Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260922_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 09/22 12Z 0.23 1209 88 5 3 0.00
Tue 09/22 13Z 0.26 1110 85 5 3 0.00
Tue 09/22 14Z 0.26 1110 84 5 3 0.00
Tue 09/22 15Z 0.28 1109 84 4 2 0.00
Tue 09/22 16Z 0.33 1109 85 5 2 0.00
Tue 09/22 17Z 0.43 0906 86 5 2 0.00
Tue 09/22 18Z 1.32 0805 87 5 2 0.00
Tue 09/22 19Z 1.82 0705 87 5 3 0.00
Tue 09/22 20Z 1.79 0706 87 5 3 0.00
Tue 09/22 21Z 1.39 0707 87 6 3 0.00
Tue 09/22 22Z 0.90 0608 87 7 3 0.00
Tue 09/22 23Z 0.60 0609 86 8 3 0.00
Wed 09/23 00Z 0.55 0611 86 10 3 0.00
Wed 09/23 01Z 0.53 0612 84 11 3 0.00
Wed 09/23 02Z 0.53 0713 82 11 3 0.00
Wed 09/23 03Z 0.53 0714 78 12 3 0.00
Wed 09/23 04Z 0.62 0815 74 11 3 0.00
Wed 09/23 05Z 0.70 0917 73 10 3 0.00
Wed 09/23 06Z 0.69 0918 69 10 3 0.00
Wed 09/23 07Z 0.63 0919 62 9 3 0.00
Wed 09/23 08Z 0.56 0819 58 7 4 0.00
Wed 09/23 09Z 0.52 0818 54 6 4 0.00
Wed 09/23 10Z 0.49 0818 50 7 4 0.00
Wed 09/23 11Z 0.49 0818 49 12 4 0.00
Wed 09/23 12Z 0.48 0818 50 19 4 0.00
Wed 09/23 13Z 0.46 0818 50 25 4 0.00
Wed 09/23 14Z 0.45 0817 51 25 4 0.00
Wed 09/23 15Z 0.44 0816 51 21 4 0.00
Wed 09/23 16Z 0.45 0714 55 13 4 0.00
Wed 09/23 17Z 0.49 0812 59 7 3 0.00
Wed 09/23 18Z 0.67 0810 61 5 3 0.00
Wed 09/23 19Z 0.73 0809 63 5 4 0.00
Wed 09/23 20Z 0.68 0709 63 5 4 0.00
Wed 09/23 21Z 0.53 0709 62 6 4 0.00
Wed 09/23 22Z 0.47 0610 61 6 4 0.00
Wed 09/23 23Z 0.48 0611 61 5 4 0.00
Thu 09/24 00Z 0.46 0611 60 4 4 0.00
Thu 09/24 01Z 0.45 0613 58 4 5 0.00
Thu 09/24 02Z 0.43 0614 54 4 5 0.00
Thu 09/24 03Z 0.40 0714 48 3 6 0.00
Thu 09/24 04Z 0.39 0714 44 3 6 0.00
Thu 09/24 05Z 0.37 0714 41 2 6 0.00
Thu 09/24 06Z 0.34 0714 35 2 6 0.00
Thu 09/24 07Z 0.33 0714 32 1 7 0.00
Thu 09/24 08Z 0.32 0714 32 2 7 0.00
Thu 09/24 09Z 0.29 0713 34 2 7 0.00
Thu 09/24 10Z 0.27 0712 33 2 7 0.00
Thu 09/24 11Z 0.25 0612 30 2 7 0.00
Thu 09/24 12Z 0.27 0613 28 3 8 0.00
Thu 09/24 13Z 0.27 0613 27 3 8 0.00
Thu 09/24 14Z 0.25 0612 29 3 8 0.00
Thu 09/24 15Z 0.23 0610 32 4 7 0.00
Thu 09/24 16Z 0.25 0610 33 4 7 0.00
Thu 09/24 17Z 0.26 0609 33 4 7 0.00
Thu 09/24 18Z 0.28 0709 32 4 7 0.00
Thu 09/24 19Z 0.27 0608 33 4 8 0.00
Thu 09/24 20Z 0.29 0608 36 4 8 0.00
Thu 09/24 21Z 0.29 0608 39 4 8 0.00
Thu 09/24 22Z 0.29 0609 40 4 8 0.00
Thu 09/24 23Z 0.29 0510 39 4 8 0.00
Run total areal avg QPF for the Central_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