Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260926_0000
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)
=== ===== === ==== ==== === === === ====
Sat 09/26 00Z 0.81 0416 71 14 9 0.00
Sat 09/26 01Z 0.83 0519 74 15 9 0.00
Sat 09/26 02Z 0.80 0519 74 13 9 0.00
Sat 09/26 03Z 0.84 0519 74 10 9 0.00
Sat 09/26 04Z 1.07 0623 73 7 9 0.00
Sat 09/26 05Z 1.32 0726 70 7 8 0.00
Sat 09/26 06Z 1.32 0727 68 7 8 0.00
Sat 09/26 07Z 1.14 0726 67 7 8 0.00
Sat 09/26 08Z 1.02 0626 65 6 8 0.00
Sat 09/26 09Z 0.96 0627 64 5 8 0.00
Sat 09/26 10Z 0.92 0627 65 5 8 0.00
Sat 09/26 11Z 0.90 0627 64 5 8 0.00
Sat 09/26 12Z 0.90 0628 63 12 8 0.00
Sat 09/26 13Z 0.86 0628 61 8 8 0.00
Sat 09/26 14Z 0.84 0627 55 9 8 0.00
Sat 09/26 15Z 0.83 0525 50 14 8 0.00
Sat 09/26 16Z 0.95 0524 50 21 8 0.00
Sat 09/26 17Z 2.13 0422 53 27 8 0.00
Sat 09/26 18Z 2.92 0422 54 33 8 0.00
Sat 09/26 19Z 3.20 0423 55 33 8 0.00
Sat 09/26 20Z 1.98 0426 54 45 8 0.00
Sat 09/26 21Z 2.20 0427 56 71 8 0.00
Sat 09/26 22Z 1.58 0428 53 64 8 0.00
Sat 09/26 23Z 1.54 0429 51 77 8 0.00
Sun 09/27 00Z 1.63 0530 54 85 7 0.00
Sun 09/27 01Z 1.68 0531 56 81 7 0.00
Sun 09/27 02Z 1.84 0533 67 90 6 0.00
Sun 09/27 03Z 1.03 0537 76 88 7 0.02
Sun 09/27 04Z 0.94 0539 82 90 7 0.02
Sun 09/27 05Z 0.98 0539 79 91 7 0.01
Sun 09/27 06Z 1.08 0539 82 90 7 0.01
Sun 09/27 07Z 0.97 0638 87 87 7 0.03
Sun 09/27 08Z 0.76 0638 93 82 9 0.07
Sun 09/27 09Z 0.70 0638 96 93 10 0.08
Sun 09/27 10Z 0.68 0638 96 90 10 0.06
Sun 09/27 11Z 0.66 0637 96 72 11 0.02
Sun 09/27 12Z 0.68 0638 96 70 11 0.06
Sun 09/27 13Z 0.72 0641 96 76 12 0.09
Sun 09/27 14Z 0.76 0743 95 82 12 0.08
Sun 09/27 15Z 0.77 0742 94 92 12 0.11
Sun 09/27 16Z 0.82 0844 96 92 12 0.10
Sun 09/27 17Z 0.81 0843 97 76 11 0.07
Sun 09/27 18Z 0.77 0942 97 72 12 0.05
Sun 09/27 19Z 0.77 0941 97 82 12 0.04
Sun 09/27 20Z 0.76 0940 97 83 12 0.04
Sun 09/27 21Z 0.76 0939 97 84 11 0.05
Sun 09/27 22Z 0.71 0937 97 80 11 0.04
Sun 09/27 23Z 0.71 0938 97 77 11 0.04
Mon 09/28 00Z 0.67 1038 97 78 12 0.05
Mon 09/28 01Z 0.62 1036 97 74 12 0.03
Mon 09/28 02Z 0.59 1035 97 80 11 0.03
Mon 09/28 03Z 0.56 1034 96 82 11 0.02
Mon 09/28 04Z 0.55 1034 96 82 12 0.02
Mon 09/28 05Z 0.53 1032 95 80 12 0.02
Mon 09/28 06Z 0.52 1031 95 84 12 0.02
Mon 09/28 07Z 0.49 1031 96 87 12 0.02
Mon 09/28 08Z 0.47 1030 96 90 12 0.02
Mon 09/28 09Z 0.48 1030 96 89 12 0.02
Mon 09/28 10Z 0.47 1029 96 90 12 0.02
Mon 09/28 11Z 0.45 1028 94 88 12 0.01
Run total areal avg QPF for the Central_Greens is: 1.37 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