 1.66 2322 91 79 -14 0.00
Mon 01/19 22Z 2.28 2425 90 74 -14 0.01
Mon 01/19 23Z 1.83 2426 85 57 -14 0.01
Tue 01/20 00Z 1.57 2427 85 62 -14 0.00
Tue 01/20 01Z 2.11 2430 85 53 -15 0.00
Tue 01/20 02Z 2.36 2431 83 50 -15 0.00
Tue 01/20 03Z 3.66 2431 81 49 -16 0.00
Tue 01/20 04Z 3.25 2531 79 53 -17 0.00
Tue 01/20 05Z 2.26 2530 80 48 -17 0.00
Tue 01/20 06Z 1.25 2530 82 51 -17 0.00
Tue 01/20 07Z 1.36 2531 88 40 -17 0.00
Tue 01/20 08Z 1.46 2630 89 48 -18 0.00
Tue 01/20 09Z 1.89 2628 89 49 -18 0.00
Tue 01/20 10Z 3.04 2627 88 61 -19 0.00
Tue 01/20 11Z 2.98 2625 84 57 -19 0.00
Tue 01/20 12Z 2.16 2625 80 55 -20 0.00
Tue 01/20 13Z 1.77 2724 74 56 -20 0.00
Tue 01/20 14Z 2.55 2723 72 56 -21 0.00
Tue 01/20 15Z 4.72 2722 72 61 -21 0.00
Tue 01/20 16Z 8.80 2721 72 65 -21 0.00
Tue 01/20 17Z 11.04 2619 75 66 -21 0.00
Tue 01/20 18Z 10.55 2618 77 68 -21 0.00
Tue 01/20 19Z 10.01 2519 75 69 -21 0.00
Tue 01/20 20Z 8.56 2520 75 68 -20 0.00
Tue 01/20 21Z 8.23 2521 77 59 -21 0.00
Tue 01/20 22Z 3.31 2622 81 55 -21 0.00
Tue 01/20 23Z 3.48 2623 82 51 -21 0.00
Wed 01/21 00Z 3.04 2625 80 50 -21 0.00
Wed 01/21 01Z 1.90 2627 75 49 -21 0.00
Wed 01/21 02Z 1.45 2628 75 45 -21 0.00
Wed 01/21 03Z 1.25 2628 77 43 -21 0.00
Wed 01/21 04Z 1.10 2627 79 44 -20 0.00
Wed 01/21 05Z 1.02 2627 80 43 -20 0.00
Wed 01/21 06Z 0.95 2627 79 41 -20 0.00
Wed 01/21 07Z 0.81 2626 78 37 -19 0.00
Wed 01/21 08Z 0.85 2628 84 28 -19 0.00
Wed 01/21 09Z 0.76 2527 81 16 -18 0.00
Wed 01/21 10Z 0.69 2526 75 13 -18 0.00
Wed 01/21 11Z 0.68 2527 69 11 -17 0.00
Wed 01/21 12Z 0.66 2527 69 13 -17 0.00
Wed 01/21 13Z 0.62 2527 67 16 -16 0.00
Wed 01/21 14Z 0.55 2525 61 24 -15 0.00
Wed 01/21 15Z 0.47 2423 56 35 -15 0.00
Wed 01/21 16Z 0.42 2322 52 78 -14 0.00
Wed 01/21 17Z 0.36 2222 42 90 -14 0.00
Wed 01/21 18Z 0.29 2022 36 92 -13 0.00
Wed 01/21 19Z 0.32 2025 41 89 -14 0.00
Wed 01/21 20Z 0.25 1926 57 89 -12 0.00
Wed 01/21 21Z 0.17 1928 74 88 -11 0.01
Wed 01/21 22Z 0.16 1935 88 90 -10 0.03
Wed 01/21 23Z 0.33 2040 91 91 -11 0.04
Thu 01/22 00Z 0.43 2041 93 91 -11 0.02
Thu 01/22 01Z 0.50 2042 94 91 -10 0.01
Thu 01/22 02Z 0.58 2141 94 92 -9 0.01
Thu 01/22 03Z 0.64 2140 94 92 -9 0.02
Thu 01/22 04Z 0.64 2238 94 86 -8 0.01
Thu 01/22 05Z 0.64 2236 92 73 -8 0.01
Run total areal avg QPF for the greens is: 0.18 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