Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260723_0600
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)
=== ===== === ==== ==== === === === ====
Thu 07/23 06Z 0.74 3125 90 41 6 0.00
Thu 07/23 07Z 0.69 3125 82 37 6 0.00
Thu 07/23 08Z 0.61 3124 79 39 6 0.00
Thu 07/23 09Z 0.57 3125 75 51 6 0.00
Thu 07/23 10Z 0.55 3124 73 50 6 0.00
Thu 07/23 11Z 0.51 3121 73 36 6 0.00
Thu 07/23 12Z 0.43 3017 70 25 7 0.00
Thu 07/23 13Z 0.44 3015 69 34 7 0.00
Thu 07/23 14Z 0.50 2914 68 40 7 0.00
Thu 07/23 15Z 0.64 2813 67 44 7 0.00
Thu 07/23 16Z 1.23 2713 67 49 7 0.00
Thu 07/23 17Z 2.88 2614 71 56 8 0.00
Thu 07/23 18Z 7.07 2615 74 49 8 0.00
Thu 07/23 19Z 10.59 2716 69 38 9 0.00
Thu 07/23 20Z 8.65 2716 66 31 9 0.00
Thu 07/23 21Z 8.17 2715 65 24 9 0.00
Thu 07/23 22Z 4.94 2714 63 22 9 0.00
Thu 07/23 23Z 1.88 2716 65 34 9 0.00
Fri 07/24 00Z 1.99 2717 63 35 10 0.00
Fri 07/24 01Z 1.45 2716 62 27 10 0.00
Fri 07/24 02Z 1.12 2715 61 25 10 0.00
Fri 07/24 03Z 1.06 2716 59 23 10 0.00
Fri 07/24 04Z 0.95 2715 59 25 9 0.00
Fri 07/24 05Z 0.84 2815 58 26 10 0.00
Fri 07/24 06Z 0.77 2814 58 25 10 0.00
Fri 07/24 07Z 0.73 2813 59 22 10 0.00
Fri 07/24 08Z 0.70 2812 61 23 9 0.00
Fri 07/24 09Z 0.71 2911 64 25 9 0.00
Fri 07/24 10Z 0.59 2910 66 23 9 0.00
Fri 07/24 11Z 0.50 2808 65 20 9 0.00
Fri 07/24 12Z 0.50 2808 61 22 9 0.00
Fri 07/24 13Z 0.42 2707 62 25 9 0.00
Fri 07/24 14Z 0.50 2505 63 26 9 0.00
Fri 07/24 15Z 0.75 2305 63 26 10 0.00
Fri 07/24 16Z 1.03 2205 62 27 10 0.00
Fri 07/24 17Z 1.61 2205 61 26 10 0.00
Fri 07/24 18Z 1.43 2204 59 26 11 0.00
Fri 07/24 19Z 1.04 2303 57 26 11 0.00
Fri 07/24 20Z 0.49 2102 56 26 12 0.00
Fri 07/24 21Z 0.32 2102 57 25 12 0.00
Fri 07/24 22Z 0.21 1802 58 23 12 0.00
Fri 07/24 23Z 0.14 1603 60 22 12 0.00
Sat 07/25 00Z 0.09 1705 60 23 12 0.00
Sat 07/25 01Z 0.09 1706 61 23 12 0.00
Sat 07/25 02Z 0.08 1806 61 23 12 0.00
Sat 07/25 03Z 0.08 1807 60 24 12 0.00
Sat 07/25 04Z 0.06 1707 61 24 12 0.00
Sat 07/25 05Z 0.05 1808 61 24 11 0.00
Sat 07/25 06Z 0.04 1806 60 24 11 0.00
Sat 07/25 07Z 0.04 1805 59 23 12 0.00
Sat 07/25 08Z 0.07 1605 58 22 12 0.00
Sat 07/25 09Z 0.14 1406 56 21 12 0.00
Sat 07/25 10Z 0.18 1408 54 20 12 0.00
Sat 07/25 11Z 0.17 1508 57 19 11 0.00
Sat 07/25 12Z 0.21 1509 61 18 11 0.00
Sat 07/25 13Z 0.22 1510 66 17 11 0.00
Sat 07/25 14Z 0.43 1510 68 16 10 0.00
Sat 07/25 15Z 0.66 1509 66 15 11 0.00
Sat 07/25 16Z 0.76 1408 63 13 11 0.00
Sat 07/25 17Z 1.24 1308 61 11 11 0.00
Run total areal avg QPF for the 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