
A warm front will approach Friday afternoon. A brief wintry mix or rain in warmer valleys is possible before a quick transition into moderate or heavy snow takes place during the Friday evening commute. 1 inch per hour snowfall rates are possible in northeastern New York and much of Vermont. Difficult travel is likely to be the main concern. Light snow will continue Friday night into Saturday. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260219_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 02/19 00Z 0.08 0209 52 28 -6 0.00
Thu 02/19 01Z 0.16 0212 53 40 -6 0.00
Thu 02/19 02Z 0.21 0314 54 47 -7 0.00
Thu 02/19 03Z 0.21 0314 54 48 -7 0.00
Thu 02/19 04Z 0.19 0313 51 43 -7 0.00
Thu 02/19 05Z 0.12 0310 46 38 -7 0.00
Thu 02/19 06Z 0.12 0309 42 36 -6 0.00
Thu 02/19 07Z 0.13 0408 37 32 -6 0.00
Thu 02/19 08Z 0.10 0406 33 32 -6 0.00
Thu 02/19 09Z 0.08 0305 30 25 -6 0.00
Thu 02/19 10Z 0.06 0304 27 17 -6 0.00
Thu 02/19 11Z 0.04 0303 25 11 -5 0.00
Thu 02/19 12Z 0.05 0303 24 11 -5 0.00
Thu 02/19 13Z 0.04 0302 24 13 -5 0.00
Thu 02/19 14Z 0.04 0502 24 14 -5 0.00
Thu 02/19 15Z 0.04 0701 25 13 -4 0.00
Thu 02/19 16Z 0.03 1001 28 23 -4 0.00
Thu 02/19 17Z 0.01 1701 32 29 -4 0.00
Thu 02/19 18Z 0.02 1802 36 33 -4 0.00
Thu 02/19 19Z 0.03 1903 40 40 -4 0.00
Thu 02/19 20Z 0.05 2103 44 36 -4 0.00
Thu 02/19 21Z 0.06 2104 47 34 -4 0.00
Thu 02/19 22Z 0.12 2305 51 38 -4 0.00
Thu 02/19 23Z 0.11 2205 53 45 -4 0.00
Fri 02/20 00Z 0.06 2104 58 46 -3 0.00
Fri 02/20 01Z 0.02 1903 62 38 -3 0.00
Fri 02/20 02Z 0.04 1904 64 25 -4 0.00
Fri 02/20 03Z 0.07 2005 69 21 -4 0.00
Fri 02/20 04Z 0.07 2006 74 14 -4 0.00
Fri 02/20 05Z 0.08 2006 79 12 -5 0.00
Fri 02/20 06Z 0.10 2007 82 13 -5 0.00
Fri 02/20 07Z 0.09 2007 82 13 -4 0.00
Fri 02/20 08Z 0.07 2006 83 14 -4 0.00
Fri 02/20 09Z 0.05 1906 81 19 -3 0.00
Fri 02/20 10Z 0.04 1905 80 28 -3 0.00
Fri 02/20 11Z 0.02 1805 79 26 -3 0.00
Fri 02/20 12Z 0.03 1706 80 28 -3 0.00
Fri 02/20 13Z 0.06 1608 82 29 -2 0.00
Fri 02/20 14Z 0.07 1611 84 30 -2 0.00
Fri 02/20 15Z 0.08 1613 83 33 -2 0.00
Fri 02/20 16Z 0.07 1614 82 38 -3 0.00
Fri 02/20 17Z 0.10 1615 78 40 -2 0.00
Fri 02/20 18Z 0.11 1616 75 56 -2 0.00
Fri 02/20 19Z 0.15 1516 78 77 -1 0.00
Fri 02/20 20Z 0.18 1417 85 90 -1 0.01
Fri 02/20 21Z 0.24 1420 89 96 -1 0.05
Fri 02/20 22Z 0.30 1322 94 97 -1 0.09
Fri 02/20 23Z 0.36 1326 95 99 -1 0.13
Sat 02/21 00Z 0.37 1328 95 99 -2 0.11
Sat 02/21 01Z 0.36 1328 95 97 -2 0.08
Sat 02/21 02Z 0.36 1328 95 85 -2 0.04
Sat 02/21 03Z 0.34 1425 96 96 -3 0.04
Sat 02/21 04Z 0.31 1422 95 94 -4 0.06
Sat 02/21 05Z 0.25 1520 95 94 -6 0.05
Sat 02/21 06Z 0.17 1618 95 93 -6 0.02
Sat 02/21 07Z 0.07 1717 95 93 -6 0.02
Sat 02/21 08Z 0.05 1814 95 93 -7 0.02
Sat 02/21 09Z 0.08 1813 96 95 -7 0.02
Sat 02/21 10Z 0.12 1912 96 96 -7 0.02
Sat 02/21 11Z 0.15 2012 97 97 -7 0.02
Run total areal avg QPF for the greens is: 0.78 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