Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260926_0000
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)
=== ===== === ==== ==== === === === ====
Sat 09/26 00Z 0.68 0416 74 14 9 0.00
Sat 09/26 01Z 0.73 0518 75 14 9 0.00
Sat 09/26 02Z 0.73 0519 73 13 9 0.00
Sat 09/26 03Z 0.78 0519 72 10 9 0.00
Sat 09/26 04Z 0.99 0622 70 8 9 0.00
Sat 09/26 05Z 1.28 0725 68 8 8 0.00
Sat 09/26 06Z 1.36 0725 67 8 8 0.00
Sat 09/26 07Z 1.19 0725 66 7 8 0.00
Sat 09/26 08Z 1.03 0624 65 6 8 0.00
Sat 09/26 09Z 0.93 0625 63 5 8 0.00
Sat 09/26 10Z 0.87 0625 62 5 8 0.00
Sat 09/26 11Z 0.86 0626 63 5 8 0.00
Sat 09/26 12Z 0.91 0627 63 10 8 0.00
Sat 09/26 13Z 0.93 0627 63 8 7 0.00
Sat 09/26 14Z 0.92 0627 58 10 8 0.00
Sat 09/26 15Z 0.88 0525 55 13 8 0.00
Sat 09/26 16Z 0.89 0523 53 17 8 0.00
Sat 09/26 17Z 1.55 0521 53 21 8 0.00
Sat 09/26 18Z 1.96 0421 55 25 8 0.00
Sat 09/26 19Z 2.16 0422 56 24 8 0.00
Sat 09/26 20Z 1.45 0424 56 31 8 0.00
Sat 09/26 21Z 1.61 0427 57 48 8 0.00
Sat 09/26 22Z 1.25 0428 54 43 8 0.00
Sat 09/26 23Z 1.26 0429 53 52 8 0.00
Sun 09/27 00Z 1.36 0530 54 62 8 0.00
Sun 09/27 01Z 1.38 0532 54 58 7 0.00
Sun 09/27 02Z 1.52 0533 62 65 7 0.00
Sun 09/27 03Z 1.01 0535 69 74 7 0.01
Sun 09/27 04Z 0.94 0537 74 81 8 0.01
Sun 09/27 05Z 0.92 0538 71 86 8 0.01
Sun 09/27 06Z 1.00 0638 73 90 7 0.01
Sun 09/27 07Z 0.97 0637 80 90 7 0.02
Sun 09/27 08Z 0.83 0638 87 87 9 0.06
Sun 09/27 09Z 0.72 0638 90 87 10 0.06
Sun 09/27 10Z 0.69 0638 91 85 10 0.04
Sun 09/27 11Z 0.66 0638 93 71 11 0.02
Sun 09/27 12Z 0.67 0738 93 67 11 0.04
Sun 09/27 13Z 0.70 0740 91 63 12 0.06
Sun 09/27 14Z 0.73 0742 90 67 12 0.05
Sun 09/27 15Z 0.75 0841 89 74 12 0.07
Sun 09/27 16Z 0.81 0842 91 75 12 0.07
Sun 09/27 17Z 0.80 0841 93 74 12 0.05
Sun 09/27 18Z 0.79 0940 92 71 12 0.04
Sun 09/27 19Z 0.80 0939 93 76 12 0.03
Sun 09/27 20Z 0.78 0938 94 75 12 0.03
Sun 09/27 21Z 0.78 0937 94 74 11 0.03
Sun 09/27 22Z 0.73 0937 94 72 12 0.02
Sun 09/27 23Z 0.72 1038 94 67 12 0.02
Mon 09/28 00Z 0.69 1038 94 71 12 0.03
Mon 09/28 01Z 0.66 1037 93 70 12 0.02
Mon 09/28 02Z 0.63 1036 94 72 12 0.02
Mon 09/28 03Z 0.60 1135 94 80 12 0.02
Mon 09/28 04Z 0.57 1133 93 82 12 0.02
Mon 09/28 05Z 0.55 1031 92 80 12 0.01
Mon 09/28 06Z 0.54 1031 92 80 12 0.01
Mon 09/28 07Z 0.52 1130 93 80 12 0.01
Mon 09/28 08Z 0.48 1128 92 83 12 0.02
Mon 09/28 09Z 0.47 1128 93 87 12 0.01
Mon 09/28 10Z 0.47 1127 92 88 12 0.01
Mon 09/28 11Z 0.44 1026 90 88 12 0.01
Run total areal avg QPF for the greens is: 0.94 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