
A Flood Watch is in effect for south-central Vermont and eastern slopes of the Adirondacks due to the potential for heavy rain. Widespread totals of 1-3 inches with localized amounts of 3-5 inches in the area could produce excessive runoff and cause flooding in low-lying or flood prone areas. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260728_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)
=== ===== === ==== ==== === === === ====
Tue 07/28 18Z 0.19 1610 91 78 15 0.00
Tue 07/28 19Z 0.39 1612 89 78 15 0.05
Tue 07/28 20Z 0.35 1613 88 79 15 0.11
Tue 07/28 21Z 0.33 1615 88 79 15 0.10
Tue 07/28 22Z 0.19 1719 92 85 15 0.16
Tue 07/28 23Z 0.11 1722 93 88 14 0.18
Wed 07/29 00Z 0.08 1724 93 89 14 0.10
Wed 07/29 01Z 0.09 1821 92 83 14 0.01
Wed 07/29 02Z 0.12 1721 95 83 14 0.01
Wed 07/29 03Z 0.18 1625 96 86 14 0.02
Wed 07/29 04Z 0.19 1629 96 85 14 0.03
Wed 07/29 05Z 0.15 1729 95 87 14 0.02
Wed 07/29 06Z 0.12 1728 95 90 14 0.03
Wed 07/29 07Z 0.17 1627 94 85 14 0.02
Wed 07/29 08Z 0.23 1628 94 88 14 0.01
Wed 07/29 09Z 0.30 1530 94 88 14 0.01
Wed 07/29 10Z 0.34 1530 95 88 14 0.02
Wed 07/29 11Z 0.41 1531 96 90 14 0.04
Wed 07/29 12Z 0.51 1431 95 90 13 0.07
Wed 07/29 13Z 0.64 1431 93 92 13 0.11
Wed 07/29 14Z 0.80 1334 94 93 13 0.16
Wed 07/29 15Z 0.90 1334 96 94 13 0.13
Wed 07/29 16Z 1.15 1335 96 91 13 0.13
Wed 07/29 17Z 0.70 1434 96 91 14 0.12
Wed 07/29 18Z 0.64 1433 97 94 13 0.15
Wed 07/29 19Z 0.54 1534 97 90 14 0.23
Wed 07/29 20Z 0.54 1429 97 92 14 0.12
Wed 07/29 21Z 0.48 1426 97 93 14 0.09
Wed 07/29 22Z 0.49 1426 96 94 14 0.06
Wed 07/29 23Z 0.53 1326 96 94 14 0.07
Thu 07/30 00Z 0.56 1326 95 94 14 0.12
Thu 07/30 01Z 0.53 1326 95 89 13 0.12
Thu 07/30 02Z 0.53 1227 96 88 13 0.05
Thu 07/30 03Z 0.53 1329 96 90 13 0.05
Thu 07/30 04Z 0.50 1329 96 93 13 0.08
Thu 07/30 05Z 0.50 1328 96 91 13 0.09
Thu 07/30 06Z 0.47 1327 94 88 14 0.04
Thu 07/30 07Z 0.42 1326 94 91 14 0.02
Thu 07/30 08Z 0.40 1325 95 93 14 0.03
Thu 07/30 09Z 0.43 1326 95 92 13 0.07
Thu 07/30 10Z 0.45 1225 94 93 13 0.04
Thu 07/30 11Z 0.47 1225 94 92 13 0.02
Thu 07/30 12Z 0.48 1225 94 93 13 0.01
Thu 07/30 13Z 0.48 1224 94 95 13 0.02
Thu 07/30 14Z 0.49 1123 94 96 13 0.02
Thu 07/30 15Z 0.51 1122 95 97 12 0.02
Thu 07/30 16Z 0.52 1020 94 96 12 0.02
Thu 07/30 17Z 0.51 1019 91 96 12 0.01
Thu 07/30 18Z 0.54 0918 88 92 12 0.01
Thu 07/30 19Z 0.56 0917 88 94 12 0.01
Thu 07/30 20Z 0.55 0816 88 95 12 0.02
Thu 07/30 21Z 0.60 0816 91 94 12 0.02
Thu 07/30 22Z 0.57 0816 89 91 12 0.03
Thu 07/30 23Z 0.53 0814 86 90 12 0.01
Fri 07/31 00Z 0.46 0813 86 91 12 0.00
Fri 07/31 01Z 0.38 0711 87 91 12 0.00
Fri 07/31 02Z 0.35 0711 87 89 12 0.00
Fri 07/31 03Z 0.32 0710 87 90 12 0.00
Fri 07/31 04Z 0.29 0710 87 92 12 0.00
Fri 07/31 05Z 0.27 0709 86 89 12 0.00
Run total areal avg QPF for the greens is: 3.29 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