Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260221_0600
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 02/21 06Z 0.13 2008 97 85 -6 0.00
Sat 02/21 07Z 0.27 2210 99 75 -7 0.00
Sat 02/21 08Z 0.33 2409 99 83 -7 0.01
Sat 02/21 09Z 0.34 2510 99 95 -7 0.01
Sat 02/21 10Z 0.29 2709 98 94 -7 0.02
Sat 02/21 11Z 0.21 2908 98 93 -7 0.02
Sat 02/21 12Z 0.16 3006 99 89 -7 0.01
Sat 02/21 13Z 0.11 3004 99 81 -7 0.01
Sat 02/21 14Z 0.06 3202 99 72 -7 0.01
Sat 02/21 15Z 0.06 0001 99 65 -7 0.00
Sat 02/21 16Z 0.08 0000 99 66 -7 0.00
Sat 02/21 17Z 0.09 2400 99 72 -7 0.01
Sat 02/21 18Z 0.08 2600 99 72 -7 0.01
Sat 02/21 19Z 0.10 0402 98 65 -7 0.01
Sat 02/21 20Z 0.15 0304 98 60 -7 0.00
Sat 02/21 21Z 0.18 0404 96 57 -8 0.00
Sat 02/21 22Z 0.22 0505 95 56 -8 0.00
Sat 02/21 23Z 0.25 0606 94 62 -8 0.00
Sun 02/22 00Z 0.27 0707 93 63 -8 0.00
Sun 02/22 01Z 0.28 0808 91 62 -8 0.00
Sun 02/22 02Z 0.27 0908 89 59 -8 0.00
Sun 02/22 03Z 0.27 0909 75 57 -7 0.00
Sun 02/22 04Z 0.28 1111 54 57 -7 0.00
Sun 02/22 05Z 0.27 1213 49 54 -7 0.00
Sun 02/22 06Z 0.25 1316 50 58 -8 0.00
Sun 02/22 07Z 0.22 1417 53 64 -8 0.00
Sun 02/22 08Z 0.18 1417 57 71 -8 0.00
Sun 02/22 09Z 0.17 1416 60 75 -7 0.00
Sun 02/22 10Z 0.16 1415 59 76 -7 0.00
Sun 02/22 11Z 0.15 1414 54 82 -7 0.00
Sun 02/22 12Z 0.13 1414 53 88 -7 0.00
Sun 02/22 13Z 0.15 1414 53 87 -7 0.00
Sun 02/22 14Z 0.18 1315 53 86 -7 0.00
Sun 02/22 15Z 0.21 1315 59 82 -7 0.00
Sun 02/22 16Z 0.25 1215 65 80 -7 0.00
Sun 02/22 17Z 0.29 1215 69 74 -7 0.00
Sun 02/22 18Z 0.31 1215 73 71 -7 0.00
Sun 02/22 19Z 0.34 1215 74 74 -7 0.00
Sun 02/22 20Z 0.37 1214 76 79 -8 0.00
Sun 02/22 21Z 0.38 1214 78 83 -8 0.00
Sun 02/22 22Z 0.37 1214 78 85 -7 0.00
Sun 02/22 23Z 0.41 1116 79 85 -8 0.00
Mon 02/23 00Z 0.46 1017 79 83 -7 0.00
Mon 02/23 01Z 0.52 0919 80 72 -8 0.00
Mon 02/23 02Z 0.56 0921 79 57 -8 0.00
Mon 02/23 03Z 0.63 0924 80 62 -8 0.00
Mon 02/23 04Z 0.61 0924 74 51 -8 0.00
Mon 02/23 05Z 0.59 0823 66 63 -8 0.00
Mon 02/23 06Z 0.60 0825 62 69 -7 0.00
Mon 02/23 07Z 0.55 0723 61 78 -7 0.00
Mon 02/23 08Z 0.54 0724 58 85 -7 0.00
Mon 02/23 09Z 0.55 0625 53 86 -7 0.00
Mon 02/23 10Z 0.61 0628 45 79 -7 0.00
Mon 02/23 11Z 0.65 0632 38 81 -6 0.00
Mon 02/23 12Z 0.66 0633 37 84 -6 0.00
Mon 02/23 13Z 0.69 0534 37 83 -7 0.00
Mon 02/23 14Z 0.68 0531 37 85 -7 0.00
Mon 02/23 15Z 0.66 0528 41 84 -8 0.00
Mon 02/23 16Z 0.68 0427 45 85 -9 0.00
Mon 02/23 17Z 0.63 0327 57 85 -10 0.00
Run total areal avg QPF for the Central_Greens is: 0.12 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