
A Frost Advisory has been issued for the northern St. Lawrence Valley, the Champlain Valley, outside of Grand Isle County in Vermont, and portions of central and southern Vermont from 2 AM to 9 AM Thursday. Frost will be less likely in areas near and along Lake Champlain, generally within 5 miles of the lake. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260923_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)
=== ===== === ==== ==== === === === ====
Wed 09/23 18Z 1.65 0706 81 10 3 0.00
Wed 09/23 19Z 1.43 0707 78 9 4 0.00
Wed 09/23 20Z 0.91 0707 78 8 4 0.00
Wed 09/23 21Z 0.58 0707 79 7 4 0.00
Wed 09/23 22Z 0.45 0708 79 6 4 0.00
Wed 09/23 23Z 0.40 0609 76 5 4 0.00
Thu 09/24 00Z 0.43 0611 74 4 5 0.00
Thu 09/24 01Z 0.46 0711 74 4 4 0.00
Thu 09/24 02Z 0.44 0712 70 4 5 0.00
Thu 09/24 03Z 0.41 0812 64 3 5 0.00
Thu 09/24 04Z 0.37 0812 57 4 5 0.00
Thu 09/24 05Z 0.32 0811 48 3 6 0.00
Thu 09/24 06Z 0.29 0711 41 3 7 0.00
Thu 09/24 07Z 0.26 0711 35 3 7 0.00
Thu 09/24 08Z 0.25 0611 32 3 7 0.00
Thu 09/24 09Z 0.26 0612 33 3 7 0.00
Thu 09/24 10Z 0.25 0611 33 3 7 0.00
Thu 09/24 11Z 0.25 0611 33 3 7 0.00
Thu 09/24 12Z 0.27 0712 32 3 7 0.00
Thu 09/24 13Z 0.26 0712 32 3 7 0.00
Thu 09/24 14Z 0.24 0711 31 3 7 0.00
Thu 09/24 15Z 0.21 0709 32 3 7 0.00
Thu 09/24 16Z 0.22 0709 33 4 7 0.00
Thu 09/24 17Z 0.22 0608 32 4 7 0.00
Thu 09/24 18Z 0.23 0608 31 4 8 0.00
Thu 09/24 19Z 0.23 0607 32 5 8 0.00
Thu 09/24 20Z 0.22 0607 35 5 8 0.00
Thu 09/24 21Z 0.26 0609 39 5 8 0.00
Thu 09/24 22Z 0.27 0609 44 5 8 0.00
Thu 09/24 23Z 0.31 0611 47 5 8 0.00
Fri 09/25 00Z 0.31 0611 48 5 8 0.00
Fri 09/25 01Z 0.33 0613 49 5 9 0.00
Fri 09/25 02Z 0.34 0613 50 5 9 0.00
Fri 09/25 03Z 0.33 0613 49 5 9 0.00
Fri 09/25 04Z 0.33 0613 46 6 9 0.00
Fri 09/25 05Z 0.31 0613 45 6 9 0.00
Fri 09/25 06Z 0.30 0613 45 6 9 0.00
Fri 09/25 07Z 0.30 0613 47 6 9 0.00
Fri 09/25 08Z 0.30 0513 48 6 9 0.00
Fri 09/25 09Z 0.31 0514 50 7 8 0.00
Fri 09/25 10Z 0.34 0515 52 7 8 0.00
Fri 09/25 11Z 0.38 0516 53 7 8 0.00
Fri 09/25 12Z 0.39 0517 51 8 8 0.00
Fri 09/25 13Z 0.43 0618 48 7 9 0.00
Fri 09/25 14Z 0.44 0617 50 8 8 0.00
Fri 09/25 15Z 0.47 0616 51 8 8 0.00
Fri 09/25 16Z 0.48 0614 49 7 8 0.00
Fri 09/25 17Z 0.41 0511 50 7 8 0.00
Fri 09/25 18Z 0.53 0410 55 7 8 0.00
Fri 09/25 19Z 1.20 0310 59 7 8 0.00
Fri 09/25 20Z 0.86 0311 60 7 8 0.00
Fri 09/25 21Z 0.56 0312 60 7 9 0.00
Fri 09/25 22Z 0.48 0314 59 7 9 0.00
Fri 09/25 23Z 0.43 0316 58 7 9 0.00
Sat 09/26 00Z 0.44 0417 57 7 9 0.00
Sat 09/26 01Z 0.46 0418 55 7 9 0.00
Sat 09/26 02Z 0.50 0518 51 6 10 0.00
Sat 09/26 03Z 0.52 0518 47 6 10 0.00
Sat 09/26 04Z 0.50 0518 42 6 10 0.00
Sat 09/26 05Z 0.49 0518 39 6 9 0.00
Run total areal avg QPF for the greens is: 0.00 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