Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260928_1800
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)
=== ===== === ==== ==== === === === ====
Mon 09/28 18Z 0.20 0807 100 95 9 0.00
Mon 09/28 19Z 0.22 0808 99 93 9 0.01
Mon 09/28 20Z 0.22 0708 99 93 8 0.01
Mon 09/28 21Z 0.24 0708 99 93 8 0.02
Mon 09/28 22Z 0.21 0608 99 92 8 0.02
Mon 09/28 23Z 0.19 0508 99 91 8 0.01
Tue 09/29 00Z 0.14 0407 98 89 9 0.01
Tue 09/29 01Z 0.13 0308 97 91 9 0.00
Tue 09/29 02Z 0.13 0308 97 91 9 0.00
Tue 09/29 03Z 0.12 0208 98 95 9 0.00
Tue 09/29 04Z 0.09 0107 97 97 9 0.01
Tue 09/29 05Z 0.04 0008 97 96 10 0.00
Tue 09/29 06Z 0.03 3509 97 94 10 0.00
Tue 09/29 07Z 0.04 3510 97 93 10 0.00
Tue 09/29 08Z 0.05 0011 96 92 10 0.00
Tue 09/29 09Z 0.04 3511 95 91 10 0.00
Tue 09/29 10Z 0.04 3512 95 88 10 0.00
Tue 09/29 11Z 0.04 3512 95 89 10 0.00
Tue 09/29 12Z 0.06 3512 95 87 10 0.00
Tue 09/29 13Z 0.06 0012 96 85 10 0.00
Tue 09/29 14Z 0.08 0012 96 83 10 0.00
Tue 09/29 15Z 0.07 0012 97 84 10 0.00
Tue 09/29 16Z 0.06 0012 97 86 9 0.00
Tue 09/29 17Z 0.06 0012 97 85 9 0.00
Tue 09/29 18Z 0.06 0011 96 84 9 0.00
Tue 09/29 19Z 0.06 0011 95 81 10 0.00
Tue 09/29 20Z 0.07 0010 93 75 10 0.00
Tue 09/29 21Z 0.08 0109 92 69 10 0.00
Tue 09/29 22Z 0.06 0010 93 66 10 0.00
Tue 09/29 23Z 0.06 0009 93 61 10 0.00
Wed 09/30 00Z 0.05 0009 93 54 10 0.00
Wed 09/30 01Z 0.03 3508 94 50 9 0.00
Wed 09/30 02Z 0.02 3507 93 47 10 0.00
Wed 09/30 03Z 0.02 3507 92 42 10 0.00
Wed 09/30 04Z 0.02 3406 89 34 10 0.00
Wed 09/30 05Z 0.03 3306 86 31 10 0.00
Wed 09/30 06Z 0.05 3307 86 26 10 0.00
Wed 09/30 07Z 0.04 3308 83 22 10 0.00
Wed 09/30 08Z 0.05 3308 81 18 10 0.00
Wed 09/30 09Z 0.03 3408 72 15 11 0.00
Wed 09/30 10Z 0.04 3309 74 16 11 0.00
Wed 09/30 11Z 0.04 3308 75 18 11 0.00
Wed 09/30 12Z 0.03 3408 73 18 11 0.00
Wed 09/30 13Z 0.03 3307 72 14 11 0.00
Wed 09/30 14Z 0.03 3306 70 14 11 0.00
Wed 09/30 15Z 0.04 3204 67 15 12 0.00
Wed 09/30 16Z 0.07 3005 66 23 11 0.00
Wed 09/30 17Z 0.10 3006 65 30 11 0.00
Wed 09/30 18Z 0.10 3006 62 34 11 0.00
Wed 09/30 19Z 0.09 3005 60 29 12 0.00
Wed 09/30 20Z 0.09 3005 59 24 12 0.00
Wed 09/30 21Z 0.10 2905 58 20 12 0.00
Wed 09/30 22Z 0.12 2805 54 15 12 0.00
Wed 09/30 23Z 0.15 2806 52 13 12 0.00
Thu 10/01 00Z 0.14 2706 51 16 12 0.00
Thu 10/01 01Z 0.16 2606 54 18 12 0.00
Thu 10/01 02Z 0.18 2607 56 18 12 0.00
Thu 10/01 03Z 0.23 2609 64 25 11 0.00
Thu 10/01 04Z 0.25 2610 73 32 11 0.00
Thu 10/01 05Z 0.23 2609 75 43 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.09 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