
A wintry mix of snow, sleet, and freezing rain will spread northward late Thursday through Friday Morning, mainly in southern Vermont and portions of northern New York. Precipitation will likely start as snow for most before transiting to a wintry mix Thursday night. Total snow and sleet accumulations up to one inch and ice accumulations up to two tenths of an inch are expected. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260304_1200
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 03/04 12Z 0.37 2918 69 17 -1 0.00
Wed 03/04 13Z 0.46 2922 65 12 -1 0.00
Wed 03/04 16Z 0.42 3020 54 8 0 0.00
Wed 03/04 17Z 0.41 2917 61 9 0 0.00
Wed 03/04 18Z 0.43 2916 65 11 -1 0.00
Wed 03/04 19Z 0.48 2816 67 14 -1 0.00
Wed 03/04 20Z 0.54 2718 64 17 -1 0.00
Wed 03/04 21Z 0.55 2718 62 19 0 0.00
Wed 03/04 22Z 0.54 2719 58 24 0 0.00
Thu 03/05 00Z 0.57 2720 59 31 0 0.00
Thu 03/05 01Z 0.55 2720 58 30 1 0.00
Thu 03/05 02Z 0.52 2719 57 28 1 0.00
Thu 03/05 03Z 0.50 2719 57 26 0 0.00
Thu 03/05 04Z 0.48 2718 56 24 0 0.00
Thu 03/05 05Z 0.45 2817 56 21 0 0.00
Thu 03/05 06Z 0.42 2816 57 20 0 0.00
Thu 03/05 07Z 0.36 2815 59 19 0 0.00
Thu 03/05 08Z 0.33 2914 63 20 0 0.00
Thu 03/05 09Z 0.28 2913 66 20 0 0.00
Thu 03/05 10Z 0.22 2910 68 21 0 0.00
Thu 03/05 11Z 0.16 2907 69 22 0 0.00
Thu 03/05 12Z 0.11 2805 71 23 0 0.00
Thu 03/05 14Z 0.07 2001 72 28 0 0.00
Thu 03/05 15Z 0.07 1602 74 29 0 0.00
Thu 03/05 16Z 0.06 1804 77 33 0 0.00
Thu 03/05 17Z 0.05 1704 77 34 0 0.00
Thu 03/05 18Z 0.05 1605 78 30 0 0.00
Thu 03/05 19Z 0.07 1607 80 27 0 0.00
Thu 03/05 20Z 0.08 1608 84 29 -1 0.00
Thu 03/05 21Z 0.10 1509 85 28 0 0.00
Thu 03/05 22Z 0.09 1510 85 30 0 0.00
Thu 03/05 23Z 0.10 1511 82 32 0 0.00
Fri 03/06 00Z 0.09 1512 82 38 0 0.00
Fri 03/06 01Z 0.11 1413 82 44 1 0.00
Fri 03/06 02Z 0.13 1415 83 51 0 0.00
Fri 03/06 03Z 0.13 1517 85 58 0 0.00
Fri 03/06 04Z 0.15 1419 86 64 0 0.01
Fri 03/06 05Z 0.17 1420 88 68 0 0.01
Fri 03/06 06Z 0.18 1421 91 72 0 0.01
Fri 03/06 07Z 0.18 1422 93 76 0 0.00
Fri 03/06 08Z 0.18 1523 94 80 0 0.00
Fri 03/06 09Z 0.18 1523 95 84 0 0.01
Fri 03/06 10Z 0.18 1522 95 89 0 0.01
Fri 03/06 11Z 0.17 1521 95 92 0 0.02
Fri 03/06 12Z 0.17 1520 95 94 0 0.03
Fri 03/06 13Z 0.17 1419 95 93 0 0.03
Fri 03/06 14Z 0.17 1419 95 90 -1 0.03
Fri 03/06 15Z 0.16 1519 94 83 -1 0.03
Fri 03/06 16Z 0.17 1519 93 74 0 0.02
Fri 03/06 17Z 0.16 1520 93 68 0 0.01
Fri 03/06 18Z 0.14 1521 93 65 0 0.01
Fri 03/06 19Z 0.14 1521 94 64 0 0.00
Fri 03/06 20Z 0.12 1620 94 68 0 0.00
Fri 03/06 21Z 0.12 1620 94 67 0 0.00
Fri 03/06 22Z 0.15 1523 93 57 0 0.00
Fri 03/06 23Z 0.12 1625 93 54 0 0.00
Run total areal avg QPF for the greens is: 0.23 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